BUSCADOR RECOLECTA

[EN] Adaptive forest management (AFM) is an urgent need because of the uncertainty regarding how changes in the climate will affect the structure, composition and function of forests during the next decades. Current research initiatives for the long-term monitoring of impacts of silviculture are scattered and not integrated into research networks, with the consequent losses of opportunities and capacity for action. To increase the scientific and practical impacts of these experiences, it is necessary to establish logical frameworks that harmonize the information and help us to define the most appropriate treatments. In this context, a number of research groups in Spain have produced research achievements and know-how during the last decades that can allow for the improvement in AFM. These groups address the issue of AFM from different fields, such as ecophysiology, ecohydrology and forest ecology, thus resulting in valuable but dispersed expertise. The main objective of this work is to introduce a comprehensive strategy aimed to study the implementation of AFM in Spain. As a first step, a network of 34 experimental sites managed by 14 different research groups is proposed and justified. As a second step, the most important AFM impacts on Mediterranean pines, as one of the most extended natural and planted forest types in Spain, are presented. Finally, open questions dealing with key aspects when attempting to implement an AFM framework are discussed. This study is expected to contribute to better outlining the procedures and steps needed to implement regional frameworks for AFM., A.J. Molina is beneficiary of an "APOSTD" fellowship (APOSTD/2019/111) funded by the Generalitat Valenciana. M. Moreno-de las Heras is beneficiary of a Serra Hunter fellowship (UB-LE-9055) funded by the Generalitat de Catalunya. F.J. Ruiz-Gomez is supported by a postdoctoral fellowship of the Junta de Andalucia (Sevilla, Spain), and the European Social Fund 2014-2020 Program (DOC_0055). The authors received national and international funding through the following projects: SILVADAPT.NET (RED2018-102719-T), ESPECTRAMED (CGL2017-86161-R), Life-FOREST CO2 (LIFE14 CCM/ES/001271), ALTERACLIM (CGL2015-69773-C2-1-P), INERTIA (PID2019-111332RB-C22-BDV), CEHYRFO-MED (CGL2017-86839-C3-2-R), DEHESACLIM (IB16185), RESILIENTFORESTS (LIFE17 CCA/ES/000063), Rhysotto (PID2019-106583RB-I00), AGL2017-83828C2-2-R, RTI2018-096884-B-C31, ESPAS (CGL2015-65569-R), and caRRRascal (RTI2018-095037-B-I00).

Moreno-Fernández, D., Camarero, J.J., García, M. et al. The Interplay of the Tree and Stand-Level Processes Mediate Drought-Induced Forest Dieback: Evidence from Complementary Remote Sensing and Tree-Ring Approaches. Ecosystems 25, 1738-1753 (2022)., Drought-induced forest dieback can lead to a tipping point in community dominance, but the coupled response at the tree and stand-level response has not been properly addressed. New spatially and temporally integrated monitoring approaches that target different biological organization levels are needed. Here, we compared the temporal responses of dendrochronological and spectral indices from 1984 to 2020 at both tree and stand levels, respectively, of a drought-prone Mediterranean Pinus pinea forest currently suffering strong dieback. We test the influence of climate on temporal patterns of tree radial growth, greenness and wetness spectral indices; and we address the influence of major drought episodes on resilience metrics. Tree-ring data and spectral indices followed different spatio-temporal patterns over the study period (1984?2020). Combined information from tree growth and spectral trajectories suggests that a reduction in tree density during the mid-1990s could have promoted tree growth and reduced dieback risk. Additionally, over the last decade, extreme and recurrent droughts have resulted in crown defoliation greater than 40% in most plots since 2019. We found that tree growth and the greenness spectral index were positively related to annual precipitation, while the wetness index was positively related to mean annual temperature. The response to drought, however, was stronger for tree growth than for spectral indices. Our study demonstrates the value of long-term retrospective multiscale analyses including tree and stand-level scales to disentangle mechanisms triggering and driving forest dieback., Ministerio de Ciencia, Innovacion y Universidades, Universidad de Alcalá, Ministerio de Ciencia e Innovación, Comunidad de Madrid, UK Research and Innovation

Adaptive forest management (AFM) is an urgent need because of the uncertainty regarding how changes in the climate will affect the structure, composition and function of forests during the next decades. Current research initiatives for the long-term monitoring of impacts of silviculture are scattered and not integrated into research networks, with the consequent losses of opportunities and capacity for action. To increase the scientific and practical impacts of these experiences, it is necessary to establish logical frameworks that harmonize the information and help us to define the most appropriate treatments. In this context, a number of research groups in Spain have produced research achievements and know-how during the last decades that can allow for the improvement in AFM. These groups address the issue of AFM from different fields, such as ecophysiology, ecohydrology and forest ecology, thus resulting in valuable but dispersed expertise. The main objective of this work is to introduce a comprehensive strategy aimed to study the implementation of AFM in Spain. As a first step, a network of 34 experimental sites managed by 14 different research groups is proposed and justified. As a second step, the most important AFM impacts on Mediterranean pines, as one of the most extended natural and planted forest types in Spain, are presented. Finally, open questions dealing with key aspects when attempting to implement an AFM framework are discussed. This study is expected to contribute to better outlining the procedures and steps needed to implement regional frameworks for AFM., A.J. Molina is beneficiary of an “APOSTD” fellowship (APOSTD/2019/111) funded
by the Generalitat Valenciana. M. Moreno-de las Heras is beneficiary of a Serra Hunter fellowship (UB-LE-9055) funded by the Generalitat de Catalunya. F.J. Ruiz-Gómez is supported by a
postdoctoral fellowship of the Junta de Andalucía (Sevilla, Spain), and the European Social Fund
2014–2020 Program (DOC_0055). The authors received national and international funding through
the following projects: SILVADAPT.NET (RED2018-102719-T), ESPECTRAMED (CGL2017-86161-R),
Life-FOREST CO2 (LIFE14 CCM/ES/001271), ALTERACLIM (CGL2015-69773-C2-1-P), INERTIA
(PID2019-111332RB-C22-BDV), CEHYRFO-MED (CGL2017-86839-C3-2-R), DEHESACLIM (IB16185),
RESILIENTFORESTS (LIFE17 CCA/ES/000063), Rhysotto (PID2019-106583RB-I00), AGL2017-83828-
C2-2-R, RTI2018-096884-B-C31, ESPAS (CGL2015-65569-R), and caRRRascal (RTI2018-095037-B-I00).

Adaptive forest management (AFM) is an urgent need because of the uncertainty regarding how changes in the climate will affect the structure, composition and function of forests during the next decades. Current research initiatives for the long-term monitoring of impacts of silviculture are scattered and not integrated into research networks, with the consequent losses of opportunities and capacity for action. To increase the scientific and practical impacts of these experiences, it is necessary to establish logical frameworks that harmonize the information and help us to define the most appropriate treatments. In this context, a number of research groups in Spain have produced research achievements and know-how during the last decades that can allow for the improvement in AFM. These groups address the issue of AFM from different fields, such as ecophysiology, ecohydrology and forest ecology, thus resulting in valuable but dispersed expertise. The main objective of this work is to introduce a comprehensive strategy aimed to study the implementation of AFM in Spain. As a first step, a network of 34 experimental sites managed by 14 different research groups is proposed and justified. As a second step, the most important AFM impacts on Mediterranean pines, as one of the most extended natural and planted forest types in Spain, are presented. Finally, open questions dealing with key aspects when attempting to implement an AFM framework are discussed. This study is expected to contribute to better outlining the procedures and steps needed to implement regional frameworks for AFM., A.J. Molina is beneficiary of an “APOSTD” fellowship (APOSTD/2019/111) funded by the Generalitat Valenciana. M. Moreno-de las Heras is beneficiary of a Serra Hunter fellowship (UB-LE-9055) funded by the Generalitat de Catalunya. F.J. Ruiz-Gómez is supported by a postdoctoral fellowship of the Junta de Andalucía (Sevilla, Spain), and the European Social Fund 2014–2020 Program (DOC_0055). The authors received national and international funding through the following projects: SILVADAPT.NET (RED2018-102719-T), ESPECTRAMED (CGL2017-86161-R), Life-FOREST CO2 (LIFE14 CCM/ES/001271), ALTERACLIM (CGL2015-69773-C2-1-P), INERTIA (PID2019-111332RB-C22-BDV), CEHYRFO-MED (CGL2017-86839-C3-2-R), DEHESACLIM (IB16185), RESILIENTFORESTS (LIFE17 CCA/ES/000063), Rhysotto (PID2019-106583RB-I00), AGL2017-83828-C2-2-R, RTI2018-096884-B-C31, ESPAS (CGL2015-65569-R), and caRRRascal (RTI2018-095037-B-I00).

The quantification of climate–growth relationships is a fundamental step in tree-ring sciences. This allows the assessment of functional responses to climate warming, particularly in biodiversity and climate-change hotspots including the Mediterranean Basin. In this region, broadleaf tree and shrub species of pre-Mediterranean, subtropical origin, have to withstand increased aridification trends. However, they have not been widely studied to assess their long-term growth responses to climate and drought. Since these species evolved under less seasonal and wetter conditions than strictly Mediterranean species, we hypothesized that their growth would mainly respond to higher precipitation and water availability from spring to early summer. Here, we quantified climate–growth relationships in five of these broadleaf species showing different leaf phenology and wood type (Pistacia terebinthus L., Pistacia lentiscus L., Arbutus unedo L., Celtis australis L., and Laurus nobilis L.) by using dendrochronology. We calculated Pearson correlations between crossdated, indexed, mean ring width series of each species (chronologies) and monthly climate variables (mean temperature, total precipitation). We also calculated correlations between the species’ chronologies and a drought index on 7-day scales. Lastly, we compared the correlation analyses with “climwin” analyses based on an information-theoretic approach and subjected to cross-validation and randomization tests. As expected, the growth of all species was enhanced in response to wet and cool conditions during spring and early summer. In some species (P. lentiscus, A. unedo, C. australis,) high prior-winter precipitation also enhanced growth. Growth of most species strongly responded to 9-month droughts and the correlations peaked from May to July, except in L. nobilis which showed moderate responses. The “climwin” analyses refined the correlation analyses by (i) showing the higher explanatory power of precipitation (30%) vs. temperature (7%) models, (ii) selecting the most influential climate windows with June as the median month, and (iii) providing significant support to the precipitation model in the case of P. terebinthus confirming that the radial growth of this species is a robust proxy of hydroclimate variability. We argue that “climwin” and similar frameworks based on information-theoretic approaches should be applied by dendroecologists to critically assess and quantify climate–growth relationships in woody plants with dendrochronological potential.

En las últimas décadas han ocurrido grandes cambios que han afectado a las masas forestales españolas. Por un lado, ha habido un aumento de las temperaturas y de los eventos climáticos extremos (sequías y heladas tardías) y por otro un abandono de las prácticas selvícolas tradicionales como consecuencia de la disminución de las rentas obtenidas del monte, y en general del ámbito rural con el consiguiente despoblamiento de las zonas rurales, así como de los cambios en la sociedad, la cual valora crecientemente la preservación de los ecosistemas naturales. En este trabajo estudiamos el impacto que están teniendo estos cambios sobre los bosques de montaña españoles. Debido a su mayor sensibilidad, se ha prestado especial atención a aquellas especies típicas de bosques templados que encuentran en la Península Ibérica su límite de distribución meridional. Se ha muestreado dos espacios naturales protegidos, el Parque Nacional de los Picos de Europa y el hayedo de Montejo de la Sierra, y cuatro especies arbóreas, Fagus sylvatica, Quercus petraea, Quercus pyrenaica y Betula pubescens. En los análisis se han empleado fundamentalmente técnicas dendrocronológicas, las cuales están basadas en el análisis de los anillos de crecimiento que quedan registrados en la madera de los árboles. En Picos de Europa la dinámica de F. sylvatica y Q. petraea ha estado vinculada a lo largo de los últimos 100 años a sucesos de mortalidad aislados asociados a eventos climáticos extremos, lo que ha favorecido a F. sylvatica, más adaptada a la competencia que Q. petraea. En El Hayedo de Montejo el factor que más ha influido sobre el crecimiento a largo plazo es el aumento de la espesura, que ha provocado el decaimiento del crecimiento en Q. petraea y especialmente en Q. pyrenaica. Estas especies se podrían ver desplazadas, si no se aplican medidas selvícolas que reviertan el proceso, por F. sylvatica, aunque esta última es mucho más sensible que Q. petraea y Q. pyrenaica frente a las heladas tardías, que podrían ser cada vez más frecuentes como consecuencia del cambio climático. ----------ABSTRACT---------- In recent decades the Spanish forests have been affected by major changes. On the one hand, there has been an increase in temperatures and extreme climatic events (droughts and late frosts) and, on the other hand, there has been an abandonment of traditional uses as a consequence of the decrease in the income obtained from the forest, and in general from the rural environment, with the consequent depopulation of rural areas, as well as increasing concern about the preservation of natural ecosystems of society. In this work we study the impact that these changes are having on Spanish mountain forests, paying special attention to those species typical of temperate forests that have their southern limit of distribution in the Iberian Peninsula due to their greater sensitivity. Two protected natural areas, the Picos de Europa National Park and the El Hayedo de Montejo forest, and four tree species, Fagus sylvatica, Quercus petraea, Quercus pyrenaica and Betula pubescens, were sampled. Dendrochronological techniques have been used to analyze the effects of climate and stand structure on tree ring growth and characterize species response and forest dynamics. In Picos de Europa, the dynamic of F. sylvatica and Q. petraea have been linked over the last 100 years to isolated mortality events associated with extreme climatic events, which has favored F. sylvatica, more adapted to competition than Q. petraea. In the El Hayedo de Montejo forest, the stand density increase has been the most influential factor in long-term growth, which has caused a decline in the growth of Q. petraea and especially Q. pyrenaica. These species could be displaced, if no silvicultural traits are applied to reverse the process, by the competition-tolerant F. sylvatica. Nevertheless, F. sylvatica is much more sensitive than Q. petraea and Q. pyrenaica to late frosts, which could become increasingly frequent as a result of climate change, so a strategy to enhance forest resilience would be maintaining mixed stands.

51 Pags.- 2 Tabls.- 9 Figs. The definitive version is available at: https://www.sciencedirect.com/science/journal/00489697, In Mediterranean areas where drought-induced forest dieback and tree mortality have been widely reported, it is still under debate how the likely risks of climate change will affect tree growth and consequently forest productivity. Increasing tree mortality has been associated not only to increased drought, but also to a lack of management in many dense pine forests and plantations, where warming may intensify tree-to-tree competition for soil water. This emphasizes the need of using silviculture to adapt dense stands of Mediterranean pine reforestations to warmer and drier conditions. Here we combined dendrochronology and C and O isotope analyses of wood in two Aleppo pine (Pinus halepensis) plantations, growing under semiarid conditions and experimentally thinned at high and moderate intensities along with control. The main aim was to understand the responses of radial growth and water use efficiency (WUEi) to different thinning intensities, and to analyze the effectiveness of thinning to enhance post-drought growth resilience. Thinning had a positive effect on growth, produced an increase of δ18O, reduced growth sensitivity to drought and decreased WUEi, suggesting a reduction of drought stress. These results were consistent across sites, and were significant even 20 years after the intervention took place. Considering the climate effects on growth through the SPEI drought index to calculate resistance and recovery indices, an increase of resistance after thinning was observed. We conclude that high thinning intensity (50% of basal area removed) is a useful silviculture intervention on Mediterranean Aleppo pine plantations that enhances their growth, and makes them less dependent on harsh climatic conditions, improving their resilience against drought and consequently making them better adapted to more unfavourable conditions., Funding for this research was provided by the Spanish “Agencia Estatal de Investigación” and the European Commission in the frame of the ERA-NET WaterWorks2015 Cofunded Call (project INNOMED). This ERA-NET is an integral part of the 2016 Joint Activities developed by the Water Challenges for a Changing World Joint Programme Initiative (Water JPI) as a result of a joint collaborative effort with the Joint Programming Initiative on Agriculture, Food Security and Climate Change (FACCE JPI). A.J. Molina is beneficiary of an ‘APOSTD’ fellowship (APOSTD/2019/111) funded by the Generalitat Valenciana. JJC acknowledges the support of FunDiver (CGL2015-69186-C2-1-R) and FORMAL (RTI2018-096884-B-C31) projects from the Spanish Ministry of Science, Innovation and Universities. The support of CEHYRFO-MED (CGL2017-86839-C3-2-R), CLICES (CGL2017-83866-C3-3-R), RESILIENT-FORESTS (LIFE17 CCA/ES/000063) and SILVADAPT.NET (RED2018-102719-T) projects is also acknowledged., Peer reviewed

The quantification of climate–growth relationships is a fundamental step in tree-ring sciences. This allows the assessment of functional responses to climate warming, particularly in biodiversity and climate-change hotspots including the Mediterranean Basin. In this region, broadleaf tree and shrub species of pre-Mediterranean, subtropical origin, have to withstand increased aridification trends. However, they have not been widely studied to assess their long-term growth responses to climate and drought. Since these species evolved under less seasonal and wetter conditions than strictly Mediterranean species, we hypothesized that their growth would mainly respond to higher precipitation and water availability from spring to early summer. Here, we quantified climate–growth relationships in five of these broadleaf species showing different leaf phenology and wood type (<i>Pistacia terebinthus</i> L., <i>Pistacia lentiscus</i> L., <i>Arbutus unedo</i> L., <i>Celtis australis</i> L., and <i>Laurus nobilis</i> L.) by using dendrochronology. We calculated Pearson correlations between crossdated, indexed, mean ring width series of each species (chronologies) and monthly climate variables (mean temperature, total precipitation). We also calculated correlations between the species’ chronologies and a drought index on 7-day scales. Lastly, we compared the correlation analyses with “<i>climwin</i>” analyses based on an information-theoretic approach and subjected to cross-validation and randomization tests. As expected, the growth of all species was enhanced in response to wet and cool conditions during spring and early summer. In some species (<i>P. lentiscus</i>, <i>A. unedo</i>, <i>C. australis</i>,) high prior-winter precipitation also enhanced growth. Growth of most species strongly responded to 9-month droughts and the correlations peaked from May to July, except in <i>L. nobilis</i> which showed moderate responses. The “<i>climwin</i>” analyses refined the correlation analyses by (i) showing the higher explanatory power of precipitation (30%) vs. temperature (7%) models, (ii) selecting the most influential climate windows with June as the median month, and (iii) providing significant support to the precipitation model in the case of <i>P. terebinthus</i> confirming that the radial growth of this species is a robust proxy of hydroclimate variability. We argue that “<i>climwin</i>” and similar frameworks based on information-theoretic approaches should be applied by dendroecologists to critically assess and quantify climate–growth relationships in woody plants with dendrochronological potential., This research was funded by Spanish Ministry of Science, Innovation, and Universities, grant number FORMAL (RTI2018-096884-B-C31)., Peer reviewed

© 2020 by the authors., The increased frequency and intensity of warming-induced droughts have triggered dieback episodes affecting many forest types and tree species worldwide. Tree plantations are not exempt as they can be more vulnerable to drought than natural forests because of their lower structural and genetic diversity. Therefore, disentangling the physiological mechanisms leading to growth decline and tree mortality can provide tools to adapt forest management to climate change. In this study, we investigated a Pinus nigra Arn. plantation situated in northern Spain, in which some trees showed canopy dieback and radial-growth decline. We analyzed how radial growth and its responses to drought events differed between non-declining (ND) and declining (D) trees showing low and high canopy defoliation, respectively, in combination with carbon (δ13C) and oxygen (δ18O) isotope ratios in tree rings. The radial growth of P. nigra was constrained by water availability during the growing season and the previous autumn. The radial growth of D trees showed higher sensitivity to drought than ND trees. This fact is in accordance with the lower drought resilience and negative growth trends observed in D trees. Both tree classes differed in their growth from 2012 onwards, with D trees showing a reduced growth compared to ND trees. The positive δ13C-δ18O relationship together with the uncoupling between growth and intrinsic water-use efficiency suggest that D trees have less tight stomatal regulation than ND trees, which could involve a high risk of xylem embolism in the former class. Our results suggest that different water use strategies between coexisting ND and D trees were behind the differences in growth patterns and point to hydraulic failure as a possible mechanism triggering dieback and growth decline., This research was funded by the Spanish Ministry of Science, Innovation, and Universities, grant number FORMAL (RTI2018-096884-B-C31)., Peer reviewed

Snow dynamics are key to understanding tree growth in mountain forests and future response to climate change. However, precise monitoring of microclimate conditions and variables related to tree growth and functioning are lacking. To advance on those issues, snow cover and microclimate conditions, tree phenology, xylogenesis, intra-annual radial growth and the concentration of sapwood and needle non-structural carbohydrates were intensively monitored in four Pinus uncinata forests along an altitudinal gradient over three years in a Pyrenean valley (NE Spain). Snow dynamics exerted strong influence on soil temperature and moisture, particularly before and during the early growing season. Soil temperature was the most relevant microclimate variable during the overall xylogenesis, mainly influencing the production of mature tracheids. Large snow accumulation resulted in later snow depletion and a consequent delay in soil warming onset. Low soil temperatures in the spring, related to prolonged snow persistence, retarded cambial reactivation and led to lower growth rate. Despite strong spatial variability among plots, wood production was determined by snow dynamics in three out of the four studied plots. This study highlights the major role played by early and late growing season soil temperatures on radial growth of mountain conifers. The results of this study suggest that a future shallower and more transitory snowpack in the studied forests, together with warmer soil and air temperatures, may increase radial growth and productivity of similar mid-latitude, young mountain forests., This study was supported by the projects: “Bosque, nieve y recursos hídricos en el Pirineo ante el cambio global” funded by Fundación Iberdrola, CGL2014-52599-P (IBERNIEVE) and CGL2017-82216-R (HIDROIBERNIEVE) funded by the Spanish Ministry of Economy and Competitiveness. ASV was supported by a pre-doctoral University Professor Training grant [FPU16/00902] funded by the Spanish Ministry of Education, Culture and Sports. EAG was supported by a pre-doctoral FPI grant [BES-2015-071466] funded by the Spanish Ministry of Economy and Competitiveness. JJC, AG and MC acknowledge funding by project RTI2018-096884-B-C31 (Spanish Ministry of Economy and Competitiveness).

12 Pags.- 34Figs.- 3 Tabls., Abstract
The negative impacts of drought on forest growth and productivity last for several years generating legacies, although the factors that determine why such legacies vary across sites and tree species remain unclear.
We used an extensive network of tree‐ring width (RWI, ring‐width index) records of 16 tree species from 567 forests, and high‐resolution climate and normalized difference vegetation index (NDVI) datasets across Spain during the common period 1982‒2008 to test the hypothesis that climate conditions and growth features modulate legacy effects of drought on forests. Legacy effects of drought were calculated as the differences between detrended‐only RWI and NDVI series (i.e. after removing long‐term growth trends) and pre‐whitened RWI and NDVI series predicted by a model including drought intensity. Superposed Epoch Analysis (SEA) was used to estimate whether legacy effects differed from random. Finally, legacy effects were related to water balance, growth persistence and variability, and tree species identity.
We found a widespread occurrence of drought legacy effects on both RWI and NDVI, but they were seldom significant. According to SEA, first‐year drought legacies were negative and different from random in 9% and 5% of the RWI and NDVI series respectively. The number of significant second‐ and third‐year legacies was substantially lower. Differences between RWI and NDVI legacies indicate that canopy greenness and radial growth responses to drought are decoupled. We found variations in legacies between tree species with gymnosperms presenting larger first‐year drought legacies than angiosperms, which were exposed to less severe droughts. Greater growth variability can explain the presence of first‐year RWI legacies in gymnosperms from dry sites despite that the relationship between growth variability and legacies was complex.
Synthesis. Accounting for species and site responses to drought provides a better understanding of the magnitude and duration of drought legacies on forest growth and productivity. Despite the widespread occurrence of growth reductions in the years during and after drought occurrence, significant legacies were not very common, mostly lasted one year, and were more widespread in gymnosperms. These are relevant factors to be considered in the future when studying the consequences of drought on forest productivity and tree growth., This study was financially supported by: Xunta de Galicia, Grant/Award Number: PGIDIT06PXIB502262PR, GRC GI‐1809; INIA, Grant/Award Number: RTA2006‐00117; CANOPEE, 2014‐2020‐FEDER funds; and Spanish Science Ministry: RTI2018‐096884‐B‐C31, RTI2018‐096884‐B‐C33, AGL2017‐83828‐C2‐2R and ENV4‐CT97‐0641 projects. GSB was supported by a ‘Juan de la Cierva Formación’ grant from MINECO (FJCI 2016‐30121). This research was supported by the BERC 2018‐2021 program, and by the Spanish Ministry of Science, Innovation and Universities through the BC3 María de Maeztu excellence accreditation (MDM‐2017‐0714) and the IBERYCA (CGL2017‐84723‐P) project. R.S.S. was supported by VULBOS project (UPO‐1263216, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014‐2020), and A.H. by PinCaR project (UHU‐1266324, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014‐2020). K.N. was supported by the Ministry of Education, Science and Sports (Republic of Slovenia, Raziskovalci‐2.1‐UL‐BF‐ C3330‐19‐952011)., Peer reviewed

© 2022 The Authors., Dieback in temperate forests is understudied, despite this biome is predicted to be increasingly affected by more extreme climate events in a warmer world. To evaluate the potential drivers of dieback we reconstructed changes in radial growth and intrinsic water-use efficiency (iWUE) from stable isotopes in tree rings. Particularly, we compared tree size, radial-growth trends, growth responses to climate (temperature, precipitation, cloudiness, number of foggy days) and drought, and changes in iWUE of declining and non-declining trees showing contrasting canopy dieback and defoliation. This comparison was done in six temperate forests located in northern Spain and based on three broadleaved tree species (Quercus robur, Quercus humilis, Fagus sylvatica). Declining trees presented lower radial-growth rates than their non-declining counterparts and tended to show lower growth variability, but not in all sites. The growth divergence between declining and non-declining trees was significant and lasted more in Q. robur (15–30 years) than in F. sylvatica (5–10 years) sites. Dieback was linked to summer drought and associated atmospheric patterns, but in the wettest Q. robur sites cold spells contributed to the growth decline. In contrast, F. sylvatica was the species most responsive to summer drought in terms of growth reduction followed by Q. humilis which showed coupled changes in growth and iWUE as a function of tree vigour. Low growth rates and higher iWUE characterized declining Q. robur and F. sylvatica trees. However, declining F. sylvatica trees became less water-use efficient close to the dieback onset, which could indicate impending tree death. In temperate forests, dieback and growth decline can be triggered by climate extremes such as dry and cold spells, and amplified by climate warming and rising drought stress., This study was supported by projects FunDiver (CGL2015-69186-C2-1-R) and FORMAL (RTI2018-096884-B-C31) from the Spanish Ministry of Science and Innovation, Innovation and Universities. C. A-M. was supported by Ramon y Cajal fellowship (RYC-2017-22830). We acknowledge the E-OBS dataset from the EU-FP6 project UERRA (http://www.uerra.eu) and the Copernicus Climate Change Service, and the data providers in the ECAandD project (https://www.ecad.eu).

Supplementary Materials: The following are available online at https://www.mdpi.com/article/
10.3390/fire4020029/s1, Paleoecological Methods; Table S1: radiocarbon (AMS-14C) data from
Arroyo de Aguas Frías site, Mountain forests are subjected to several pressures including historical land-use changes and climate warming which may lead to shifts in wildfire severity negatively impacting tree species with low post-fire growth resilience. This is the case of relict Mediterranean Scots pine (Pinus sylvestris) forests in the Sierra de Gredos mountains (central Spain). We reconstructed the historical fire regime of these forests since 1700 by using paleoecology, historical ecology and dendroecology. We detected an increase in charcoal accumulation rate and coprophilous fungi in peat bogs during the late 19th century when the pine pollen percentage sharply decreased, historical records of fire peaked and many trees showed growth suppressions. We inferred an increased wildfire incidence during the late 19th century, which could have shaped the current distribution of Scots pine forests. This shift in fire-forest interactions can be explained by the uncontrolled use of mountain forests and grasslands due to the dissolution of “Mesta”, one of the major and lasting transhumance livestock associations in Europe. Integrating historical human and climate influences on fire regimes allows decomposing the resilience and conservation components of relict forests, Peer reviewed

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Attribution (CC BY) license., In Mediterranean seasonally dry regions, the rise in dieback and mortality episodes observed in pine afforestations has been related to higher drought intensity and lack of appropriate management, which enhance competition between trees for water and light. However, there is little understanding of the benefits of silviculture for plantations under seasonal drought stress. A combination of dendrochronology and wood C and O isotope analyses was used in three Black pine (Pinus nigra) plantations to work out the responses of radial growth (BAI, basal area increment) and water-use efficiency (WUEi) to thinning treatments (removal of 40% of the stand basal area). Thinning had a positive effect on BAI and WUEi, reduced drought sensitivity, and reduced the temporal dependence on the previous year’s growth. These results were significant even 13–14 years after thinning and coherent for the three study sites. Differences were found between the sites regarding the physiological mechanisms of adaptation. In two sites, we inferred the enhanced WUEi was due to increased photosynthetic rates (A) at constant stomatal conductance (gs). In the third site, which had higher tree density and therefore competition, we inferred increases in both A and gs, with the former being proportionally larger than the latter., Funding for this research was provided by the “Agencia Estatal de Investigación” of Spain (CSIC) in the frame of the ERA-NET WaterWorks2015 co-funded Call (project PCIN-2017-020/INNOMED). This ERA-NET is an integral part of the 2016 Joint Activities developed by the Water Challenges for a Changing World Joint Programme Initiative (Water JPI) as a result of a joint collaborative effort with the Joint Programming Initiative on Agriculture, Food Security and Climate Change (FACCE JPI). Funding was also provided by the project EFA210/16/PIRAGUA, co-funded by the European Regional Development Fund (ERDF) through the Interreg V Spain-France-Andorre Programme (POCTEFA 2014-2020) of the European Union. The authors also acknowledge support from the Spanish Ministry of Science, Innovation and Universities through the research projects FORMAL (RTI2018-096884-B-C31) and CLICES (CGL2017-83866-C3-3-R)., Peer reviewed

Tree plantations have been proposed as suitable carbon sinks to mitigate climate change. Drought may reduce their carbon uptake, increasing their vulnerability to stress and affecting their growth recovery and resilience. We investigated the recent growth rates and responses to the climate and drought in eight Atlas cedar (Cedrus atlantica) plantations located along a wide climate gradient from wetter sites in south-eastern France and north Spain to dry sites in south-eastern Spain. The cedar growth increased in response to the elevated precipitation from the prior winter to the current summer, but the influence of winter precipitation on growth gained importance in the driest sites. The growth responsiveness to climate and drought peaked in those dry sites, but the growth resilience did not show a similar gradient. The Atlas cedar growth was driven by the total precipitation during the hydrological year and this association strengthened from the 1980s onwards, a pattern related to the winter North Atlantic Oscillation (NAO). High winter NAO indices and drier conditions were associated with lower growth. At the individual level, growth resilience was related to tree age, while growth recovery and year-to-year growth variability covaried. Plantations’ resilience to drought depends on both climate and tree-level features., This research was funded by the Spanish Ministry of Economy, Industry and Competitiveness: FORMAL (RTI2018-096884-B-C31) project and SilvAdapt RED2018 102719 T project., Peer reviewed

11 páginas, 6 figuras, 2 tablas, Alpine treelines are expected to shift upward due to climate warming, whereas warmer conditions can have negative impacts on forests located near the xeric, equatorward limit of the distribution of tree species (rear edge). We compare tree populations forming the distribution limits of mountain pine (Pinus uncinata) in north-eastern Spain: two cold-limited alpine treeline populations, and a rear-edge drought-prone stand. In the treelines, trees were sampled in three altitudinal belts to evaluate within-site variations considering the forest, the transitional ecotone and the treeline. Tree growth was markedly higher in one of the treeline sites (Tesso), particularly in the forest belt, as compared to the other treeline (Las Cutas), and to the warmest rear-edge stand. Tree growth in the rear-edge population depended on June precipitation. Trees presented also comparatively smaller leaves with higher Specific Leaf Area (SLA) there than in the two treelines. Regarding the differences between altitudinal belts within the treelines, treeline soils showed lower N concentrations and a lower content of sand than in forests. Soil microbiota was dominated by bacteria in the treeline and by fungi in the forest, although with differences between sites. Soil characteristics and microbial composition were strongly related, whereas its relationship with tree growth and functional traits was less clear. The marked differences in leaf traits and growth response to climate found when comparing treeline and rear-edge sites highlights the biogeographical uniqueness of sites forming the equatorward distribution limit. The greater tree growth in the Tesso treeline as compared to Las Cutas indicate that interactions between climate and physical and chemical properties of the soil influence tree growth and its interactions with soil microbial communities in the treeline. A better understanding of plant-soil feedbacks may help to understand the future dynamics of tree populations forming the species’ climatic and geographic limits of distribution., This study was supported by projects: LMP242_18 (Gobierno de Aragón co-financed by FEDER European Funds), FORMAL (ref. RTI2018–096884-B-C31; Spanish Ministry of Science, Innovation and Universities) and the project “CLU-2019–05 – IRNASA/CSIC Unit of Excellence”, funded by the Junta de Castilla y León and cofinanced by the European Union (ERDF “Europe drives our growth”). We acknowledge the E-OBS dataset from the EU-FP6 project UERRA (http://www.uerra.eu) and the Copernicus Climate Change Service, and the data providers in the ECA&D project (https://www.ecad.eu). The authors thank Virginia Gascón (IRNASA-CSIC) for her valuable task in laboratory analyses, Peer reviewed

13 Págs., Rear-edge tree populations forming the equatorward limit of distribution of temperate species are assumed to be more adapted to climate variability than central (core) populations. However, climate is expected to become more variable and the frequency of climate extremes is forecasted to increase. Climatic extreme events such as heat waves, dry spells and spring frosts could become more frequent, and negatively impact and jeopardize rear-edge stands. To evaluate these ideas, we analyzed the growth response of trees to successive spring frosts in a mixed forest, where two temperate deciduous species, Fagus sylvatica L. (European beech) and Quercus petraea (Matt.) Liebl. (sessile oak), both at their southernmost edge, coexist with the Mediterranean Quercus pyrenaica Willd. (Pyrenean oak). Growth reductions in spring-frost years ranked across species as F. sylvatica > Q. petraea > Q. pyrenaica. Leaf flushing occurred earlier in F. sylvatica and later in Q. pyrenaica, suggesting that leaf phenology was a strong determinant of spring frost damage and stem growth reduction. The frost impact depended on prior climate conditions, since warmer days prior to frost occurrence predisposed to frost damage. Autumn Normalized Difference Vegetation Index data showed delayed leaf senescence in spring-frost years and subsequent years as compared with pre-frost years. In the studied forest, the negative impact of spring frosts on Q. petraea and especially on F. sylvatica growth, was considerably higher than the impacts due to drought. The succession of four spring frosts in the last two decades determined a trend of decreasing resistance of radial growth to frosts in F. sylvatica. The increased frequency of spring frosts might prevent the expansion and persistence of F. sylvatica in this rear-edge Mediterranean population., The National Parks Autonomous Agency (2483S/2017, 2481S/2017); the Autonomous Community of Madrid (P2013/ MAE-2760); the Spanish Ministry of Economy, Industry and Competitiveness (AGL2016-76769-C2-1-R, RTI2018-096884-B-C31); and the Spanish Ministry of Education, Culture and Sports (FPU15/03533 to A.R-.C.)., Peer reviewed

21 páginas, figuras, 4 tablas, Rear-edge populations at the xeric distribution limit of tree species are particularly vulnerable to forest dieback triggered by drought. This is the case of silver fir (Abies alba) forests located in Southwestern Europe. While silver fir drought-induced dieback patterns have been previously explored, information on the role played by nutritional impairment is lacking despite its potential interactions with tree carbon-water balances. We performed a comparative analysis of radial growth, intrinsic water-use efficiency (iWUE), oxygen isotopes (δ18 O) and nutrient concentrations in leaves of declining (DD) and non-declining (ND) trees in silver fir in four forests in the Spanish Pyrenees. We also evaluated the relationships among dieback predisposition, intraspecific trait variation (wood density and leaf traits) and rhizosphere soil physical-chemical properties. The onset of growth decline in DD trees occurred more than two decades ago, and they subsequently showed low growth resilience against droughts. The DD trees presented consistently lower foliar concentrations of nutrients such as P, K, Cu and Ni than ND trees. The strong effects of foliar nutrient status on growth resilience indices support the key role played by mineral nutrition in tree functioning and growth before, during and after drought. In contrast, variability in wood density and leaf morphological traits, as well as soil properties, showed weak relationships with tree nutritional status and drought performance. At the low elevation, warmer sites, DD trees showed stronger climate-growth relationships and lower δ18 O than ND trees. The uncoupling between iWUE and δ18 O, together with the positive correlations between P and K leaf concentrations and δ18 O, point to deeper soil/bedrock water sources and vertical decoupling between nutrient and water uptake in DD trees. This study provides novel insights into the mechanisms driving silver fir dieback and highlights the need to incorporate tree nutrition into forest dieback studies., This study was financially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) via competitive grant RTI2018-096884-B-C31 (FORMAL project), RTI2018-096884-B-C33 (LESENS project) and by the Government of Aragón via competitive grant LMP242_18. AG acknowledges financial support from the Spanish Ministry of Science and the AEI through the Ramón y Cajal grant (RyC2020- 030647-I). JIQ acknowledges the financial support from Spanish Ministry of Science through the project (PID2019-107382RB-I00). JMI acknowledges financial support from the Project “CLU-2019-05—IRNASA/CSIC Unit of Excellence”, funded by the Junta de Castilla y León and cofinanced by the European Union (ERDF “Europe drives our growth”). RSS and JCL acknowledge the financial support from the Andalusian government (P20_00813 VUERCLIM), (IE19_074 UPO DendroOlavide) and (UPO-1263216 VULBOS), and from the Spanish Ministry of Science trough the project (EQC2018-005303-P), Peer reviewed

 Instituto de Ciencias Forestales (ICIFOR), The important role that forests play in the global carbon cycle has led to the implementation of management practices to enhance long-term carbon storage in forests. Obtaining information about how forest biomass varies at different successional stages is therefore essential. In this study, we aimed (i) to determine the relationship between stand live biomass and the degree of naturalness (i.e. the degree to which forests dynamics are driven by natural processes in the absence of anthropogenic influences) in undisturbed, mature forests, and (ii) to establish the upper threshold of live biomass stock that is dependent on site quality, by using the site form (SF) index (dominant height-diameter relationship). We assessed live biomass stocks in a total of 10 undisturbed mixed and pure mature silver fir (Abies alba Mill.) and European beech (Fagus sylvatica L.) stands across the Spanish Pyrenees. We used dendrochronology and chrono-functional indicators to assess the degree of naturalness and to detect growth releases as proxies for past disturbance. We compared data from the mature plots and data from the Spanish National Forest Inventory (NFI), for similar forest types and SF values, to determine whether maximum live biomass values were reached in the plots. We observed that live biomass stock was generally independent of naturalness. The forests characterized by the lowest degrees of naturalness held similar amounts of live tree biomass as those characterized by the highest degrees of naturalness, including old-growth forests. Although some stands had undergone severe disturbance in the past, in all but two plots the live biomass stocks reached maximum values at the respective SF values, unlike in the NFI plots. The study findings contribute to the body of evidence supporting the existence of an upper threshold of live biomass stock represented by undisturbed mature stands. Maximum live carbon stock appears to be reached at earlier stages than the old-growth stage. This finding has consequences for biomass and carbon management and may be useful for developing forest policies involving carbon sequestration aimed at mitigating climate change., This work was supported by the Spanish Ministry of Science, Innovation and Universities (projects AGL2016-76769-C2-2-R, RTI2018-096884-B-C31 (JJC), and RTI2018-096884-B-C33 (RSS)). The authors received financial support from the following organizations: the Spanish Ministry of Education through the FPU program ( FPU16/03057 ) (JAMV); the Spanish Secretariat of State for Research, Development and Innovation through a JdC-I fellowship (CPC); the VULBOS project [ UPO - 1263216 , FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020 ] (RSS); the PinCaR project ( UHU - 1266324 , FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020 ) (AH); Marche Polytechnic University through the Campus World project (MC); and projects AGL2015-73190-JIN , PID2019-110273RB-I00 and RYC-2017-23389 from the Spanish Ministry of Science and Innovation (DMB)., Peer reviewed

24 Pág., Intra-annual wood density fluctuations are valuable indicators of the role of the local climate and provenance origins on tree growth. These intra-ring wood features were the most informative about local adaptation and phenotypic plasticity ofPinus halepensisMill. in a provenance trial. This highlights the importance of taking provenance into account when selecting forest reproductive material to mitigate the effects of climate change. Context: It is essential to disentangle the influence of climate from the effect of provenance on inter- and intra-annual wood traits to identify populations’ responses to climate changes. This will be even more relevant in the drought-prone Mediterranean region, where species have high genetic differentiation among populations. Aims: We investigated the effects of provenance and climate driving Pinus halepensis Mill. wood traits, as imprinted phenotypic adaptations to the Mediterranean climate. Methods: Inter- and intra-annual wood trait variation (ring-, early-, and latewood width, wood density) was studied by microdensitometry in 8 provenances from Spain, France, Greece, and Italy in a common-garden experiment. We related wood traits and density fluctuations with inter-annual climate variations at the trial site and the provenance origin. Results: Provenances showed distinct responses to climate regarding tree growth, wood density, and intra-annual fluctuations. Density fluctuations in latewood were more frequent than in earlywood. Climate at the provenance origin was a more important force for density fluctuations than climatic variations at the planting site, with different trends between coastal and inland provenances, and higher frequency of latewood fluctuations in provenances from arid and semiarid sites. Conclusion: Differences in P. halepensis wood density fluctuations confirmed the imprinted origin provenance control in response to climate variations and indicated a relation with local adaptation of these xylem anatomical features. Moreover, the position of these fluctuations in rings reflected the high plasticity of P. halepensis to cope with high intra-seasonal variability of climatic conditions. This underlines the importance of considering tree-ring features for the selection of provenances in reforestation material for conservation and silvicultural programs., AH is supported by PinCaR project (UHU-1266324, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014–2020); JV (SFRH/BPD/105656/2015) and FC (SFRH/ BPD/111307/2015) were supported by postdoctoral research grants from FCT with funds from POPH (Portuguese Operational Human Potential Program), QREN Portugal (Portuguese National Strategic Reference Framework), and FSE (European Social Fund). RSS was supported by the Spanish Ministry of Economy, Industry and Competitiveness by the postdoctoral grant (IJCI-2015-25845, MCIU funds), CoMo-ReAdapt (CGL2013-48843-C2-1-R) project, RTI2018-096884-B-C31 and RTI2018-096884-B-C33 projects (Ministry of Ministry of Science, Innovation and Universities, Spain), and VULBOS project (UPO-1263216, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014–2020)., Peer reviewed

Assessing tree growth patterns and deviations from expected climate baselines across wide environmental gradients is fundamental to determine forest vulnerability to drought. This need is particularly compelling for the southernmost limit of the tree species distribution where hot droughts often trigger forest dieback processes. This is the case of some silver fir (Abies alba) populations located in southwestern Europe (Spanish Pyrenees) which present ongoing dieback processes since the 1980s. We sampled 21 silver fir stands showing different dieback intensity, assessed using defoliation levels, quantified their growth patterns and characterized their responses to climate. Then, we assessed growth deviations from climatic predictions using the process-based Vaganov-Shashkin (VS) growth model. The forests showing most intense dieback, i.e. highest defoliation levels, were mainly located in low-elevation sites of the western Pyrenees. Trees in these stands displayed the lowest growth rates and the highest year-to-year variability in growth and their growth was limited by late-summer evaporative demand. In eastern and central Pyrenees, we detected a mild growth limitation by low soil moisture during the late growing season and positive growth recovery in recent years with respect to a climate baseline. Decreasing growth trajectories were the most common pattern, while rising trends were common in stands with low dieback in eastern and central Pyrenees. Our results portend systematic spatial variability of growth trends across the Pyrenean silver fir populations forming the south-western distribution limit of the species in Europe. Decoupling of growth between eastern and western populations observed in the recent decades suggests contrasting vulnerability to climate change, and more importantly, the decoupling of growth patterns in western clusters could be used as an early-warning signal of impending dieback. Consequently, we foresee future dieback events to have more detrimental effects in the western compared with the eastern Pyrenees., We thank the following projects funded by the Spanish Ministry of Economy (CGL2015-69186-C2-1-R) and the Spanish Ministry of Science, Innovation and Universities (RTI2018-096884-B-C31). C. Valeriano acknowledges funding by a FPI grant (PRE2019-089800) associated to project RTI2018-096884-B-C31. J. Tumajer was supported by Charles University (UNCE HUM/018). A. Gazol is supported by the Ramón y Cajal Program of the Spanish MICINN under Grant RyC2020-030647-I, and by CSIC and Science and Innovation Ministry under grants PIE-20223AT003 and PID2021-123675OB-C43, respectively, also by TED2021-129770B-C21. G. Sangüesa-Barreda was supported by a Postdoctoral grant (IJC2019-040571-I) funded by MCIN/AEI /10.13039/501100011033. R. Sánchez-Salguero and JC. Linares were supported by VULBOS (UPO-1263216) and VURECLIM (P20_00813) projects, both by FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020; and supported by EQC2018-004821-P and IE19_074 UPO projects cofounded by Spanish “Plan Estatal de Investigación Científica y Técnica y de Innovación 2017-2020” and Plan Andaluz de Investigación, Desarrollo e Innovación (PAIDI 2020)., Peer reviewed

Droughts are becoming more frequent in the Mediterranean basin due to warmer conditions. Droughts negatively impact forests growth for several years, often generating negative legacies or carryover effects. However, these legacies differ among tree species, sites and drought characteristics and have been mainly studied considering tree growth or canopy greenness, but ignoring reproductive phenomena. Here, we compare the legacy effects of drought on acorn and male inflorescence production and radial growth by using a 19-year series of 150 Quercus ilex individuals in three stands located in north-eastern Spain. We evaluate the relationships between monthly climate variables, tree-ring width, acorn production and male inflorescence production. For the two driest years considered (2005 and 2012), when very few acorns were produced, we did not find negative legacy effects on acorn production in the three years following droughts. The production of male inflorescences did not show any significant legacy after drought, although its annual variation was related to the climatic conditions of the year before acorn ripening. Acorn production was higher than expected for some of these years, apparently following the pattern of tree growth recovery with a certain lag. This compensatory response of acorn production differed between the two analysed droughts, in accordance with different conditions of drought timing and post-drought climate conditions. Even though few negative legacy effects of growth and acorn production were found, we confirmed the negative effect of drought stress on tree growth and acorn production, linked to dry winter conditions. Our findings confirm that drought features (timing, duration, intensity) and post-drought climate conditions influence tree growth and reproduction legacies., This research was funded by Spanish Ministry of Science, Innovation and Universities, grant number FORMAL (RTI2018-096884-B-C31) to JJC., Peer reviewed

Some widely distributed timber species, such as oaks, are vulnerable to low soil water availability and drought. Therefore, selecting broadleaved minor species with lower sensitivity to drought could be an alternative in seasonally dry areas. However, the growth performance of these minor hardwood species is unknown, particularly under warm and dry conditions at the southern limit of their distribution range. We assessed the radial growth response to drought by correlating tree-ring and climate data in coexisting service trees (Sorbus domestica) and two oak species (Quercus faginea, Quercus pyrenaica). Trees were sampled in three Mediterranean sites located in Spain with different precipitation patterns. We used the Vaganov–Shashkin (VS) growth model to infer the main climate constraints of growth. To ascertain whether climate is changing tree phenology, we also simulated changes in xylem onset and cessation timings and compared them with leaf falling dates in service trees. Service trees showed a trend towards advancing leaf fall, but this was not related to xylem growth. Oaks responded more to a drought index than service trees. The strongest responses corresponded to droughts peaking from spring to summer, but oaks tended to respond to longer droughts (9–13 months) than service trees (2–7 months). These different responses are due to the positive responses of all species to high precipitation in the growing season, but the sensitivity of oak growth to warm summer conditions and increased atmospheric water demand. The VS model indicated a more bimodal growth pattern in services trees than in oaks, which could allow the former to recover better after a dry summer. Service trees could be more widely used as a source of valuable timber wood under Mediterranean continental conditions., The support of Spanish Ministry of Science grant number RTI2018-096884-B-C31 is acknowledged. FC was supported by the R&D unit CFE (FCT/UIDB/04004/2020)., Peer reviewed

Local differentiation at distribution limits may influence species' adaptive capacity to environmental changes. However, drivers, such gene flow and local selection, are still poorly understood. We focus on the role played by range limits in mountain forests to test the hypothesis that relict tree populations are subjected to genetic differentiation and local adaptation. Two alpine treelines of mountain pine (Pinus uncinata Ram. ex DC) were investigated in the Spanish Pyrenees. Further, an isolated relict population forming the species' southernmost distribution limit in north-eastern Spain was also investigated. Using genotyping by sequencing, a genetic matrix conformed by single nucleotide polymorphisms (SNPs) was obtained. This matrix was used to perform genotype-environment and genotype-phenotype associations, as well as to model risk of non-adaptedness. Increasing climate seasonality appears as an essential element in the interpretation of SNPs subjected to selective pressures. Genetic differentiations were overall weak. The differences in leaf mass area and radial growth rate, as well as the identification of several SNPs subjected to selective pressures, exceeded neutral predictions of differentiation among populations. Despite genetic drift might prevail in the isolated population, the Fst values (0.060 and 0.066) showed a moderate genetic drift and Nm values (3.939 and 3.555) indicate the presence of gene flow between the relict population and both treelines. Nonetheless, the SNPs subjected to selection pressures provide evidences of possible selection in treeline ecotones. Persistence in range boundaries seems to involve several selective pressures in species' traits, which were significantly related to enhanced drought seasonality at the limit of P. uncinata distribution range. We conclude that gene flow is unlikely to constrain adaptation in the P. uncinata rear edge, although this species shows vulnerability to future climate change scenarios involving warmer and drier conditions., Belén Méndez-Cea is recipient of a UCM Santander predoctoral fellowship (CT42/18-CT43/18), Isabel García-García is recipient of a predoctoral fellowship (FPU18/01153). This research was funded by projects LMP242_18 (Gobierno de Aragón, co-financed by FEDER European Funds), FORMAL (ref. RTI2018–096884-B-C31; Spanish Ministry of Science, Innovation and Universities) and the project “CLU-2019–05 – IRNASA/CSIC Unit of Excellence”, funded by the Junta de Castilla y León and co-financed by the European Union (ERDF “Europe drives our growth”)., Peer reviewed

Extreme climate events such as late spring frosts (LSFs) negatively affect productivity and tree growth in temperate beech forests. However, detailed information on how these forests recover after such events are still missing. We investigated how LSFs affected forest cover and radial growth in European beech (Fagus sylvatica L.) populations located at different elevations at four sites in the Italian Apennines, where LSFs have been recorded. We combined tree-ring and remote-sensing data to analyse the sensitivity and recovery capacity of beech populations to LSFs. Using daily temperature records, we reconstructed LSF events and assessed legacy effects on growth. We also evaluated the role played by elevation and stand structure as modulators of LSFs impacts. Finally, using satellite images we computed Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and LAI (Leaf Area Index) to evaluate the post-LSF canopy recovery. The growth reduction in LSF-affected trees ranged from 36 % to 84 %. We detected a negative impact of LSF on growth only during the LSF year, with growth recovery occurring within 1–2 years after the event. LSF-affected stands featured low vegetation indices until late June, i.e. on average 75 days after the frost events. We did not find a clear relationship between beech forest elevation and occurrence of LSFs defoliations. Our results indicate a high recovery capacity of common beech and no legacy effects of LSFs., JJC acknowledges funding by project RTI2018-096884-B-C31 of the Spanish Ministry of Economy, Industry and Competitiveness., Peer reviewed

© 2023 The Author(s). Published by Elsevier GmbH. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)., Tree phenology is sensitive to climate warming and changes in seasonal precipitation. Long xylogenesis records are scarce, thus limiting our ability to analyse how radial growth responds to climate variability. Alternatively, process-based growth models can be used to simulate intra-annual growth dynamics and to better understand why growth bimodality varies along temperature and precipitation gradients. We used the Vaganov-Shashkin (VS) growth model to analyse the main climatic drivers of growth bimodality in eight trees and shrubs conifers (four pines and four junipers) across Spain. We selected eleven sites with different continentality degree and spring/autumn precipitation ratios since we expected to find pronounced bimodal growth in less continental sites with spring and autumn precipitation peaks. The VS model successfully simulated annual growth rates at all sites as a function of daily temperature and soil moisture data. Bimodal growth patterns clustered into less continental sites showing low spring/autumn precipitation ratios. This finding agrees with observed climate-growth associations showing that growth was enhanced by wet-cool winter-to-spring conditions, but also by wet autumn conditions in the most bimodal sites. We observed a stronger growth bimodality in pines compared to junipers. We discuss the spatial variability of climate drivers in bimodality growth pattern and how increasing continentality and shifts in seasonal precipitation could affect growth patterns. Bimodality could be an advantageous response to overcome summer drought in Mediterranean forests. The ability of some species to reactivate growth during autumn might determine their capacity to withstand increasing summer aridity., This work was supported by project RTI2018–096884-B-C31 and by FPI grant (ref. PRE2019–089800) to CV from the Spanish Ministry of Science. RSS was supported by DendrOlavide I (EQC2018–005303-P), Ministry of Science, Innovation and Universities, Spain; DendrOlavide II (IE19_074 UPO), VURECLIM (P20_00813) and VULBOS (UPO-1263216) Junta de Andalucía, Fondos Europeos de Desarrollo Regional. JT received the support from Charles University (UNCE/HUM 018). VS was grateful for the support of RSF project (# 22–14–00048)., Peer reviewed

© 2023 The Author(s). Published by Elsevier GmbH. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/)., The growth responses to climate variability are still unknown in locally threatened conifers from dry regions, but this information is necessary for improving the conservation of relict populations under increasing aridification. We characterized the radial growth patterns and responses to climate of Tetraclinis articulata, a Cupressaceae tree endemic to the western Mediterranean Basin, in a relict population located in southwestern Spain (Doñana) and two populations from the northern Morocco where the species core habitat is found (Tétouan, Ifarten). We assessed climate-growth relationships by using tree-ring width, climate data, drought and North Atlantic Oscillation (NAO) indices. Climate-growth analyses were refined using the climwin R package to select the most informative statistical models. The main climatic constraints of growth were inferred by using the process-based Vaganov-Shashkin (VS) model explicitly considering non-linear climate-growth relationships. Tetraclinis articulata growth was favored by wet conditions from the prior autumn to the spring of the growth year. In Doñana, warmer May conditions led to growth decline but this negative effect could be reversed by wet-warm conditions in the prior late autumn. Growth in the two Moroccan sites was constrained by 6- to 18-month long droughts peaking in summer, which account for cumulative water deficit since the previous autumn. Winter and early spring precipitation were the main climate drivers of growth in the Moroccan T. articulata populations, and their year-to-year variability was linked to the NAO. The VS model simulations showed that T. articulata growth is enhanced by wet soil conditions in late winter and early spring, probably recharging shallow soil water pools. The VS model also confirmed that warmer spring-summer conditions could amplify drought stress and threaten the long-term persistence of the relict Doñana population., This research was funded by Spanish Ministry of Science and Innovation (TED2021–129770B-C21 project). CV was supported by a PhD grant (PRE2019-089800) associated to project RTI2018–096884-B-C31 from Spanish Ministry of Science and Innovation. ARC is supported by a "Margarita Salas" post-doctoral fellowship (RCMS-22-G1T6IW-17-NLHJ80) from the Universidad Politécnica de Madrid (Spain). PZF was supported by a Fulbright Scholar grant through the Moroccan-American Commission for Educational & Cultural Exchange (MACECE). The authors thank ICTS-RBD (Infraestructura Científica y Técnica Singular-Reserva Biológica de Doñana) funded by ICTS-MICIN program and to the managers of Doñana Protected Area for its help in accessing and sampling the Doñana relict population., Peer reviewed

© 2024 The Authors. Published by Elsevier GmbH. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)., The olive tree is an iconic component of Mediterranean agricultural landscapes. Many monumental olive trees are regarded as millennial individuals, but their ages cannot be estimated through tree ring dating. Alternatively, 14C-dating of pith wood sample provides age estimates for these old trees. However, published age estimates indicate that most ages of old olive trees range between 200 and 700 years. Nevertheless, some rare individuals may be millennial or even older. Here we report the oldest dated olive tree, sampled in the so-called Noah olive grove in Bshaaleh (northern Lebanon), and having an age of 1161 ± 131 years according to 14C dating. By measuring tree diameter, ring counting, and 14C wood dating in old olive trees in Mediterranean countries an equation was obtained to estimate the 14C-estimated age of old olive trees: age = 37.56 + 1.835 diameter. We conclude that most monumental olive trees are centennial but not millennial, with very old trees probably restricted to harsh sites where trees show slow growth rates., This study was funded by project RTI2018-096884-B-C31 (Spanish Ministry of Science)., Peer reviewed

© 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)., Warming temperatures and droughts are driving widespread forest dieback and growth decline worldwide. In forests experiencing dieback, declining trees may exhibit altered climate memory of growth, indicative of physiological impairment. Thus, we evaluated climate-growth responses of trees in four drought-disturbed forests dominated either by gymnosperms (Abies alba, Pinus sylvestris) or angiosperms (Fagus sylvatica, Quercus humilis) in Northern Spain, where we compared responses of declining (heavily defoliated) and non-declining (slightly or not defoliated) trees. To disentangle the effects of forest dieback and past climate on tree growth, we applied the stochastic antecedent modeling (SAM) framework to annual tree-ring widths to quantify climatic memory. Declining trees had lower recent growth than non-declining conspecifics. All species responded positively to precipitation and temperature, independent of their vigor class, except for declining silver fir (A. alba) and European beech (F. sylvatica) individuals, which showed a negative effect of warmer temperatures on growth. Declining trees of these two species were also more sensitive to recent temperature and precipitation conditions, whilst climatic conditions further into the past were more important for non-declining trees. Silver fir and European beech from both vigor classes were also coupled to climate conditions during markedly different seasons, with dry summer conditions particularly affecting declining trees. Declining and non-declining Scots pine (P. sylvetris) and pubescent oak (Q. humilis) trees did not show different responses to past climate. While drought-triggered dieback differentially impacted silver fir and European beech individuals, Scots pine and pubescent oak trees suffered from a chronic process of loss in tree growth and vigor. Our results highlight the differences in climate sensitivity and climate memory of tree growth in forests experiencing ongoing dieback., We acknowledge funding provided by projects FUNDIVER (CGL2015–69186-C2–1-R and CGL2015–69186-C2–2-R projects) and FORMAL (RTI2018–096884-B-C31 and RTI2018–096884-B-C32) from the Spanish Ministry of Science and Innovation. We thank the interest and guidance of J.M. Vadillo and Estella forest guards (Navarra Govt.) and the help in the field and the lab of M. Colangelo. We acknowledge the E-OBS dataset from the EU-FP6 project UERRA (http://www.uerra.eu) and the Copernicus Climate Change Service, and the data providers in the ECAD project (https://www.ecad.eu). K. Ogle acknowledges the support of the National Science Foundation, Advances in Biological Informatics program (grant #1458867)., Peer reviewed

Observational, correlative approaches are one of the backbones of dendrochronology. For instance, climate-growth relationships are usually quantified by calculating Pearson correlations. However, the ability to detect these relationships and the probability of declaring significant correlations by chance pose multiple challenges to such correlative framework. The R climwin package, developed a few years ago within the discipline of animal ecology, overcomes these limitations. In this paper we apply climwin to study relationships between climate and tree-ring widths and anatomy to show the advantages of using this package in the field of dendrochronology. This package allows calculating several models considering multiple windows relating a response variable to the climatic factors at different time resolutions. Then, the most parsimonious model is selected through an information-theoretic approach and randomization tests are computed to establish the significance of the selected model. We compare analyses based on Pearson correlations with climwin results using several environmental drivers (climate variables, drought indices, river flow), response variables (tree-ring width, tracheid lumen area and cell-wall thickness), and tree species from ecologically contrasting sites (cold- and water-limited conifers, Mediterranean riparian ash forests). Analyses of climate-growth/anatomy relationships based on the use of climwin showed several advantages over simple Pearson correlations: (i) they did not depend on the use of arbitrary time intervals of fixed duration, (ii) they allowed reducing probabilities associated with type I and II errors, (iii) they resulted in more consistent findings, (iv) they increased the capacity to detect differences between sites or periods in a time series, and (v) they provided more explanatory power., JJC acknowledges funding by projects SED-IBER (BBVA Foundation), CGL2015-69186-C2-1-R and RTI2018-096884-B-C31 (Spanish Ministry of Science)., Peer reviewed

© 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/), Climate change can lead to the simultaneous occurrence of extreme droughts and heat waves increasing the frequency of compound events with unknown impacts on forests. Here we use two independent datasets, a compiled database of tree drought mortality events and the ICP-Forest level I plots, to study the impacts of the simultaneous occurrence of hot summers, with elevated vapour pressure deficit (VPD), and dry years on forest defoliation and mortality across Europe. We focused on tree drought mortality and background mortality rates, and we studied their co-occurrence with compound events of hot summers and dry years. In total, 143 out of 310 mortality events across Europe, i.e. 46% of cases, corresponded with rare compound events characterized by hot summers and dry years. Over the past decades, summer temperature increased in most sites and severe droughts resulted in compound events not observed before the 1980s. From the ICP-Forest plots we identified 291 (1718 trees) and 61 plots (128 trees) where severe defoliation and mortality, respectively, were caused by drought. The analyses of these events showed that 34% and 27% of the defoliation and mortality cases corresponded with rare compound climate events, respectively. Background mortality rates across Europe in the period 1993–2013 presented higher values in regions where summer temperature and VPD more steeply rose, where drought frequency increased. The steady increase in summer temperatures and VPD in Southern and Eastern Europe may favor the occurrence of compound events of hot summers and dry conditions. Giving that both, local and intense tree drought mortality events and background forest mortality rates, are linked to such compound events we can expect an increase in forest drought mortality in these European regions over the next decades., This study was supported by project FORMAL (RTI2018-096884-B-C31) from the Spanish Ministry of Science, Innovation and Universities., Peer reviewed

© 2021 The Author(s). Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/., Legacies of past climate conditions and historical management govern forest productivity and tree growth. Understanding how these processes interact and the timescales over which they influence tree growth is critical to assess forest vulnerability to climate change. Yet, few studies address this issue, likely because integrated long-term records of both growth and forest management are uncommon. We applied the stochastic antecedent modelling (SAM) framework to annual tree-ring widths from mixed forests to recover the ecological memory of tree growth. We quantified the effects of antecedent temperature and precipitation up to 4 years preceding the year of ring formation and integrated management effects with records of harvesting intensity from historical forest management archives. The SAM approach uncovered important time periods most influential to growth, typically the warmer and drier months or seasons, but variation among species and sites emerged. Silver fir responded primarily to past climate conditions (25–50 months prior to the year of ring formation), while European beech and Scots pine responded mostly to climate conditions during the year of ring formation and the previous year, although these responses varied among sites. Past management and climate interacted in such a way that harvesting promoted growth in young silver fir under wet and warm conditions and in old European beech under drier and cooler conditions. Our study shows that the ecological memory associated with climate legacies and historical forest management is species-specific and context-dependent, suggesting that both aspects are needed to properly evaluate forest functioning under climate change., Marqués was supported by a FPI grant from the University of Alcalá; G. Sangüesa-Barreda was supported by a Juan de la Cierva-Formación grant from MINECO (FJCI 2016-30121). We acknowledge funding provided by projects FUNDIVER (Spanish Ministry of Economy and Competitiveness, MINECO, Spain; CGL2015-69186-C2-1-R and CGL2015-69186-C2-2-R projects), FORMAL (MINECO, Spain; RTI2018-096884-B-C31 and RTI2018-096884-B-C32), and the National Science Foundation, Advances in Biological Informatics (#1458867)., Open Access funding provided by ETH Zurich., Peer reviewed

© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)., There is debate on which tree species can sustain forest ecosystem services in a drier and warmer future. In Europe, the use of non-native timber species, such as Douglas fir (Pseudotsuga menziesii [Mirb.] Franco), is suggested as a solution to mitigate climate change impacts because of their high growth resilience to drought. However, the biogeographical, climatic and ecological limits for widely planted timber species still need to be defined. Here, we study the growth response to climate variables and drought of four Douglas fir plantations in northern Spain subjected to contrasting climate conditions. Further, we measure wood density in one of the sites to obtain a better understanding of growth responses to climate. Correlative analyses and simulations based on the Vaganov–Shaskin process-based model confirm that growth of Douglas fir is constrained by warm and dry conditions during summer and early autumn, particularly in the driest study site. Minimum wood density increased in response to dry spring conditions. Therefore, planting Douglas fir in sites with a marked summer drought will result in reduced growth but a dense earlywood. Stands inhabiting dry sites are vulnerable to late-summer drought stress and can act as “sentinel plantations”, delineating the tolerance climate limits of timber species., This research was funded by: (i) a “Ramón y Cajal” postdoctoral Program of the SPANISH MINISTRY OF SCIENCE, INNOVATION AND UNIVERSITIES under Grant RyC2020-030647-I (A.G.) and (ii) the SPANISH MINISTRY OF SCIENCE, INNOVATION AND UNIVERSITIES, grant number RTI2018-096884-B-C31. A.G. received funding from PIE-20223AT003 of CSIC., Peer reviewed

R scripts showing how to use climwin package with tree-ring width and anatomy chronologies. The databases needed to use the scripts are included., [FILES]

1. climwin with dendro and anatomy.R

R script in which climwin is used to study the growth/anatomy-climate relationships of 5 species with weekly time resolution.

2. climwin with the river flow.R

R script in which climwin is used to study the growth-river flows relationships of 2 sites with monthly time resolution.

3. Pinus sylvestris model.R

R script in which climwin is used to fit a multiple linear regression.

4. RingWidths.csv

Database of detrended growths and anatomical variables needed to run the R scripts.

Abbreviations:

LA - lumen area

CWT - cell wall thickness

ew - earlywood

lw - latewood

Ps - Pinus sylvestris (Corbalán site)

Aa - Abies alba (Paco Ezpela site)

VA1 - Valdelinares (Pinus uncinata)

AL - Alcalá de la Selva (Pinus sylvestris)

CO - Olmedilla (Pinus nigra)

AC - Alto de Cabra (Pinus pinaster)

VH - Valbona (Pinus halepensis)

5. climate.rds

Database of climate needed to run the R scripts.

Abbreviations:

T - Temperature

Tmax - Maximum temperature

Tmin - Minimum temperature

P - Precipitation

spei - Standardized Evapotranspiration Precipitation Index using a range of time scales (1, 3, 6, 9, 12, 24, 36 and 48 months) over which water deficits and surplus accumulate are considered.

6. Fraxinus.csv

Database of detrended growths of Fraxinus needed to run the R scripts.

7. River flow.csv

Database of river flow needed to run the R scripts.

8. readme.txt

txt file explaining the details of the data.

(2021-07-01), [METHODOLOGY]

We aim to identify the most likely climate variables driving the growth and wood anatomy

of the species using climwin package.

We used the weekly resolved climate data and a randomization technique to find, for each climate variable, the most relevant period of the year in which climate was most related to growth according to climwin. To identify the most likely climate predictors of the growth and wood anatomy features and the most relevant time window (the most influential period of the year for individual climate variables), we fitted simple linear regressions with the growth/anatomy variables as the response variables and the climate variables as predictors. The mean of each factor in each time window considered was used as the aggregate statistics. For each factor all possible window lengths (periods of year) at weekly resolution (but monthly resolution for the flow river) was calculated and the one with the lowest ΔAICc compared to the null model (i.e., including the intercept only) was selected. Finally, randomization tests were calculated using 1000 repetitions to calculate pΔAICc (the likelihood that a climatic signal is real). October 1 of the previous year was established as the threshold for the beginning of the windows and November 31 of the year of growth as the limit for the end of the windows. A minimum length of two weeks was pre-defined.

A multiple linear regression were fitted using P. sylvestris pine lumen area chronology, without distinguishing between earlywood and latewood, as the response variable and including the climate variables found to be statistically significant. For building the model with climwin we followed this procedure: (i) among the simple linear models calculated with climwin for the response variable, the model with the lowest ∆AICc was selected; (ii) using this model as baseline model, we introduced the rest of climatic variables one by one in order to fit all possible two-factor models, obtaining for each model ∆AICc, climate windows and p∆AICc; and (iii) the models with p∆AICc < 0.05 were selected. Finally, only a model with two climate variables met this condition. If more significant models with different climatic variables had been found, the whole process would have to be repeated including the model with two climatic factors with lower ∆AICc in the baseline model. Multicollinearity was avoided by controlling the variance inflation factor (VIF)., Ministerio de Economía y Competitividad: CGL2015-69186-C2-1-R
Agencia Estatal de Investigación: RTI2018-096884-B-C31, Peer reviewed

© 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)., Pollarded woodlands are iconic components of European rural landscapes. Pollarding is a traditional management technique used to obtain timber and firewood. However, these woodlands are subjected to different stressors in rapidly depopulating rural regions under continental Mediterranean areas where riparian black poplar (Populus nigra) pollards are widespread but still understudied. First, the rapid rural depopulation has lead to the abandonment of pollarding creating trees with abundant, thick and heavy branches. Second, climate warming and alteration of river flows reduce soil moisture which could contribute to growth decline of riparian pollards. We investigated how these stress factors have impacted radial growth in seven sites located in four river basins of southern Aragón, north eastern Spain. We used dendrochronology to reconstruct the changes in radial growth during the period 1890–2020 and to assess how growth has responded to changes in temperature, precipitation and river flow variability. Since 1900 growth suppressions, probably corresponding to pollarding events, occurred in several decades (1910s, 1960s, 1980s and 1990s) and showed a high variability among sites and river basins. Suppressions peaked during the 1940s, probably associated to intense pollarding related to high timber and firewood demand after the Spanish Civil War. Poplar radial growth increased in response to high precipitation and river flow from March to April, particularly in sites located away of river banks. Pollarding abandonment and declines in soil moisture availability threaten the persistence of veteran black poplars. Active management through pollarding and protection should be implemented to preserve these iconic, anthropogenic woodlands due to their multiple ecological and cultural services., This study was supported by project FORMAL (RTI2018-096884-B-C31) from the Spanish Ministry of Science and Innovation., Peer reviewed

© 2022 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made., 1. Understanding the mechanisms underlying community stability has become an urgent need to protect ecosystems from global change and resulting biodiversity loss. While community stability can be influenced by species richness, synchrony in annual fluctuations of species, species stability and functional traits, the relative contributions of these drivers to stability are still unclear. In semi-natural grasslands, land-use changes such as fertilization might affect stability by decreasing richness and influencing year-to-year fluctuations. In addition, they can promote long-term directional trends, shifting community composition and influencing grassland maintenance. Thus, it is important to consider how species and community stability vary year-to-year but also in the long term., 2. Using a 14-year vegetation time series of a species-rich semi-natural Mediterranean grassland, we studied the relative importance of richness, synchrony, species stability and functional traits on community stability. To assess land-use change effects on stability, we applied a fertilization treatment. To distinguish stability patterns produced by year-to-year fluctuations from those caused by long-term trends, we compared the results obtained using a detrending approach from those without detrending., 3. Independently of the treatment and approach applied, the most stable communities were those composed of asynchronous species with low specific leaf area. Fertilization decreased year-to-year and long-term community stability by increasing community-weighted mean of specific leaf area, decreasing species stability or also reducing richness in the case of year-to-year stability. Additionally, traits such as seed mass had an indirect effect on stability through synchrony. Long-term trends appeared in control and fertilized plots (due to fertilization), decreasing community and species stability and leading to differences in the relationships found between community stability and some of its drivers. This reflects the importance of accounting for the effect of temporal trends on community and species stability using both a long-term and a year-to-year approach., 4. Synthesis. Stability is influenced by richness, synchrony and functional traits. Fertilization decreases species and community stability by promoting long-term trends in species composition, favouring competitive species and decreasing richness. Studying stability at the community level and species level, and accounting for the effect of trends is essential to understand stability and its drivers more comprehensively., This research was funded by Fundación Caja Navarra (Programa ‘Tú Eliges, Tú Decides’, ref. 10833) and Universidad de Navarra (projects ‘Biodiversity Data Analytics and Environmental Quality’ and ‘Red de Observatorios de la Biodiversidad de Navarra (ROBIN)’). M.V. is supported by Departamento de Educación, Gobierno de Navarra (Ayudas predoctorales para la realización de programas de doctorado de interés para Navarra; Plan de Formación y de I + D 2018). A.G. is supported by project FORMAL (ref. RTI2018-096884-B-C31; Ministerio de Ciencia, Innovación y Universidades) and by the Ramon y Cajal Program of the Spanish Ministerio de Ciencia e Innovación under Grant RyC2020-030647-I. L.G. is supported by long-term research development project of the Czech Academy of Sciences (No. RVO 67985939)., Peer reviewed

© 2022 Gazol, Oliva, Valeriano, Colangelo and Camarero. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms., Drought is an important driver of forest dynamics in the Mediterranean region. The forecasted increase in drought frequency and severity can notably influence tree growth, forest structure, composition and productivity. Understanding how coexisting tree species respond to drought is thus crucial to understand which are less vulnerable and will perform better in a warmer and drier world. To assess drought vulnerability, we used dendrochronology to study the radial growth trends and responses to a drought index of four pine species (Pinus halepensis, Pinus pinea, Pinus nigra, and Pinus sylvestris) coexisting in North-eastern Spain. We reconstructed the growth of each species and evaluated their short- and long-term growth response to drought for the common period 1980–2017. The growth of the four pine species depended on water availability and high early spring temperatures impacted the growth of P. nigra and P. sylvestris negatively. The occurrence of a severe drought between 2005 and 2007 lead to marked growth reductions in the four species, but it was greater in magnitude in P. pinea and P. halepensis in 2005, and in P. nigra in 2007. The results of basal area increment models at the individual tree level suggested that P. halepensis trees grow more than the rest of species. After accounting for age and drought effects, P. nigra and P. sylvestris displayed negative growth trends in the 2008–2017 period while P. pinea and P. halepensis displayed positive growth trends. P. sylvestris was the most resistant species and P. pinea the less resistant. Conversely, P. halepensis and P. pinea were slightly more resilient than P. sylvestris. Moreover, P. sylvestris was the species displaying the highest autocorrelation and the lowest coefficient of variation in ring-width indices. A marked drop in the autocorrelation of P. pinea ring-width index was observed in response to the 2005 drought. These results indicate that all study species are vulnerable to drought but in different degrees. The strong resilience capacity of P. halepensis suggests that it will better thrive in a drier future, but mixed pine forests, such as the one here studied, may contract or become rare due to the strong sensitivity of P. pinea to drought and the lower post-drought performance of P. nigra and P. sylvestris., We acknowledge funding from the Barcelona Provincial Council (Diputació de Barcelona), by project RTI2018-096884-B-C31 and by FPI grant (ref. PRE2019-089800) to CV (Spanish Ministry of Science). AG and JO were also supported by the Ramon y Cajal Program of the Spanish MICINN under Grants RyC2020-030647-I and RYC-2015-17459, respectively. This research has received funding from PIE-20223AT003 of CSIC., Peer reviewed

© 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)., Mountain forests affect spatial and temporal variability of snow processes through snow interception and by modifying the energy balance of snowpack. The high sensitivity of snow cover to seasonal temperatures in mid–latitude mountains is well known and is of particular interest with regard to a future warmer climate. The snowpack in the Pyrenees is expected to be the most impacted by climate change in the Mediterranean mountains, where future climate trends project rising temperatures and decreasing precipitation. This study analyzes how changes in temperature and precipitation can affect current forest–snow interactions in four forests, located near each other but under contrasting topographic settings, in the Spanish Pyrenees. This understanding will allow us to anticipate the future hydrological responses of Pyrenean forested mountain basins. The research was accomplished by performing a sensitivity analysis using simulations from the Cold Regions Hydrological Model (CRHM) and by comparing forest canopy sites (F) vs. openings (O). The CRHM platform focuses on the incorporation of physically based descriptions of snow–dominated regions hydrological processes. It was found that forest cover induced different snowpack sensibility to climatic change conditions in the studied forests. Delayed onset of snow accumulation (F: 13 days·°C−1; O: 5 days·°C−1) and reduced snowpack duration (F: 28 %·°C−1; O: 23 %·°C−1) under warmer temperatures were more intense in areas beneath the forest canopy compared to openings. A lower annual peak of snow water equivalent (SWE) (F: 81 mm·°C−1; O: 129 mm·°C−1), earlier melt-out date (F: 8 days·°C−1; O: 10 days·°C−1) and slower melting rates (F: 0.4 mm·day−1·°C−1; O: 0.5 mm·day−1·°C−1) with increasing temperatures were more intense in forest openings. The forest–driven reduction in snowpack duration (40%) was significantly enhanced with warming (10% per °C). Lower precipitation (20% precipitation reduction) could increase the response of this forest effect to warming (32%), while higher precipitation (20% precipitation increment) could reduce it (−26%). There was relevant topographic variability in the forest−snow interactions in response to climate change among the study stands, despite their proximity., This study was supported by the projects: “Bosque, nieve y recursos hídricos en el Pirineo ante el cambio global” funded by Fundación Iberdrola, CGL2014-52599-P (IBERNIEVE) and CGL2017-82216-R (HIDROIBERNIEVE) funded by the Spanish Ministry of Economy and Competitiveness. ASV was supported by a pre–doctoral University Professor Training grant [FPU16/00902] funded by the Spanish Ministry of Education, Culture and Sports. JJC acknowledges funding by project RTI2018-096884-B-C31 (Spanish Ministry of Economy and Competitiveness)., Peer reviewed

© 2022 The Authors. Published by Elsevier GmbH. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/), Females of woody dioecious species usually expend more resources on reproduction than males. Therefore, it is expected that females incur greater costs of reproduction than males, and, as a result, trade-offs between reproduction and growth should emerge. The aim of this study is to test those hypotheses by analyzing the differences between genders regarding radial growth (basal area increment) and wood carbon isotope composition (δ13C), a proxy of water-use efficiency. We compared these two variables in males and females of four dioecious tree species inhabiting drought-prone Mediterranean sites in Spain (Pistacia terebinthus, Ilex aquifolium, Juniperus thurifera and Ailanthus altissima). We analyzed the influence of sex on the radial growth patterns throughout the tree life considering the growth stage of individuals, the differences in the response of genders to climate variables (air temperature, precipitation and drought severity), and the δ13C during a severe drought period. One site was studied for each species and 21–33 trees per species were sampled in each site. No differences in growth were found between genders for any of the four species throughout their life span. No significant interactions between gender and precipitation were found, although A. altissima males were more responsive to summer (June-July) temperature. No differences in δ13C were found between genders excepting for P. terebinthus, indicating that the males of this species show a less efficient water use during drought events than the females. These results do not support the broad assumption that females of woody dioecious plants show lower growth and are less water-use efficient than males or that they respond differently to precipitation variability, except for P. terebinthus during drought events. Further analyses could be performed in other dioecious species inhabiting seasonally dry regions to confirm or reject our conclusions., This work was supported by the Spanish Ministry of Science, Innovation and Universities [Grant no. RTI2018-096884-B-C31]., Peer reviewed

© 2022 The Author(s). Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/., Drought-induced forest dieback can lead to a tipping point in community dominance, but the coupled response at the tree and stand-level response has not been properly addressed. New spatially and temporally integrated monitoring approaches that target different biological organization levels are needed. Here, we compared the temporal responses of dendrochronological and spectral indices from 1984 to 2020 at both tree and stand levels, respectively, of a drought-prone Mediterranean Pinus pinea forest currently suffering strong dieback. We test the influence of climate on temporal patterns of tree radial growth, greenness and wetness spectral indices; and we address the influence of major drought episodes on resilience metrics. Tree-ring data and spectral indices followed different spatio-temporal patterns over the study period (1984–2020). Combined information from tree growth and spectral trajectories suggests that a reduction in tree density during the mid-1990s could have promoted tree growth and reduced dieback risk. Additionally, over the last decade, extreme and recurrent droughts have resulted in crown defoliation greater than 40% in most plots since 2019. We found that tree growth and the greenness spectral index were positively related to annual precipitation, while the wetness index was positively related to mean annual temperature. The response to drought, however, was stronger for tree growth than for spectral indices. Our study demonstrates the value of long-term retrospective multiscale analyses including tree and stand-level scales to disentangle mechanisms triggering and driving forest dieback., D M-F is supported by a “Juan de la Cierva Formación” post-doctoral fellow (FJC2018-037870-I) from the Spanish Ministry of Science and Innovation and AV-S by the Ministry of Universities through a FPU doctoral fellowship (FPU17/03260). We acknowledge support from grants "Data Driven Models of Forest Drought Vulnerability and Resilience across spatial and temporal Scales: Application to the Spanish Climate Change Adaptation Strategy" (DARE: RTI2018-096884-B-C32) and FORMAL (RTI2018-096884-B-C31) from the Spanish Ministry of Science, Innovation and Universities, Spain. We also thank the support of the Community of Madrid Region under the framework of the multi-year Agreement with the University of Alcalá (Stimulus to Excellence for Permanent University Professors, EPU-INV/2020/010) and the University of Alcalá “Ayudas para la realización de Proyectos para potenciar la Creación y Consolidación de Grupos de Investigación.” E.R.L. was funded by a UKRI Future Leaders Fellowship (MR/T019832/1)., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature., Peer reviewed

Tree-ring data has been widely used to inform about tree growth responses to drought at the individual scale, but less is known about how tree growth sensitivity to drought scales up driving changes in forest dynamics. Here, we related tree-ring growth chronologies and stand-level forest changes in basal area from two independent data sets to test if tree-ring responses to drought match stand forest dynamics (stand basal area growth, ingrowth, and mortality). We assessed if tree growth and changes in forest basal area covary as a function of spatial scale and tree taxa (gymnosperm or angiosperm). To this end, we compared a tree-ring network with stand data from the Spanish National Forest Inventory. We focused on the cumulative impact of drought on tree growth and demography in the period 1981–2005. Drought years were identified by the Standardized Precipitation Evapotranspiration Index, and their impacts on tree growth by quantifying tree-ring width reductions. We hypothesized that forests with greater drought impacts on tree growth will also show reduced stand basal area growth and ingrowth and enhanced mortality. This is expected to occur in forests dominated by gymnosperms on drought-prone regions. Cumulative growth reductions during dry years were higher in forests dominated by gymnosperms and presented a greater magnitude and spatial autocorrelation than for angiosperms. Cumulative drought-induced tree growth reductions and changes in forest basal area were related, but initial stand density and basal area were the main factors driving changes in basal area. In drought-prone gymnosperm forests, we observed that sites with greater growth reductions had lower stand basal area growth and greater mortality. Consequently, stand basal area, forest growth, and ingrowth in regions with large drought impacts was significantly lower than in regions less impacted by drought. Tree growth sensitivity to drought can be used as a predictor of gymnosperm demographic rates in terms of stand basal area growth and ingrowth at regional scales, but further studies may try to disentangle how initial stand density modulates such relationships. Drought-induced growth reductions and their cumulative impacts have strong potential to be used as early-warning indicators of regional forest vulnerability., This study was financially supported by Xunta de Galicia, Grant/Award Number PGIDIT06PXIB502262PR, GRC GI-1809; INIA, Grant/Award Number RTA2006-00117; CANOPEE, 2014-2020-FEDER funds, Spanish Science Ministry RTI2018-096884-B-C31, RTI2018-096884-B-C33, AGL2017-83828-C2-2R, RTI2018-096884-B-C3,1 and RTI2018-096884-B-C32 projects. Gabriel Sangüesa-Barreda was supported by a “Juan de la Cierva-Formación” grant from MINECO (FJCI 2016-30121). Antonio Gazol and Paloma Ruiz-Benito were supported by a project “2018 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation.” Ana-Maria Hereş was supported by the project PN-III-P1-1.1-TE-2019-1099 financed by the Romanian Ministry of Education and Research through UEFISCDI. Raúl Sánchez-Salguero was supported by VULBOS project (UPO-1263216, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020). Paloma Ruiz-Benito was supported by the Community of Madrid Region under the framework of the multi-year Agreement with the University of Alcalá (Stimulus to Excellence for Permanent University Professors, EPU-INV/2020/010) and the University of Alcalá “Ayudas para la realización de Proyectos para potenciar la Creación y Consolidación de Grupos de Investigación.” Andrea Hevia was supported by PinCaR project (UHU-1266324, FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimiento, Empresas y Universidad 2014-2020)., Peer reviewed

Diplodia shoot blight is an emergent forest disease in Europe caused by Diplodia sapinea. The short-term impacts of the pathogen on tree physiology are well known, but its capacity to cause mortality has been poorly documented.

We compared the survival of four pine species affected by Diplodia shoot blight following a hailstorm: Pinus sylvestris, P. nigra, P. pinea and P. halepensis. In the case of P. sylvestris, survival in the hail-affected sites was compared with survival in other sites affected by Diplodia shoot blight with no hailstorm records. Mortality and crown condition were recorded over two years. Dendrochronological analyses were conducted to assess growth responses to drought and to test the influence of radial growth before the outbreak of Diplodia shoot blight on survival. The endophytic community, as well as the abundance of D. sapinea, was quantified by metabarcoding and qPCR respectively, and were correlated with crown damage.

Crown damage was the best predictor of mortality across species. Pinus sylvestris experienced a much higher rate of mortality than P. nigra, P. pinea and P. halepensis. Two years after the outbreak, P. halepensis was the only species that could recover crown condition. Mortality was found to be unrelated to radial growth prior the outbreak. Drought responses did not correlate with mortality differences across pine species or sites. In the case of P. sylvestris, mortality was initially higher amongst diseased trees in areas affected by hailstorms than in sites not affected by hailstorms, however it tended to equalise after two years. Amongst P. sylvestris trees, crown damage correlated with a higher abundance of the pathogen. Signs of competition amongst endophytes were observed between non-defoliated and defoliated Scots pine trees following hailstorms.

Our study shows that D. sapinea can cause a significant mortality to P. sylvestris. The legacy effects of crown damage can last for at least two years after an outbreak. During this time, crown damage is a good predictor of survival, and can help managers decide which trees remove after an outbreak., The authors would like to acknowledge the financial support from the Barcelona Provincial Council (Diputació de Barcelona). J.O. was supported by the “Ramón y Cajal” fellowship RYC-2015-17459 from the Spanish Ministry of Science, Innovation and Universities. J.J.C. acknowledges funding by project FORMAL (RTI2018-096884-B-C31) from the Spanish Ministry of Science, Innovation and Universities., Peer reviewed

© 2022 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)., Trees grow at night, when the vapor pressure deficit (VPD) is low enough. Therefore, intra-annual density fluctuations (IADFs) should be formed when the VPD drops below a certain threshold. This idea is tested by assessing climate-latewood IADF relationships in six conifer species under Mediterranean climate conditions. Hourly climate and dendrometer data were analyzed for years with elevated IADF production in two species (Pinus halepensis, Juniperus thurifera). Lastly, climate–growth relationships were evaluated in two drought-prone sites to assess the relative role of minimum vs. maximum temperatures as growth drivers. Latewood IADF production was positively related to growth rate. IADFs were more abundant when monthly or 10-day long precipitation was high in the late growing season (August and September). According to dendrometer data, growth mainly occurred in early night (20–2 h) and early morning (6–8 h). This growth window corresponded to rainy periods with VPD below a minimum threshold associated with summer storms. Latewood IADFs are produced in response to these wet late-summer conditions, which could be related to bimodal growth. These associations are in line with correlations showing that high minimum (night) rather than maximum (day) temperatures reduce growth. This last idea should be further checked in drought-prone forests using global tree-ring databases., This research was funded by the SPANISH MINISTRY OF SCIENCE, INNOVATION AND UNIVERSITIES, grant number RTI2018-096884-B-C31., Peer reviewed

datasheet.xlsx

Data used in the analyses, consists on two sheets:
- boxplotindices: data with stability, synchrony and richness values for each plot or community, the approach used to calculate each index (long-term or year-to-year), and the treatment applied in each plot (control or fertilized).

- matrixalldatacom: data used to carry out the analyses at the community level. For each community it is given: the number of the plot or community, stability, synchrony, richness, functional composition and diversity of the five traits studied, and treatment (control or fertilized). For each of these variables there are two columns, one with the variable calculated using the long-term approach (named "longterm_" or "cum_") and the other one for the variable calculated using the year-to-year approach (named "yeartoyear_" or "mean_").

- matrixalldataspp: data used to carry out the analyses at the species level. For each species it is given: species name, long-term and year-to-year stability, species values for the five traits studied, and treatment (control or fertilized). Missing values are indicated by NAs., Understanding the mechanisms underlying community stability has become an urgent need in order to protect ecosystems from global change and resulting biodiversity loss. While community stability can be influenced by richness, synchrony in annual fluctuations of species, species stability and functional traits, the relative contributions of these drivers to stability are still unclear. In semi-natural grasslands, land-use changes such as fertilization might affect stability by decreasing richness and influencing year-to-year fluctuations. In addition, they can promote long-term directional trends, shifting community composition and influencing grassland maintenance. Thus, it is important to consider how species and community stability vary year-to-year but also in the long term.

Using a 14-year vegetation time series of a species-rich semi-natural Mediterranean grassland, we studied the relative importance of richness, synchrony, species stability and functional traits on community stability. To assess land-use change effects on stability, we applied a fertilization treatment. To distinguish stability patterns produced by year-to-year fluctuations from those caused by long-term trends, we compared the results obtained using a detrending approach from those without detrending.

Stability is influenced by richness, synchrony and functional traits. Fertilization decreases species and community stability by promoting long-term trends in species composition, favouring competitive species and decreasing richness. Studying stability at the community and species level, and accounting for the effect of trends is essential to understand stability and its drivers more comprehensively., [Methods] Study site and experimental design: In 2003, 12 plots of 15x5 m (hereafter called macro-plots) were established inside an area of 5500 m2. Half of the macro-plots (six) were used as control plots and half were fertilized with sewage sludge in a single event in 2003, applying manually to the soil surface 5 kg m-2 . The sludge came from a municipal urban wastewater treatment plant located in Tudela (Navarra, Spain), and it was sludge previously dried to 28% dry matter by centrifugation. To accurately assess vegetation changes, a 1x1 m permanent plot was placed in the centre of each macro-plot. Every year for 14 consecutive years (from 2004 to 2017), at the end of June, vegetation was sampled by R. Ibáñez, who identified and recorded every vascular plant species present in each of the permanent plots. The 1x1 m permanent plots were divided into 100 10x10 cm subplots to measure species abundance (frequency) by counting the number of 10x10 cm subplots in which the species was present (presence was recorded if shoots overlapped with the sampling unit/subplot, not according to rooted plants). Richness, synchrony and stability measures: Species richness in each permanent plot was measured both as cumulative species richness, counting the number of species found at least once in a permanent plot during the 14 years of the study, and as mean species richness, averaging the number of species found in a permanent plot over the 14 years (Lepš et al., 2018). Community-level synchrony for each permanent plot was calculated using the log variance ratio index (“Logvar”), which is the log-transformation of the ratio of observed to expected variance (i.e. the ratio of variance of the total community abundance to the sum of variances of the abundance of each species; Lepš et al., 2018; Roscher et al., 2011). Stability at both the community and the species level was calculated as the inverse of the coefficient of variation (CV-1) across years of cumulative or individual species abundances in each permanent plot. In order to distinguish the patterns produced by long-term trends from those caused by year-to-year fluctuations, we also used the three-term local quadrat variance detrending method (T3; Hill, 1973), which consists in calculating the variance in three year time periods, to remove the effect of long-term trends both on synchrony and stability indices (Lepš, Götzenberger, et al., 2019). Thus, we calculated synchrony (log variance ratio) and stability (CV-1) indices using both the non-detrending (hereafter “long-term” synchrony and stability) and the T3-detrending approach (hereafter “year-to-year” synchrony and stability; for which the original variance used in the log variance ratio index or in the inverse of the coefficient of variation was replaced by the three-term local-quadrat variance) (Valencia, de Bello, Lepš, et al., 2020). All synchrony and stability indices were calculated using the calc_sync function of the package “tempo” in R (Lepš, Götzenberger, et al., 2019). Plant functional traits and indices: We obtained data for five functional traits (plant height, Leaf Dry Matter Content or LDMC, Specific Leaf Area or SLA, Leaf Area or LA and Seed Mass or SM) for most of the species present in the 1x1 m permanent plots (data available for 98%, 78%, 84%, 98% and 85% of the species, respectively). Trait data were collected in-situ. Although the number of individuals measured for each trait varied, traits were measured following the protocols provided by Cornelissen et al. (2003). Missing data were obtained from BROT, a trait database for Mediterranean Basin species (Tavşanoğlu & Pausas, 2018), or from TRY database (Kattge et al., 2020). Mean trait values and abundance data for each species were used to calculate community functional composition and functional diversity for the five traits studied. Functional composition was measured as the Community Weighted Mean (CWM; Garnier et al., 2004) and functional diversity as the Rao Quadratic Index (Rao, 1982), which is the sum of pairwise functional distances between species weighted by relative abundance (Mouchet et al., 2010). To calculate these indices, we used the function dbFD of the “FD” package in R (Laliberté & Legendre, 2010; Laliberté et al., 2014). Data analysis: To study how fertilization influenced stability, synchrony and species richness at the community level, and to test if the values displayed by these indices and their response to fertilization changed depending on the approach used to calculate them (e.g. long-term or year-to-year), we carried out three multiple linear regression models using as response variables the stability, synchrony or species richness index in each plot, respectively. As explanatory variables we used the treatment applied in each plot (i.e. control or fertilized), the approach used to calculate the index (i.e. long-term or year-to-year stability and synchrony, and cumulative or mean species richness), and the interaction between both. In order to discover the main drivers of community stability, we used different linear regression models to test for relationships between community stability (long-term and year-to-year) and synchrony, richness, functional composition and diversity of the five traits studied and treatment. The explanatory variables were calculated in different ways depending on if we studied long-term or year-to-year stability, so that the variables would as well reflect “accumulated” or “yearly” values. For long-term stability we used long-term synchrony and cumulative species richness, and the functional composition and diversity indices were calculated using the cumulative abundance of each species across all years. By contrast, for year-to-year stability we used year-to-year synchrony and mean species richness across years, and the functional composition and diversity were calculated separately for each plot and year and then averaged across all years. This way, the first type of models was more focused on detecting processes acting across years and promoting trends, while the second type was focused on year-to-year processes. We build linear regression models by first running simple regression models for each explanatory variable and then applied multiple regression models with synchrony, richness, treatment and the functional indices selected as significant or marginally significant in the simple models. We then studied stability at the species level. Species stability was averaged over control and over fertilized plots. As we found some extreme values corresponding to highly stable species (Brachypodium retusum (Pers.) P.Beauv. and Aphyllanthes monspeliensis L.), we log transformed average species stability. We tested for relationships between log-transformed species stability (long-term and year-to-year) and the five functional traits studied. We first used simple models for each trait and when a certain trait was significant we did multiple models using trait, treatment and the interaction between both as explanatory variables. On the other hand, we also studied how fertilization influenced species stability, checking if results changed when using the long-term or year-to-year approach. We calculated the Pearson’s correlation coefficient and applied a paired t-test to test for differences in species stability between control and fertilized plots and between the long-term and year-to-year approach. All analyses were carried out with the lm, cor.test and t.test functions in R software (v. 4.0.3; R Core Team, 2020)., Fundación Caja Navarra, Award: Ref. 10833 (Programa “Tú Eliges, Tú Decides”), University of Navarra, Award: Project “Biodiversity Data Analytics and Environmental Quality”, University of Navarra, Award: Project “Red de Observatorios de la Biodiversidad de Navarra (ROBIN)”, Departamento de Educación, Award: Ayudas predoctorales para la realización de programas de doctorado de interés para Navarra; Plan de Formación y de I+D 2018, Ministerio de Ciencia e Innovación, Award: Ref. RTI2018-096884-B-C31 (Project FORMAL), Czech Academy of Sciences, Award: No. RVO 67985939, Peer reviewed

indicescom.R: calculation of richness, synchrony and stability indices at the community level.

functionalindicescom.R: calculation of functional composition (Community Weighted Mean) and diversity (Rao) for the five traits studied (plant height, Leaf Dry Matter Content, Specific Leaf Area, Leaf Area, Seed Mass), at the community level.

spstabilityindices.R: calculation of stability indices at the species level.

models_boxplots.R: R script for multiple linear regression models analysing the relationship between richness, synchrony or stability values and the approach used (long-term or year-to-year), treatment (control or fertilized) and the interaction between approach and treatment.

models_stability_communitylevel.R: R script for simple and multiple linear regression models analysing the drivers of long-term and year-to-year community stability.

SEMs.R: R script for Piecewise Structural Equation Models analysing the relationships between long-term and year-to-year community stability and their drivers.

models_stability_splevel.R: R script for simple and multiple linear regression models analysing the relationship between long-term and year-to-year species stability and functional traits.

spstability.R: R script for Pearson's correlations and paired t-tests analysing the effects of treatment and long-term trends on species stability., Understanding the mechanisms underlying community stability has become an urgent need in order to protect ecosystems from global change and resulting biodiversity loss. While community stability can be influenced by richness, synchrony in annual fluctuations of species, species stability and functional traits, the relative contributions of these drivers to stability are still unclear. In semi-natural grasslands, land-use changes such as fertilization might affect stability by decreasing richness and influencing year-to-year fluctuations. In addition, they can promote long-term directional trends, shifting community composition and influencing grassland maintenance. Thus, it is important to consider how species and community stability vary year-to-year but also in the long term.

Using a 14-year vegetation time series of a species-rich semi-natural Mediterranean grassland, we studied the relative importance of richness, synchrony, species stability and functional traits on community stability. To assess land-use change effects on stability, we applied a fertilization treatment. To distinguish stability patterns produced by year-to-year fluctuations from those caused by long-term trends, we compared the results obtained using a detrending approach from those without detrending.

Stability is influenced by richness, synchrony and functional traits. Fertilization decreases species and community stability by promoting long-term trends in species composition, favouring competitive species and decreasing richness. Studying stability at the community and species level, and accounting for the effect of trends is essential to understand stability and its drivers more comprehensively., Fundación Caja Navarra Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100006671
Award Number: Ref. 10833 (Programa "Tú Eliges, Tú Decides"), Universidad de Navarra Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100004435
Award Number: Project "Biodiversity Data Analytics and Environmental Quality", Universidad de Navarra Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100004435
Award Number: Project "Red de Observatorios de la Biodiversidad de Navarra (ROBIN)", Departamento de Educación, Gobierno de Navarra Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100003425
Award Number: Ayudas predoctorales para la realización de programas de doctorado de interés para Navarra; Plan de Formación y de I+D 2018, Ministerio de Ciencia, Innovación y Universidades Crossref Funder Registry ID: http://dx.doi.org/10.13039/100014440
Award Number: Ref. RTI2018-096884-B-C31 (Project FORMAL), Czech Academy of Sciences Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100004240
Award Number: No. RVO 67985939, Peer reviewed

Plants require a number of essential elements in different proportions for ensuring their growth and development. The elemental concentrations in leaves reflect the functions and adaptations of plants under specific environmental conditions. However, less is known about how the spectrum of leaf elements associated with resource acquisition, photosynthesis and growth regulates forest biomass along broad elevational gradients. We examined the influence of leaf element distribution and diversity on forest biomass by analyzing ten elements (C, N, P, K, Ca, Mg, Zn, Fe, Cu, and Mn) in tree communities situated every 100 meters along an extensive elevation gradient, ranging from the tropical forest (80 meters above sea level) to the alpine treeline (4200 meters above sea level) in the Kangchenjunga Landscape in eastern Nepal Himalayas. We calculated community-weighted averages (reflecting dominant traits governing biomass, i.e., mass-ratio effect) and functional divergence (reflecting increased trait variety, i.e., complementarity effect) for leaf elements in a total of 1,859 trees representing 116 species. An increasing mass-ratio effect and decreasing complementarity in leaf elements enhance forest biomass accumulation. A combination of elements together with elevation explains biomass (52.2% of the variance) better than individual elemental trait diversity (0.05% to 21% of the variance). Elevation modulates trait diversity among plant species in biomass accumulation. Complementarity promotes biomass at lower elevations, but reduces biomass at higher elevations, demonstrating an interaction between elevation and complementarity. The interaction between elevation and mass-ratio effect produces heterogeneous effects on biomass along the elevation gradient. Our research indicates that biomass accumulation can be disproportionately affected by elevation due to interactions among trait diversities across vegetation zones. While higher trait variation enhances the adaptation of species to environmental changes, it reduces biomass accumulation, especially at higher elevations., This study was supported by the National Natural Science Foundation of China (Grant No. 42030508) and the Second Tibetan Plateau Scientific Expedition and Research Program (Grant No. 2019QZKK0301). Nita Dyola was supported by CAS-TWAS President’s Fellowship Program for International Ph.D. students. Josep Peñuelas was supported by Spanish Government (Grant Nos. PID2019-110521GB-I00 and TED2021-132627B-I00), the Catalan Government (Grant No. SGR 2017-1005) and the Fundación “Ramón Areces” (Grant No. CIV-P20A6621). J. Julio Camarero was supported by the Spanish Government (Grant No. RTI2018-096884-B-C31). The Department of National Parks and Wildlife Conservation, Government of Nepal, is especially acknowledged for granting research permission., Peer reviewed

<p>R scripts showing how to use climwin package with tree-ring width and anatomy chronologies. The databases needed to use the scripts are included.</p>
<p></p>
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<p>FILES </p>
<p>--------------------------</p>
<p> </p>
<p>1. climwin with dendro and anatomy.R</p>
<p></p>
<p>R script in which climwin is used to study the growth/anatomy-climate relationships of 5 species with weekly time resolution.</p>
<p></p>
<p>2. climwin with the river flow.R</p>
<p></p>
<p>R script in which climwin is used to study the growth-river flows relationships of 2 sites with monthly time resolution. </p>
<p></p>
<p>3. Pinus sylvestris model.R</p>
<p></p>
<p>R script in which climwin is used to fit a multiple linear regression.</p>
<p></p>
<p>4. RingWidths.csv</p>
<p></p>
<p>Database of detrended growths and anatomical variables needed to run the R scripts. </p>
<p></p>
<p>Abbreviations:</p>
<p>LA - lumen area </p>
<p>CWT - cell wall thickness</p>
<p>ew - earlywood</p>
<p>lw - latewood</p>
<p>Ps - Pinus sylvestris (Corbalán site)</p>
<p>Aa - Abies alba (Paco Ezpela site)</p>
<p>VA1 - Valdelinares (Pinus uncinata)</p>
<p>AL - Alcalá de la Selva (Pinus sylvestris)</p>
<p>CO - Olmedilla (Pinus nigra)</p>
<p>AC - Alto de Cabra (Pinus pinaster)</p>
<p>VH - Valbona (Pinus halepensis)</p>
<p></p>
<p>5. climate.rds</p>
<p></p>
<p>Database of climate needed to run the R scripts.</p>
<p></p>
<p>Abbreviations:</p>
<p>T - Temperature</p>
<p>Tmax - Maximum temperature</p>
<p>Tmin - Minimum temperature</p>
<p>P - Precipitation</p>
<p>spei - Standardized Evapotranspiration Precipitation Index using a range of time scales (1, 3, 6, 9, 12, 24, 36 and 48 months) over which water deficits and surplus accumulate are considered.</p>
<p></p>
<p>6. Fraxinus.csv</p>
<p></p>
<p>Database of detrended growths of Fraxinus needed to run the R scripts.</p>
<p></p>
<p>7. River flow.csv</p>
<p></p>
<p>Database of river flow needed to run the R scripts.</p>
<p></p>
<p>8. readme.txt</p>
<p></p>
<p>txt file explaining the details of the data.</p>
<p> </p>

Forest dieback is manifested as widespread loss of tree vigor, growth decline and high mortality rates. Forest dieback is becoming increasingly frequent and extended, particularly in drought-prone regions. This is the case of the south-western Spanish Pyrenees, where keystone species such as Silver fir reach their xeric and southern distribution limits. While dieback of this species has been widely documented in this area, we still lack methodologies to forecast the vulnerability of these forests in response to increasing drought stress so as to anticipate their potential dieback in the future. Here we study multiple features of Silver fir forests and trees to evaluate whether previous growth rates and their growth trends are valid predictors of forest dieback. Further, we validate our methodology revisiting two Silver fir sites sampled two decades ago. The defoliation degree was strongly related with radial growth, and growth trends differed between moderately to highly defoliated trees and non-defoliated trees. Forests showing dieback, i.e., those in which 25% of the sampled trees showed defoliation > 50%, were located at low elevation and received less rainfall in summer than forests showing no dieback. Trees showing high defoliation presented lower growth rates than non-defoliated trees. Moreover, we ratified that defoliation has increased considerably over the last two decades in one of the two revisited sites, but we were unable to accurately forecast growth trends in both sites, particularly in the site not showing dieback. The retrospective assessment of growth rates and trends offers valuable information on the vulnerability of Silver fir trees to drought. However, we are still far from being able to forecast the vulnerability of Silver fir forests to increasing drought. A systematic monitoring of growth across a wide tree-ring network of sites might provide valuable information to advance in this direction.

Global climate change is expected to further raise the frequency and severity of extreme events, such as droughts. The effects of extreme droughts on trees are difficult to disentangle given the inherent complexity of drought events (frequency, severity, duration, and timing during the growing season). Besides, drought effects might be modulated by trees’ phenotypic variability, which is, in turn, affected by long-term local selective pressures and management legacies. Here we investigated the magnitude and the temporal changes of tree-level resilience (i.e., resistance, recovery, and resilience) to extreme droughts. Moreover, we assessed the tree-, site-, and drought-related factors and their interactions driving the tree-level resilience to extreme droughts. We used a tree-ring network of the widely distributed Scots pine (Pinus sylvestris) along a 2, 800 km latitudinal gradient from southern Spain to northern Germany. We found that the resilience to extreme drought decreased in mid-elevation and low productivity sites from 1980–1999 to 2000–2011 likely due to more frequent and severe droughts in the later period. Our study showed that the impact of drought on tree-level resilience was not dependent on its latitudinal location, but rather on the type of sites trees were growing at and on their growth performances (i.e., magnitude and variability of growth) during the predrought period. We found significant interactive effects between drought duration and tree growth prior to drought, suggesting that Scots pine trees with higher magnitude and variability of growth in the long term are more vulnerable to long and severe droughts. Moreover, our results indicate that Scots pine trees that experienced more frequent droughts over the long-term were less resistant to extreme droughts. We, therefore, conclude that the physiological resilience to extreme droughts might be constrained by their growth prior to drought, and that more frequent and longer drought periods may overstrain their potential for acclimation.

Drought stress has induced dieback episodes affecting many forest types and tree species worldwide. However, there is scarce information regarding drought-triggered growth decline and canopy dieback in Mediterranean deciduous oaks. These species face summer drought but have to form new foliage every spring which can make them vulnerable to hotter and drier conditions during that season. Here, we investigated two stands dominated byQuercus frainettoTen. andQuercus canariensisWilld. and situated in southern Italy and Spain, respectively, showing drought-induced dieback since the 2000s. We analyzed how radial growth and its responses to climate differed between non-declining (ND) and declining (D) trees, showing different crown defoliation and coexisting in each stand by: (i) characterizing growth variability and its responsiveness to climate and drought through time, and (ii) simulating growth responses to soil moisture and temperature thresholds using the Vaganov-Shashkin VS-lite model. Our results show how growth responsiveness to climate and drought was higher in D trees for both oak species. Growth has become increasingly limited by warmer-drier climate and decreasing soil moisture availability since the 1990s. These conditions preceded growth drops in D trees indicating they were more vulnerable to warming and aridification trends. Extremely warm and dry conditions during the early growing season trigger dieback. Changes in the seasonal timing of water limitations caused contrasting effects on long-term growth trends of D trees after the 1980s inQ. frainettoand during the 1990s inQ. canariensis. Using growth models allows identifying early-warning signals of vulnerability, which can be compared with shifts in the growth responses to warmer and drier conditions. Our approach facilitates establishing drought-vulnerability thresholds by combining growth models with field records of dieback.