BUSCADOR RECOLECTA

<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>
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<p>FILES </p>
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<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>

Proyecto de investigación que busca conocer la importancia relativa del aumento de la espesura y del cambio climático en el decaimiento del crecimiento radial observado en los árboles de El Hayedo de Montejo.

DESCRIPCIÓN DE LOS DATOS

Crecimientos radiales de Fagus sylvatica, Quercus petraea y Quercus pyrenaica muestreados en El Hayedo de Montejo. Los crecimientos están medidos con una precisión de 0.01 mm. Los archivos están en formato txt pero ordenados según el formato rwl. La primera columna de los archivos de crecimientos es el código de los testigos de madera muestreados: los cuatro primeros caracteres indican la parcela (por ejemplo P086); el quinto carácter es 0 o B, indicando B que ese árbol es el segundo muestreado de esa especie en esa misma parcela (se muestreó un árbol por especie y parcela salvo en algunas parcelas donde se muestrearon más árboles para tener una muestra total de al menos 20 individuos por especie); el sexto carácter indica el número de testigo (se tomaron dos por árbol).

Perímetros en 2018 a 1´3 metros de altura en cm de aquellos árboles en los que se midieron los crecimientos. Al igual que los crecimientos, estos datos están ordenados por especie y parcela, indicando con la letra B el segundo árbol muestreado de una misma especie en una misma parcela.

Evolución de la competencia entre 1994 y 2015 del arbolado adyacente a los pies muestreados en área basimétrica (m2/ha) y tanto por uno de dicha área basimétrica que corresponde a cada una de las especies principales. Son datos de competencia estimados con geoestadística (ver apartado de metodología) a partir de datos reales obtenidos en inventarios realizados en 1994, 2005 y 2015.

ARCHIVOS

1. Crecimiento_radial_Q_petraea.txt

Archivo txt, ordenado según el formato rwl, con los crecimientos radiales de esta
especie en centésimas de milímetro.

2. Crecimiento_radial_Q_pyrenaica.txt

Archivo txt, ordenado según el formato rwl, con los crecimientos radiales de esta
especie en centésimas de milímetro.

3. Crecimiento_radial_F_sylvatica.txt

Archivo txt, ordenado según el formato rwl, con los crecimientos radiales de esta
especie en centésimas de milímetro.

4. Perimetros.csv

Archivo csv con los perímetros en cm obtenidos a una altura de 1´3 m en los mismos
árboles en los que se midieron los crecimientos.

5. Competencia.csv

Archivo csv con las estimaciones de la competencia del vecindario para el periodo
1994-2015 en las parcelas en las que se barrenaron los árboles.

3. readme.txt

Archivo txt explicando los detalles de los datos.

Many factors can influence tree growth over time such as different forest management practices, climate or tree-to-tree interactions, especially in mixed forests. We show in this work how the temporal growth patterns for
Scots pine and European beech depend on thinning intensity (0%, 20% and 40% extraction of basal area),
canopy type (pine-beech vs. pine patches), throughfall and their interactions. To fulfill this objective we
monitored radial growth of both species using band dendrometers during a 6-year long period including two
very dry years. Temporal growth patterns differed between both species. Whereas Scots pine showed two main
peaks of growth in May-June and October, European beech mainly grew from May to early September even
when throughfall was very limited. Effects of thinning on growth generally increased for both species during dry
periods both at the seasonal and annual scales. The treatment with 20% of thinning intensity was the most
effective at the annual scale for enhancing growth of both species. However, increases in growth due to thinning
were much higher in beech than in pine and lasted longer. Thinning effects on pine were higher in mixed canopy
than in pure canopy and appeared to be modulated by throughfall. Global differences in pine growth between
canopy types as a function of throughfall increased during the main growing season as beech canopy developed.
Growth of Scots pine, but not that of European beech, generally increased with throughfall which suggests that
pine might be more dependent for its growth on water from the soil surface layer while beech would depend
more on water from deeper soil layers. Our findings have implications to select the most convenient thinning
treatments and canopy type under a potential climate change scenario characterized by warmer conditions, more
severe droughts and less throughfall., We are thankful to the Public University of Navarre for supporting
this study through a grant to fund Cardil's Postdoctoral studies. This
study has been carried out within the framework of the projects
AGL2006-08288 and AGL2009-11287 financed by Ministerio de
Economía y Competividad (Spain). Camarero JJ acknowledges the
support of the Fundiver Spanish project (Spanish Ministry of
Economy and Competitiveness, project CGL2015-69186-C2-1-R).

Tree mortality is a key factor influencing forest functions and dynamics, but our understanding of the mechanisms leading to mortality and the associated changes in tree growth rates are still limited. We compiled a new pan-continental tree-ring width database from sites where both dead and living trees were sampled (2970 dead and 4224 living trees from 190 sites, including 36 species), and compared early and recent growth rates between trees that died and those that survived a given mortality event. We observed a decrease in radial growth before death in ca. 84% of the mortality events. The extent and duration of these reductions were highly variable (1-100 years in 96% of events) due to the complex interactions among study species and the source(s) of mortality. Strong and long-lasting declines were found for gymnosperms, shade- and drought-tolerant species, and trees that died from competition. Angiosperms and trees that died due to biotic attacks (especially bark-beetles) typically showed relatively small and short-term growth reductions. Our analysis did not highlight any universal trade-off between early growth and tree longevity within a species, although this result may also reflect high variability in sampling design among sites. The intersite and interspecific variability in growth patterns before mortality provides valuable information on the nature of the mortality process, which is consistent with our understanding of the physiological mechanisms leading to mortality. Abrupt changes in growth immediately before death can be associated with generalized hydraulic failure and/or bark-beetle attack, while long-term decrease in growth may be associated with a gradual decline in hydraulic performance coupled with depletion in carbon reserves. Our results imply that growth-based mortality algorithms may be a powerful tool for predicting gymnosperm mortality induced by chronic stress, but not necessarily so for angiosperms and in case of intense drought or bark-beetle outbreaks.

Severe droughts have the potential to reduce forest productivity and trigger tree mortality. Most trees face several drought events during their life and therefore resilience to dry conditions may be crucial to long-term survival. We assessed how growth resilience to severe droughts, including its components resistance and recovery, is related to the ability to survive future droughts by using a tree-ring database of surviving and now-dead trees from 118 sites (22 species, >3,500 trees). We found that, across the variety of regions and species sampled, trees that died during water shortages were less resilient to previous non-lethal droughts, relative to coexisting surviving trees of the same species. In angiosperms, drought-related mortality risk is associated with lower resistance (low capacity to reduce impact of the initial drought), while it is related to reduced recovery (low capacity to attain pre-drought growth rates) in gymnosperms. The different resilience strategies in these two taxonomic groups open new avenues to improve our understanding and prediction of drought-induced mortality.

The Popocatépetl volcano resumed its eruptive activity in 1994 and is still active. The largest eruption recorded during this new stage of activity occurred in December 2000. We traced the volcanic activity signal in tree-rings from Pinus hartwegii trees located in the north slope of the volcano, located at ∼3 km from the volcanic cone. Annually resolved tree-ring widths, elemental and stable δ13C and δ18O isotope composition were measured during the period 1989-2014 to study the effects of the volcanic activity on trees. Our results indicate a high increase in the concentration of metal elements (Co, Cr, Cu, Fe, Li, Mo, Ni, Pb, Rb, Sr, Ti, Zn) in tree rings following the major 2000 volcanic eruption, compared to the pre-eruption period from 1989 to 1993. Other chemical elements such as Al, K and S peaked 2 years later, in the 2003 tree ring, that matched with the formation of a very narrow ring that year. This sharp reduction of growth was probably driven by a combination of harsh climatic conditions (drought) with the lagged negative effects of the 2000 eruption. Carbon isotope discrimination (Δ13C) and δ18O increased from 1995 to 2006, suggesting reduced stomatal conductance, photosynthetic activity and water use efficiency due to the large dust veil covering the study zone. The variation of relevant elements (Ca, Mn) showing significant correlations with tree growth, Δ13C and δ18O can be attributed to the selective availability of elements following the soil acidification caused by the volcanic activity. Our findings suggest that the recent activity of the Popocatépetl might have increased tree vulnerability, as reflected in the sharp reduction of growth following the drought recorded 2 years after the large eruption of December 2000. Our results warn about the cumulative negative effects of volcanic activity and harsh climatic conditions on tree growth and functioning.

Despite the importance of species interaction in modulating the range shifts of plants, little is known about the responses of coexisting life forms to a warmer climate. Here, we combine long-term monitoring of cambial phenology in sympatric trees and shrubs at two treelines of the Tibetan Plateau, with a meta-analysis of ring-width series from 344 shrubs and 575 trees paired across 11 alpine treelines in the Northern Hemisphere. Under a spring warming of +1°C, xylem resumption advances by 2-4 days in trees, but delays by 3-8 days in shrubs. The divergent phenological response to warming was due to shrubs being 3.2 times more sensitive than trees to chilling accumulation. Warmer winters increased the thermal requirement for cambial reactivation in shrubs, leading to a delayed response to warmer springs. Our meta-analysis confirmed such a mechanism across continental scales. The warming-induced phenological mismatch may give a competitive advantage to trees over shrubs, which would provide a new explanation for increasing alpine treeline shifts under the context of climate change. Under warmer springs at the alpine treeline, growth reactivation is advanced in trees, but delayed in shrubs. This phenological mismatch creates a competitive edge for trees and offers a novel explanation for the dynamics of alpine treeline in the face of climate change.

Drought is one of the key natural hazards impacting net primary production and tree growth in forest ecosystems. Nonetheless, tree species show different responses to drought events, which make it difficult to adopt fixed tools for monitoring drought impacts under contrasting environmental and climatic conditions. In this study, we assess the response of forest growth and a satellite proxy of the net primary production (NPP) to drought in peninsular Spain and the Balearic Islands, a region characterized by complex climatological, topographical, and environmental characteristics. Herein, we employed three different indicators based on in situ measurements and satellite image-derived vegetation information (i.e., tree-ring width, maximum annual greenness, and an indicator of NPP). We used seven different climate drought indices to assess drought impacts on the tree variables analyzed. The selected drought indices include four versions of the Palmer Drought Severity Index (PDSI, Palmer Hydrological Drought Index (PHDI), Z-index, and Palmer Modified Drought Index (PMDI)) and three multi-scalar indices (Standardized Precipitation Evapotranspiration Index (SPEI), Standardized Precipitation Index (SPI), and Standardized Precipitation Drought Index (SPDI)). Our results suggest that—irrespective of drought index and tree species—tree-ring width shows a stronger response to interannual variability of drought, compared to the greenness and the NPP. In comparison to other drought indices (e.g., PDSI), and our results demonstrate that multi-scalar drought indices (e.g., SPI, SPEI) are more advantageous in monitoring drought impacts on tree-ring growth, maximum greenness, and NPP. This finding suggests that multi-scalar indices are more appropriate for monitoring and modelling forest drought in peninsular Spain and the Balearic Islands.

1. Biotic stressors such as hemiparasites have a profound impact on forest functioning. However, predicting the future incidence of these stressors on forests remains challenging because climate-based distribution does not consider tree-hemiparasite interactions or the impacts of extreme climate events on stressors'' performance.
2. We use species distribution models (SDMs) and ecophysiological and demographic field data to assess whether climatic suitability is a proxy for the performance of the hemiparasite mistletoe (Viscum album) in two forests with contrasting climatic conditions. Two host tree species representing wet-cold (Scots pine) and dry-warm (Aleppo pine) conditions were selected. We fitted SDMs based on climate variables, and measured different ecophysiological variables capturing cold- (photoinhibition) and drought tolerance (intrinsic water-use efficiency, iWUE). We also assessed demographic variables related to seed germination and establishment rates of mistletoe through a translocation experiment.
3. Species distribution models showed a high climatic suitability of mistletoe in both forests. Mistletoes living in the Scots pines site presented a higher cold tolerance, while those inhabiting the Aleppo pine site showed a higher iWUE. Seedlings coming from local seeds showed a lower mortality than seedlings coming from translocated seeds. Germination and seedling establishment showed temporal mismatches when comparing local and translocated seeds.
4. Synthesis. Habitat suitability predicted by SDMs based on climate data and field performance were related in this mistletoe species. However, ecophysiological and demographic variables indicated a lower fitness of mistletoe in the dry-warm site associated with drought stress. In conclusion, predicted climate suitability based on SDMs forecasts should be refined using field data on actual performance and considering plant-to-plant interactions and extreme climate events.

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.

Individual differences in the access to deep soil water pools may explain the differential damage among coexisting, conspecific trees as a consequence of drought-induced dieback. We addressed this issue by comparing the responses to a severe drought of three Mediterranean oak species with different drought tolerance, Quercus pubescens L. and Quercus frainetto Ten., mainly thriving at xeric and mesic sites, respectively, and Quercus cerris L., which dominates at intermediate sites. For each species, we compared coexisting declining (D) and non-declining (ND) trees. The stable isotope composition (d2H, d18O) of xylem and soil water was used to infer a differential use of soil water sources. We also measured tree size and radial growth to quantify the long-term divergence of wood production between D and ND trees and non-structural carbohydrates (NSCs) in sapwood to evaluate if D trees presented lower NSC values. The ND trees had access to deeper soil water than D trees except in Q. frainetto, as indicated by significantly more depleted xylem water values. However, a strong d2H offset between soil and xylem water isotopes observed in peak summer could suggest that both tree types were not physiologically active under extreme drought conditions. Alternative processes causing deuterium fractionation, however, could not be ruled out. Tree height and recent (last 15-25 years) growth rates in all species studied were lower in D than in ND trees by 22 and 44%, respectively. Lastly, there was not a consistent pattern of NSC sapwood concentration; in Q. pubescens, it was higher in ND trees while in Q. frainetto, the D trees were the ones exhibiting the higher NSC concentration. We conclude that the vulnerability to drought among conspecific Mediterranean oaks depends on the differential access to deep soil water pools, which may be related to differences in rooting depth, tree size and growth rate.

Key message: Competitive interactions change over time and their influence on tree growth is intensified during drought events in marginal Scots pine populations. Abstract: Competition is a key factor driving forest dynamics and stand structure during the course of stand development. Although the role neighbourhood competition on stand dynamics has received increasing attention, the response of competition to environmental fluctuations and stand development remains poorly explored. We evaluated changes in competition during stand development in a dry-edge Scots pine relict population located in Central Spain. Typically, tree-to-tree interactions have been investigated through static competition measurements, which usually lack the temporal variation associated to natural forest development and environmental conditions. Here, we assessed how individual and neighbourhood components of competition evolved along a 35-year period, and we related competition dynamics to population structure and drought levels. On six plots, 508 trees were mapped and diameters at breast height (DBH) were measured. Two increment cores were taken from target trees to derive basal area increment (BAI), and neighbourhood was reconstructed back to 1980. Results provide insights into inter-annual variability in competition effects and their role on tree radial growth depending on climatic conditions. From the year 2005 onwards, both individual and neighbourhood components of competition showed a decoupled pattern over time. This effect was particularly pronounced during the extreme drought in 2012, in which the individual component decreased, whereas the neighbourhood component increased. In addition, climatic variability modulated the competition effects during stand development. This approach of evaluating competition dynamics proves to be promising for studying forest stand development and the influence of climate impacts on tree populations subjected to xeric conditions.

As the global climate warms, increased aridity is expected to become a major determinant of forest productivity and tree growth. In gymnosperms, wood density quantified at seasonal to annual scales can be related to changes in tracheid lumen size due to alterations in soil water availability. In this way, minimum wood density (MND) has been shown to respond negatively to early growing-season precipitation in several conifers because dry conditions reduce tracheid lumen size and consequently increase MND. We investigated if this relationship between spring precipitation and MND applies to four conifer species (Abies alba, Pinus sylvestris, Pinus nigra, Juniperus thurifera) in NE Spain from mesic (A. alba, P. sylvestris) to xeric (P. nigra, J. thurifera) conditions. We further assessed how climate, precipitation, and drought-affected tree-ring width (TRW) and MND at several time scales to test if water shortage in spring increases MND and decreases TRW over time and seasonally. Lastly, we quantified the post-drought MND recovery. We found the strongest negative correlations between MND and spring precipitation in P. nigra followed by J. thurifera. In these two species, the associations between MND and 9-month long droughts peaked in early spring (P. nigra, r =-0.73; J. thurifera, r =-0.50). Juniperus thurifera presented a better post-drought recovery (decrease in MND), followed by P. nigra and P. sylvestris. We conclude that MND is a reliable and accurate proxy of drought severity during spring in conifers subjected to seasonal water shortage. MND can be used as an early-warning indicator of short- A nd long-term changes in the responses of trees to water shortage.

Drought is one of the key natural hazards impacting net primary production and tree growth in forest ecosystems. Nonetheless, tree species show different responses to drought events, which make it difficult to adopt fixed tools for monitoring drought impacts under contrasting environmental and climatic conditions. In this study, we assess the response of forest growth and a satellite proxy of the net primary production (NPP) to drought in peninsular Spain and the Balearic Islands, a region characterized by complex climatological, topographical, and environmental characteristics. Herein, we employed three different indicators based on in situ measurements and satellite image-derived vegetation information (i.e., tree-ring width, maximum annual greenness, and an indicator of NPP). We used seven different climate drought indices to assess drought impacts on the tree variables analyzed. The selected drought indices include four versions of the Palmer Drought Severity Index (PDSI, Palmer Hydrological Drought Index (PHDI), Z-index, and Palmer Modified Drought Index (PMDI)) and three multi-scalar indices (Standardized Precipitation Evapotranspiration Index (SPEI), Standardized Precipitation Index (SPI), and Standardized Precipitation Drought Index (SPDI)). Our results suggest that—irrespective of drought index and tree species—tree-ring width shows a stronger response to interannual variability of drought, compared to the greenness and the NPP. In comparison to other drought indices (e.g., PDSI), and our results demonstrate that multi-scalar drought indices (e.g., SPI, SPEI) are more advantageous in monitoring drought impacts on tree-ring growth, maximum greenness, and NPP. This finding suggests that multi-scalar indices are more appropriate for monitoring and modelling forest drought in peninsular Spain and the Balearic Islands

Climate change in the Mediterranean, associated with warmer temperatures andmore frequent droughts, is expected to impact forest productivity and the functioning of forests ecosystems as carbon reservoirs in the region. Climate warming can positively affect forest growth by extending the growing season, whereas increasing summer drought generally reduces forest productivity and may cause growth decline, trigger dieback, hamper regenera- tion, and increase mortality. Forest management could potentially counteract such negative effects by reducing stand density and thereby competition for water. The effectiveness of such interventions, however, has so far mostly been evaluated for short time periods at the tree and stand levels, which limits our confidence regarding the efficacy of thinning interventions over longer time scales under the complex interplay between climate, stand structure, and forest management. In this study, we use a century-long historical data set to assess the effects of climate and management on forest productivity. We consider rear-edge Scots pine (Pinus syl- vestris) populations covering continental and Mediterranean conditions along an altitudinal gradient in Central Spain. We use linear mixed-effects models to disentangle the effects of alti- tude, climate, and stand volume on forest growth and ingrowth (recruitment and young trees' growth). We find that warming tends to benefit these tree populations, warmer winter temperature has a significant positive effect on both forest growth and ingrowth, and the effect is more pronounced at low elevations. However, drought conditions severely reduce growth and
ingrowth, in particular when competition (stand volume) is high. We conclude that summer
droughts are the main threat to Scots pine populations in the region, and that a reduction of
stand volume can partially mitigate the negative impacts of more arid conditions. Mitigation
and adaptation measures could therefore manage stand structure to adopt for the anticipated impacts of climate change in Mediterranean forest ecosystems., Ministerio de Economía y Competitividad, Ministerio de Ciencia e Innovación, Universidad de Alcalá

Climate warming is significantly affecting the composition and function of forest ecosystems. However, the forest responses to climate change in sub-humid and temperate areas are understudied compared with cold and semi-arid areas. Here, we investigate the radial-growth responses of two subalpine conifer species along an elevational gradient located in the Qinling Mountains, a sub-humid and temperate area situated in central China. Three sites dominated by larch (<i>Larix chinensis</i> Beissn.) and two other sites dominated by fir (<i>Abies fargesii</i> Franch.) located at different elevations were sampled. <i>L. chinensis</i> at a higher elevation showed more common and stronger climatic signals than <i>A. fargesii</i> at a lower elevation. The radial growth of <i>L. chinensis</i> was limited by low pre-growing season temperatures and showed an increasing growth trend in the last few years. On the other hand, <i>A. fargesii</i> growth was limited by summer water shortage and it was characterized by a declining trend in the most recent decade. Consequently, <i>L. chinensis</i> would benefit from climate warming, whereas <i>A. fargesii</i> could be regarded as a vulnerable tree species to warming-induced drought stress., This work was funded by the National Natural Science Foundation of China (41601192 and 41525001),
and China Postdoctoral Science Foundation (2015M572591). J.J.C. thanks the support of the CGL2015-69186-C2-1-R
project (Spanish Ministry of Economy).

Treeline ecotones are considered early-warning monitors of the effects of climate warming
on terrestrial ecosystems, but it is still unclear how tree growth at treeline will track the forecasted temperature rise in these cold environments. Here, we address this issue by analysing and projecting growth responses to climate on two different cold-limited alpine treelines: Pinus uncinata Ram. in the Spanish Pyrenees and Larix sibirica Ledeb. in the Russian Polar Urals. We assess radial-growth changes as a function of tree age and long-term climate variability using dendrochronology and a process-based model of tree growth. Climate-growth relationships were compared considering young (age < 50 years) and old trees (age > 75 years) separately. Warm summer conditions enhanced radial growth, particularly after the 1980s, in the Polar Urals sites, whereas growth was positively related to warm spring and winter conditions in the Pyrenees sites. These associations were stronger in young than in old trees for both tree species and regions. Forecasted warm conditions are expected to enhance growth rates in both regions, while the growing season is forecasted to lengthen in the Pyrenees treelines, mostly in young trees. The observed age-related responses to temperature also depend on the forecasted warming rates. Although the temperature sensitivity is overall increasing for young trees, those responses seem more divergent, or even reversed, throughout the contrasting emission scenarios. The RCP 8.5 emission scenario corresponding to the most pronounced warming and drier conditions (+4.8 ◦C) could also amplify drought stress in young trees from the Pyrenees treelines. Our modelling approach provides accessible tools to evaluate functional thresholds for tree growth in treeline ecotones under warmer conditions., We are very grateful for several projects financed by “Organismo Autónomo de Parques Nacionales” (projects 12/2008 and 387/2011). This study was also supported by the following projects funded by the Spanish Ministry of Economy, Industry and Competitiveness: AMB95-0160, REN2002-04268-C02, CGL2011-26654, CGL2015-69186-C2-1-R (FunDiver), CGL2013-48843-C2-1-R (CoMo-ReAdapt); by the TreeClim ERA.Net RUS Pilot Joint Call for Collaborative S&T Projects (funded under the 7th European Framework Programme for Research and Development) and by the Russian Scientific Foundation under grant RSF-17-14-01112 in part connected with the Polar Urals data sampling and working with article text. RSS is supported by Spanish Ministry of Economy, Industry and Competitiveness Postdoctoral grant (IJCI-2015-25845, FEDER funds)., Peer reviewed

35 páginas, 6 figuras, 2 tablas.--This is a post-peer-review, pre-copyedit version of an article published in Forest Ecology and Management. The final authenticated version is available online at: https://doi.org/10.1016/j.foreco.2020.118625, Mixed forests are expected to be more productive and resilient against disturbances than pure forests. However, tree to tree interactions are complex and vary depending on tree characteristics and multiple site features including soil properties. Such complexity is not normally accounted for in studies of mixing effects on tree response to drought. Here, we evaluate if neighbourhood tree identity influence soil biotic and abiotic characteristics in three mature, mixed Silver fir (Abies alba) forests. Further, we investigate the relationships between radial growth response to drought, tree characteristics (growth rate, size and competition pressure), tree neighbourhood, and soil physico-chemical and biological properties. Patterns of covariation between tree size, competition pressure, soil microbial composition, and growth recovery after drought were observed among different neighbourhood types. Slow-growing, small Silver fir trees experiencing high competitive pressure were associated with higher proportions of Scots pine (Pinus sylvestris) in the neighbourhood, high soil C:N ratios, and showed a faster growth recovery after drought. A neighbourhood dominated by broadleaf species (mainly European beech, Fagus sylvatica) was associated with high biomass of arbuscular mycorrhizal fungi, and low biomass of Gram-positive bacteria and Eukaryote, together with lower tree growth recovery. Therefore, coexistence with other Silver fir, Scots pine or European beech trees is associated to different covariation patterns of tree, soil and drought performance variables of the target Silver fir trees. Finally, our study remarks that combining tree, soil and neighbour variables at individual level helps to understand patterns of tree growth and growth response to drought under different stand mixtures, We thank Michele Colangelo and Elena Granda for their help during fieldwork in Orússite. We also thank Elena La hoz and Virginia Gascón for their valuable task in laboratory analyses. We thank Manuel Pizarro for drawing Fig.1. XSM is supported by FPI predoctoral grant from the Spanish Ministry of Economy, Industry and Competitiveness (BES-2016-077676). This study was supported by the project FunDiver (CGL2015-69186-C2-1-R) funded by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO), Peer reviewed

Forest decline induced by climate change is a global phenomenon that affects many
tree species, mainly in drought-prone areas as the Mediterranean region. In southern
Italy, several oak species have shown decline symptoms and elevated mortality since
the 2000s due to drought stress. However, it remains to be answered whether decline
occurred alone or whether a pathogen was also involved. To this aim, we compared
two coexisting oak species in a forest located in southern Italy which are assumed to be
less (Quercus cerris) and more tolerant to drought (Quercus pubescens). We sampled
fifteen couples of neighboring declining (D) and non-declining (ND) trees of both species.
Wood cores were taken from all trees to perform dendrochronological analyses to detect
the decline onset and link it to potential climatic drivers. Carbon isotope ratios (d13C)
were analyzed in wood of the two vigor classes to compare their water-use efficiency.
Phytophthora presence was also assessed in soil samples from ten D-ND couples of
trees per species. The oak species most affected by drought-induced decline in terms
of leaf shedding and mortality was Q. cerris, i.e., the least tolerant to drought. In both
species, the D trees showed a reduced growth rate compared with ND trees from 2000
onward when drought and warming intensified. Q. pubescens showed higher growth
sensitivity to precipitation, temperature and drought than Q. cerris. This sensitivity to
climate was magnified in D trees whose growth decreased in response to warm and dry
conditions during the prior winter and the late summer. The Q. pubescens D trees were
more efficient in their water use than ND trees before the growth divergence between D
and ND trees amplified. In the studied area, Phytophthora quercina was isolated from
40% of the sampled trees, and tended to be more frequent amongst ND than amongst
D trees. Our data suggests that droughts and warm summer conditions triggered oak
decline. The high prevalence of P. quercina in the studied area warrants further study as
a potential predisposing factor., This research was supported by the project “Alarm of Forest Mortality in Southern Italy” (Gorgoglione Administration, Basilicata Region, Italy) and by the CGL2015-69186-C2-1-R project (Spanish Ministry of Science).

Individual differences in the access to deep soil water pools may explain the differential damage among coexisting, conspecific trees as a consequence of drought-induced dieback. We addressed this issue by comparing the responses to a severe drought of three Mediterranean oak species with different drought tolerance, Quercus pubescens L. and Quercus frainetto Ten., mainly thriving at xeric and mesic sites, respectively, and Quercus cerris L., which dominates at intermediate sites. For each species, we compared coexisting declining (D) and non-declining (ND) trees. The stable isotope composition (δ2H, δ18O) of xylem and soil water was used to infer a differential use of soil water sources. We also measured tree size and radial growth to quantify the long-term divergence of wood production between D and ND trees and non-structural carbohydrates (NSCs) in sapwood to evaluate if D trees presented lower NSC values. The ND trees had access to deeper soil water than D trees except in Q. frainetto, as indicated by significantly more depleted xylem water values. However, a strong δ2H offset between soil and xylem water isotopes observed in peak summer could suggest that both tree types were not physiologically active under extreme drought conditions. Alternative processes causing deuterium fractionation, however, could not be ruled out. Tree height and recent (last 15-25 years) growth rates in all species studied were lower in D than in ND trees by 22 and 44%, respectively. Lastly, there was not a consistent pattern of NSC sapwood concentration; in Q. pubescens, it was higher in ND trees while in Q. frainetto, the D trees were the ones exhibiting the higher NSC concentration. We conclude that the vulnerability to drought among conspecific Mediterranean oaks depends on the differential access to deep soil water pools, which may be related to differences in rooting depth, tree size and growth rate., This research was financially supported by the project OT4CLIMA (Italian Ministry of Education, University and Research (MIUR), Project N. ARS01_00405) ‘Advanced EO Technologies for studying climate change impacts on the environment’ and by the project ‘Alarm of forest mortality in Southern Italy’ (Gorgoglione Administration, Basilicata Region, Italy). M.C. was supported by the PhD program from the University of Basilicata (Italy). J.J.C. acknowledges funding by the project CGL2015-69186-C2-1-R project (Spanish Ministry of Economy). We acknowledge the E-OBS dataset from the EU-FP6 project UERRA (http://www.uerra.eu) and the data providers in the ECA&D project (https://www.ecad.eu).

Tracheids fulfil most wood functions in conifers
(mechanical support and water transport) and earlywood
tracheids account for most hydraulic conductivity within
the annual tree ring. Dry conditions during the early
growing season, when earlywood is formed, could lead to
the formation of narrow tracheid lumens and a dense earlywood.
Here, we assessed if there is a negative association
between minimum wood density and early growing-season
(spring) precipitation. Using dendrochronology, we studied
growth and density data at nine forest stands of three
Pinaceae species (Larix sibirica, Pinus nigra, and Pinus
sylvestris) widely distributed in three cool–dry Eurasian
regions from the forest-steppe (Russia, Mongolia) and Mediterranean (Spain) biomes. We measured for each
annual tree ring and the common 1950–2002 period the
following variables: earlywood and latewood width, and
minimum and maximum wood density. As expected, dry
early growing season (spring) conditions were associated
with low earlywood production but, most importantly, to
high minimum density in the three conifer species. The
associations between minimum density and spring precipitation
were stronger (r = -0.65) than those observed with
earlywood width (r = 0.57). We interpret the relationship
between spring water availability and high minimum density
as a drought-induced reduction in lumen diameter,
hydraulic conductivity, and growth. Consequently, forecasted
growing-season drier conditions would translate into
increased minimum wood density and reflect a reduction in
hydraulic conductivity, radial growth, and wood formation.
Given the case-study-like nature of this work, more
research on other cold–dry sites with additional conifer
species is needed to test if minimum wood density is a
robust proxy of early season water availability., We acknowledge the support of Spanish Ministry
of Economy Projects (Fundiver, CGL2015-69186-C2-1-R). Tree-ring density data were obtained and analysed under support of
Russian Science Foundation (Project 14-14-00295).

Insect outbreaks of increasing frequency and severity in forests are predicted due to climate change. Insect herbivory is known to promote physiological changes in forest trees. However, little is known about whether these plant phenotypic adjustments have cascading effects on tree microbial symbionts such as fungi in roots and foliage. We studied the impact of defoliation by the pine processionary moth in two infested Pinus nigra forests through a multilevel sampling of defoliated and non-defoliated trees. We measured tree growth, nutritional status and carbon allocation to chemical defenses. Simultaneously, we analyzed the putative impact of defoliation on the needle endophytes and on the soil fungal communities. Higher concentrations of chemical defenses were found in defoliated trees, likely as a response to defoliation; however, no differences in non-structural carbohydrate reserves were found. In parallel to the reductions in tree growth and changes in chemical defenses, we observed shifts in the composition of needle endophytic and soil fungal communities in defoliated trees. Defoliated trees consistently corresponded with a lower biomass of ectomycorrhizal fungi in both sites, and a higher alpha diversity and greater relative abundance of belowground saprotrophs and pathogens. However, ectomycorrhizal alpha diversity was similar between non-defoliated and defoliated trees. Specific needle endophytes in old needles were strongly associated with non-defoliated trees. The potential role of these endophytic fungi in pine resistance should be further investigated. Our study suggests that lower biomass of ectomycorrhizal fungi in defoliated trees might slow down tree recovery since fungal shifts might affect tree-mycorrhizal feedbacks and can potentially influence carbon and nitrogen cycling in forest soils., J.J.C. acknowledges the support of the CGL2015-69186-C2-1-R and RTI2018-096884-B-C31 projects (Spanish Ministry of Science), and L.S. and R.Z. acknowledge support from MCIU/AEI/FEDER/UE grants FUTURPIN AGL2015-68274-C3-2-R and RESILPINE RTI2018-094691-B-C33 and from Xunta de Galicia‐GAIN grant IN607A2016/013. J.O. and J.G.A. were supported by a Ramón y Cajal fellowship (RYC-2015-17459; RYC-2016-20528, respectively) and J.A.B. was supported by the Serra-Hunter Program-Generalitat de Catalunya.

Forest dieback and mortality events induced by drought stress are widely reported.
However, few studies have jointly examined the role played by drought on growth and mortality in
tree species inhabiting floodplain forests. Here, we focused on mortality events occurring since the
early 2000s on large areas in a floodplain forest located within the Ticino regional park in Northwest
Italy, where affected native (pedunculate oak, Quercus robur L.) and introduced tree species (black
locust, Robinia pseudoacacia L.) coexist. We related growth with climate data and drought severity to
discern if these species were similarly affected by drought. Then, we: (i) evaluated the presence of
pathogens of the genus Phytophthora in recently dead oak trees since this was the most affected species
and pathogens are often associated with oak decline cases; and (ii) compared xylem vessel diameter
and tree-ring C isotope discrimination ( 13C) to highlight differences in water-use strategies between
living and dead trees in both species. The radial growth of living and dead trees started diverging
in the 1970s, although only after warm-drought periods occurred during 1990s did this divergence
become significant. Growth of trees that died responded more negatively to drought than in the
case of living trees. Moreover, trees that died formed smaller xylem vessels in the past than living
trees and also showed more negative 13C values in both tree species, indicating a higher intrinsic
water-use efficiency in living than in dead trees. The pathogen Phytophthora cinnamomi Rands was
only detected in one recently dead tree, suggesting that it is unlikely that dead oaks were predisposed
to drought damage by the pathogen. We conclude that a climate shift from wet to warm-dry summer
conditions in the early 1990s triggered forest dieback and induced mortality in both tree species.
Temperate floodplain forests are susceptible to drought-induced dieback. The drought-sensitivity of
both species could lead to successional shifts driven by a reduction of N inputs through N-fixing by
black locust and the replacement of oak by drought-tolerant species., This research was funded by the projects “Convenzione Rotondella” (Rotondella Administration, Basilicata Region, Italy) and CGL2015-69186-C2-1-R project (Spanish Ministry of Economy). M.C. was supported by the PhD program from the course of Agricultural, Forest and Food Science at the University of Basilicata (Italy)

An improved understanding of how tree species will respond to warmer conditions and longer droughts requires comparing their responses across different environmental settings and considering a multi-proxy approach. We used several traits (tree-ring width, formation of intra-annual density fluctuations - IADFs, wood anatomy, Δ13C and δ18O records) to retrospectively quantify these responses in three conifers inhabiting drought-prone areas in northwestern Mexico. A fir species (Abies durangensis) was studied in a higher altitude and slightly rainier site and two pine species were sampled in a nearby, lower drier site (Pinus engelmannii, Pinus cembroides). Tree-ring-width indices (TRWi) of the studied species showed a very similar year-to-year variability likely indicating a common climatic signal. Wood anatomy analyses done over 3.5 million measured cells, showed that P. cembroides lumen area was much smaller than in the other two species and it remained constant along all the studied period (over 64 years). Instead, cell wall thickness was widest in P. engelmannii and this species presented the highest amount of intra-annual density fluctuations. Climate and wood anatomy correlations pointed out that lumen area was positively affected by winter precipitation for all studied species, while cell-wall thickness was negatively affected by this season's precipitation in all species but P. cembroides. Stable isotope analysis showed significantly lower values of Δ13C for P. cembroides and no significant δ18O differences between the three species, although they shared a common decreasing trend. With very distinct wood anatomical traits (smaller cells, compact morphology), P. cembroides stood out as the better adapted species in its current environment and could be less affected by future drier climate. P. engelmannii and A. durangensis showed high plasticity at wood anatomical level, allowing them to promptly respond to seasonal water availability but likely gives few advantages on future climate scenarios with longer and frequent drought spells., We are very grateful to Maria Elena Gelain, Department of Comparative Biomedicine and Food Science, University of Padua, for allowing us access to the D-sight 2.0 System automatic scanner (Grandi Attrezzature fund, University of Padua). Funding was provided by Mexican CONACYT (CB-2013/222522-A1-S-21471) and COCYTED (FOMIX-2017) projects also by the Spanish Ministry of Economy of Competitiveness project (Fundiver, CGL2015-69186-C2-1-R) and (MINECO/FEDER grant number AGL2015-68274-C3-3-R). We also thank PIDCAF-UJED, DendroRed (https://dendrored.ujed.mx).

Over recent decades, forest management in Europe has increasingly moved towards the emulation of natural dynamics. Natural dynamics in beech-oak forests leads to the formation of monospecific beech stands, the oak usually being excluded or restricted to sites with poor growing conditions. However, beech is more vulnerable than oak to drought and high temperatures. In this study, we examine whether climate change could attenuate the dominance of beech and improve the competitive capacity of oak in an old-growth temperate forest located in the “Picos de Europa” National Park, northern Spain. We used a dendroecological approach to reconstruct the competitive capacity of beech and oak and developed a projection for the 21st century based on forecasted climate conditions under three different emission scenarios. Beech is the dominant tree species in the studied forest, where the disturbance regime has favored the replacement of oak by beech. In general oaks are older than beeches and most of the small trees are beeches. Our results show that this substitution process may weaken due to the vulnerability of beech to warmer and drier conditions. Climate change will benefit oak growth over beech over the course of the 21st century, as was observed in the late 20th century. However, the natural gap dynamic benefits beech due to its greater shade-tolerance. Therefore, if the resilience of the ecosystem is to be increased, management strategies favoring oak regeneration are necessary given the better adaptation of oak to climate change.

The effects of climate change on forest growth are not homogeneous across tree species distribution ranges because of inter-population variability and spatial heterogeneity. Although latitudinal and thermal gradients in growth patterns have been widely investigated, changes in these patterns along longitudinal gradients due to the different timing and severity of regional droughts are less studied. Here, we investigated these responses in Mediterranean Black pine (Pinus nigra Arn.). We built a tree-ring width dataset comprising 77 forests (1202 trees) across the Mediterranean Basin. The biogeographical patterns in growth patterns and the relationships between growth and mean temperature, precipitation, drought and atmospheric circulations patterns (NAO -North Atlantic Oscillation-, SOI -Southern Oscillation Index- and MOI -Mediterranean Oscillation index-) were analyzed. Then, we evaluated the spatial and temporal growth synchrony between and within east and west populations. We found different growth and climate patterns in west vs. east Black pine populations, although in both regions growth was driven by similar temperature and precipitation variables. MOI significantly influenced tree growth, whilst NAO and SOI showed weaker effects. Growth of east and west Black pine populations desynchronized after the 1970s when several and uncoupled regional droughts occurred across the Mediterranean Basin. We detected a climate shift from the 1970s to the 1980s affecting growth patterns, changing growth-climate relationships, and reducing forest growth from west to east Black pine forests. Afterwards, climate and growth of east and west populations became increasingly more divergent. Our findings imply that integral bioclimatic and biogeographical analyses across the species distribution area must be considered to adequately assess the impact of climate change on tree growth under warming and more arid conditions.

Context: In recent decades, two major factors have influenced tree growth in many forests: climate warming, which is associated with aridification and negative growth trends in many Mediterranean forests, and abandonment of forest management, resulting from forest policy in conjunction with rural depopulation in Europe, often leading to an increase in competition and a decrease in growth.
Aims: Here we study growth trends in a mixed forest of Fagus sylvatica, Quercus petraea and Quercus pyrenaica, where the abandonment of traditional uses in the 1960s has been followed by an increase in tree density. In this forest, both F. sylvatica and Q. petraea reach their south-westernmost limits of distribution.
Methods: Using dendrochronological methods and growth modeling, we assess the importance of climate warming on the shifts in competitive growth advantage of these three coexisting tree species and the relative importance of climate and competition on growth trends.
Results and conclusions: Q. petraea and especially F. sylvatica, showed favorable evolution of their competitive capacity, despite the increase in temperatures that has occurred in the area in recent decades. F. sylvatica presented the lowest sensitivity to climate. Under the current climate and forest structure conditions, competition is the most limiting factor on tree growth for the two oak species.

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.