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Ongoing climatic change is threatening the survival of drought-sensitive tree species, such as silver fir (Abies alba). Drought-induced dieback had been previously explored in this conifer, although the role played by tree-level genetic diversity and its relationship with growth patterns and soil microsite conditions remained elusive. We used double digest restriction-site-associated DNA sequencing (ddRADseq) to describe different genetic characteristics of five silver fir forests in the Spanish Pyrenees, including declining and non-declining trees. Single nucleotide polymorphisms (SNPs) were used to investigate the relationships between genetics, dieback, intraspecific trait variation (functional dendrophenotypic traits and leaf traits), local bioclimatic conditions, and rhizosphere soil properties. While there were no noticeable genetic differences between declining and non-declining trees, genome–environment associations with selection signatures were abundant, suggesting a strong influence of climate, soil physicochemical properties, and soil microbial diversity on local adaptation. These results provide novel insights into how genetics and diverse environmental factors are interrelated and highlight the need to incorporate genetic data into silver fir forest dieback studies to gain a better understanding of local adaptation.

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).

19 Pags.- 15 Figs., We analyzed the impacts of drought severity on a variety of sectors in a topographically complex basin (the upper Aragón basin 2181 km2) in the Central Spanish Pyrenees. Using diverse data sources including meteorological and hydrological observations, remote sensing and tree rings, we analyze the possible hydrological implications of drought occurrence and severity on water availability in various sectors, including downstream impacts on irrigation water supply for crop production. Results suggest varying responses in forest activity, secondary growth, plant phenology, and crop yield to drought impacts. Specifically, meteorological droughts have distinct impacts downstream, mainly due to water partitioning between streamflow and irrigation channels that transport water to crop producing areas. This implies that drought severity can extend beyond the physical boundaries of the basin, with impacts on crop productivity. This complex response to drought impacts makes it difficult to develop objective basin-scale operational definitions for monitoring drought severity. Moreover, given the high spatial variability in responses to drought across sectors, it is difficult to establish reliable drought thresholds from indices that are relevant across all socio-economic sectors. The anthropogenic impacts (e.g. water regulation projects, ecosystem services, land cover and land use changes) pose further challenges to assessing the response of different systems to drought severity. This study stresses the need to consider the seasonality of drought impacts and appropriate drought time scales to adequately assess and understand their complexity., This work was supported by the research projects CGL2017-82216-R, PCI2019-103631, and PID2019-108589RA-I00 financed by the Spanish Commission of Science and Technology and FEDER; CROSSDRO project financed by the AXIS (Assessment of Cross(X) - sectoral climate Impacts and pathways for Sustainable transformation), JPI-Climate co-funded call of the European Commission and INDECIS which is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462). Dhais Peña-Angulo received a “Juan de la Cierva” postdoctoral contract (FJCI-2017-33652 Spanish Ministry of Economy and Competitiveness, MEC).

Background and Objectives—Coexisting tree and shrub species will have to withstand more arid conditions as temperatures keep rising in the Mediterranean Basin. However, we still lack reliable assessments on how climate and drought affect the radial growth of tree and shrub species at intra- and interannual time scales under semi-arid Mediterranean conditions. Materials and Methods—We investigated the growth responses to climate of four co-occurring gymnosperms inhabiting semi-arid Mediterranean sites in northeastern Spain: two tree species (Aleppo pine, Pinus halepensis Mill., Spanish juniper, Juniperus thurifera L.) and two shrubs (Phoenicean juniper, Juniperus phoenicea L., Ephedra nebrodensis Tineo ex Guss.). First, we quantified the intra-annual radial-growth rates of the four species by periodically sampling wood samples during one growing season. Second, we quantified the climate–growth relationships at an interannual scale at two sites with different soil water availability by using dendrochronology. Third, we simulated growth responses to temperature and soil moisture using the forward, process-based Vaganov‒Shashkin (VS-Lite) growth model to disentangle the main climatic drivers of growth. Results—The growth of all species peaked in spring to early summer (May–June). The pine and junipers grew after the dry summer, i.e., they showed a bimodal growth pattern. Prior wet winter conditions leading to high soil moisture before cambium reactivation in spring enhanced the growth of P. halepensis at dry sites, whereas the growth of both junipers and Ephedra depended more on high spring–summer soil moisture. The VS-Lite model identified these different influences of soil moisture on growth in tree and shrub species. Conclusions—Our approach (i) revealed contrasting growth dynamics of co-existing tree and shrub species under semi-arid Mediterranean conditions and (ii) provided novel insights on different responses as a function of growth habits in similar drought-prone regions.

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).

Climate warming is expected to positively alter upward and poleward treelines which are controlled by low temperature and a short growing season. Despite the importance of treelines as a bioassay of climate change, a global field assessment and posterior forecasting of tree growth at annual scales is lacking. Using annually resolved tree-ring data located across Eurasia and the Americas, we quantified and modeled the relationship between temperature and radial growth at treeline during the 20th century. We then tested whether this temperature–growth association will remain stable during the 21st century using a forward model under two climate scenarios (RCP 4.5 and 8.5). During the 20th century, growth enhancements were common in most sites, and temperature and growth showed positive trends. Interestingly, the relationship between temperature and growth trends was contingent on tree age suggesting biogeographic patterns in treeline growth are contingent on local factors besides climate warming. Simulations forecast temperature–growth decoupling during the 21st century. The growing season at treeline is projected to lengthen and growth rates would increase and become less dependent on temperature rise. These forecasts illustrate how growth may decouple from climate warming in cold regions and near the margins of tree existence. Such projected temperature–growth decoupling could impact ecosystem processes in mountain and polar biomes, with feedbacks on climate warming. climate warming, forest limit, growth model, mountain ecosystems, tree rings acceptedVersion

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).

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., We examined tree growth resilience of Scots pine along a 2,800 km latitudinal gradient from southern Spain to north‐eastern Germany using 615 adult trees from 30 different sites. We found that the resilience of Scots pine to extreme drought decreased in mid‐elevation and low productivity sites from 1980–1999 to 2000–2011 due to more frequent and severe droughts in the later period. We 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 during the pre‐drought period.

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 by Quercus frainetto Ten. and Quercus canariensis Willd. 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&ndash, 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 in Q. frainetto and during the 1990s in Q. 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.

21 Pags.- 5 Figs.- 1 Appendix. - Suppl. Data., This study links tree-ring growth and gross primary production for a variety of forest types under different environmental conditions across Spain. NOAA-AVHRR satellite imagery data were combined with dendrochronological records and climate data at a fine spatial resolution (1.21 km2) to analyze the interannual variability of tree-ring growth and vegetation activity for different forest biomes from 1981 to 2015. Specifically, we assessed the links between tree-ring width indices (TRWi), the Normalized Difference Vegetation Index (NDVI) and a variety of environmental conditions, represented by climatic variables (air temperature, precipitation, evapotranspiration and water balance) and elevation. The impact of these variables on tree growth was assessed by means of the Predictive Discriminant Analysis (PDA). Results reveal a general positive and significant relationship between inter-annual variability of the NDVI at a high spatial resolution (1.21 km2) and tree-ring growth. Maximum correlations between NDVI and tree-ring growth were recorded when cumulative NDVI values were considered, in some cases covering long time periods (6–10 months), suggesting that tree growth is mainly related to Gross Primary Production (GPP) at annual scale. The relationship between tree-ring growth and inter-annual variability of the NDVI, however, strongly varies between forest types and environmental conditions., This work was supported by the research projects CGL2014-52135-C03-01, CGL2015-69186-C2-1-R, CGL2015-69985-R, CGL2013-48843-C2-1-R, AGL2014-53822-C2-1-R, (BFU2010-21451), PCIN-2015-220, CGL2016-81706-REDT and CGL2017-82216-R financed by the Spanish Commission of Science and Technology and FEDER, 1560/2015: Herramientas de monitorización de la vegetación mediante modelización ecohidrológica en parques continentales financed by the Red de Parques Nacionales, IMDROFLOOD financed by the Water Works 2014 co-funded call of the European Commission, CROSSDRO financed by the AXIS (Assessment of Cross(X) – sectorial climate Impacts and pathways for Sustainable transformation) JPI-Climate co-funded call of the European Commission and INDECIS, which is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462). Financed by the Spanish Commission of Science and Technology and FEDER, and INDECIS, which is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by FORMAS (SE), DLR (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462). Natalia Martin-Hernandez was supported by a doctoral grant by the Aragon Regional Government, Marina Peña-Gallardo was granted by the Spanish Ministry of Economy and Competitiveness and Miquel Tomas-Burguera was supported by a doctoral grant by the Spanish Ministry of Education, Culture and Sport. Raúl Sánchez-Salguero, Antonio Gazol and Gabriel Sangüesa-Barreda were supported by Postdoctoral grants (IJCI-2015-25845, MINECO-FPDI 2013-16600 and FJCI 2016-30121, respectively; FEDER funds). This work also benefited from funding from Xunta de Galicia (PGIDIT06PXIB502262PR, GRC GI-1809, ROCLIGAL-10MDS291009PR), INIA (RTA2006-00117), and Interreg V-A POCTEFA (CANOPEE, 2014-2020-FEDER funds) projects.

Dendroprovenancing studies frequently use site chronologies to identify the origin of archaeological and historical timber. However, radial growth (tree-ring width, TRW) of tree species is influenced by both local and regional climate scales. Here we investigate how the use of annually-resolved Blue Intensity (BI) measurements can enhance dendroprovenancing precision of black pine (Pinus nigra Arn.) and Scots pine (P. sylvestris L.) on the Iberian Peninsula. Principal Component Gradient Analyses (PCGA) was used to assess geographical patterns of annual variation in different TRW and BI proxies of pine trees from two mountain ranges in the Central System and Andalusia in Spain. Local climate-growth relationships were quantified to identify underlying causes of identified groups with diverse growth patterns. Two distinct elevational groups were observed when performing PCGA on latewood BI time series with the response to summer drought as the main factor causing the differences. Both P. nigra and P. sylvestris BI time series were found to be more related to summer drought at low elevation sites showing an increase in sensitivity at lower latitudes. PCGA of TRW time series allowed to discriminate between trees from Andalusia and Central System within the elevation groups. February and October temperatures were found to be the main climatic factors causing the differences in TRW time series among the high- elevation sites, whereas for low-elevation trees it was the average winter temperature influencing TRW. A subsequent leave-one-out analyses confirmed that including latewood BI time series improves the precision of dendroprovenancing of pine wood in the Iberian Peninsula.

Climate reconstructions based on tree-ring features rely on the assumption that growth drivers are mainly meteorological variables. Consequently, annually resolved and absolutely dated temperature reconstructions in high-elevation conifer forests are mainly based on tree-ring width (TRW) and maximum wood density (MXD). However, long-term and annually resolved chronologies of chemical elements are scarce despite they could complement TRW- and MXD-based reconstructions. Here, we used a novel non-destructive method by applying Micro X-ray fluorescence (μXRF) to wood samples of old mountain pine (Pinus uncinata) trees from two Pyrenean high-elevation forests. We tested if Calcium (Ca) relative concentration, as estimated through μXRF, is a valuable proxy of long-term climatic and environmental changes in two sites with basic and acid soils, respectively. We compared the climate sensitivity of TRW, MXD and Ca by using calculating correlations with monthly climate data (mean temperature and total precipitation). Then, we built linear regressions to predict temperatures for the period 1900–2009. Prior-autumn and spring temperatures were positively related to TRW, MXD and Ca. However, Ca series revealed a high sensitivity to temperatures during the prior winter and spring but also to summer precipitation. We confirm the potential of long-term wood-chemistry studies based on the μXRF non-destructive technique to reconstruct environmental changes.

Drought-induced forest dieback is causing reductions in productivity, increasing tree mortality and impairing terrestrial carbon uptake worldwide. However, the role played by long-term nutrient imbalances during drought-induced dieback is still unknown. To improve our knowledge on the relationships between dieback and nutrient imbalances, we analysed wood anatomical traits (tree-ring width and wood density), soil properties and long-term chemical information in tree-ring wood (1900-2010) by non-destructive Micro X-ray fluorescence (μXRF) and destructive (ICP-OES) techniques. We studied two major European conifers with ongoing drought-induced dieback in mesic (Abies alba, silver fir) and xeric (Pinus sylvestris, Scots pine) sites. In each site we compared coexisting declining (D) and non-declining (ND) trees. We used dendrochronology and generalized additive and linear mixed models to analyse trends in tree-ring nutrients and their relationships with wood traits. The D trees presented lower growth and higher minimum wood density than ND trees, corresponding to a smaller lumen area of earlywood tracheids and thus a lower theoretical hydraulic conductivity. These differences in growth and wood-anatomy were more marked in silver fir than in Scots pine. Moreover, most of the chemical elements showed higher concentrations in D than in ND trees during the last two-five decades (e.g., Mn, K and Mg), while Ca and Na increased in the sapwood of ND trees. The Mn concentrations, and related ratios (Ca:Mn, Mn:Al and P:Mn) showed the highest differences between D and ND trees for both tree species. These findings suggest that a reduced hydraulic conductivity, consistent with hydraulic impairment, is affecting the use of P in D trees, making them more prone to drought-induced damage. The retrospective quantifications of Mn ratios may be used as early-warning signals of impending dieback.

Ring-width series are important for diverse fields of research such as the study of past climate, forest ecology, forest genetics, and the determination of origin (dendro-provenancing) or dating of archaeological objects. Recent research suggests diverging climate-growth relationships in tree-rings due to the cardinal direction of extracting the tree cores (i.e. direction-specific effect). This presents an understudied source of bias that potentially affects many data sets in tree-ring research. In this study, we investigated possible direction-specific growth variability based on an international (10 countries), multi-species (8 species) tree-ring width network encompassing 22 sites. To estimate the effect of direction-specific growth variability on climate-growth relationships, we applied a combination of three methods: An analysis of signal strength differences, a Principal Component Gradient Analysis and a test on the direction-specific differences in correlations between indexed ring-widths series and climate variables. We found no evidence for systematic direction-specific effects on tree radial growth variability in high-pass filtered ring-width series. In addition, direction-specific growth showed only marginal effects on climate-growth correlations. These findings therefore indicate that there is no consistent bias caused by coring direction in data sets used for diverse dendrochronological applications on relatively mesic sites within forests in flat terrain, as were studied here. However, in extremely dry, warm or cold environments, or on steep slopes, and for different life-forms such as shrubs, further research is advisable., Swiss National Science Foundation, grant no. P0ZHP1_162299. A. Buras received funding from the German Academic Exchange Service (DAAD). CGL2015-69186-C2-1-R project (Spanish Ministry of Economy). DAAD-Conacyt scholarship. OLDPINE (AGL2017-83828-C2-2R) project (Spanish Ministry of Economy, Industry and Competitiveness, MINECO). Ministry of Education, Youth, and Sports of CR within the National Sustainability Program I (NPUI), grant number LO1415, the Czech Science Foundation (18-17295S). Ministry of Research and Innovation, CNCS – UEFISCDI, project number PN-III-P1-1.1-TE-2016-1508, within PNCDI III (BIOCARB). CoMo-ReAdapt (CGL2013-48843-C2-1-R, Spanish Ministry of Economy, Industry and Competitiveness, Spain), LESENS (RTI2018-096884-B-C33, Ministry of Science, Innovation and Universities, Spain).

Producción Científica, 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., Ministerio de Economía projects: (CGL2015-69186-C2-1-R (Fundiver)), (CGL2015-69985-R (CLIMED)),( CGL2013-48843-C2-1-R (CoMo-ReAdapt)),( AGL2014-53822-C2-1-R (SATIVA)),( XIRONO (BFU2010-21451)),( CGL2014-52135-C03-01), (PCIN-2015-220), and (CGL2016-81706-REDT (Ecometas Network)), (1560/2015 (ECOHIPRO)), Xunta de Galicia, projects:(PGIDIT06PXIB502262PR, GRC GI-1809, ROCLIGAL-10MDS291009PR), INIA (RTA200600117) e Interreg V-A POCTEFA (CANOPEE, 2014-2020-fondos FEDER), Ministerio de Economía y Empresa, postdoctoral grants (MINECO-FPDI 2013-16600; fondos FEDER), Postdoctoral grants (IJCI-2015-25845)

Warmer and drier climatic conditions are projected for the 21st century; however, the role played by extreme climatic events on forest vulnerability is still little understood. For example, more severe droughts and heat waves could threaten quaternary relict tree refugia such as Circum-Mediterranean fir forests (CMFF). Using tree-ring data and a process-based model, we characterized the major climate constraints of recent (1950–2010) CMFF growth to project their vulnerability to 21st-century climate. Simulations predict a 30% growth reduction in some fir species with the 2050s business-as-usual emission scenario, whereas growth would increase in moist refugia due to a longer and warmer growing season. Fir populations currently subjected to warm and dry conditions will be the most vulnerable in the late 21st century when climatic conditions will be analogous to the most severe dry/heat spells causing dieback in the late 20th century. Quantification of growth trends based on climate scenarios could allow defining vulnerability thresholds in tree populations. The presented predictions call for conservation strategies to safeguard relict tree populations and anticipate how many refugia could be threatened by 21st-century dry spells.

The first large-scale network of tree-ring chronologies from the western Mediterranean (WM; 32°N–43°N, 10°W–17°E) is described and analyzed to identify the seasonal climatic signal in indices of annual ring width. Correlation and rotated empirical orthogonal function analyses are applied to 85 tree-ring series and corresponding gridded climate data to assess the climate signal embedded in the network. Chronologies range in length from 80 to 1129 years. Monthly correlations and partial correlations show overall positive associations for Pinus halepensis (PIHA) and Cedrus atlantica (CDAT) with winter (December–February) and spring (March–May) precipitation across this network. In both seasons, the precipitation correlation with PIHA is stronger, while CDAT chronologies tend to be longer. A combination of positive correlations between growth and winter–summer precipitation and negative partial correlations with growing season temperatures suggests that chronologies in at least part of the network reflect soil moisture and the integrated effects of precipitation and evapotranspiration signal. The range of climate response observed across this network reflects a combination of both species and geographic influences. Western Moroccan chronologies have the strongest association with the North Atlantic Oscillation.

Crown defoliation is extensively monitored across European forests within the International Co-operative Programme (ICP) as a proxy of forest health. Climate warming and drought are assumed to be the major drivers of tree growth and crown defoliation, particularly in seasonally dry areas such as the Mediterranean Basin. Here we analyse how climate, drought, and atmospheric processes are related to defoliation time series of five oak and five pine species that are dominant across Spanish ICP monitoring forest plots. We found that warmer and drier conditions during April were linked to enhanced defoliation. Warm April conditions were also related to high values of the Atlantic Multi-decadal Oscillation (AMO), thereby indicating large-scale links between atmospheric processes, temperature, and defoliation patterns. The temperature-defoliation association was species-specific since some tree species from wet sites showed a weak association (e.g., Quercus robur L.) whereas others from dry sites (e.g., Quercus ilex L.) presented the strongest associations. The latter tree species could be considered vulnerable to heat stress in terms of leaf shedding. We also explored if defoliation was related to radial growth and found negative associations in relatively dry areas. Warmer and drier conditions linked to increasing AMO values are connected to the post-1990s rise of defoliation in Spanish ICP forest plots. Combined incorporation of defoliation and growth into mortality models can provide insights into assessments of forest vulnerability., We thank the support of projects CGL2015-69186-C2-1-R, CGL2013-48843-C2-1-R, and RTA 2010-00065 (Spanish Ministry of Economy and Competitiveness and FEDER funds). We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).

The European Dendroecologial Fieldweek (EDF) provides an intensive learning experience in tree-ring research that challenges any participant to explore new multidisciplinary dendro-sciences approaches within the context of field and laboratory settings. Here we present the 25th EDF, held in Asturias, NW Spain, in summer 2014. The course, with 33 participants and 10 instructors from 18 countries included advanced training in dendrochronology skills, an overview of tree-ring broad fields and methodological basics to deal with specific research questions as well as applied advanced micro-projects in dendroarchaeology (DAR), dendroclimatology (DCL), dendrogeomorphology (DGM), forest dynamic (FD) and plant anatomy (PA). The results demonstrated the potential of tree-ring research in the Asturias region. The DAR group researched archaeological samples from different contexts (Oviedo cathedral choir stalls, Segovia cathedral roof timbers, Ribadeo shipwreck ship timbers and Bronze Age site charcoal) and explored the supply of wood in different periods. The DCL group established that the Quercus robur and Castanea sativa ring-width measurements show weak climate-growth correlations, where for many trees this is likely caused by management. The strength of the climatic signal could be enhanced using undisturbed settings. The DGM group found that Corylus avellana and Salix spp. are challenging species for dendrogeomorphological studies. Debris-flow events were detected by the presence of tension wood, growth reduction and scars, and their incidences were also supported by local meteorological data. The FD group found that tree growth decreases with increasing competition, a pattern more pronounced in C. sativa than in Pinus sylvestris forest plantations. The results indicate that wood production could be increased by applying thinning treatments on C. sativa. The PA group showed that xylem conduits and phloem area are organized according to the common needs for water supply to leaves and obtain photosynthetic products, regardless site growing conditions for P. sylvestris and Tusilago farfara. In conclusion, this EDF has been a model for interdisciplinary research and international collaboration that has demonstrated that high-quality research and education can be conducted within one week. The EDFs provide an important service to the dendrochronological community and demonstrate the usefulness of this educational-scientific and multi-cultural experience.

Mediterranean pine forests display high resilience after extreme climatic events such as severe droughts. However, recent dry spells causing growth decline and triggering forest dieback challenge the capacity of some forests to recover following major disturbances. To describe how resilient the responses of forests to drought can be, we quantified growth dynamics in plantations of two pine species (Scots pine, black pine) located in south-eastern Spain and showing drought-triggered dieback. Radial growth was characterized at inter- (tree-ring width) and intra-annual (xylogenesis) scales in three defoliation levels. It was assumed that the higher defoliation the more negative the impact of drought on tree growth. Tree-ring width chronologies were built and xylogenesis was characterized 3 years after the last severe drought occurred. Annual growth data and the number of tracheids produced in different stages of xylem formation were related to climate data at several time scales. Drought negatively impacted growth of the most defoliated trees in both pine species. In Scots pine, xylem formation started earlier in the non-defoliated than in the most defoliated trees. Defoliated trees presented the shortest duration of the radial-enlargement phase in both species. On average the most defoliated trees formed 60% of the number of mature tracheids formed by the non-defoliated trees in both species. Since radial enlargement is the xylogenesis phase most tightly related to final growth, this explains why the most defoliated trees grew the least due to their altered xylogenesis phases. Our findings indicate a very limited resilience capacity of drought-defoliated Scots and black pines. Moreover, droughts produce legacy effects on xylogenesis of highly defoliated trees which could not recover previous growth rates and are thus more prone to die., We thank the support of Junta de Andalucía and project GESBOME (P06-RNM-1890) and AEMET (Agencia Estatal de Meteorología) for providing meteorological data. JC acknowledges the support of the Excellence Network “Red de Ecología Terrestre para afrontar los retos del Cambio Global—ECOMETAS” (CGL2014-53840-REDT) of the Spanish Ministry of Economy. RS thanks the support of project CoMo-ReAdapt (CGL2013-48843-C2-1-R) and postdoctoral fellowship of (FEDER-Programa de Fortalecimiento de las capacidades en I+D+i de las Universidades 2014-2015, Junta de Andalucía). RN acknowledges the support of the project LIFE13 ENV/ES/001384 “Development of technical guidelines for carbon sequestration and dynamization of carbon compensation in forests” and QUERCUSAT (CLG2013-40790-R). GG acknowledges the granting of a predoctoral fellowship from FPI program (BES-2011-050172) by the Spanish Ministry of Economy and Competitivity (Project BFU 2010-21451). This work was carried out under the framework of the EU COST Action FP 1106 (Studying Tree Responses to extreme Events: a SyntheSis, STReESS).

Aim of the study: We assessed the ability of the 3-PG process-based model to accurately predict growth of Pinus sylvestris and P. nigra plantations across a range of sites, showing declining growth trends, in southern Spain.Area of study: The study area is located in “Sierra de Los Filabres” (Almería).Material and methods: The model was modified in fifteen parameters to predict diameter (DBH, cm), basal area increment (BAI, cm2 yr-1) and leaf area index (LAI, m2 m-2) in healthy trees and trees showing declining growth. We assumed that a set of specific physiological parameters (stem partitioning ratio-pFS20, maximum litterfall rate-γFx, maximum canopy conductance-gCx, specific leaf area for mature aged stands-σ1, age at which specific leaf area = ½ (σ0 + σ1), age at full canopy cover-tc, and canopy boundary layer conductance-gB) included in 3-PG would be suitable for predicting growth decline related to climate conditions. The calibrated model was evaluated using dendrochronological and LAI data obtained from plots.Main results: Observed and simulated DBH showed a high correlation (R2 > 0.99) between modelled and measured values for both species. In contrast, modelled and observed BAI showed lower correlation (R2 < 0.68). Sensitivity analysis on 3-PG outputs showed that the foliage parameters - maximum litterfall rate, maximum canopy conductance, specific leaf area for mature aged stands, age at which specific leaf area, and age at full canopy cover - were important for DBH and BAI predictions under drought stress.Research highlights: Our overall results indicated that the 3-PG model could predict growth response of pine plantations to climatic stress with desirable accuracy in southern Spain by using readily available soil and climatic data with physiological parameters derived from experiments.Keywords: Hybrid process model; forest management models; growth prediction; Pinus spp, Parameterization; forest decline.

39 páginas, 5 tablas, 6 figuras, 2 figuras suplementarias. -- This is a pre-copyedited, author-produced version of an article accepted for publication in Tree Physiology following peer review. The version of record [J. J. Camarero, G. Guada, R. Sánchez-Salguero, E. Cervantes; Winter drought impairs xylem phenology, anatomy and growth in Mediterranean Scots pine forests. Tree Physiol 2016; 36 (12): 1536-1549] is available online at: http://dx.doi.org/10.1093/treephys/tpw077, Continental Mediterranean forests face drought and cold stress. Drought and cold spells are climate extremes which can impair the recovery and resilience capacity of some Mediterranean forests. Climate warming could amplify the negative effects on forests of climate extremes by altering phenology phases (premature dehardening) and by magnifying drought stress. Here we capitalize on a winter-drought induced dieback triggered by a cold spell which occurred in December 2001 and affected Scots pine forests in E. Spain. We assessed post-dieback recovery by quantifying and comparing radial growth and xylem anatomy of non-declining (crown cover > 50%) and declining (crown cover ≤ 50%) trees in two sites (VP, Villarroya de los Pinares; TO, Torrijas). We also characterized aboveground productivity in site VP and xylogenesis in both sites during 2005. Dieback caused legacy effects since needle loss, a 60% reduction in aboveground biomass and radial-growth decline characterized declining trees three years after these dieback symptoms started in spring 2002. Declining trees formed collapsed tracheids in the 2002-ring earlywood, particularly in the most affected VP site where xylogenesis differences between non-declining and declining trees were most noticeable. The lower growth rates of declining trees were explained by a shorter duration of their major xylogenesis phases. In the site VP the radial-enlargement and wall-thickening of tracheids were significantly reduced in declining trees as compared to non-declining trees, and this was because these phases tended to start earlier and end later in non-declining than in declining trees. Gompertz models fitted to tracheid production predicted that maximum growth rates occurred 11-12 days earlier in non-declining than in declining trees. The formation of radially-enlarging tracheids was enhanced by longer days in both study sites and also by wetter conditions in the driest TO site, but this xylogenesis sensitivity to climate was reduced in declining trees. Winter-drought induced dieback impairs xylem anatomy and phenology, aboveground productivity, xylogenesis and growth in Mediterranean Scots pine populations. Affected stands show a costly post-dieback recovery challenging their resilience ability., JJC acknowledges the support of the Excellence Network “Red de Ecología Terrestre para afrontar los retos del Cambio Global—ECOMETAS” (CGL2014-53840-REDT) of the Spanish Ministry of Economy.

Forests play a key role in the carbon balance of terrestrial ecosystems. One of the main uncertainties in global change predictions lies in how the spatiotemporal dynamics of forest productivity will be affected by climate warming. Here we show an increasing influence of climate on the spatial variability of tree growth during the last 120 y, ultimately leading to unprecedented temporal coherence in ring-width records over wide geographical scales (spatial synchrony). Synchrony in growth patterns across cold-constrained (central Siberia) and drought-constrained (Spain) Eurasian conifer forests have peaked in the early 21st century at subcontinental scales (∼1,000 km). Such enhanced synchrony is similar to that observed in trees co-occurring within a stand. In boreal forests, the combined effects of recent warming and increasing intensity of climate extremes are enhancing synchrony through an earlier start of wood formation and a stronger impact of year-to-year fluctuations of growing-season temperatures on growth. In Mediterranean forests, the impact of warming on synchrony is related mainly to an advanced onset of growth and the strengthening of drought-induced growth limitations. Spatial patterns of enhanced synchrony represent early warning signals of climate change impacts on forest ecosystems at subcontinental scales. T.A.S. is supported by ERANET-MUNDUS (Euro-Russian Academic Network-Mundus) (European Commission). V.R.d.D. is supported by the Ramón y Cajal Program (Contract RYC-2012-10970). Support for this work was provided by European Union projects ForMAT (Sensitivity of tree growth to climate change and growth modelling from past to future) (Contract ENV4-CT97-0641), ISONET (400 years of annual reconstructions of European climate variability using a high resolution isotopic network) (Contract EV K2-2001-00237), and MILLENNIUM (European climate of the last millennium) (Contract GOCE 017008); the Russian Science Foundation (Project 14-14-00295); the Catalan Government (Project 2014 SGR 1141); Studying Tree Responses to Extreme Events: A Synthesis (STReESS) COST (European Cooperation in Science and Technology) Action FP1106; and Spanish Projects CGL2011-26654 and CGL2013-48843-C2-1-R (Spanish Ministry of Economy and Competitiveness).

The current scenario of global warming has resulted in considerable uncertainty regarding the capacity of forest trees to adapt to increasing drought. Detailed ecophysiological knowledge would provide a basis to forecast expected species dynamics in response to climate change. Here, we compare the water balance (stomatal conductance, xylem water potential, needle osmotic adjustment) of Abies pinsapo, a relict drought-sensitive Mediterranean fir, along an altitudinal gradient. We related these variables to soil water and nutrient availability, air temperature, atmospheric water potential, and vapour pressure deficit during two consecutive years. Our results indicate that A. pinsapo closed stomata rapidly over a very narrow range of soil water availability and atmospheric dryness. This isohydric response during water stress suggests that this relict conifer relied on the plant hormone abscisic acid to maintain closed stomata during sustained drought, instead of needle desiccation to passively drive stomatal closure, needle osmotic adjustment or a plastic response of the xylem to different levels of water availability. Both the soil and foliar nutrient contents suggest that the studied populations are not limited by nutrient deficiencies, and drought was stronger in the warmer low-elevation areas.

Sánchez-Salguero, R. et al.- 37 páginas, Scots pine forests subjected to continental Mediterranean climates undergo cold winter temperatures and drought stress. Recent climatic trends towards warmer and drier conditions across the Mediterranean Basin might render some of these pine populations more vulnerable to drought-induced growth decline at the Southernmost limit of the species distribution. We investigated how cold winters and dry growing seasons drive the radial growth of Scots pine subject to continental Mediterranean climates by relating growth to climate variables at local (elevational gradient) and regional (latitudinal gradient) scales. Local climate-growth relationships were quantified on different time scales (5-, 10- and 15-days) to evaluate the relative role of elevation and specific site characteristics. A negative water balance driven by high maximum temperatures in June (low-elevation sites) and July (high-elevation sites) was the major constraint on growth, particularly on a 5- to 10-day time scale. Warm nocturnal conditions in January were associated with wider rings at the high-elevation sites. At the regional scale, Scots pine growth mainly responded positively to July precipitation, with a stronger association at lower elevations and higher latitudes. January minimum temperatures showed similar patterns but played a secondary role as a driver of tree growth. The balance between positive and negative effects of summer precipitation and winter temperature on radial growth depends on elevation and latitude, with low-elevation populations being more prone to suffer drought and heat stress; whereas, high-elevation populations may be favoured by warmer winter conditions. This negative impact of summer heat and drought has increased during the past decades. This interaction between climate and site conditions and local adaptations is therefore decisive for the future performance and persistence of Scots pine populations in continental Mediterranean climates. Forecasting changes in the Scots pine range due to climate change should include this site-related information to obtain more realistic predictions, particularly in Mediterranean rear-edge areas. © 2015 Elsevier B.V., We were glad to be able to use the E-OBS dataset (EU- project ENSEMBLES) and the data providers in the ECA&D project (http://www.ecad.eu), and thank Dr. Geert Jan van Oldenborgh for his assistance with these data. We are grateful to the researchers who provided data on the International Tree-Ring Data Bank. This study was funded by the projects CoMo-ReAdapt (CGL2013-48843-C2-1-R) and FORRISK (Interreg IV B SUDOE 2007-2013). The authors thank CENEAM, Montes de Valsaín and OAPN and all participants involved in the International Tree-Ring Summer School carried out in 2012 in Valsaín (Segovia-Spain), especially to Kenza Garah, María Tabakova, Virginia Garófano-Gómez and Clara Rodriguez-Morata. R. Sánchez-Salguero is grateful for the financial support of University of Córdoba-Campus de Excelencia ceiA3 and “Fondo Europeo de Desarrollo Regional (FEDER)-Programa de Fortalecimiento de las capacidades en I + D + i de las Universidades 2014–2015, Junta de Andalucía”. We are grateful to Silvia Dingwall for the language review. This work has been carried out under the framework of the COST FP1106 network STReESS.

To assess if tree age may modulate the main climatic drivers of radial growth, two relict Pinus nigra subsp. salzmannii populations (María, most xeric site; Mágina, least xeric site) were sampled in southern Spain near the limits of the species range. Tree-ring width residual chronologies for two age groups (mature trees, age ≤ 100 years (minimum 40 years); old trees, age > 100 years) were built to evaluate their responses to climate by relating them to monthly precipitation and temperature and a drought index (DRI) using correlation and response functions. We found that drought is the main driver of growth of relict P. nigra populations, but differences between sites and age classes were also observed. First, growth in the most xeric site depends on the drought severity during the previous autumn and the spring of the year of tree-ring formation, whereas in the relatively more mesic site growth is mainly enhanced by warm and wet conditions in spring. Second, growth of mature trees responded more to drought severity than that of old trees. Our findings indicate that drought severity will mainly affect growth of relict P. nigra populations dominated by mature trees in xeric sites. This conclusion may also apply to similar mountain Mediterranean conifer relicts., This project was funded through DIVERBOS (CGL2011-30285-C02-02) and INIA-RTA (RTA2010-00065-00-00). R. Sánchez-Salguero acknowledges a FPU (Formación de Profesorado Universitario) grant (AP2007-04747) (Ministerio de Educación, Spain). We also acknowledge the financial support from University of Córdoba-Campus de Excelencia CEIA3 and AEMET (Agencia Estatal de Meteorologia) for providing meteorological data. We thank Francisca de la Hoz and Angela Merino for their support during field works, and R. Arias for his assistance in the laboratory. J. J. Camarero thanks the support of ARAID and Globimed.

In a context of global change, climate impacts can trigger defoliation processes in different forest species. The ICP Forests network estimates the level of forest defoliation over time in different European countries. Those data are used to related defoliation with potential causal factors. In European Southwestern forests, climate change appears to be the detonating factor of generalized defoliation. The objectives of this study were (i) identity defoliation trends in forest trees at network of Spanish ICP Forests monitoring plots and, (ii) find out if there are underlying climate factors that trigger defoliation process along the time. The spatiotemporal synchronization of the defoliation response was analyzed with cross-correlation using COFECHA software. The relationship between the 88 climatic variables proposed and defoliation was analyzed using Correlated Component Regression models (CCR models) and Discriminant Analysis (DA). The significance of the variables in each model was compared using contingency tables. A peak of defoliation was observed in the mid-1990s with no recovered to the initial values of the early 1990s. The behavior of the different tree species with respect to defoliation, synchronized both in time and space, involves one or several factors that have a general and similar effect on forests in Spain. The most significant factors related to defoliation were the thermal-related factors, particularly average temperatures in April and June and the thermal oscillation of both the current year and the previous year. Only one drought indicator as statistically significant was identified (A, duration of aridity in months) and suggests that it is of limited relevance in the Spanish forest defoliation conditions. © 2014 Elsevier B.V.

Touchan, R.... et al., This report describes an international summer course, >Tree Rings, Climate, Natural Resources, and Human Interaction>, held in Valsaín, Spain, in summer of 2012. The course, with 14 participants from three countries (Spain, Algeria, and Russia), included basic training in dendrochronology skills as well as applied projects in dendroclimatology, dendroecology and dendrogeomorphology. Copyright © 2013 by The Tree-Ring Society., This International Summer School was carried out in collaboration with the Laboratory of Tree-Ring Research, University of Arizona, from the United States, and IGME (Instituto Geológico y Minero de España), IPE-CSIC (Instituto Pirenaico de Ecología - Consejo Superior de Investigaciones Científicas), ARAID foundation, INIA-CIFOR (Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria-Centro de Investigación Forestal) and University of Córdoba, from Spain. The organizers sincerely thank the CENEAM (National Center for Environmental Education), Montes de Valsaín and OAPN (Organismo Autónomo de Parques Nacionales) from the Ministerio de Agricultura, Alimentación, y Medio Ambiente in Spain for the support and facilities to organize this course. We thank Drs. Rafael Herrera, Mar Génova and Guillermo Gea-Izquierdo for their contributions in the course. We thank AEET (Asociación Española de Ecología Terrestre) from Spain for generous grants provided to students. We thank the course sponsors: Tree-Ring Society, National Science Foundation-USA (Grant AGS-Paleo Perspectives on Climate Change Program 1103314), Regents Instruments, Beta Analytic, and Cox Analytical Systems.

Machaerium scleroxylon (morado) is an important timber species from the lowland tropical dry forests in Bolivia. We followed a dendrochronological approach to (i) evaluate the responses of radial growth to climatic variables and atmospheric circulation patterns, and (ii) quantify the growth rate in order to estimate the Minimum Logging Diameter (MLD), age, and optimal cutting rotation. We measured tree-ring width in wood discs taken from ten randomly selected mature individuals. We used previous histological analyses to distinguish and visually crossdate tree rings. Despite the existence of false rings, lenses and wedging rings, the species showed defined annual ring boundaries, thus enabling a tree-ring chronology analysis. Correlations between residual ring-width indices and monthly climatic variables (temperature and rainfall) and atmospheric circulation patterns (El Niño-Southern Oscillation) index were calculated. Growth showed a significant positive correlation with monthly rainfall and a negative correlation with mean temperature during the late rainy season (i.e. from December up to March). A positive correlation found between the ring width and ENSO indices indicates that the growth of M. scleroxylon was significantly affected by atmospheric circulation patterns. Growth rate is slow in morado, suggesting a MLD of 50 cm and an optimal cutting cycle longer than 40 years depending on each site. Copyright © 2013 by The Tree-Ring Society.

The southernmost European natural and planted pine forests are among the most vulnerable areas to warming-induced drought decline. Both drought stress and management factors (e.g., stand origin or reduced thinning) may induce decline by reducing the water available to trees but their relative importances have not been properly assessed. The role of stand origin - densely planted vs. naturally regenerated stands - as a decline driver can be assessed by comparing the growth and vigor responses to drought of similar natural vs. planted stands. Here, we compare these responses in natural and planted Black pine (Pinus nigra) stands located in southern Spain. We analyze how environmental factors - climatic (temperature and precipitation anomalies) and site conditions - and biotic factors - stand structure (age, tree size, density) and defoliation by the pine processionary moth - drive radial growth and crown condition at stand and tree levels. We also assess the climatic trends in the study area over the last 60. years. We use dendrochronology, linear mixed-effects models of basal area increment and structural equation models to determine how natural and planted stands respond to drought and current competition intensity. We observed that a temperature rise and a decrease in precipitation during the growing period led to increasing drought stress during the late 20th century. Trees from planted stands experienced stronger growth reductions and displayed more severe crown defoliation after severe droughts than those from natural stands. High stand density negatively drove growth and enhanced crown dieback, particularly in planted stands. Also pine processionary moth defoliation was more severe in the growth of natural than in planted stands but affected tree crown condition similarly in both stand types. In response to drought, sharp growth reduction and widespread defoliation of planted Mediterranean pine stands indicate that they are more vulnerable and less resilient to drought stress than natural stands. To mitigate forest decline of planted stands in xeric areas such as the Mediterranean Basin, less dense and more diverse stands should be created through selective thinning or by selecting species or provenances that are more drought tolerant. © 2013 Elsevier B.V., We are grateful for support from the Spanish FPU PhD Grant program (AP2007-04747) (Ministerio de Educación, Spain) and the financial support from University of Córdoba-Campus de Excelencia ceiA3 to the first author, and the MEC Project INTERBOS (CGL2008-04503-CO3-02), DIVERBOS (CGL2011-30285-C02-02); and AEMET (Agencia Estatal de Meteorologia) for providing meteorological data. We thank the support of “Agencia Andaluza del Agua y Medio Ambiente” (J.M. Ruiz-Navarro and all the members of “Red de Equilibrios Biológicos de Andalucía”) and Consejería de Medio Ambiente, Junta de Andalucía. We thank J.M. Grau, F. Artero, A. Carmen, M. Sanchez Gonzalez and M. Minaya for the laboratory and fieldwork support. MAZ and RSS were supported by SUM2008-00004-C03.01 (INIA) and CEXTREME; FP7-ENV-2008-1-226701. AFC and RSS were supported by INIA-RTA (RTA2010-00065-00-00). The first author thanks members of WSL for their useful comments. J.J. Camarero thanks ARAID and collaborative efforts within the Globimed network (http://www.globimed.net).

Drought has been frequently discussed as a trigger for forest decline. Today, large-scale forest decline is observed at the rear edge of Mediterranean forests, with drought identified as the most likely driver. The vulnerability of Mediterranean mountain plantations to regional climatic variations; however, is poorly understood. In this paper, we analyze the impact of biotic and abiotic factors on the growth and vigor of two pine species in drought-prone areas. We assess the main factors influencing crown defoliation and radial growth to develop a predictive model of forest decline risk for pine plantations at the dry edge of the species range. Dendrochronological data were collected on 50 plots for Pinus nigra subsp. salzmanii and 40 plots for Pinus sylvestris. We examined tree size, competition, site characteristics and climate variables related to decline of pine plantations. Correlation and principal component analysis (PCA) were used to identify the correlates of decline with crown condition and growth, separately. Logistic regression and generalized linear models were used to study the relationship between canopy defoliation and growth, respectively, for P. nigra and P. sylvestris. Explanatory variables were introduced in a stepwise selection. The PCA revealed three main axes, associated with climate, competition and physiographic variables. Those three axes were associated with crown damage and basal area growth, respectively. Probability of crown damage was associated with tree size, competition and climate conditions. P. sylvestris was more sensitive than P. nigra to summer potential evapotranspiration effects. Also, climate and competition were the two main drivers affecting basal area growth. Unlike crown defoliation, physiography had an important effect. Within each species, there was a divergence between healthy and damaged trees, mainly related to competition factors. On the other hand, growth trends as an independent variable were not included in the crown damage probability model in a stepwise selection. However, declining growth found in trees at higher crown defoliation and drier sites may imply a greater vulnerability to decline, suggesting an enhanced die-off risk. The sharp growth reduction and widespread defoliation in declining pine plantations make their future persistence in xeric sites subject to frequent and severe droughts unlikely under expected warmer and drier conditions in the future. © 2012 Elsevier B.V.

[EN] The negative impacts of severe drought on the growth and vigor of tree species and their relationship with forest decline have not been properly evaluated taking into account the differential responses to such stress of trees, sites and species. We evaluated these responses by quantifying the changes in radial growth of plantations of four pine species (Pinus sylvestris, Pinus nigra, Pinus pinaster, Pinus halepensis) which showed distinct decline and defoliation levels in southeastern Spain. We used dendrochronological methods, defoliation records, linear mixed models of basal area increment and dynamic factor analysis to quantify the responses of trees at the species and individual scales to site conditions and drought stress. In the region a temperature rise and a decrease in spring precipitation have led to drier conditions during the late twentieth century characterized by severe droughts in the 1990s and 2000s. As expected, the defoliation levels and the reductions in basal area increment were higher in those species more vulnerable to drought-induced xylem embolism (P. sylvestris) than in those more resistant (P. halepensis). Species adapted to xeric conditions but with high growth rates, such as P. pinaster, were also vulnerable to drought-induced decline. The reduction in basal area increment and the defoliation events occurred after consecutive severe droughts. A decrease in spring precipitation, which is the main driver of radial growth, is the most plausible cause of recent forest decline. The sharp growth reduction and widespread defoliation of the most affected pine plantations of Scots pine make their future persistence in drought-prone sites unlikely under the forecasted warmer and drier conditions. © 2011 Springer Science+Business Media B.V., We thank the support of Junta de Andalucía, project GESBOME (P06-RNM-1890), project INTERBOS (CGL2008-04503-CO3-02) and a FPU grant (AP2007-04747, MCI, Spain) to the first author. We thank J. Bautista and A. Herrero for their help in the field and the support of Natural Park of Sierra de Baza and EGMASA. J.J. Camarero thanks ARAID and collaborative efforts within Globimed network. We thank R. Calama for his help with statistical analyses. We also thank Dr. S. Donner and three anonymous reviewers for their constructive comments.