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Impacts of climate warming on forests vigour are forecasted to increase in magnitude. Yet it remains unclear how stand characteristics and competition modulate the relationship between tree growth and gross primary production with drought. Here, we studied how the spatial variation in stand density, basal area and height modulates tree growth (Basal Area Increment, BAI and stand growth), summer NDVI, as well as their responses to drought (Standardized Precipitation-Evapotranspiration Index, SPEI) in 56 Aleppo pine (Pinus halepensis Mill.) planted forests located in Northeast Spain. Long-term BAI responses to SPEI were strongly determined by stand density, suggesting that competition modulates Aleppo pine growth responses to drought. Along this, summer NDVI also displayed strong associations with SPEI. NDVI was mostly related with stand growth, suggesting canopy densification drives NDVI pattern and trends. Short-term BAI and NDVI responses to severe droughts were mainly independent of stand characteristics. In the studied region, drought is a universal factor limiting Aleppo pine secondary growth and canopy greening. However, the results suggest that stand density modulates Aleppo pine growth responses to drought on the long-term, reducing the growth in densest stands. Denser stands with larger trees are the ones that present higher NDVI values, suggesting that canopy activity depends more on stand canopy coverage than on secondary growth rate and its response to drought. In these Mediterranean pines, canopy activity and secondary growth are temporally coupled but spatially decoupled.

Producción Científica, Standard procedures to obtain high-quality images of wood samples have become a bottleneck in the digitization of dendrochronology. Digitization is currently dominated by flatbed scanners, but the use of these devices is limited by sample length and surface flatness. Although several solutions based on digital photography have been published, they lack effective digitization processes or are too expensive to be widely adopted. Free open-source software and hardware has emerged as an alternative to create research tools that combine reduced costs with high reliability. Here we present CaptuRING, an open-source tool for wood sample digitization combining a do-it-yourself hardware based on Arduino® with a DSLR camera and a free open-source software with an easy-to-use graphical user interface. We compared CaptuRing with image acquisition from a standard flatbed scanner Epson® V750PRO. CaptuRING outperforms scanner image resolution and sharpness, while it removes sample size limitations. Moreover, CaptuRing performs this task in less than half of the time needed by Epson® V750PRO flatbed scanner. CaptuRING emerges as a reliable and low-cost tool to capture high-resolution images of wood samples boosting current digitization processes. The combination of free open software and hardware empowers dendrochronology to advance in wood sample digitization., Junta de Castilla y León, project OUTBREAK (VA171P20) and (IR2020-1-UVA08), Ministerio de Ciencia, Innovación y Universidades, grant number (CGL2017-87309-P) (MGH PRE2018-084106) and project PROWARM (PID2020-118444GA-I00), Universidad Politécnica de Madrid (through Project RP200060107)

Prumnopitys andina is a South American podocarp with a restricted distribution in southern Andean temperate forests, and is severely threatened due to habitat loss. Despite much dendrochronological...

Intraspecific variation in plant defences is expected to be the result of adaptive and plastic responses to environmental conditions, where trade-offs between growth and defences are thought to play a key role shaping phenotypic patterns in defensive investment. Axial resin ducts are costly defensive structures that remain imprinted in the tree rings of conifers, therefore being a valuable proxy of defensive investment along the trees’ lifespan. We aimed to disentangle climate-driven adaptive clines and plastic responses to both spatial and temporal environmental variation in resin duct production, and to explore growth-defence trade-offs. To that aim, we applied dendrochronological procedures to quantify annual growth and resin duct production during a 31-year-period in a Mediterranean pine species, including trees from nine populations planted in two common gardens. Both genetic factors and plastic responses modulated annual resin duct production. However, we found no evidence of adaptive clines with climate gradients driving population differentiation. Our results revealed a marked physiological trade-off between growth and defences, where the slope of the trade-off was genetically variable and associated with climatic gradients. Our results help to enlighten the evolutionary patterns and genetic basis of defensive allocation within species, particularly revealing a key role of growth-defence trade-offs.

Producción Científica, Macaronesian laurel forests are the only remnants of a subtropical palaeoecosystem dominant during the Tertiary in Europe and northern Africa. These biodiverse ecosystems are restricted to cloudy and temperate insular environments in the North Atlantic Ocean. Due to their reduced distribution area, these forests are particularly vulnerable to anthropogenic disturbances and changes in climatic conditions. The assessment of laurel forest trees’ response to climate variation by dendrochronological methods is limited because it was assumed that the lack of marked seasonality would prevent the formation of distinct annual tree rings. The aims of this study were to identify the presence of annual growth rings and to assess the dendrochronological potential of the most representative tree species from laurel forests in Tenerife, Canary Islands. We sampled increment cores from 498 trees of 12 species in two well-preserved forests in Tenerife Island. We evaluated tree-ring boundary distinctness, dating potential, and sensitivity of tree-ring growth to climate and, particularly, to drought occurrence. Eight species showed clear tree-ring boundaries, but synchronic annual tree rings and robust tree-ring chronologies were only obtained for Laurus novocanariensis, Ilex perado subsp. platyphylla, Persea indica and Picconia excelsa, a third of the studied species. Tree-ring width depended on water balance and drought occurrence, showing sharp reductions in growth in the face of decreased water availability, a response that was consistent among species and sites. Inter-annual tree-ring width variation was directly dependent on rainfall input in the humid period, from previous October to current April. The four negative pointer years 1995, 1999, 2008 and 2012 corresponded to severe drought events in the study area. This study gives the first assessment of dendrochronological potential and tree-ring climate sensitivity of tree species from the Tenerife laurel forest, which opens new research avenues for dendroecological studies in Macaronesian laurel forests., Ministerio de Ciencia, Innovación y Universidades (projects PID2019-109906RA-I00, PID2020-118444GA-100 and PID2019-106908RA-I00/AEI/10.13039/501100011033), Ministerio de Ciencia, Innovación y Universidades (predoctoral contract PRE2018-084106), Ministerio de Economía, Industria y Competitividad (project CGL2017-87309-P and postdoctoral grant IJC2019-040571-I), Junta de Castilla y León (projects VA113G19 and IR2020-1-UVA08), Universidad de Valladolid (predoctoral contract 113-2019PREUVA22), Comunidad de Madrid (project S2018/EMT-4338)

Producción Científica, Tree pollarding was a dominant management strategy of European forests for centuries creating open agroforestry landscapes with important cultural and environmental values. This traditional practice has been widely abandoned in last decades with a subsequent impact in terms of biodiversity and cultural loss. Central Spain hosts the largest and best-preserved area of pollarded narrow-leaved ash (Fraxinus angustifolia Vahl.) woodlands in Europe. The main aim of this research is to obtain rigorous historical records of pollarding frequency to get adequate information for traditional ash management. We used dendrochronological techniques to evaluate temporal changes of pollarding frequency and rotation length. We analysed the stand level synchrony and the effect of land property on pollarding activity from 322 trees growing in eight pollard stands in Central Spain. Pollarding events were unequivocally identified at tree level by a characteristic change in growth pattern. We identified 2426 tree-level pruning events with the first event dated in 1777. Historical pruning recurrence ranged between 5 and 10 years with higher pollarding frequency on private lands. Pruning events within each site were synchronous, suggesting the existence of a rotational schema within each stand. Pruning frequency decreased drastically in the 1970s matching with the depopulation of rural areas and the general abandonment of traditional practices. Pollarding practices have recovered in recent decades although with lower intensity and lacking the synchronic historical patterns. Providing technical and economic support to make this traditional activity profitably would have strong environmental revenue due the multiple ecosystem services provided by pollarded ashes., iuFOR Institute Unit of Excellence" of the University of Valladolid, funded by the Junta de Castilla y León and co-financed by the European Union (ERDF "Europe drives our growth") project (CLU-2019-01), Ministerio de Ciencia e Innovación y Agencia Estatal de Investigación - MCIN/AEI/10.13039/501100011033 project PROWARM (PID2020-118444GA-100),(IJC2019-040571-I),(grant PRE2018-084106), Junta de Castilla y León, projects, (VA171P20) and (IR2020-1-UVA08), Publicación en abierto financiada por el Consorcio de Bibliotecas Universitarias de Castilla y León (BUCLE), con cargo al Programa Operativo 2014ES16RFOP009 FEDER 2014-2020 DE CASTILLA Y LEÓN, Actuación:20007-CL - Apoyo Consorcio BUCLE

Producción Científica, The ability of trees to endure for millennia, surpassing human lifetimes, and survive the most destructive human and natural hazards is astonishing. But what is the ecological role of tree longevity? Are old trees more than impressive nature wonders? Can ancient trees become effective genetic reservoirs able to recover bygone ecosystems? Oceanic islands are ideal ecosystems to address these questions, as they have experienced recent and intense human-induced environmental changes. In the Canary Islands in the northeastern Atlantic Ocean, human colonization since the fifth century BCE (Rodríguez-Varela et al., 2017) added logging, fire, and grazing pressure to a territory already experiencing regular volcanic activity. Tenerife Island is the most populated island of the Canary Islands archipelago and harbors the largest subalpine ecosystems in the entire Macaronesian Biogeographic Region. Woodlands in the Tenerife subalpine environment were once formed by the Canary Island juniper (Juniperus cedrus Webb. & Berthel.; hereafter juniper; Machado & Galván, 2012, García-Cervigón et al., 2019), but historical human pressure restricted its distribution to inaccessible spots, away from human activity, such as cliffs. [parte del texto], Comunidad de Madrid, Grant/Award Number: REMEDINAL TE-CM (S2018/EMT-4338), Junta de Castilla y León-Consejería de Educación, Grant/Award Numbers: (VA113G19), (VA171P20) y (IR2020-1-UVA08), Ministerio de Ciencia e Innovación, Grant/Award Numbers: LAUREL (PID2019-109906RA-I00), (PRE2018-084106) and PROWARM (PID2020-118444GA-100), Ministerio de Economía, Industria y Competitividad. Grant/Award Number: (IJC2019-040571-I), Secretaría de Estado de Investigación, Desarrollo e Innovación, Grant/Award Number: spRING (CGL2017-87309-P)

Trees’ growth responses to climate may depend on tree age and site conditions. In dioecious species, sex adds an extra level of complexity due to differential reproductive effort between the sexes and potentially sex-related dimorphic growth. Araucaria araucana is a long-lived dioecious conifer with outstanding morphological and functional adaptations considered an excellent model to explore interactions between radial growth, climate variability and reproductive effort. We assessed the potential dimorphism of growth rates of the sexes, the effects of site, tree age and sex on the individual climatic responses, and the growth-climate-cone production relationships of A. araucana in two environmentally contrasted sites at the Andes of south-central Chile. We quantified tree-ring growth, its dependence on weather variability, and the relationships of cone production with growth and climate. We found site-dependent sexually-dimorphic growth rates, with females growing more in the warmer site while males growing more in the colder site. Resource allocation to growth was dependent on weather conditions prior to the growing season. Clear effects of site conditions, tree sex and age on the responses of individual tree growth to climate were identified. A more resilient response to drought stress occurred in the colder site and female trees’ growth showed tighter limitations by winter snow cover. Warm conditions in spring and summer exerted an age-dependent detrimental effect on growth, which is coherent with earlier xylogenesis resumption in younger trees. Cone production was strongly dependent on antecedent weather conditions up to seven years prior to seed dispersal that induced female cone primordia formation and favoured fertilization of female cones and soil nutrient uptake. The revealed lagged connections between vegetative growth, weather cues and cone production point towards a long-term life strategy for A. araucana.

Warming-related growth decrease on southern Fagus sylvatica forests has been observed in different regions; however, whether it is a generalized fact or not remains unclear. Here we investigate the geographical pattern on growth response of the southwestern European beech forests to the warming climate shift which started in the 1980s. We sampled 15 beech forests (215 trees) across four climatically contrasting regions (Mediterranean, Pyrenean, low- and high-elevation Atlantic areas) near the southern distribution limit of the species in the Iberian Peninsula. Dendrochronological analyses were carried out to evaluate the growth of European beech since the 1950s. Growth responses quantified as pointer years, abrupt growth changes and long-term growth trends were compared between periods (before and after the 1980s climate shift), geographical regions and tree sizes. Analyses of the studied variables indicated a growth decrease in basal area increment after the climate shift in three of the four studied regions. Pyrenean stands were not negatively influenced by the climate shift, although an increase in the frequency of negative abrupt growth changes was also found there. Growth after the climate shift presented divergent patterns depending on the geographical region. Although Mediterranean and Atlantic stands presented different indicators of constrained growth, Pyrenean stands showed rising long-term growth trends. Such results suggest that regional characteristics differentially determine the growth response of the southern European beech forests to recent warming periods. Iberian beech forests located at the Pyrenees would benefit from forecasted warming conditions, whereas Atlantic and Mediterranean forests would be more prone to suffer warming-related growth decline.

Induced defences in conifers are an effective strategy that allows individuals to increase resistance against pests and pathogens by optimizing associated costs. Studies exploring inducibility of defences in conifers have usually been conducted in young individuals (i.e., seedlings and saplings) whereby effects were addressed within weeks or months after induction, limiting knowledge and generalization of long-term patterns in mature individuals growing under natural conditions. In addition, few studies have explored how plasticity and genetic differentiation among populations may affect the inducibility of defences in mature trees. We took advantage of two long-term Pinus pinaster common gardens to explore the interactive and independent contribution of genetic differentiation (i.e., variation among populations) and the environment (i.e., plasticity between sites) as drivers of variation in short-term, long-term and systemic inducibility of chemical defences (resin flow, non-volatile resin, phenolics) in response to simulated herbivore damage associated with jasmonate signalling. We provide evidence that the external application of methyl jasmonate increased the production of resin based defences in mature P. pinaster trees for at least two years after its application. We found that inducibility of defences did not differ among populations, but was rather contingent on local environmental conditions. Systemic effects of methyl jasmonate were also observed and suggest that induced responses likely involve complex within-individual reallocation of chemical defences. Our results contribute to better understanding of the ecological and evolutionary relevance of induced defence strategies in conifers and have important implications for integrating forest management practices aiming to improve forest health and resistance to pests and pathogens., This study was supported by the Spanish Government (MINECO/FEDER) grants COMPROPIN (AGL2010-18724) and RESILPIN (RTI2018-094691-B-C33), and the Xunta de Galicia-GAIN grant (IN607/2021/03). CVG received funding from the FPI Grant programme (MINECO-Spain BES-2016–076624) and from a Xunta de Galicia-GAIN/Fulbright postdoctoral fellowship (IN606B 2021/004).

Climate warming is driving an advance of leaf unfolding date in temperate deciduous forests, promoting longer growing seasons and higher carbon gains. However, an earlier leaf phenology also increases the risk of late frost defoliation (LFD) events. Compiling the spatiotemporal patterns of defoliations caused by spring frost events is critical to unveil whether the balance between the current advance in leaf unfolding dates and the frequency of LFD occurrence is changing and represents a threaten for the future viability and persistence of deciduous forests. We combined satellite imagery with machine learning techniques to reconstruct the spatiotemporal patterns of LFD events for the 2003-2018 period in the Iberian range of European beech (Fagus sylvatica), at the drier distribution edge of the species. We used MODIS Vegetation Index Products to generate a Normalized Difference Vegetation Index (NDVI) time series for each 250 × 250 m pixel in a total area of 1,013 km2 (16,218 pixels). A semi-supervised approach was used to train a machine learning model, in which a binary classifier called Support Vector Machine with Global Alignment Kernel was used to differentiate between late frost and non-late frost pixels. We verified the obtained estimates with photointerpretation and existing beech tree-ring chronologies to iteratively improve the model. Then, we used the model output to identify topographical and climatic factors that determined the spatial incidence of LFD. During the study period, LFD was a low recurrence phenomenon that occurred every 15.2 yr on average and showed high spatiotemporal heterogeneity. Most LFD events were condensed in 5 yr and clustered in western forests (86.5% in one-fifth of the pixels) located at high elevation with lower than average precipitation. Elevation and longitude were the major LFD risk factors, followed by annual precipitation. The synergistic effects of increasing drought intensity and rising temperature combined with more frequent late frost events may determine the future performance and distribution of beech forests. This interaction might be critical at the beech drier range edge, where the concentration of LFD at high elevations could constrain beech altitudinal shifts and/or favor species with higher resistance to late frosts.

Navaea phoenicea (Malvaceae) is a flagship shrub species endemic to Tenerife Island in the Canary archipelago and is included as Endangered on the Spanish Red List. We conducted a comprehensive census and monitored the structure of eight accessible populations over 10 years to develop a stage-based demographic matrix model and performed deterministic and stochastic projections. To determine the longevity of individuals, we conducted a dendrochronological study on ten collected dry samples. The censuses showed a clear, gradual decline, and the total population was around half that in previous studies. The yearly finite growth rate was strongly correlated with annual rainfall. Survival rates of seedlings were low, and high elasticity values were allocated to the larger, reproductive individuals, which showed the highest survival rates. The age of the oldest individual was 32 years, while the average age inferred from dendrochronology was 18 years. These results point to a lower longevity of individuals with respect to the values calculated by demographic models. The findings of this study suggest the importance of the preservation of reproductive individuals and their habitat, as well as the need to re-adopt legal measures of greater protection for the species, This research was funded by the CSIC Intramural project 2006-3-OI-028, Spanish Ministry of Science and Innovation research project CGL2007-66516 to JFA and a personal grant FPI 0266/2005 from Madrid Regional Government (European Social Fund) to AGFdC

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

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.

Quercus pyrenaica is one of the most widespread species in pure or mixed stands across the Iberian Peninsula. It mostly occurs in mountain areas within the Mediterranean region, but also dominates forests along the boundary to the Atlantic northern Iberia. Given this role as a transitional species, the understanding of its behavior is of great relevance in a context of climate change. We analyzed five Q. pyrenaica stands in northwestern Iberia, located along a transect of increasing elevation in the Atlantic/Mediterranean biogeographical boundary. Tree-ring chronologies were obtained by measuring the earlywood vessel size, and the radial increment on a representative number of trees. Three variables were used, namely (i) the hydraulically-weighted diameter for the earlywood vessels in the first row (DH-r1), (ii) for vessels outside this row (DH-nr1), and (iii) the latewood width (LW). Variable chronologies were compared to monthly meteorological records, and to the North Atlantic Oscillation index (NAO). LW variation was controlled by water availability during late spring-early summer all throughout the study area, but differences among sites were mostly driven by the presence of abrupt growth changes linked to forest disturbance regime. In contrast, earlywood responses were modulated by the topographic position. The three low-elevation sites, located at windward of a central mountain range, were related to environmental conditions during quiescence, whereas the two others responded at the moment of wood formation; DH-r1 was more controlled by climate than DH-nr1. The close association between NAO and vessel size was in accordance with the elevation gradient. Our results showed relevant signals related to micro-, meso-, and macroclimatic conditions, and pointed out to the existence of cause-effect relationships. Therefore, the combined time-series analysis of earlywood vessels and latewood increment is a powerful tool to understand the ecological behavior of marcescent oaks in marginal populations, which often dominate transitional areas.

We obtained tree-ring chronologies for pedunculate oak along an altitudinal gradient of four sites in NW Iberia, which covers most of the species range within the region. Trees grow under Atlantic climate, with a rainfall maximum in autumn-winter, and a minimum during summer, but lacking a remarkable drought. Chronologies included several earlywood anatomical features and ring widths, which were compared to each other. Latewood width and a subset of six earlywood variables were selected for further analyses, considering the period 1954–2003. The lowest site considerably differed from the rest of the gradient due to its milder conditions. Earlywood and latewood were unrelated at the three upper sites, and both compartments responded to different climatic factors. Hydraulic conductivity determined by vessel size was used to describe tree performance, which was modulated by temperature along the gradient. We hypothesize that the main processes involved are the timing of earlywood formation and carbohydrate dynamics. Water availability during late spring and summer affected latewood width, but only at low elevation. This paper illustrates the complexity of analyzing climate-growth relationships in oceanic areas under the absence of a prevailing limiting factor, while providing a feasible explanation of potential mechanisms involved.

The long-term history of fire regimes in the Mediterranean Andes of Chile is almost unknown. Subalpine woodlands of Austrocedrus chilensis include long-lived trees resilient to low-intensity fires, which can provide valuable tree-ring-based information about fire history. In this work, we performed an annually resolved multicentury reconstruction of past fires from fire-scar records identified in relict Austrocedrus wood found on steep highly-eroded and rocky slopes with coarser fuel structure in the upper Cachapoal Valley, central Andes of Chile. We compared this fire record with historical land-use changes and extensive reconstructions of regional precipitation and temperature, as well as large-scale climatic patterns. The highest fire frequencies were recorded in the Spanish settlement period (1541–1750), when land-clearing activities, cattle ranching, agriculture, and mining practices became widespread after the Spanish conquest. At an interannual time scale, fire occurrence and precipitation were unconnected during the Spanish settlement. By contrast, in the indigenous period (1200–1540), under the influence of the aboriginal Chiquillanes people, fires occurred in wet years with high vegetation productivity. In the livestock grazing period (1751–1950), when large cattle ranches were established, fires occurred in dry years after a wet year. Fires in this period were likely ignited under conditions of high fuel flammability to improve plant production and promote intensive livestock grazing. At a multidecadal time scale, fires were more frequent in cold periods throughout the whole record. These findings suggest that herbaceous fuel accumulation and flammability, modulated by climate variation and human land uses, were the main factors promoting fires spread in this Mediterranean subalpine area. Our research emphasizes the importance of relict Austrocedrus wood for fire history reconstruction and expands knowledge about fire regime shifts over the past eight centuries in southern South America.

AIM: We investigate the effects of the environmental and geographical processes driving growth resilience and recovery in response to drought in Mediterranean Pinus pinaster forests. We explicitly consider how intraspecific variability modulates growth resilience to drought. LOCATION: Western Mediterranean basin. METHODS: We analysed tree rings from a large network of 48 forests (836 trees) encompassing wide ecological and climatic gradients, including six provenances. To characterize the major constraints of P. pinaster growth under extremely dry conditions, we simulated growth responses to temperature and soil moisture using a process‐based growth model coupled with the quantification of climate–growth relationships. Then, we related growth–resilience indices to provenance and site variables considering different drought events. RESULTS: Pinus pinaster displayed strong variation in growth resilience across its distributional range, but common patterns were found within each provenance. Post‐drought resilience increased with elevation and drier conditions but decreased with spring precipitation. Trees from dry sites were less resistant to drought but recovered faster than trees from wet sites. MAIN CONCLUSIONS: Resilience strategies differed among tree provenances: wet forests showed higher growth resistance to drought, while dry forests presented faster growth recovery, suggesting different impacts of climate warming on forest productivity. We detected geographically structured resilience patterns corresponding to different provenances, confirming high intraspecific variability in response to drought. This information should be included in species distribution models to simulate forest responses to climate warming and forecasted aridification.

Mexican beech (Fagus grandifolia subsp. mexicana) has been classified as an endangered species because of its restricted distribution. The current distribution of Mexican beech, which is considered a Miocene relict, is limited to Tropical Montane Cloud Forests (TMCF) in the mountains of the Sierra Madre Oriental in eastern Mexico. We used dendroclimatic techniques to evaluate the effects of climate variability on the growth of Mexican beech within three forest fragments. The independent chronologies developed for the three sites were 152–178 years long. Cross-sections helped to assess the quality of the crossdating and detect false rings. Over the last 180 years, Mexican beech trees have lower mean radial growth than rates exhibited by other Fagus species. Mexican beech growth appears to be influenced by growing-season temperatures, especially mean maximum temperature. The response appears to be positive at the beginning of the growing season but becomes negative later. These results suggest that the persistence of Fagus-dominated forests in Mexico is dependent on local-scale climatic conditions of the TMCF. Mexican beech forests are associated with micro-climatic conditions that will control the fate of these forests in the face of on-going climate change.

The impact of climate on xylem structure and function has been profusely studied for a variety of species in the last decades, but the ecological role of ring porosity under increasing levels of environmental stress has been scarcely assessed. In this study, we analyse the timing of earlywood vessels occlusions by tyloses in two ring-porous species with contrasting ecological strategies ( Quercus robur and Q. pyrenaica ) along a seasonal drought gradient, and relate it to variations in earlywood vessel diameter and radial growth obtained from tree-ring series. The number of trees showing tyloses increased in summer as a result of more frequent cavitation events under drier conditions, and was more reduced for the more drought-tolerant Q. pyrenaica , which had a higher hydraulic diameter ( D h ) but lower latewood increments. D h values decreased towards the wettest sites, and were negatively related to warm and rainy conditions in winter. Our results showed that large earlywood vessel diameters are not necessarily accompanied by high rates of tyloses formation or limited growth in summer. We hypothesize that trees in seasonal environments can take advantage from large earlywood vessels, because benefits from a more efficient hydraulic system during favourable periods are higher than the risk of xylem impairment in summer.

Tetraclinis articulata is a xerothermic Mediterranean conifer native from NW Africa that grows under semiarid conditions in the Atlas Mountains. This species is particularly well adapted to water scarcity and forms xeric woodlands subjected to recurring drought, aridification and overexploitation. Wood of T. articulata has been considered of limited dendrochronological value due to abundant anatomical anomalies in their growth rings. We studied tree-ring growth and tree-ring features to check its dendrochronological potential and evaluate their climatic signals and drought legacy effects at two semiarid sites with contrasting elevation in Morocco. Tree-ring boundaries were properly identified on wood cores from 60 to 68% of the sampled trees. Intra-annual wood density fluctuations (IADF), microrings, missing rings and rings with undefined limits were most abundant at the low-elevation coastal site than at the mountain site. Microring and missing ring abundance was inversely related to tree-ring growth, independent of cambial age, and mostly dependent on drought occurrence. IADF frequency was independent of tree-ring growth but inversely related to cambial age. A complex response of IADF formation to cool March to June conditions was found at the low-elevation coastal site, while IADF formation in the mountain site was related to May water availability. Undefined ring limits were observed only at the low-elevation site, showing positive relationships with elevated maximum temperatures in previous winter. Previous winter rainfall favored radial growth, but a significant legacy effect of water availability was evident up to three years prior to growth. Tree-ring growth was mostly related to water availability 33 and 26 months prior to growth at low-elevation and mountain sites, respectively. The obtained results reveal a very plastic cambial activity and a strong ability of T. articulata to withstand drought even for long periods.

Oceanic islands ecosystems are among the most endangered in the world, as the effects of ongoing climate change may potentially combine with other pre-existing drivers of plant population decline. In the Canary Islands, nitrogen-fixing Teide broom (Spartocytisus supranubius) is a keystone species in the Teide National Park high mountain ecosystem. However, recruitment failure due to introduced herbivores and dieback episodes are decimating its populations. We explored the role of climate as a potential driver of Teide broom mortality. We analyzed annual rings of Teide broom to reconstruct the impact of climate on secondary growth, intrinsic water use efficiency (iWUE) and mortality, and to explore the potential for growth rates and levels of resilience to act as indicators of mortality risk. We found that higher precipitation from October to February improved Teide broom secondary growth, whereas iWUE increased with high July–August temperatures. Extreme drought events in 2001 and 2012 strongly reduced secondary growth and resulted in subsequent plant death. Individuals that subsequently died had lower growth rates, poorer capacity for growth recovery after drought events and marginally higher iWUE than those which survived. More frequent recurrence of extreme drought events in the future would increase the frequency of dieback episodes, and the combination of a decline in mature individuals and lower recruitment rates due to exotic herbivore pressure would mean an uncertain future for the Teide broom. Our results indicate how global change may impact keystone species in protected areas and highlight the need for urgent implementation of proactive conservation policies.

International audience; Increased drought frequency and severity may reshape tree species distribution in arid environments. Dioecious tree species may be more sensitive to climate warming if sex-related vulnerability to drought occurs, since lower performance of one sex may drive differential stress tolerance, sex-related mortality rates and biased sex ratios. We explored the effect of sex and environment on branch hydraulic (hydraulic conductivity and vulnerability to embolism) and trunk anatomical traits in both sexes of the dioecious conifer Juniperus thurifera L. at two sites with contrasting water availability. Additionally, we tested for a trade-off between hydraulic safety (vulnerability to embolism) and efficiency (hydraulic conductivity). Vulnerability to embolism and hydraulic conductivity were unaffected by sex or site at branch level. In contrast, sex played a significant role in xylem anatomy. We found a trade-off between hydraulic safety and efficiency, with larger conductivities related to higher vulnerabilities to embolism. At the anatomical level, females' trunk showed xylem anatomical traits related to greater hydraulic efficiency (higher theoretical hydraulic conductivity) over safety (thinner tracheid walls, lower Mork's Index), whereas males' trunk anatomy followed a more conservative strategy, especially in the drier site. Reconciling the discrepancy between branch hydraulic function and trunk xylem anatomy would require a thorough and integrated understanding of the tree structure-function relationship at the whole-plant level. Nevertheless, lower construction costs and higher efficiency in females' xylem anatomy at trunk level might explain the previously observed higher growth rates in mesic habitats. However, prioritizing efficiency over safety in trunk construction might make females more sensitive to drought, endangering the species' persistence in a drier world.

Conifers have evolved different chemical and anatomical defences against a wide range of antagonists. Resin ducts produce, store and translocate oleoresin, a complex terpenoid mixture that acts as both a physical and a chemical defence. Although resin duct characteristics (e.g., number, density, area) have been positively related to biotic resistance in several conifer species, the literature reporting this association remains inconclusive. Axial resin ducts recorded in annual growth rings are an archive of annual defensive investment in trees. This whole-life record of defence investment can be analysed using standard dendrochronological procedures, which allows us to assess interannual variability and the effect of understudied drivers of phenotypic variation on resin-based defences. Understanding the sources of phenotypic variation in defences, such as genetic differentiation and environmental plasticity, is essential for assessing the adaptive potential of forest tree populations to resist pests under climate change. Here, we reviewed the evidence supporting the importance of resin ducts in conifer resistance, and summarized current knowledge about the sources of variation in resin duct production. We propose a standardized methodology to measure resin duct production by means of dendrochronological procedures. This approach will illuminate the roles of resin ducts in tree defence across species, while helping to fill pivotal knowledge gaps in plant defence theory, and leading to a robust understanding of the patterns of variation in resin-based defences throughout the tree’s lifespan.

Extreme climatic events, such as late frosts in spring during leaf flush, have considerable impacts on the radial growth of temperate broadleaf trees. Albeit, all broadleaved species are potentially vulnerable, damage depends on the particularities of the local climate, the species, and its phenology. The impact of late spring frosts has been widely investigated in the Northern Hemisphere, but the potential incidence in Southern Hemisphere tree species is still poorly known. Here, we reconstruct spring frost occurrence at 30 stands of the deciduous tree Nothofagus pumilio in its northern range of distribution in the Patagonian Andes. We identified tree ring-width reductions at stand level not associated with regional or local drought events, matching unusual minimum spring temperatures during leaf unfolding. Several spring frosts were identified along the northern distribution of N. pumilio, being more frequent in the more continental Argentinean forests. Spring frost in 1980 had the largest spatial extent. The spring frosts in 1980 and 1992 also induced damages in regional orchards. Spring frost damage was associated with (i) a period of unusually warm temperatures at the beginning of leaf unfolding, followed by (ii) freezing temperatures. This study helps expand our understanding of the climatic constraints that could determine the future growth and dynamics of Andean deciduous forests and the potential use of tree-rings as archives of extreme events of spring frosts in northern Patagonia.

Climate change is increasing the frequency of extreme climate events, causing profound impacts on forest function and composition. Late frost defoliation (LFD) events, the loss of photosynthetic tissues due to low temperatures at the start of the growing season, might become more recurrent under future climate scenarios. Therefore, the detection of changes in late-frost risk in response to global change emerges as a high-priority research topic. Here, we used a tree-ring network from southern European beech (Fagus sylvatica L.) forests comprising Spain, Italy and the Austrian Alps, to assess the incidence of LFD events in the last seven decades. We fitted linear-mixed models of basal area increment using different LFD indicators considering warm spring temperatures and late-spring frosts as fixed factors. We reconstructed major LFD events since 1950, matching extreme values of LFD climatic indicators with sharp tree-ring growth reductions. The last LFD events were validated using remote sensing. Lastly, reconstructed LFD events were climatically and spatially characterized. Warm temperatures before the late-spring frost, defined by high values of growing-degree days, influenced beech growth negatively, particularly in the southernmost populations. The number of LFD events increased towards beech southern distribution edge. Spanish and the southernmost Italian beech forests experienced higher frequency of LFD events since the 1990s. Until then, LFD events were circumscribed to local scales, but since that decade, LFD events became widespread, largely affecting the whole beech southwestern distribution area. Our study, based on in-situ evidence, sheds light on the climatic factors driving LFD occurrence and illustrates how increased occurrence and spatial extension of late-spring frosts might constrain future southern European beech forests' growth and functionality. Observed alterations in the climate-phenology interactions in response to climate change represent a potential threat for temperate deciduous forests persistence in their drier/southern distribution edge.

To counteract the effects of herbivores and pathogens, conifers have developed a sophisticated resin-based defensive system. Since defences are costly, trees must continuously accommodate defensive investment throughout plastic responses to environmental stimuli. However, the extent of such responses can differ at the intra-specific level (i.e. genetic variation in plasticity). Here we examined whether and to what extent year-to-year climate fluctuations, an important source of environmental heterogeneity during the trees' life, drive plasticity in defensive allocation of a widespread pine species. Specifically, we quantified interannual variation in resin duct production along a 31-year-period in 174 Pinus pinaster trees of nine range-wide populations grown in two common gardens in Central Spain. We aimed to explore (i) patterns of interannual variation (i.e., temporal plasticity) in resin duct production among populations and sites, (ii) whether such patterns are linked to plastic responses to interannual variation in climate conditions (i.e., climatic plasticity), and (iii) whether plastic responses to climate differ among populations (i.e., genetic variation in plasticity) and sites. We found large interannual plasticity in resin duct production (22.8 % of total variance), with temporal patterns differing among sites and populations. Climate conditions during the early growth period significantly affected the annual differentiation of resin ducts. Particularly, April precipitation had a positive overall effect on resin duct production. Inversely, warmer conditions in April had a negative effect but only in certain populations, which demonstrates genetic variation in climate sensitivity of resin duct formation. Despite significant effects of certain climate variables on annual resin duct production, climate only accounted for a small proportion of the total interannual variation (up to 3.8 % of interannual variation explained by climate factors). This suggests that alternative factors such as trade-offs with growth and temporal variation in biotic and non-climatic abiotic conditions likely contribute to explain interannual fluctuations in defensive investment.

The climate response and resilience of tree growth to drought events have been widely reported for forests from the Northern Hemisphere. However, studies are much scarcer in the extra-tropical forests of southern South America. Mediterranean and Temperate forests of Chile are suffering from a moderate warming and a sustained precipitation decrease, occurring on top of an unprecedented megadrought since 2010. This study evaluated tree-growth patterns, the climate response and drought resilience of nine secondary Nothofagus obliqua forests across a latitudinal gradient from Mediterranean to Temperate climate in the Andes of Chile (35.7° to 40.3° S). Moreover, to improve the understanding of the spatial variation in productivity patterns, this research assessed trends in the maximum Normalized Difference Vegetation Index (peak in the NDVI) across the gradient for 2001–2018. Tree-growth patterns were highly influenced by stand dynamics, with steep decreasing trends in most of the stands related to a gradual canopy closure. Productivity trends had a flat pattern north of 38oS, but positive trends south of this latitude, which were mostly attributed to stand development. Tree growth was positively related to precipitation in all the sites, with annual and summer rainfall being more important in the north (Mediterranean climate) and south (Temperate climate), respectively. Conversely, maximum temperature had a negative effect on growth in most of the studied forests. This implies that projected warmer and drier conditions may have a detrimental effect on N. obliqua growth during coming decades. The two northern stands, located at the species dry range edge, were among the most resilient to drought and have not been strongly affected by the current megadrought in the area. Overall climate conditions, however, do not define the tolerance of stands to droughts, likely because local environmental and forests conditions play a key role. Although droughts have not strongly impacted the growth of N. obliqua across its distribution so far, future studies should assess the effects of the current long-term megadrought on growth resilience, and physiological studies should address the impacts of droughts and heat waves on forest function beyond what growth can unveil.

Summary Environmental conditions and the structure of the dormant cambium are assumed to affect seasonal patterns of cambial activity, hence controlling allocation of non-structural carbohydrates (NSC) to growth. However, seasonal dynamics of xylogenesis, and their connections with NSC content and dormant cambium size, have been rarely assessed along an environmental gradient. We monitored xylogenesis and leaf phenology during 2012 and 2013, and NSC in 2012, for the drought-sensitive Quercus robur and the drought-tolerant Quercus pyrenaica along a water-availability gradient in the north-western Iberian Peninsula, and analysed dependencies of xylem production and phenology on the number of cells in dormant cambium. Study oak species showed comparable seasonal fluctuations in cambial activity and NSC content, despite Q. pyrenaica had a shorter growing season and a lower wood production than Q. robur. A sharp drop in spring NSC levels at all study sites evidenced that stored carbohydrates were crucial for earlywood formation. Under drier conditions, both species extended the growing period in spring and autumn, but reduced and even stopped xylogenesis in summer, showing an enhanced NSC accumulation before dormancy. A higher number of cells in dormant cambium of large dominant oaks accounted for their wider xylem increments and longer active periods. Our study demonstrates that xylogenesis is modulated by predisposing effects of dormant cambium size on xylem production and growing season length. Moreover, the high plasticity of cambial activity in deciduous oaks would confer resistance against recurrent summer drought through the improvement of the NSC status. A lay summary is available for this article.

El ancho de los anillos de crecimiento y las fluctuaciones intra-anuales de densidad de la madera (IADF) contienen información sobre los factores ambientales que controlan el desarrollo de las especies forestales. En este trabajo se evaluaron los efectos del clima sobre el crecimiento radial y la formación de IADF en una plantación de Austrocedrus chilensis en Valdivia, Chile. Se calcularon la cronología media de crecimiento radial y la distribución anual de frecuencias de IADF de 20 árboles y se estudió su relación con la precipitación, la temperatura y los índices de El Niño Oscilación del Sur (ENSO) y Oscilación Antártica (AO) en el período 1975-2010. Se utilizaron análisis de correlación y regresión múltiple para estudiar la relación crecimiento-clima y la prueba t de comparación de medias para contrastar diferencias entre años con y sin IADF. Se observó una relación inversa del crecimiento con la precipitación del verano previo y la temperatura máxima durante el período de crecimiento, evidenciando condiciones de estrés por exceso de precipitación y elevadas temperaturas estivales. Los años con máxima frecuencia de IADF en la madera de A. chilensis fueron aquellos en que se produjo un episodio El Niño, que en el área de estudio causa veranos secos y cálidos, seguidos por un mes de septiembre lluvioso. No se observaron relaciones significativas con AO. La interacción entre el clima local y ENSO ha controlado la formación de fluctuaciones intra-anuales de la densidad de la madera de A. chilensis en Valdivia.

The adaptive potential and genetic background of tree species will determine their performance and vitality under changing climate conditions. How environment and genotype influence secondary growth and their climate sensitivity in boreal and temperate conifers has been fairly studied. Provenance studies assessing the genetic variation in plasticity of radial growth, however, are scarce in Mediterranean tree species. We explored the impact of climate on tree-ring growth in Pinus pinaster based on plantation sites and genetic background. We assessed the climate sensitivity, plastic response of growth, and intraspecific genetic differentiation of pines from 10 provenances planted in two trials in south-central Spain. Trees from areas with a climate similar to that of the planting sites showed greater growth rates. Higher within-site than among-site similitude in inter-annual growth variation was evidenced by similar growth patterns in each trial test, irrespective of seed provenance. We found positive growth responses to mild conditions in late winter, and to wet and cloudy conditions in spring and early summer. Greater site-dependent than genetically-driven control was observed on growth sensitivity to climate. Central Spanish seed sources were better able to withstand the combination of stressful environmental conditions in the test sites. Inter-site environmental variation was the factor that explained a higher number of growth responses to climate variation. The significant “genetic × environment” interaction on radial growth suggested that genotypic determinants were strongly modulated by plastic adaptations due to local conditions. The site-dependent relationships of provenance climate responses with the conditions at origin also reflected the prevailing local adaptation to site constraints. Since plastic response of P. pinaster trees to local environment has more influence than its genetic predisposition, assessing the spatio-temporal variation of growth sensitivity to climate becomes increasingly important.

Quantifying intraspecific genetic variation and phenotypic plasticity of traits involved in drought tolerance is essential to forecast forest tree vulnerability to climate change. Tree ring analysis was applied to retrospectively assess the resistance, recovery and resilience of a Mediterranean pine in the face of extreme climate episodes. We combined a dendrochronological approach with the analysis of common-garden tests to disentangle genetic, environment and genetic-by-environment effects in growth responses of 10 P. pinaster populations to two extreme climatic events. Trees were 43 years old and had experienced two intense droughts, in 1995 and 2005. Drought events caused drastic reductions in secondary growth, but trees showed high capacity to recover pre-drought growth rates. The differences in the characteristics of the two drought events and the environmental distance between sites strongly modulated maritime pine responses to extreme droughts. However, a common among-population signal across sites and events was detected in the drought response strategy. Among-population variation in response to extreme droughts was evident for the resistance and recovery components, two strategies that appeared to trade-off between each other. Populations from Atlantic climates showed higher resistance but lower recovery capacity, whereas Mediterranean origins prioritised recovery over resistance. Mediterranean populations showed a more conservative strategy that indicated an adaptive advantage under water stress, reflected in greater long-term survival. The abovementioned relationships were clear in the site where the impact of the drought events was strongest, but not in the more favourable site. Differences in relationships between sites reflect that strategies of populations to cope with drought are strongly context dependent. Based on these results, we infer that future extreme droughts will differentially affect P. pinaster populations across the natural range of the species. Immediate effects will be more evident in Mediterranean areas but, in the long term, population persistence in the face of climate change will be more compromised for Atlantic origins. Because local environmental conditions can considerably modulate responses to extreme events, special attention is required to define appropriate management practices to mitigate the impact of future droughts.

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)

International audience; Deciphering climatic factors limiting cambial activity is critical to forecast the potential of trees to respond to ongoing climatic change. We explored multiple xylem traits, including tree-ring width, inter-annual micro-density variation and intra-annual density fluctuations (IADF), to unveil the climatic factors constraining cambial activity of a Mediterranean conifer (Pinus pinaster) along a continental-aridity gradient. Secondary growth responded mainly to water availability, explaining as much as 64.7% of earlywood growth variance for earlywood growth. The continuous and non-overlapping timing of the climatic signals of earlywood and late wood growth reflected a continuous water limitation of secondary growth along the growing season. Drought also had an extraordinary impact on minimum (D-min) and maximum (D-max) density, with maximal explained variances reaching 47.4% and 39.1%, respectively. D-min was negatively associated to water availability during the initiation of earlywood formation, whereas D-max responded positively to water availability during two distinct periods: previous winter and the initiation of latewood formation. IADFs in the latewood were quite common along the gradient, occurred in 21-51% of the rings, and responded to episodes of high rainfall and elevated temperature at different phases of latewood formation. Xylem traits identity outperformed site as a driver of climatic signal, revealing the potential of a multi-proxy approach to unveil multiple facets of the xylogenetic cycle. Cambial plasticity, i.e. the ability to adjust the xylogenesis rate and to arrest and resume cambial activity to exploit favorable climatic windows, was critical for Pinus pinaster to thrive within wide climatic envelopes. Nevertheless, the pervasive effect of water availability on all analyzed traits indicates that forthcoming reduced precipitation and increased evapotranspiration, as predicted by climate change models, will negatively impact P. pinaster secondary growth along its whole environmental range.

Semiarid woodlands dominated by calden ( Prosopis caldenia Burkart) thrive at the dry edge of the Argentinean Pampas. While the area of original woodlands shrinks due to deforestation, adjacent areas experience the advance of calden. The aim of this study was to determine the factors that favoured recruitment of calden along its natural range and in adjacent grasslands and ecotone woodlands. Eight sampling sites were selected in the original calden's woodlands, in the grassland and in the ecotone. Standard dendrochronological techniques were applied to estimate establishment dates, date fire events and growth releases. Recruitment of calden was massive and episodic. Two recruitment events were noticed in the woodland area in the 1790s and 1870s, which coincided, respectively, with the first settlement of aborigines and the generalised use of fire. Two periods with contrasted patterns of calden establishment were distinguished in the 20th century: 1920–1969 with an abundant recruitment that started with land abandonment by foreigner colonizers, and 1970–2010 with almost no regeneration. Tree establishment was linked to fire. Sheep numbers had a positive effect on growth release of calden. Calden recruitment should be considered a multi-causal process that integrates the effects of several factors mostly driven by anthropogenic land-use changes.

In this work, an individual-based approach was used to assess the relative importance of tree age, size, and competition in modulating the individual dendroclimatic response of Quercus robur L. This was performed in a multi-aged forest in northwestern Spain under a wet Atlantic climate. All trees in five replicated forest stands with homogeneous soil conditions were mapped and inter-tree competition was quantified with a distance-dependent competition index. Tree rings of cored trees were crossdated and total age was estimated on individuals where the pith was missed. The climatic response was evaluated by bootstrapped correlations of individual tree-ring chronologies with climatic records. Inter-annual growth variation, i.e., mean sensitivity, was independent of tree age and bole diameter, but modulated by competition. Water excess in previous summer-autumn and spring negatively affected growth, while warmer September conditions favored growth. Individual response to climate was independent of tree age, but related to the joint effect of tree bole diameter and competition. Larger oaks in less competitive environments responded more plastically to climatic stress, while smaller trees under high competition levels were less responsive to climate. Strong inter-tree competition reduced growth plasticity but amplified the vulnerability of smaller oaks to the particularly rainy conditions of the study area. These findings suggest that inter-tree competition is a relevant size-mediated extrinsic factor that can potentially modulate individual radial growth variation and its response to limiting climatic conditions in temperate deciduous forests. This study highlights the value of individual-based approach as a useful tool that informs about the relative contribution of factors modulating the climatic response of tree-ring growth.

16 Pags.- 3 Tabls.- 5 Figs., Forecasted increase drought frequency and severity may drive worldwide declines in forest productivity. Species‐level responses to a drier world are likely to be influenced by their functional traits. Here, we analyse forest resilience to drought using an extensive network of tree‐ring width data and satellite imagery. We compiled proxies of forest growth and productivity (TRWi, absolutely dated ring‐width indices; NDVI, Normalized Difference Vegetation Index) for 11 tree species and 502 forests in Spain corresponding to Mediterranean, temperate, and continental biomes. Four different components of forest resilience to drought were calculated based on TRWi and NDVI data before, during, and after four major droughts (1986, 1994–1995, 1999, and 2005), and pointed out that TRWi data were more sensitive metrics of forest resilience to drought than NDVI data. Resilience was related to both drought severity and forest composition. Evergreen gymnosperms dominating semi‐arid Mediterranean forests showed the lowest resistance to drought, but higher recovery than deciduous angiosperms dominating humid temperate forests. Moreover, semi‐arid gymnosperm forests presented a negative temporal trend in the resistance to drought, but this pattern was absent in continental and temperate forests. Although gymnosperms in dry Mediterranean forests showed a faster recovery after drought, their recovery potential could be constrained if droughts become more frequent. Conversely, angiosperms and gymnosperms inhabiting temperate and continental sites might have problems to recover after more intense droughts since they resist drought but are less able to recover afterwards., This study was financially supported by the Spanish Ministry of Economy 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). The study was also funded by IMDROFLOOD (Water Works 2014, EC) and INDECIS (European Research Areas for Climate Services) projects. 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. RSS and AG were supported by Postdoctoral grants (IJCI‐2015‐25845 and MINECO‐FPDI 2013‐16600; FEDER funds).

RESUMEN Nothomyrcia fernandeziana (Hook. & Arn.) Kausel es una especie endemica de los bosques de la isla Robinson Crusoe (RC), Archipielago de Juan Fernandez, Chile. Aristotelia chilensis (Molina) Stuntz es una especie invasora introducida en la isla a mediados del siglo XIX que compite con las especies endemicas, poniendo en riesgo su conservacion. Los patrones de crecimiento radial permiten inferir estrategias biologicas de las plantas lenosas como longevidad, tolerancia a la sombra y capacidad competitiva, caracteristicas de gran importancia para los programas de conservacion. Los objetivos de este trabajo fueron caracterizar los anillos de crecimiento de ambas especies y estudiar sus patrones de crecimiento con el objeto de aportar conocimiento base que contribuya a la conservacion de los bosques endemicos de RC. Se realizo el estudio anatomico y dendrocronologico de los anillos de crecimiento en secciones transversales del tronco de ambas especies en RC, asi como de A. chilensis en su area de distribucion natural en Chile continental. La madera de ambas especies presento anillos de crecimiento bien diferenciados. N. fernandeziana mostro un crecimiento juvenil reducido, arboles longevos y alta capacidad de liberacion del crecimiento (aumento superior al 100% del promedio de los valores de ancho de anillos de los 10 anos previos al evento). A. chilensis, sin embargo, presento una alta tasa de crecimiento durante su ontogenia y escasa longevidad, comportandose como especie pionera en RC al igual que en su area de distribucion natural. Sobre la base de estos resultados, se recomienda actuar favoreciendo el establecimiento de N. fernandeziana a la sombra de A. chilensis, propiciando la gradual sustitucion de la especie invasora por especies endemicas de RC.