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AimsWe aimed to evaluate how climatic fluctuations influence the plasticity of anatomical vessel traits and the width of annual tree-rings of two relict-endemic Mexican Magnolia species. Notwithstanding, few studies have assessed the drought effect on vessel traits in tropical montane cloud trees of eastern Mexico.MethodsThrough digital images of growth rings, we assessed the tree radial growth rate, age of the trees and plasticity in vessel traits regarding climatic fluctuations of the Mexican Magnolia species studied. We compared vessel density, hydraulic diameter and percentage of conductive area in drought years (DY) and non-drought years (NDY) in two Mexican Magnolia species.Important FindingsFor the first time, the plasticity that occurs in porous wood vessel traits to long-term climatic fluctuations was analysed for two endangered Magnolia species (Magnolia vovidesii and M. schiedeana) from two tropical montane cloud forests in Mexico. We found that temperature and precipitation were strongly associated with differences in tree-ring width when DY and NDY were compared. Our analyses revealed that a high plasticity in vessel anatomy of diffuse-porous wood was related to temperature and/or water availability for both Magnolia species studied. We concluded that anatomical adaptations to DY resulted in a substantial reduction in vessel traits when compared with NDY, and that the plastic adaptations played an essential role in water transport and safety for the survival of the studied species during stressful long periods.

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)

Identificador de proyecto: Marie Sklodowska-Curie grant agreement No 101029581, Long-term records of tree-ring width (TRW), latewood maximum density (MXD) and blue intensity (BI) measurements on conifers have been largely used to develop high-resolution temperature reconstructions in cool temperate forests. However, the potential of latewood blue intensity (LWBI), less commonly used earlywood blue intensity (EWBI), and delta (difference between EWBI and LWBI, dBI) blue intensity in Mediterranean tree species is still unexplored. Here we developed BI chronologies in moist-elevation limits of the most southwestern European distribution of Pinus nigra subsp. salzmanii Arnold. We tested whether BI variables derived from tree rings of black pine are better proxies than ring-width variables to reconstruct long-term changes in climatic factors and water availability. For this we applied correlations and regression analyses with daily and monthly climate data, a spatial and temporal drought index (Standardized Precipitation-Evapotranspiration Index-SPEI) and Vapour Pressure Deficit (VPD), as well as atmospheric circulation patterns: North Atlantic Oscillation (NAO), Southern Oscillation Index (SOI) and Western Mediterranean Oscillation (WeMO). We found a positive relation between black pine growth (RW) and temperature during the winter preceding the growing season. Among all variables LWBI and dBI were found to be more sensitive than TRW to SPEI at low-elevation site, with EWBI series containing an opposite climatic signal. LWBI and dBI were significantly related to June and September precipitation at high-elevation site. Winter VPD was related with higher EWI and LWI series, whereas dBI and EWBI were related with January SOI and February NAO. We confirm the potential of long-term dBI series to reconstruct climate in drought-prone regions. This novel study in combination with other wood anatomical measurements has wide implications for further use of BI to understand and reconstruct environmental changes in Mediterranean conifer forests., Wageningen University & Research, Universidade de Santiago de Compostela, University of Amsterdam

We investigated how temperature patterns affect cambial activity and leaf phenology of oak across a wide range of natural woodlands at its southwestern distribution boundary. Understanding the climatic control of wood formation in dominant species is very relevant to infer tree responses to ongoing environmental changes and their impact on the carbon cycle. We selected nine sites along two elevation gradients from the coastline in northwestern Iberia, and sampled ten trees per site biweekly during 2012 and 2013. Leaf and cambial phenological phases were related to mean air temperature for 10–60 day running periods along the year to identify the most relevant time windows for cambium and leaf phenophases, and the relationships among them. The first earlywood vessels expanded before the appearance of small leaves, and subsequently underwent maturation to meet water requirements for full leaf unfolding. The advance or delay of cambial reactivation and budburst varied among sites and years modulated by spring temperature, and were respectively maximized by maximum and minimum values. Temperature can modify the onset of early phenophases of primary and secondary growth differently, and also the synchronicity between them. However, the maturation of the first earlywood vessels is necessary to undergo full leaf extension.

Northwestern Iberia is characterized for being an Atlantic/Mediterranean transitional area, where the most natural forests contain certain species, typical from either biogeographic region, growing under limiting conditions due to their marginal location. In order to identify the main climatic factors controlling growth, and thus better understand how they impact wood formation processes of the key tree species in these ecosystems, we analyzed tree rings of two somehow contrasting oaks (Quercus robur, Atlantic; and Q. pyrenaica, sub-Mediterranean) at their distribution boundary towards the Mediterranean region. For this, two nearby sites with slightly different regime of water availability were selected for each species. We developed chronologies of radial increment (expressed as latewood width) and functional anatomical traits (size and number of earlywood vessels) for the last decades, and also monitored wood formation along two growing seasons. Our results suggest that the combination of anatomical traits and radial growth constitute a useful tool to understand the behavior of these species in boundary distribution areas. We found some differences between sites, especially for Q. pyrenaica, but the main factors controlling growth were clearly identified at all sites. Earlywood characteristics were mainly related to temperature, whereas latewood width responded to precipitation, regardless of the species. However, vessels of low-elevation Q. robur seemed to be controlled by factors affecting carbohydrate balance, while those of high-elevation Q. pyrenaica were associated to spring conditions for growth resumption. Summer water availability was linked to a wider latewood for both species. In addition, the analysis of xylogenesis carried out at all sites was essential to interpret climate responses by providing evidences for the existence of a cause-effect relationship.

Aim Spatial variations of environmental conditions translate into biogeographical patterns of tree growth. This fact is used to identify the origin of timber by means of dendroprovenancing. Yet, dendroprovenancing attempts are commonly only based on ring‐width measurements, and largely neglect additional tree–ring variables. We explore the potential of using wood anatomy as a dendroprovenancing tool, and investigate whether it increases the precision of identifying the origin of oak wood. Since different tree–ring variables hold different information on environmental conditions prevailing at specific times of the growing season—which vary between source regions—we hypothesize that their inclusion allows more precise dendroprovenancing. Location Europe, Spain. Taxon Quercus robur L., Quercus petraea (Matt.) Liebl., Quercus faginea Lam., Quercus pyrenaica Willd. Methods We sampled four oak species across Northern Spain, i.e. from the Basque country and Cantabria and—in the Basque country—from low to high elevation (topographic/latitudinal gradient). We measured multiple tree–ring variables to (a) extract complementary variables; (b) present statistical relations among them; (c) analyse region‐specific variation in their patterns based on time–series of individual trees; and (d) determine underlying climate–growth relationships. Leave‐one‐out analysis was used to test whether a combination of selected variables allowed dendroprovenancing of a randomly selected tree within the area. Results A combination of latewood width (LW) and earlywood vessel size was used to pinpoint the origin of oak wood with higher precision than ring width or LW only. Variation in LW pinpointed the wood to east and west areas, whereas variation in vessels assigned wood to locations along a latitudinal/topographic gradient. The climatic triggers behind these gradients are respectively an east–west gradient in June–July temperature and a north–south gradient in winter/spring temperatures. The leave‐one‐out analyses supported the robustness of these results. Main conclusions Integration of multiple wood–xylem anatomical variables analysed with multivariate techniques leads to higher precision in the dendroprovenancing of ring‐porous oak species. This research work is part of the ForSEAdiscovery project (Forest Resources for Iberian Empires: Ecology and Globalization in the Age of Discovery), and was funded by the Marie Curie Actions programme of the European Union (PITN‐2013‐607545). This work was supported by a postdoc fellowship of the German Academic Exchange Service (DAAD) SI

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.

A quantitative method was tested to describe crown phenophases in relation to water content and to secondary growth in ring-porous species, based on the hypothesis that new shoots require hydrated tissues to maintain the necessary turgor for extension, leading to a reduction in dry matter content (DMC). We collected a three-year-old branch from 11 Quercus pyrenaica Willd. trees at 10-day intervals to estimate DMC of newly developing buds, leaves, and twigs, and processed two opposite stem microcores for xylogenesis. Branch phenophases and shoot length were recorded in the field. The DMC of all organs decreased during crown development, with a minimum in early June, followed by a gradual increase up to initial values in late September. The shoot extension period concurred with the lowest DMC, but also with the beginning of earlywood maturation in the main stem, suggesting a high tissue hydration only when earlywood vessels become functional to fulfill enough water requirements for shoot and leaf extension. These results confirm the usefulness of DMC to accurately quantify the phenology of primary growth from bud swelling up to full leaf extension, as a complement to qualitative methods. This variation in DMC appears to be linked to secondary growth as a result of earlywood vessel development.

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.

Combined dendrochronological and archival research revealed the history of construction and subsequent repairs to the roof structures of Segovia Cathedral, the last gothic cathedral built in Spain. Although this iconic building has been extensively documented by different scholars, the completion date of the 16th century original sacristy was uncertain. Furthermore, disaster struck the building on two occasions, in the 17th and 18th centuries. First, on September 1614, lightning hit the bell tower and fire spread through the roof of the nave. Then, on 1 November 1755, the Lisbon earthquake shook the cathedral building. However, the extent of the damage caused by these events was unknown. Our combined research revealed that the trees used to make the tie-beams of the sacristy were cut in the late summer/winter months of 1676/77, one century later than the completion date, suggesting that this part of the original sacristy was renewed when a new one was built together with the offices in an annexed building. Furthermore, absolute dates obtained for the nave indicate that the trees used to build the current roof structure were cut in the autumn/winter of 1614/15, which implies that the 16th century original roof must have burned down entirely due to the lightning fire. A historical document registering the purchase of the wood to repair this structure in 1614 confirms this information. Finally, the damage caused by the Lisbon earthquake must have compromised the structural integrity of the roof, as the support timbers used to reinforce it belong to small trees cut in the spring or summer of that same year 1755. Archival research revealed that the roofs were inspected a few weeks after the earthquake, and that repairs were carried out in 1756. This suggests that the wood to prop up the structure was most likely purchased shortly after the inspection (probably in a nearby saw mill where cheap wood from trees cut in the summer of 1755 was available), and before the repairs took place.

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).

Studies on the provenance of wood for shipbuilding contribute widely to the fields of archaeology, anthropology, environmental history, cultural geography, and palaeoclimatology. The development of reference datasets to determine the date and provenance of shipwreck timbers is therefore a paramount undertaking. Here we compile and present recent advances in the development of tree-ring chronologies, stable strontium isotope ratios and chemical biomarkers aimed to determine the date and provenance of Iberian shipwreck timbers. A set of oak and pine tree-ring chronologies have been developed from living trees covering the past 500 and 800 years, respectively, and have served to confirm the provenance of the wood used in an 18th-century Spanish ship of the Royal Navy. Stable strontium isotopic signatures have been obtained from soil and living trees at 26 sites throughout the Iberian Peninsula, providing a climate-independent geochemical network to source the origin of historic timbers. However, retrieving the original isotopic signature from waterlogged samples remains unsuccessful, stressing the need to develop effective protocols to separate the seawater signal from the original strontium isotope ratios in the wood. Analyses of organic compounds in wood of living trees have proven suitable to discriminate species and provenances, but results on shipwreck timbers are inconclusive and should be further explored. Our regional approach has the potential to be expanded to other areas and archaeological timbers from different periods throughout the Anthropocene. We highlight the strengths and weaknesses of the techniques presented when applied to waterlogged wood, propose GIS tools to interpret and visualize combined results, and stress the need to expand these type of reference datasets to allow for multiproxy dendroprovenancing approaches This research, and particularly authors MDD, SR, MT, FH, LA, and PG, was funded by the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP72007-2013) under REA grant agreement no. PITN-GA 2013-607545. MDD has also received funding from the Dutch Research Council [Nederlandse Organisatie voor Wetenschappelijk Onderzoek, grant number 016.Veni.195.502] SI

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.

We selected two sites dominated by the sub-Mediterranean oak Quercus pyrenaica Willd. close to its distribution boundary in northwestern Iberia, within a mountain region with a high winter precipitation. The sites differed in their soil water regime, corresponding to the edge of a peat bog, and to a moderate slope. We obtained tree-ring chronologies of total ring width (RW), and mean earlywood vessel area (MVA); their responses to climatic factors were compared for the period 1945–2002. RW presented a higher chronology quality than MVA, but was rather independent of climate, probably because of the presence of recurrent growth reductions. In contrast, MVA was closely related to precipitation during April and May, whereby a high water availability was coupled to smaller vessels. We found remarkable differences between the climatic signal of both stands, as trees growing on the peat soil responded later and with considerably lower intensity. We hypothesize that spring waterlogging causes that the response at the wettest site occurs only when soil desiccation begins, which results in a delayed climatic signal, and also lower intra- and inter-annual variation due to more homogeneous conditions. Climate–growth relationships at the driest site were mainly associated with the first row, whereas it is vessels expanding later in the season that show this relation for the moist site. Our results confirm that MVA chronologies are reliable proxies of both regional and local climatic conditions, but only a careful optimization by selecting vessel subsets does provide a complete view of their potential.

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.

Many anatomical features in trees result from their reaction to fluctuating environmental conditions, and some can be measured and dated. Recently, quantitative wood anatomy has been used to build time series, and consequently to study the responses of trees through time. This involves the application of dendrochronological techniques, although some methodological adaptations are necessary when using anatomical variables. Until now, the study of continuous anatomical series has proven to be very promising when applied to the earlywood vessels of ring-porous trees, due to their great physiological relevance. In this paper, we review the main aspects that must be considered when building continuous series of earlywood vessel features of ring-porous trees as compared to ‘classical’ dendrochronology. We first discuss the procedures for building individual series and chronologies, starting with the selection of variables, examining their statistical properties, and assessing how crossdating and detrending should be adapted. We also show that time series of earlywood vessels usually exhibit a low common signal, but in contrast are strongly related to climate, and often reveal responses not recorded by the classical dendrochronological variables. In addition, we deal with the optimization of environmental signals, by first evaluating multiple potential variables to be used, and indicate how to reduce their number according to the relations among them. As earlywood variables are basically determined by vessel number or vessel size, we discuss the search for the most appropriate variable to characterize vessel number, as well as the advantage of progressively selecting earlywood vessels attending to their size and position. Finally, we extend the application of these methodologies to diffuse-porous species as compared to ring-porous trees, and show that the climatic signal contained in their anatomical features is also relevant, provided that vessels are carefully selected upon their location within the ring.

Wood anatomical features may be visible on the microscopic as well as on the macroscopic scale. While the former can often be quantified by detailed wood anatomical analyses, the latter are often treated as qualitative features or as binary variables (present/absent). Macroscopic tree-ring features can be quantified in terms of frequency, intensity, or classified according to their position within a tree ring, like intra-annual density variations (IADFs) in conifers or frost rings in earlywood or latewood. Although some of these tree-ring features, like e.g. missing rings or IADFs are often seen as anomalies, hampering dendrochronologists to perform proper crossdating of tree-ring series, many of these properties are formed under extreme environmental stress or heavy impact, and could mark these extreme events by the manifestation in the wood anatomical structures throughout the lifespan of trees. The described tree-ring features form discrete time-series of extreme events. For example, flood rings may be marked by lunar-shaped earlywood vessels or enlarged latewood vessels in ring-porous oaks. White earlywood rings and light rings indicate reduced cell wall thickness and lignification occurring in very cold years. Frost rings result from cambial cell death during abrupt cooling events in the growing season. Missing rings and IADFs are mainly caused by drought events. Characteristic variations in earlywood vessel size, shape, or number in ring-porous oak species are markers for flood events, defoliation, heat stress, or drought. Traumatic resin ducts may be triggered by a range of biotic or environmental stressors, including wounding, fires or mechanical factors. Reaction wood is indicative of mechanical stress, often related to geomorphic events. In many cases anatomical responses are unspecific and may be caused by different stressors or extreme events. Additionally, the sensitivity of trees to form such features may vary between species, or between life stages within one species. We critically evaluate the indicative value of different wood anatomical tree-ring features for environmental reconstructions.

Key messageWe sampled Pinus nigra cones in 29 trees in an age range of 90 to 725 years. The mother tree age did not significantly influence the pinecone or pine seed size, seed germination capacity, or plant size or vigor displayed during the first year of growth in the nursery.ContextPinus nigra Arn. ssp. salzmannii is a long-lived Mediterranean species, with millenary trees residing in an old-growth forest in the Cazorla Mountain Range in SE Spain which is home to the oldest known trees in the Iberian Peninsula.AimsThis study aimed to assess how the mother tree age in Pinus nigra influences seed viability, germination capacity, and the seedling survival and growth during the first year under nursery conditions.MethodsTwenty-nine trees aged 90 to 725 years were selected and 60 cones were harvested per tree to study the cone characteristics (size and weight), seed viability, and germination capacity in relation to the mother tree age. Eighty germinated seeds per tree were transferred to the nursery and seedling survival and growth were measured after the first growing season.ResultsSignificant between-tree differences were detected for cone characteristics (cone and seed weight, number of seeds per cone), as well as for germination capacity. Notably, however, the mother tree age did not significantly influence the aforementioned parameters.ConclusionForest management and regeneration practices of Pinus nigra should take into account that trees of this species up to at least 725 years old produce seeds with a fairly high reproductive capacity.

El Museo de Belas Artes de A Coruña incorpora en sus fondos, por una donación particular en el año 1948, una talla de madera policromada y estofada de inicios del siglo XVIII. En el año 2016, debido al estado de deterioro de la pieza, se inició su proceso de restauración. Este proceso no solo consistió en revertir la pieza a su apariencia estética inicial sino que se complementó con un estudio iconográfico y con una caracterización completa de la madera y del recubrimiento dorado a través de la Tomografía Computerizada (TC) y la Microscopía Electrónica de Barrido (SEM-EDX). La utilización de estas técnicas analíticas ha permitido visualizar el interior y el exterior de la pieza, generar un registro virtual 3D con información estructural, evaluar el estado de conservación de la madera e identificar el tipo de recubrimiento dorado (pan de oro y purpurinas procedentes de antiguas restauraciones). El estudio dendrocronológico, aunque no ha sido concluyente para datar la madera debido al bajo número de anillos presentes en el tronco (representados tan solo 27 años), ha servido sin embargo para evaluar los límites y la potencialidad del uso de la dendrocronología basada en exámenes tomográficos no destructivos en tallas de madera. El proceso de restauración y el estudio iconográfico realizado también se describen en este trabajo. Ambos han ayudado a poner en valor expositivo la pieza y a identificar la identidad del Santo representado que en un origen, fue catalogado como San Gregorio, con dudas sobre su identidad como San Benito y que finalmente es asignado como San Bernardo.

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)

We analysed climate–growth relationships for two ring-porous oak species (Quercus robur L. and Q. pyrenaica Willd.) at one site in northwestern Spain. Increment cores from 12 living trees per species were taken for ring and earlywood vessel measurements, considering three width variables (for earlywood, latewood, and the whole ring) and six anatomical variables (based on vessel area distribution, number of vessels, and conductivity) in the earlywood. We used standard dendrochronological procedures and compared each mean series with meteorological records of temperature, precipitation, and estimates of soil water content. Earlywood width was negatively related to precipitation in the previous late season for Q. robur, but it was controlled by the previous spring temperature for Q. pyrenaica. These responses were highly dependent on vessel number and probably related to carbohydrate storage dynamics but differed between species. Vessel size showed a stronger relationship to climate and was mainly coupled to water excess during the winter for Q. robur but dependent on quiescence temperature for Q. pyrenaica; also, climatic signal in vessel size was maximized by the largest vessels for Q. pyrenaica but only increased slightly for Q. robur. Consequently, vessel parameters showed a much stronger climate signal than ring width and were successful at highlighting the differences between both oak species.

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).

We studied the relation between xylem and leaf phenology, and how environmental factors can modify the growth rhythm of Quercus pyrenaica Willd. on the boundary of its northwestern distribution. For this, wood formation and leaf phenology were monitored in 2012 and 2013 at five sites along an altitudinal gradient. Ten trees were randomly sampled at each site every 10–12 days, their leaf phenological stage recorded, and a microcore extracted to study cambial activities. These events were related to each other, as well as to air temperature for 10–60 day running periods along the year, in order to identify the association between processes, and the most relevant time windows for the onset and cessation of tree growth. The first earlywood vessels began their expansion before budburst, and leaf unfolding occurred when at least the first row of earlywood vessels had undergone maturation. However, the temperature regime did not explain the beginning of cell maturation, whereas the cessation of cell enlargement was delayed by maximum temperature, and to a greater extent by thermal amplitude provided that water is available. Primary and secondary growth of Q. pyrenaica were clearly synchronized at all sites, confirming that the maturation of the first earlywood vessels is essential for crown development. This strong synchronicity suggests that temperature is not the main factor for the beginning of primary and secondary growth; on the contrary, the cessation of wood formation appears to be more dependent on temperature, though also modulated by precipitation.

Wood formation of Quercus robur and Q. pyrenaica is similar along the growing season, mostly differing in the initial earlywood vessels, which are formed later but faster for Q. pyrenaica. We monitored leaf phenology and wood formation during the growing season of 2010 on two oak species (Quercus robur L. and Quercus pyrenaica Willd.) in the northwestern Iberian Peninsula to provide a detailed description of cambial dynamics, with a special focus on earlywood, and to relate phenological phases to simultaneous cambial processes. For this, we used visual survey of buds and leaves, and microscopic observations of microcores taken from stems on the same dates. Sampling intervals were weekly in the early season, and more spaced afterwards. There were no differences in cambial processes among individuals of the same species, whereas some phases of cambial dynamics and phenology were simultaneous for the two species. Cambial reactivation began in middle March, and bud burst was achieved in early May (6 weeks later) for both species, but they differed in the time required for the expansion of vessels in the first row. Vessel enlargement in Q. robur started at the beginning of April, and lasted for 1 month, while it began 2 weeks later in Q. pyrenaica and spanned only 2 weeks. The beginning of secondary wall lignification in the first vessel row was contemporary to bud burst. Earlywood formation lasted until mid-June, when latewood vessels and fibres started to be much more abundant in all individuals. Radial growth ceased in middle September. The total duration of earlywood formation lasted for 3 months in both species, while latewood formation took around two and a half months.

Tree-ring growth of Pinus canariensis at high elevation on Tenerife, Canary Islands, is thought to be principally controlled by drought-induced stress. Aspect of mountain slopes on this oceanic island strongly influences local water input, with trade winds maintaining humid weather conditions on windward slopes, while leeward slopes remain much more arid. We tested whether P. canariensis tree-ring growth is controlled by local water availability and the large-scale climatic pattern of the North Atlantic Oscillation (NAO) along its elevation range on windward and leeward slopes on Tenerife. Wood cores were taken from 6 stands on windward and 6 on leeward slopes at elevations of 1120 to 1930 m. We found outstanding differences between windward and leeward slopes with regard to tree growth responses to local climate and NAO. Responsiveness to winter temperature was greater in windward stands, while tree growth in leeward stands was mainly controlled by total annual rainfall, which was strongly linked to NAO variation. Tree-ring growth was dependent on water input throughout the whole leeward slope, but elevation gradients were not relevant for tree growth dynamics. The unique exception was the lowest windward stand, located within the most humid environment on Tenerife, which experienced detrimental effects both of rainfall in late winter-spring and heat in summer. We conclude that slope aspect and exposure to trade winds are mostly driving P. canariensis growth. Prospects of growth of this species should consider that NAO-driven drought stress may affect populations on leeward slopes, where drier conditions could become limiting in the future., The staff of Corona Forest Natural Park of Tenerife facilitated access to field sites. V.R. benefited from a visiting fellowship to the University of La Laguna, funded by Consellería de Innovación e Industria, Xunta de Galicia, and research contracts by INIA-Xunta de Galicia and CSIC, partially funded by the European Social Fund. This research was partially funded by Consellería de Innovación e Industria, Xunta de Galicia (PGIDIT06PXIB502262PR), and INIA, Spanish Ministry of Science and Innovation (RTA2006- 00117).

Non-structural carbohydrates (NSC) play a central role in the construction and maintenance of a tree's vascular system, but feedbacks between the NSC status of trees and wood formation are not fully understood. We aimed to evaluate multiple dependencies among wood anatomy, winter NSC, and phenology for coexisting temperate (Quercus robur) and sub-Mediterranean (Q. pyrenaica) oaks along a water-availability gradient in the NW Iberian Peninsula. Sapwood NSC concentrations were quantified at three sites in December 2012 (N = 240). Leaf phenology and wood anatomy were surveyed in 2013. Structural equation modelling was used to analyse the interplay among hydraulic diameter (Dh), winter NSC, budburst date, and earlywood vessel production (EVP), while the effect of Dh and EVP on latewood width was assessed by using a mixed-effects model. NSC and wood production increased under drier conditions for both species. Q. robur showed a narrower Dh and lower soluble sugar (SS) concentration (3.88–5.08 % dry matter) than Q. pyrenaica (4.06–5.57 % dry matter), but Q. robur exhibited larger EVP and wider latewood (1403 µm) than Q. pyrenaica (667 µm). Stem diameter and Dh had a positive effect on SS concentrations, which were related to an earlier leaf flushing in both species. Sapwood sugar content appeared to limit EVP exclusively in Q. pyrenaica. In turn, Dh and EVP were found to be key predictors of latewood growth. Our results confirm that sapwood SS concentrations are involved in modulating growth resumption and xylem production in spring. Q. pyrenaica exhibited a tighter control of carbohydrate allocation to wood formation than Q. robur, which would play a role in protecting against environmental stress in the sub-Mediterranean area. This work was supported by the Spanish Ministry of Economy and Competitiveness (research projects BFU-21451 and CGL2012-34209) with European Regional Development Fund, and by Xunta de Galicia (research projects 10MDS291009PR and GRC2015/008). Gonzalo Pérez-de-Lis received a PhD FPU-ME grant(grantnumberAP2010-4911)fundedbytheSpanishMinistry of Education. The work was partially inspired within the FPS COST Action FP1106 – STReESS and Ecometas net CGL201453840REDT SI

Time series of tree-ring anatomical features are important to understand the functional role of xylem plasticity over the life span of trees, and thus to reconstruct past ecological and climatic conditions. Holm oak (Quercus ilex L.) is a drought-tolerant tree widely distributed in the Mediterranean Basin. Chronologies of tree-ring width (TRW), vessel lumen area [maximum (MAX) and mean (MVA)] and vessel density (VD) were developed for the period 1942–2001. Each ring was divided into three sections to compare the intra-annual variation of vessel features with the climate conditions during the growing season. The common variability of tree-growth and vessel features was analyzed using a principal component analysis (PCA). Vessel lumen area (MAX and MVA) and TRW loaded positively on the first axis (PC1), whereas VD from the first and second part of the ring (VD1 and VD2) loaded negatively, suggesting that these variables share a common variance. On the other hand, VD in the last third of the ring (VD3) loaded positively on second axis (PC2). PC1 showed a strong positive correlation with precipitation during the hydrological year (prior October–September) and a negative correlation with temperature in spring (April–May), while PC2 showed a negative correlation with precipitation in June. Our results showed that TRW and vessel lumen area were mainly dependent on moisture conditions along the growing season, while vessel density probably plays an important role in the balance between hydraulic conductivity and safety to embolism to better adjust the hydraulic system to water availability.

In this paper, we present the package detrendeR, a Graphical User Interface to facilitate the visualization and analysis of dendrochronological data, using the R computing environment. This package offers an easy way to perform most of the traditional tasks in dendrochronology: detrending, chronology building and graphical presentation of time series. The advantage of detrendeR, compared with the program ARSTAN, is the graphical interface that provides the user with an easy way to use R language, rich in graphics and handling routines, with no need to type commands. The detrendeR uses a simple and familiar dialog-box interface and it can read Tucson decadal-format files (*.rwl and *.crn) as well as plain text files. In addition, detrendeR has the ability to test temporal changes of the common signal using moving intervals. The detrendeR should make it easier to perform detrending and chronology building of tree-ring series, taking advantage of the R statistical programming environment.

Summer water stress is the main limiting factor for Pinus pinaster growth under Mediterranean climate, but no information on limiting physiographic and climatic factors under Atlantic conditions is available for this species. We hypothesize that water availability during the active period limits P. pinaster growth, with stands nearby the Atlantic-Mediterranean boundary being more sensitive to summer drought stress. We analyzed the inter- and intra-annual climatic response of this species at ten monospecific stands in a transitional area between the Atlantic and Mediterranean biogeographical regions in Galicia, NW Spain. Mean sensitivity of radial growth consistently decreased with increasing elevation, and growth variation was quite similar for the earlywood, latewood or total ring widths, suggesting a strong intra-annual coherency of radial growth. Growth patterns were site dependent and geographically structured, with three groups of stands showing different climatic responses. As expected for sites suffering from summer drought stress, water availability enhances growth in western and southern Galicia, showing negative responses to maximum temperatures and positive to water availability. In northern Galicia, away from the Atlantic-Mediterranean boundary, water surplus in the rainy seasons negatively influenced growth. This was probably due to the combined effects of seasonal water-logging stress and the reduction of solar radiation associated with cloudiness, which would limit photosynthetic rates in winter and spring. Local variations of water availability strongly controlled the physiological processes that determine growth dynamics of P. pinaster in NW Spain, contributing to its geographical structure and contrasting sensitivity., This research was funded by Dirección Xeral de Investigación, Desenvolvemento e Innovación, Xunta de Galicia (PGIDIT06PXIB502262PR).

We investigated whether vessel time series of Holm oak (Quercus ilex L.), a diffuse to semi-ring-porous species, can record a climatic signal which differs from the signal encoded in tree-ring width (TRW). The study was conducted in ten Q. ilex trees from a coppice stand in northeast Spain. Chronologies of TRW, mean vessel area (MVA) and maximum vessel area (MAX) were developed and correlated with climate data, for the period 1985–2004 (20 years). Our results indicate that vessel features contain environmental information that is different from that stored in TRW. MAX chronologies correlate better to early spring precipitation (April–May) than TRW chronologies, and so does MVA of the largest 20–25 vessels from the first third of the ring with late spring precipitation (May–June). Also, the combination of MVA and TRW is a better predictor of summer precipitation. This explorative study clearly shows that vessel features can complement the climatic signal of TRW increasing the resolution of the climate reconstructions for the Mediterranean region.

Holm oak (Quercus ilex L.) is a long-lived species widely distributed across the Mediterranean Basin, with po- tential value for dendrochronology and dendroclimatology. However, tree-ring dating in Q. ilex is a complex task that has limited the number of dendrochronological studies using this evergreen species. In the present work, it was investigated if old Q. ilex trees showed annual tree rings and whether they can be used as climate proxies. A long tree-ring chronology (126 years) of Q. ilex was developed using cross sections of 20 trees from the Guadiana river basin (Portugal). The high correlation among tree-ring series suggested that tree growth was controlled mainly by climate. Response function analysis showed a positive correlation between tree-ring width and precipitation from October(t-1) of the previous year to January(t) of the current year and in May(t). Tree-ring width was negatively correlated with the North Atlantic oscillation that exerts a strong influence on the precipitation over Iberia. Negative pointer years were triggered by dry years and became more frequent during the last decade of the 20th century. In conclusion, it is possible to accurately date old Q. ilex trees, and their tree rings could be used for climate reconstructions across the Mediterranean. Resume ´ : Le chene vert (Quercus ilex L.), une espece longevive tresr epandue dans le bassin mediterraneen, a une valeur potentielle en dendrochronologie et dendroclimatologie. Cependant, la datation des cernes annuels de Q. ilex est une tache complexe qui a limitele nombre d'etudes dendrochronologiques chez cette espece sempervirente. Dans cette etude, nous avons examinesi les vieilles tiges de Q. ilex montrent des cernes annuels et si ces cernes peuvent etre utilises comme te ´- moins du climat. Une longue chronologie (126 ans) de Q. ilex aetedeveloppeeapartir des sections radiales de 20 arbres provenant du bassin de la riviere Guadiana (Portugal). La forte correlation entre les series dendrochronologiques indiquait que la croissance des arbres est controlee principalement par le climat. L'analyse d'une fonction de reponse a montrequ'il y avait une correlation positive entre la largeur des cernes annuels et la precipitation du mois d'octobre(t-1) de l'annee pre ´- cedente au mois de janvier(t) de l'annee en cours et celle du mois de mai(t). La largeur des cernes annuels etaient negative- ment correleeal'oscillation nord-atlantique qui exerce une forte influence sur la precipitation au-dessus de la peninsule iberique. Les annees caracteristiques negatives etaient dues ades annees seches et elles sont devenues plus frequentes du- rant la derniere decennie du 20 e siecle. En conclusion, il est possible de dater avec exactitude les vieilles tiges de Q. ilex et leurs cernes annuels pourraient etre utilises pour les reconstitutions du climat partout en Mediterranee. (Traduit par la Redaction)

We assessed the seasonal climatic response of 2 Pinus and 2 Quercus tree species in a littoral island in northwest Spain, analyzing earlywood, latewood, and total ring widths. We used bootstrapped response functions to identify the variables controlling growth, and we estimated the pure and shared effects of local climate components (temperature and water balance) and a large-scale atmospheric pattern (North Atlantic Oscillation, NAO) on tree growth using a variance partitioning approach. For all species, the response functions showed stronger climatic signals in latewood and total ring than in earlywood. The pure effects of temperature, water balance, and NAO on tree growth were significant. However, a null shared effect between local climate and NAO was evidenced due to the absence of a direct link between NAO in the previous autumn and the other significant climatic variables. Pinus pinaster was the species most sensitive to local climate, mainly to water availability during its active period...

Chronologies of earlywood vessel size of ring- porous trees contain valuable ecological information, but long preparation procedures limit their application in eco- logical studies. Recent and fast techniques for wood surface preparation combined with automated image analysis are reducing the work needed to build chronolo- gies, but might also entail measurement inaccuracy. In this study, we aim to evaluate the effect of a possible effi- ciency-accuracy trade-off on ecological signal strength. To this end, we compare measurements of mean vessel area from two recent and fast procedures carried out on sanded wood surfaces with a reference procedure based on an accurate survey from thin sections. Measurements were performed on increment cores of 15 sessile oaks (Quercus petraea (Mattuschka) Liebl.) for the period 1956-2006. Dissimilarities in results with the reference procedure were quantified and evaluated. Our data show that the workload can be reduced by more than 20-fold when using the highly automated procedure. Signal weakening caused by mea- surement errors is negligible for vessels (6,000 lm 2 and can be easily compensated by increasing the sample size. Manual correction of misrecognized vessels hardly reduced this error further. The new procedures constitute a major step towards an efficient and accurate analysis of early- wood vessel chronologies of ring-porous tree species.

Aim In this study, we evaluate the importance of the mean earlywood vessel size of oaks as a potential proxy for climate in mesic areas. Location The study was conducted in Switzerland at three forest sites dominated by oak (Quercus petraea and Q. pubescens). The three sites were in different climatic zones, varying mainly in terms of precipitation regime. Methods Three 50-year-long site chronologies of mean earlywood vessel size and tree-ring widths were obtained at each site and related to monthly meteorological records in order to identify the main variables controlling growth. The responses of mean vessel size to climate were compared with those of the width variables to evaluate the potential climatic information recorded by the earlywood vessels. Results The results show that the mean vessel size has a different and stronger response to climate than ring-width variables, although its common signal and year-to-year variability are lower. This response is better in particular at mesic sites, where it is linked to precipitation during spring, i.e. at the time of vessel formation, and is probably related to the occurrence of only a few processes controlling vessel growth, whereas radial increment is controlled by multiple and varying factors. Main conclusions The mean earlywood vessel size of oak appears to be a promising proxy for future climate reconstructions of mesic sites, where radial growth is not controlled by a single limiting factor.

Sixty individual ring-width series of oak (Quercus robur L.) from six sites in the northwestern Iberian Peninsula, ranging from 50 to 120 years, were grouped using hierarchical cluster analysis with different types of distance measures. Euclidean distances as well as other linkage distances based on statistics used to crossdate tree-ring series (Gleichlaufigkeit and coefficient of correlation with its corresponding t-value) were compared. In addition, a new distance measure based on a corrected inversion of the Student's t is proposed in the present paper, which takes into consideration the number of years used for series comparison. The Euclidean distances, commonly used in ecological analyses, inefficiently identified homogeneous units of trees based on their ring-width patterns. Among crossdating statistics, the correlation coefficient was more effective than Gleichlaufigkeit, but the most satisfactory results were obtained when 1/t was used as distance measure. Finally, these methods of cluster analys...

The analysis of time series of wood cell anatomical features (such as the earlywood vessels of ring-porous trees) is a successful approach to understand the effect of environmental factors on tree growth and thus constitutes a valuable source of information about past environmental conditions. However, despite the rising interest in analyzing wood anatomical time series, little or no attention has been paid to establish an adequate sample of cells in order to minimize the risk of missing a valuable environmental signal. In order to contribute to such methodological bases, this paper is aimed at (1) identifying a representative sample of earlywood vessels within a tree, which encode the same climatic information, and (2) assessing if it is preferable to obtain the sample of vessels along one or two radii. Four individuals of sessile oak (Quercus petraea (Mattuschka) Liebl.) and sweet chestnut (Castanea sativa Mill.) were harvested and all their earlywood vessel lumina were measured along two 40-mm wide radial strips. Measured vessels were selected stepwise while increasing the tangential width of the wood section from 1 to 40 mm, analyzing at each step (1) the common signal of chronologies and (2) the correlation to the main climatic variables controlling growth. Additionally, both radii in each tree were analyzed together and separately. The results showed that a total tangential width of 10 mm was enough to stabilize the climatic signal with improvement when distributed along two different radii, but a slightly larger tangential width was required to reach an optimal common signal. We suggest that, at least for the case of these two species growing at this specific climatic context, two 5-mm increment cores ensure a representative vessel selection.

• The aim of this study was to identify the climatic signal contained in the earlywood vessel size of the ring-porous chestnut (Castanea sativa) and the physiological processes involved in the underlying mechanisms. • In order to assign the encoded signal to a specific physiological process, bud phenology and vessel formation were monitored along an elevation transect and chronologies of the size of the first row of earlywood vessels were retrospectively correlated with 40 yr of early spring temperatures. • The first vessels appeared in late April to early May, after encoding both a negative temperature signal in February-March (during tree quiescence) and a positive temperature signal in early April (at the time of resumption of shoot growth). • We hypothesize that February and March temperatures affect cambial sensitivity to auxin, preconditioning tree responses later in the season. Furthermore, April temperature is related to tree activation whereby new hormone production fosters vessel expansion. © The Authors (2006).

Summary •W ood anatomical features measured in dated tree rings have often proven to be of ecological value. However, little is known about the suitability and power of such measurements studied in a year-to-year basis as is done in dendrochronology. • The present work is based on a comparative analysis of 60 dated time-series of earlywood features of chestnut ( Castanea sativa ) grown in the climatic context of the Southern part of the Swiss Alps. • It has been shown that the earlywood vessel area is a suitable ecological indicator. This variable, although not very sensitive, contains environmental information that is different from that stored in all other ring-width and earlywood features we considered. The vessel size is mainly related to the temperature during two physiologically crucial periods for vessel growth: the end of the previous vegetation period (during reserve storage) and the onset of cambial activity (during cell division and vessel differentiation). • Our work shows that the mean vessel size of the ring-porous chestnut contains ecophysiological information that can be used for research in dendrochronology.

Earlywood vessel lumen areas were measured in 72 consecutive tree rings in wood cores from oak (Quercus robur L.) trees in a maritime woodland. This anatomical time series was statistically correlated with climate data for the same time span. There was a strong dependence of earlywood vessel lumen area on rainfall between February and April, which reflects the role of water availability in vessel ontogeny. By inversion, earlywood vessel lumen areas can be used as a proxy to reconstruct spring precipitation beyond the archived weather records. Such information may be of value in the context of climate change.

The ample distribution of common beech (Fagus sylvatica) across Europe implies that this key tree species occurs under a broad variety of climatic conditions despite its sensitivity to drought stress. Iberian beech rear-edge (southernmost) forests are located along the boundary between the Eurosiberian and Mediterranean biogeographical regions. Therefore, those forests are considered to be sensitive monitors of the effects of warming-induced drought stress on marginal tree populations. We evaluate if the radial growth of Iberian beech populations is mainly constrained by drought. Since previous findings indicated that El Niño-Southern Oscillation (ENSO) teleconnections may influence the rainfall regime in northern Spain, we also assessed if beech response to drought and water availability is modulated by this large-scale climatic pattern. We compared the recent growth patterns and responses to climate across a network of 30 tree-ring site chronologies established throughout northern Spain where beech forests are subjected to contrasting climatic conditions. Iberian beech populations located near or within the Mediterranean biogeographical region were the most sensitive to June water deficit. However, the dependency of beech growth on drought stress near the rear-edge of the species was mitigated where cloudy conditions prevail in summer, namely in mesic stands located in the Eurosiberian region. Drought stress in the latter populations was alleviated by cloudiness, which in turn depended on ENSO, and this effect on growth has been intensifying for the last decades. We prove that the sensitivity of rear-edge populations to drought, in terms of growth reduction, is greatly modulated by local or regional environmental gradients, but also by the influence of large-scale climatic variation., This work was partially funded by Fundación para el Fomento de la Investigación Científica Aplicada y la Tecnología, Asturias Regional Government (PB-REC98-04), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Spanish Government (RTA2006-00117), Spanish Economy and Competitiveness (CGL2011-26654) and Agriculture and Environment (OAPN, 387/2011) Ministries projects. JJC acknowledges the support of ARAID.

We review the current state of dendroarchaeology in the Iberian Peninsula and discuss its potential, outlining the particular relevance and complexity of this territory and its material heritage for dendroarchaeological studies. Whereas dendrochronology is used throughout the rest of Europe to answer questions about cultural heritage, the application of dendroarchaeology in the Iberian Peninsula has been remarkably underrepresented in comparison to dendroecology and dendroclimatology. Existing tree-ring chronologies in this territory have a widespread geographical coverage, but are often too short to allow dendroarchaeological studies, resulting in inadequate assessments of material heritage made of wood in and originating from the Iberian Peninsula. However, different studies have demonstrated that dendroarchaeology has a great potential in the area. This review illustrates the rich variety of Iberian material heritage from different periods and cultures covering over 8000 years that could profit from dendrochronological research. Future research possibilities in relation to the available Iberian heritage in Spain, Portugal and worldwide are proposed. © 2015.

Key message: Earlywood vessel features indicate different adaptations of Quercus petraea and Q. pyrenaica, which are probably related with their corresponding Atlantic and sub-Mediterranean ecological requirements. We studied the climatic signal of the earlywood anatomy of a temperate [Quercus petraea (Mattuschka) Liebl.] and a sub-Mediterranean (Quercus pyrenaica Willd.) oak species growing under similar climatic conditions in a transitional area between the Atlantic and Mediterranean regions of the Iberian Peninsula. We hypothesized that both species react differently in their wood anatomy due to their contrasting ecological requirements, and we test the usefulness of earlywood anatomical features to study the behaviour of these ring-porous oaks upon climate. For this, we measured the earlywood vessels, and obtained annual series of several anatomical variables for the period 1937-2006 using dendrochronological techniques, considering whether the vessels belonged to the first row or not. After optimizing the data set by principal component analysis and progressive filtering of large vessels, we selected maximum vessel area and total number of vessels as they resulted to be the optimal variables to describe vessel size and number, respectively. Vessel size of Q. pyrenaica was dependent on precipitation along the previous growing season, whereas it did not show any clear climatic response for Q. petraea. On the contrary, vessel number was related to winter temperature for both species. These relationships observed between climate and anatomy appeared to be stable through time. The results obtained reinforce the utility of earlywood vessel features as potential climate proxies. © 2013 Springer-Verlag Berlin Heidelberg., Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), MICINN (RTA2006-00117)

Forest dieback is usually triggered by climatic extremes, even if tree decline can be caused by diverse biotic and abiotic stressors acting synergistically on tree vitality. Many case studies worldwide illustrate the global importance of drought-induced forest dieback under a context of climate warming. However, forest decline is also occurring in regions that are not water-limited, but where increasing rainfall and exceptionally rainy events are observed. Here we assessed the influence of inter-tree competition, regional water availability, and largescale climate variation on the decline and death of pedunculate oak (Quercus robur) in an Atlantic rainy forest in NW Spain. All healthy, declining, and dead trees in four replicated forest stands were mapped, and inter-tree competition was individually quantified with a distance-dependent competition index. Long-term variation of annual radial growth was analyzed on a selection of individuals per stand, and its dependence on climate variation was examined by correlation analysis with monthly climatic records. Trees under intense competition showed higher mortality risk. Increasing rainfall and the large-scale climatic pattern El Niño-Southern Oscillation (ENSO) have influenced tree growth during recent decades, acting as long-term stressors. A detrimental effect of water surplus during both the year preceding growth and spring of the current year has been noticed since 1980. Extremely rainy conditions in 2001 resulted in strong short-term stress that killed trees suffering from intense competition and wetness-induced stress. Our findings support that water excess is a relevant triggering factor for dieback of dominant forest trees in rainy temperate deciduous forest. This pattern is possible in regions where increasing precipitation and more frequent and intense rainfall extremes, associated with global climate warming, are happening. Since climate warming may lead to higher total annual rainfall, and to an increase in frequency and intensity of extreme precipitation events, forest dieback episodes associated with wetter conditions may become more common in the future., This study was supported by Consellería de Innovación e Industria, Xunta de Galicia (PGIDIT06PXIB502262PR), and Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Ministerio de Ciencia e Innovación (RTA2006-00117).