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Old-growth forests have an important role in maintaining animal and plant diversity, are important carbon (C) reservoirs and are privileged sites to study long-term plant physiological responses, long-term forest dynamics and climate change impact on forest ecosystems. Several studies have highlighted how old-living trees undergo age-related declines with hydraulic limitations and reduction in photosynthesis, though some recent works have suggested that such a decline is not always observed. Our study aims at understanding the role of atmospheric CO2 increase on tree C uptake and stomatal conductance (gs) in old-living trees by analysing the long-term patterns of tree growth and intrinsic water use efficiency (iWUE) in three old-growth forests in the Balkans (Bosnia-Herzegovina and Montenegro), using dendrochronology and isotopic analysis. We hypothesised a long-term increase in iWUE in the studied old-growth forests, mostly related to enhanced photosynthesis rather than reduced stomatal conductance. Tree cores were sampled from dominant silver fir (Abies alba Mill.) trees in each forest. Tree-ring widths were measured and basal area increments (BAI) were assessed for each sampled tree and, from the six longest chronologies, five decades were chosen for cellulose extraction, its isotopic analysis (δ13C, δ18O), iWUE and leaf water 18O evaporative enrichment above the source water (Δ18OL) determination. We observed a continuous and significant increase in iWUE from 1800 to 2010 in the sampled dominant trees at all the three old-growth forests. Our BAI data and our estimates of Δ18OL across the study period support the idea that enhanced photosynthesis rather than reduced stomatal conductance is the major driver of the measured iWUE increase. Thus, our results support some recent findings challenging the hypothesis that iWUE in forests is primarily the result of a CO2-induced reduction in stomatal conductance as well as the so called hydraulic limitation hypothesis.

Spatial interactions between trees influence forest community succession. The objective of this study was to investigate how shifts in forest composition and proximity between tree species affect stand development over time in mixed forest systems. At six locations across the Fishlake National Forest, Utah, USA, in stands where facilitation has been documented previously, tree-ring samples were collected from aspen and subalpine fir trees. Basal area increment was calculated to characterize the effects of the proximity of overstory trees on multidecadal growth responses of aspen and subalpine fir in aspen-dominant and mixed aspen–conifer stands. Subalpine fir seedlings were established next to aspen (within 10 cm) when aspen was between 15 and 120 years old with a mean age of 60 years. Aspen and subalpine fir growth rates were reduced with increasing conifer abundance. Aspen trees growing next to a proximate subalpine fir tree had slower growth rates over time than aspen trees growing independently. Growth rates of subalpine fir in aspen-dominated stands were similar when growing independently or near aspen trees. However, subalpine fir in conifer-dominated stands maintained higher growth rates when growing next to an aspen tree than when growing independently. The data suggest that as stand competition increases with conifer abundance, the proximity of overstory trees increases competitive exclusion of aspen while having a beneficial growth effect on subalpine fir. These results underscore the importance of maintaining natural fire regimes in forest systems that keep competitive interactions in balance.

The need to understand the carbon sequestration ability of trees under current and future climatic scenarios is fundamental to predict the role of forest in counterbalancing the global warming. In this study, we investigated the carbon sequestration ability of Pinus sylvestris L. in a setting of pure and mixed forests with Quercus petraea (Matt.) Liebl. in Central Poland. Beside the traditional growth measures, i.e., Ring Width, Basal Area Increment, and wood density, we utilized also a new Index called BAIden, which combines Basal Area Increment and mean ring wood density to depict the carbon sequestration ability of trees. Pinus sylvestris showed different sensitivity to climatic variability depending on tree admixture, while the Basal Area Increment and wood density presented few differences between pure and mixed forests. According to the BAIden index, carbon accumulation in P. sylvestris showed similar sensitivity to climatic variability in pure and mixed forests. The new index was also informative on the main climatic drivers of carbon sequestration. Considering future climatic scenarios, the carbon sequestration ability of P. sylvestris will be facilitated by rising temperatures in late winter-early spring and reduced by decreasing precipitation and rising temperatures during summer. Finally, we discussed the perspective and applicability of BAIden for further studies on carbon sequestration ability under climate change.

Recent changes commonly observed in forests growth could be the result of a combination of different climatic and non-climatic factors, such as rising atmospheric [CO2], temperature changes, atmospheric N deposition and drought stress. These effects are difficult to assess, however, due to the superimposition of age-related changes. After removing age effects through a novel approach, this study quantifies the effects on tree growth of global change, and assesses the relationship with individual environmental drivers and their relative importance. Generalized Additive Mixed Models (GAMMs) were applied to decouple the non-linear effects of age and co-occurring environmental changes on basal area increments (BAI) series, as derived from tree rings in a Pseudotsuga menziesii stand chronosequence of four different age classes (65-, 80-, 100- and 120-year-old). The model could explain about 57% of the overall variation in BAI as a function of age and a selected set of predictors, including water availability in the current summer and at the end of previous growing season; together with age, winter-spring mean temperature was found to be the most important predictor. After accounting for age-related effects, a significant decrease in BAI was observed in Douglas fir over the last decades. No significant impact of atmospheric [CO2] and atmospheric N deposition were detected.

One of the most important proxy archives for past climate variation is tree rings. Tree-ring parameters offer valuable knowledge regarding how trees respond and adapt to environmental changes. Trees encode all environmental changes in different tree-ring parameters. In this study, we analyzed how air temperature is encoded in different Norway spruce tree-ring proxies along an altitude gradient in an intramountain valley of the Carpathians. The study area, in the Gheorgheni region, Romania (Eastern Carpathians), has a mountain climate with a frequent temperature inversion in winter. The climate–growth relationship was analyzed for two contrasting altitudes: low elevation, i.e., below 1000 m a.s.l., and high elevation, i.e., above 1500 m a.s.l. Two local weather stations, one in the valley and the other on the upper part of the mountains, provide daily temperatures (Joseni—750 m a.s.l. and Bucin—1282 m a.s.l.). The bootstrap Pearson correlation between cumulative daily temperature data and three tree-ring proxies (tree-ring width—TRW, basal area increment—BAI, and blue intensity—BI) was computed for each series. The results show that elevation modulates the climate response pattern in the case of BI, and remains relatively similar for TRW and BAI. The winter temperature’s positive influence on spruce growth was observed in both TRW and BAI chronologies. Additionally, the BAI chronology highlights a positive relationship with summer temperature. The highest correlation coefficient (r = 0.551, p < 0.05, n = 41) was recorded between BI residual chronology from high elevation series and summer/autumn temperature from the upper-part weather station for a cumulative period of 59 days (the second half of August to the beginning of October). Our results show that, for this intramountain valley of the Eastern Carpathians, different tree-ring proxies capture different climate signals.

Alterações ambientais podem implicar mudanças nas características de um ecossistema e alterar a vegetação local, sobretudo o crescimento das espécies. Este estudo objetivou avaliar o crescimento de Araucaria angustifolia em relação a uma alteração ambiental, ocorrida com a implantação de lagoas artificiais nas proximidades dos indivíduos, nos anos de 1974 e 1976. Foram coletadas duas amostras radiais diametralmente opostas do lenho de nove indivíduos adultos de A. angustifolia, com o uso de um trado de incremento. As amostras foram processadas seguindo a metodologia clássica de dendrocronologia. Para avaliar as mudanças no crescimento de cada indivíduo foram calculados os incrementos em área basal. As relações entre o crescimento radial e o clima, para os períodos anterior e posterior à alteração ambiental, foram analisadas a partir de testes de correlação entre a cronologia e os dados históricos mensais de precipitação pluviométrica e temperatura média, utilizando o coeficiente de Pearson. O incremento em área basal individual indicou um aumento no crescimento em período próximo à alteração ambiental para algumas das árvores. A correlação entre os índices dos anéis de crescimento e os dados meteorológicos históricos indica uma resposta distinta entre os períodos anterior e posterior à implantação das lagoas. Pode-se inferir que a alteração ambiental, associada a outros fatores, como a temperatura no verão e a precipitação no verão e no inverno, modificou alguns padrões de resposta no seu crescimento. Made available in DSpace on 2018-12-14T00:08:59Z (GMT). No. of bitstreams: 1 2018P.BotossoEBAlteracao.pdf: 376973 bytes, checksum: 3dcc0344cb5b1f511bce7889108f9c5a (MD5) Previous issue date: 2018-12-13 Seção ciências agrárias.

© The Author(s). 2019. Background: Environmental change has resulted in changes in forest growth in Europe during the last century. This has consequences for the products and services delivered by forest. Mixing tree species is often proposed as a strategy to deal with the consequences of climate change. Diversifying forests is believed to result in higher productivity and increased growth stability. Tree species diversity is therefore expected to affect long-term trends in tree radial growth. However, this has not yet been studied. In this paper we study the effect of diversity on the radial growth and its long-term trends for beech and oak trees growing along a gradient of tree species diversity in the loamy region of central Belgium (from monocultures to mixed forests patches up to three species). Results: We found that beech trees have a higher radial growth whereas oak trees have a lower one when growing in mixtures. The contrasting diversity-productivity relationship observed for beech and oak is in agreement with their ranking in shade tolerance, where oaks suffer increased competition in mixed oak patches. Overall, in monocultures and mixtures, an increasing radial growth trend of + 2% for the period 1927–2015 and 21% for the period 1899–2015 was found for beech and oak, respectively. Tree species diversity did not alter the shape of this detected long-term radial growth trend. Nevertheless, for oak a lower year-to-year variability in radial growth is found in mixtures indicating ahigherresilience. Conclusion: We conclude that diversity impacts the average radial growth and its variability (only in the case of oak) but not the shape of the long-term trend in radial growth of beech and oak trees growing in the loamy region of central Belgium. ispartof: FOREST ECOSYSTEMS vol:6 issue:1 status: published

The increased frequency and intensity of warming-induced droughts have triggered dieback episodes affecting many forest types and tree species worldwide. Tree plantations are not exempt as they can be more vulnerable to drought than natural forests because of their lower structural and genetic diversity. Therefore, disentangling the physiological mechanisms leading to growth decline and tree mortality can provide tools to adapt forest management to climate change. In this study, we investigated a Pinus nigra Arn. plantation situated in northern Spain, in which some trees showed canopy dieback and radial-growth decline. We analyzed how radial growth and its responses to drought events differed between non-declining (ND) and declining (D) trees showing low and high canopy defoliation, respectively, in combination with carbon (&delta, 13C) and oxygen (&delta, 18O) isotope ratios in tree rings. The radial growth of P. nigra was constrained by water availability during the growing season and the previous autumn. The radial growth of D trees showed higher sensitivity to drought than ND trees. This fact is in accordance with the lower drought resilience and negative growth trends observed in D trees. Both tree classes differed in their growth from 2012 onwards, with D trees showing a reduced growth compared to ND trees. The positive &delta, 13C-&delta, 18O relationship together with the uncoupling between growth and intrinsic water-use efficiency suggest that D trees have less tight stomatal regulation than ND trees, which could involve a high risk of xylem embolism in the former class. Our results suggest that different water use strategies between coexisting ND and D trees were behind the differences in growth patterns and point to hydraulic failure as a possible mechanism triggering dieback and growth decline.

Research Highlights: We investigated the competitive interactions among three tree species (interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), interior spruce (Picea glauca [Moench] Voss &times, Picea engelmannii Engelm.), and lodgepole pine (Pinus contorta Dougl. Ex Loud. var. latifolia Englem.)) in multi-aged stands in central British Columbia, Canada. Background and Objectives: Understanding competitive interactions among tree species in mixed-species stands is fundamental to supporting silvicultural decision-making in such stands. Using the periodic annual basal area increment for single trees as our dependent variable, we investigated whether neighboring trees competed with subject trees independently of species identity. We also examined the differences in single-tree basal area growth among the three conifer species over time under different levels of competition. Materials and Methods: We developed several spatially explicit, single-tree basal area growth models for interior Douglas-fir, interior spruce, and lodgepole pine using data from 16 plots in two blocks of a long-term study (five measurements over a 21-year period) on the response to pre-commercial thinning. We compared these equations to assess whether intraspecific or interspecific competition predominated. We also examined the differences in basal area growth among the three conifer species over time under different levels of competition. Results: We found asymmetrical relationships between the conifer trees and their neighbors for all species, indicating that the main driver limiting growth in these stands is aboveground competition for light. There was evidence of higher intraspecific competition for small (&lt, 10.0 cm DBH) interior Douglas-fir in one block. However, there was no general pattern among larger subject trees with respect to the identity of neighborhood competitive effects and the equivalence of neighbors. We observed a higher level of basal area growth over time for interior Douglas-fir than for lodgepole pine and interior spruce, irrespective of the competition intensity and, not surprisingly, the growth rate declined with increasing competition levels for the three species. Conclusions: Our results provide an understanding of how interior Douglas-fir stands will develop over time and information on species interactions that could help forest managers explore different silvicultural options and their effects on individual tree growth in these complex stands.

Tree growth is strongly influenced, among other factors, by climate. Much knowledge regarding climate–growth relationships has been gained by studying tree rings. However, sufficient tree-ring data is rarely available if climate effects are required to be representative for large spatial scales, for example, in order to be used in scenario models to estimate forest development under climate change. Alternative data sources include large-scale forest inventories, although these usually provide lower temporal resolutions than tree rings. When working with temporally sparsely-resolved growth data, the question of how climate–growth relationships aggregate over time becomes relevant. To overcome this trade-off between spatial representativeness and temporal resolution, this study aims at optimally using the information contained in the annual resolution of tree rings to derive recommendations regarding the choice of climate variables for modeling tree growth based on forest inventories. We evaluated for Picea abies and Fagus sylvatica, which part of the year (spring, summer, vegetation period, whole year) and whether mean or extreme climatic conditions within inventory intervals should be taken into consideration. A three-step approach was used: (1) we used response functions to quantify the effect of monthly precipitation and temperature on annual basal area increments, (2) we temporally aggregated the annual basal area increments to hypothetical intervals of five and ten years, and correlated them with climate means and extremes – from different parts of the year – within the aggregated intervals, and (3) we fitted linear mixed-effects models to simultaneously quantify the effects of the climate variables, site characteristics and the years of the hypothetical inventories. The results did not generally differ between both species. Variables based on conditions during the whole year and partly during spring performed better than variables based on conditions during summer or the vegetation period. Defining the year as the period between October of the previous year and September of the current year allows possible lag effects of previous autumn and winter conditions to be taken into consideration. Mean climatic conditions reached or exceeded the correlations of the extremes and mostly performed similar to or better than the extremes in the models. Our results indicate that these relationships are insensitive to the often arbitrarily determined years, in which inventories take place. These findings can serve as basic recommendations for the choice of climate variables when modeling climate effects on multi-year growth of P. abies and F. sylvatica in the European lowlands.

Measurements of physical tree crown dimensions were of subjective character in the past, even though they can be considered important for the management of many silvicultural operations, such as timing of thinning operations. In our study we investigated if and how measures of physical crown dimensions of trees differed when quantified conventionally versus based on 3D-terrestrial laser scanning and how they are related to basal area increment. Some 24 randomly selected predominant or dominant beech trees between 90 and 110 yrs of age and of varying height were used as study trees. We hypothesized that tree crown dimensions obtained from scans are more closely related to tree radial growth than those obtained from conventional field measurements. It was found that from a variety of compared crown size characteristics the scan-based tree attributes mean crown radius, maximum area of the crown and crown projection area were most closely related to individual tree growth. We conclude that the horizontal extension of a tree crown in general is to be considered one of the most important drivers of tree growth. We also conclude that terrestrial laser scanning is a powerful tool to reliably measure physical crown dimensions and TLS-based measurements are more reliable than conventional ones.

Wood formation is the primary biological process through which carbon is durably sequestered in woody plants, and is thus a major contributor to mitigate climate change. We analyzed the tree growth patterns of four conifer species across the Iberian Peninsula (IP) based on a dense dendrochronological network (179 sites) combined with a high resolution climate dataset. Generalized linear-mixed models were used to predict the potential tree growth of different pine species under different climate conditions considering different age classes. We found a strong age dependency of tree growth, significant variations across the climate gradients, and a significant interaction of both age and climate effects on the four species considered. Overall, Pinus halepensis was the species with the highest climate sensitivity and the highest growth rates in all age classes and across its distribution area. Due to its stronger plastic character and its potential adaptability, Pinus halepensis was demonstrated to be the most suitable species in terms of tree growth and potentiality to enhance carbon sequestration in the IP. Since its potential distribution largely exceeds its actual distribution, P. halepensis arises as a key species to cope with future climate conditions and to keep fixing carbon regardless of the climatic circumstances.

Coskuner, Kadir Alperen/0000-0001-5249-1604; Ozturk, Murat/0000-0003-1405-036X WOS: 000441963100009 Mistletoe infection results in substantial growth losses in mistletoe-infected forests. This study reports and evaluates the results of retrospective analyses of radial growth of Scots pine (Pinus sylvestris) in relation to the level of infection of pine mistletoe (Viscum album ssp. austriacum). A total of 43 Scots pine trees were destructively sampled from different sites. Of these trees, 14 were uninfected and 29 were infected. Infection classes were determined using six-class dwarf mistletoe rating system (DMRS). All needle and mistletoe biomass were removed completely and weighed for each sampled tree. Subsamples from needles and all mistletoe biomass were taken to the laboratory for oven-dried weight determinations. Five-cm-thick wood discs were cut from the stem at the breast height (1.3m) to determine annual basal area increment for the last 25years. In addition to DMRS, new infection classes were created using mistletoe-to-needle biomass (MB/NB) ratio. The results showed that the radial growth losses could be as much as 41% to 64% at different infection levels. The rate of growth loss in relation to DMRS and MB/NB ratio was similar, but with a larger variability in DMRS values. The results showed that both DMRS rating and MB/NB ratio seem to be important for quantifying growth loss on Scots pine trees infected with mistletoe. The results of this study can also be invaluable in modelling the effects of mistletoe on the growth of Scots pine trees. Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [112O258] The Scientific and Technological Research Council of Turkey (TUBITAK), Grant/Award Number: 112O258

Drought-triggered declines in forest productivity and associated die-off events have increased considerably due to climate warming in the last decades. There is an increasing interest in quantifying the resilience capacity of forests against climate warming and drought to uncover how different stands and tree species will resist and recover after more frequent and intense droughts. Trees form annual growth rings that represent an accurate record of how forest growth responded to past droughts. Here we use dendrochronology to quantify the radial growth of different forests subjected to contrasting climatic conditions in Spain during the last half century. Particularly, we considered four climatically contrasting areas where dominant forests showed clear signs of drought-induced dieback. Studied forests included wet sites dominated by silver fir (Abies alba) in the Pyrenees and beech (Fagus sylvatica) stands in northern Spain, and drought-prone sites dominated by Scots pine (Pinus sylvestris) in eastern Spain and black pine (Pinus nigra) in the semi-arid south-eastern Spain. We quantified the growth reduction caused by different droughts and assessed the short-and long-term resilience capacity of declining vs. non-declining trees in each forest. In all cases, drought induced a marked growth reduction regardless tree vigor. However, the capacity to recover after drought (resilience) at short- and long-term scales varied greatly between declining and non-declining individuals. In the case of beech and silver fir, non-declining individuals presented greater growth rates and capacity to recover after drought than declining individuals. For Scots pine, the resilience to drought was found to be lower in recent years regardless the tree vigor, but the growth reduction caused by successive droughts was more pronounced in declining than in non-declining individuals. In the black pine forest an extreme drought induced a marked growth reduction in declining individuals when accounting for age effects on growth rates. We demonstrate the potential of tree-ring data to record short- and long-term impacts of drought on forest growth and to quantify the resilience capacity of trees.

This paper addresses the response of adult sprout-origin sessile oaks (Quercus petraea (Matt.) Liebl.) to a strong release. Our research plot was established at the Training Forest Enterprise of Mendel University in Brno (Czech Republic) at the turn of 2008/2009. The plot is situated on a plateau with mesotrofic soil in a beech-oak forest vegetation zone at an altitude of 410 m above sea level. Tree responses were monitored using precise girth measurements. During the first year after the release, the basal area increment showed a positive correlation with only the tree diameter. During the second and third year, the basal area increment was also correlated with the release intensity. During the third year, the basal area increment was explained by the tree diameter, the crown shape, and the release intensity as well as individual types of epicormic shoot occurrence. The occurrence of epicormic shoots in the lower part of the trunks and umbel-shaped crowns increased the basal area increment. In the first, second and third year after thinning, the model explained 11.79%, 11.25% and 28.99%, respectively, of the basal area increment variability. Adult trees of sprout origin responded to a strong release very early (within two years) after felling.

Outbreak insects are among the major biotic disturbances affecting Mediterranean forests by reducing their growth and vitality through severe defoliations. Despite their relevance for the management of these drought-prone areas, we lack information on the relationships between growth, canopy cover and insect defoliations at ample spatial and temporal scales. Here, we combine remote sensing (vegetation indexes) and dendrochronological information (basal area increment, BAI) to assess the effects of pine processionary moth (Thaumetopoea pityocampa, PPM) defoliations on growth and cover changes of several pine species, mainly focusing on Pinus nigra. We compared both datasets with a long-term field survey of PPM stand defoliations carried out in eastern Spain during the period 1970-2012. Lastly, we fitted linear-mixed models of BAI using as predictors climatic variables and a multi-scalar drought index to distinguish drought-related growth reductions from those attributed to PPM outbreaks. PPM severe defoliations mainly affected edge or low-density stands. Several vegetation indices (Moisture Stress Index, Normalized Burn Ratio and Normalized Difference Infrared Index) reflected the cover decrease corresponding to severe PPM defoliations. We found that trees affected by various severe PPM defoliations took at least 2. years to recover BAI values similar to those observed before the outbreak. The combined use of remote sensing and dendrochronology allows monitoring the impact of PPM defoliations from stands to trees, and these are valuable approaches to forecast outbreaks and their effects on Mediterranean forest. We consider both powerful tools to further assess the interacting effects of climate warming and PPM dynamics on drought-prone forests. © 2014 Elsevier B.V., This study was supported by projects PROCLIM and CGL2011-26654 financed by La Caixa-Aragón Government and the Spanish Commission of Science and Technology-FEDER, respectively. JJC acknowledges support by ARAID. We sincerely thank J. D. Galván, A.Q. Alla and the personal from the Forest Health Laboratory (Mora de Rubielos, Gobierno de Aragón) for the help in the field works. The authors acknowledge the Landsat scenes provided by the European Space Agency (ESA) in the context of the project C1P.15257.

We investigated long-term responses (since 1850) of Fagus sylvatica (Luxembourg; central Europe) to shifts in temperature, precipitation, and nitrogen deposition by analyzing diameter at breast height (DBH) increment, basal area increment (BAI), and tree-ring stable isotopes (δ13C, δ15N). We compared stands on soils with contrasting water supply (Regosols and Cambisols with an available water capacity of ca. 40 and 170 mm, respectively) and of two different age classes (ca. 60 vs. 200 years). All stands showed a peak in DBH increment in the decade 1978–1987, but a decline in increment growth in subsequent decades. In addition, BAI declined in mature stands in the last two decades. Decreasing increment rates were attributable to an increasing drought limitation of stands, mainly induced by increasing temperatures in the last two decades. Contrary to our expectations, stands on Cambisols showed a similar susceptibility to shifts in temperature and precipitation as stands on Regosols, suggesting a strong adaptation of the respective ecotypes grown at dryer sites. This result was in line with long-term trends for tree-ring δ13C signatures, which did not differ significantly between stands on Cambisols and Regosols. Climate impacts on tree-ring δ15N signatures were low. High spring precipitation and temperatures caused increasing and decreasing δ15N values, respectively, but only in mature stands on Cambisols. Stands on Regosols tended to have lower δ15N values than stands on Cambisols. Decreasing δ15N values in recent decades suggest an increasing impact of allochthonous N loads with isotopically lighter N. We investigated long-term responses (since 1850) of Fagus sylvatica (Luxembourg; central Europe) to shifts in temperature, precipitation, and nitrogen deposition by analyzing diameter at breast height (DBH) increment, basal area increment (BAI), and tree-ring stable isotopes (δ13C, δ15N). We compared stands on soils with contrasting water supply (Regosols and Cambisols with an available water capacity of ca. 40 and 170 mm, respectively) and of two different age classes (ca. 60 vs. 200 years). All stands showed a peak in DBH increment in the decade 1978–1987, but a decline in increment growth in subsequent decades. In addition, BAI declined in mature stands in the last two decades. Decreasing increment rates were attributable to an increasing drought limitation of stands, mainly induced by increasing temperatures in the last two decades. Contrary to our expectations, stands on Cambisols showed a similar susceptibility to shifts in temperature and precipitation as stands on Regosols, suggesting a strong adaptation of the respective ecotypes grown at dryer sites. This result was in line with long-term trends for tree-ring δ13C signatures, which did not differ significantly between stands on Cambisols and Regosols. Climate impacts on tree-ring δ15N signatures were low. High spring precipitation and temperatures caused increasing and decreasing δ15N values, respectively, but only in mature stands on Cambisols. Stands on Regosols tended to have lower δ15N values than stands on Cambisols. Decreasing δ15N values in recent decades suggest an increasing impact of allochthonous N loads with isotopically lighter N.

New forest management approaches aim to ensure high biodiversity and climatic adaptability. Silvicultural practices can alter tree-tree interactions and thus influence forest structure and composition. However, knowledge of the interacting effects of competitive and abiotic stress in tree communities is still limited. We assessed growth dynamics of European beech Fagus sylvatica in oligo- to eutrophic lowland beech forests by quantifying variation in the importance and intensity of competitive interactions among adult trees along a productivity gradient defined by nutrient availability and hydrological characteristics. We further predicted changes in competition indices with various levels of crowding for different forest types. Basal area growth of 1819 canopy trees was analysed using forest inventory data. Competition response of adult trees was inconsistent among forest types. For small timber trees, the intensity (absolute effect) and importance (effect relative to abiotic constraints) of competition decreased with increasing abiotic stress. Growth responses of medium and large timber trees, however, revealed an opposite trend. Thus, in tree communities, competition effects did not follow a general pattern, because tree maturation altered the responsiveness of trees to environmental stress. Resource dependency of competition effects was most pronounced for large timber trees, with lowest sensitivity to changes in crowding conditions occurring on fertile sites. For small and medium timber trees, however, competition effects were strongest in dense stands, with lowest sensitivity to changes in crowding conditions on resource-limited sites. Synthesis and applications. Tree-tree interactions in beech forests showed a clear pattern which depended on tree maturation and resource supply. This highlights the importance of considering tree size-related changes along environmental gradients in regional growth models. Our findings indicate that management practices could facilitate both timber production and nature conservation demands by adapting thinning approaches to age- and resource-related tree growth patterns. We propose a distinct reduction in thinning intensity, particularly for larger beech trees growing on sites with optimum below-ground resources. This would increase the permanent stand volumes and promote natural stand dynamics, which in turn would benefit biodiversity typical of old-growth beech forest ecosystems. Tree-tree interactions in beech forests showed a clear pattern which depended on tree maturation and resource supply. This highlights the importance of considering tree size-related changes along environmental gradients in regional growth models. Our findings indicate that management practices could facilitate both timber production and nature conservation demands by adapting thinning approaches to age- and resource-related tree growth patterns. We propose a distinct reduction in thinning intensity, particularly for larger beech trees growing on sites with optimum below-ground resources. This would increase the permanent stand volumes and promote natural stand dynamics, which in turn would benefit biodiversity typical of old-growth beech forest ecosystems.

An individual-tree growth model was developed with data from 54 permanent plots of Scots pine (Pinus sylvestris L.) located in Galicia (northwestern Spain). The study involved two model fitting approaches, one considering constant growth and mortality rates in the period between two consecutive inventories, and another considering variable growth and mortality rates in the same period. The individual-tree growth model was based on annual basal area growth, height growth and survival probability. The model included variables from groups pertaining to tree size, competition and age. Weighted regression was used as a tool for dealing with missing height observations in model fitting. Evaluation of the model via simulation of growth and mortality in the period between inventories showed that the variable growth rate approach provided slightly better results than the constant growth rate approach. The final model was consistent with expected diameter growth, height growth, dominant height growth, stand basal area growth and reduction in number of stems per hectare.

13 páginas, 7 figuras, 1 tabla., We aimed to gain knowledge on the changes in intrinsic water use efficiency (iWUE) in response to increasing atmospheric CO2 concentrations and climate change over the last century. We investigated the variation in the iWUE of mature Fagus sylvatica trees located in the higher, central and lower altitudinal forest limits (HFL, CFA and LFL) of one of the southernmost sites of beech distribution in Europe, the Montseny Mountains in Catalonia (northeast Spain), during the last century by analysing the δ13C of their tree rings. Pre- and post-maturation phases of the trees presented different trends in δ13C, Δ13C, Ci (internal CO2 concentration), iWUE and basal area increment (BAI). Moreover, these variables showed different trends and absolute values in the LFL than in the other altitudinal sites, CFA and HFL. Our results show the existence of an age effect on δ13C in the CFA and HFL (values increased by ca. 1.25‰ coinciding with the BAI suppression and release phases, previous to maturation). These age-related changes were not found in the LFL, whose beech trees arrived to maturation earlier and experienced drier conditions during the suppression phase. In the last 26 years of comparable mature trees, the increase of iWUE deduced from the Δ13C analyses was ca. 10% in LFL, ca. 6% in CFA and not significant in HFL. These results show that climate change towards more arid conditions accounted for these higher Δ13C-values and increases in the LFL more than the continuous increase in atmospheric CO2 concentrations. This increased iWUE in the LFL did not avoid a decline in growth in these lowest altitudes of this beech southern range-edge as a result of warming. Furthermore, since there was no apparent change in iWUE and growth in the beech forests growing in the more standard-adequate environments of higher altitudes in the last 26 years, the rate of sequestration of C into temperate ecosystems may not increase with increasing atmospheric CO2 concentrations as predicted by most models based on short-term small scale experiments., This research was supported by Spanish Government CGL2004-01402/BOS and REN2006-4025/BOS grants, the EC ALARM (GOCE-CT-2003-506675) and NITROEUROPE (GOCE017841) Projects, and a Fundación BBVA 2004 and a Catalan government SGR2005-00312 grants.

Alpine treelines are often induced by a threshold of minimum temperatures above which tree growth is generally not possible anymore. However, this worldwide pattern may not account for more drought-prone mountains, where changes in precipitation can also affect ecosystem functioning and productivity at higher elevations. Here, we aim to determine if tree-ring formation in ecotones along the Pyrenees indeed primarily depends on temperature means or also reflects hydroclimatic changes. The mean duration of the growing season at Pyrenean treelines was 177 days, lasting from mid-May to early November, which corresponds to a mean root-zone temperature of 8.2 °C. Temperatures during the early and late growing season were most critical for mountain pine growth at highest elevations, and above average spring temperatures also contributed to radial enlargement of tracheids. Sites showing more similar soil temperatures also presented more similar long-term growth trends indicating that local conditions trace regional influences on growth. Nevertheless, more wet conditions in summer enhanced growth at treelines subjected to more Mediterranean influence and therefore having a higher summer water deficit. A broader perspective reveals that soil moisture availability during spring and summer, however, also influence ring width formation at other treelines located in mid-latitude mountains separating temperate and semi-arid biomes. Our results suggest re-evaluating the idea of purely temperature-limited treelines, especially in mid-latitude mountains that experience moisture seasonality or where precipitation decreases with increasing elevation. © 2015, Springer-Verlag Berlin Heidelberg., E. González de Andrés acknowledges the support of an FPI fellowship (Economy and Innovation Ministry, Spain). We sincerely thank Jeff Diez for revising a draft of the manuscript. Conflict of interest J. Julio Camarero was supported by projects 387/2011 (OAPN, Agriculture an Environment Ministry, Spain) and CGL2011-26654 (Economy and Innovation Ministry, Spain). U. Büntgen was further supported by the Operational Programme of Education for Competitiveness of the Ministry of Education, Youth, and Sports of the Czech Republic (No. CZ.1.07/2.3.00/20.0248). The authors declare that they have no conflict of interest.

Fil: Landesmann, Jennifer B. Universidad Nacional del Comahue. Instituto de Investigaciones en Biodiversidad y Medioambiente. Laboratorio Ecotono; Argentina. Fil: Landesmann, Jennifer B. Consejo Nacional de Investigaciones Científicas y Técnica. Instituto de Investigaciones en Biodiversidad y Medioambiente. Laboratorio Ecotono; Argentina. Fil: Gowda, Juan H. Universidad Nacional del Comahue. Instituto de Investigaciones en Biodiversidad y Medioambiente. Laboratorio Ecotono; Argentina. Fil: Gowda, Juan H. Consejo Nacional de Investigaciones Científicas y Técnica. Instituto de Investigaciones en Biodiversidad y Medioambiente. Laboratorio Ecotono; Argentina. Fil: Garibaldi, Lucas Alejandro. Universidad Nacional de Río Negro. Instituto de Investigaciones en Recursos Naturales, Agroecología y Desarrollo Rural; Argentina. Fil: Garibaldi, Lucas Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Recursos Naturales, Agroecología y Desarrollo Rural; Argentina. Fil: Kitzberger, Thomas. Universidad Nacional del Comahue. Instituto de Investigaciones en Biodiversidad y Medioambiente. Laboratorio Ecotono; Argentina. Fil: Kitzberger, Thomas. Consejo Nacional de Investigaciones Científicas y Técnica. Instituto de Investigaciones en Biodiversidad y Medioambiente. Laboratorio Ecotono; Argentina. Fire severity and extent are expected to increase in many regions worldwide due to climate change. Therefore, it is crucial to assess the relative importance of deterministic vs. stochastic factors producing remnant vegetation to understand their function in the persistence of fire-sensitive plants. Vegetation remnants (areas within the landscape that have not burned for a considerable amount of time) may occur stochastically or in more predictable locations (fire refuges) where physical conditions decrease fire severity. Our aim was to determine if remnant forests of the fire-sensitive conifer Austrocedrus chilensis are associated with biophysical attributes that allow persistence in a fire-prone Patagonian landscape. We conducted a multi-scale approach, determining attributes of forest remnants and their surroundings (matrices) through remote sensing and field-based biophysical and functional characteristics, and quantifying how tree survival probability relates to microsite conditions. Trees within remnants displayed abundant fire scars, were twofold older and had threefold larger growth rates than matrix trees. Remnants were associated with high rocky cover and elevated topographical positions. Tree survival increased in hilltops, eastern aspects, and with sparse vegetation. Trees within remnants experienced severe reductions in growth during droughts. Our results suggest that A. chilensis remnants are mainly the result of refuges, where environmental conditions increase fire survival, but also increase susceptibility to drought. A trade-off between fire survival and drought vulnerability may imply that under increasing drought and fire severity, locations that in the past have served as refuges may reduce their ability to allow the persistence of fire-sensitive taxa.

Theory predicts that the postindustrial rise in the concentration of CO2 in the atmosphere (ca) should enhance tree growth either through a direct fertilization effect or indirectly by improving water use efficiency in dry areas. However, this hypothesis has received little support in cold-limited and subalpine forests where positive growth responses to either rising ca or warmer temperatures are still under debate. In this study, we address this issue by analyzing an extensive dendrochronological network of high-elevation Pinus uncinata forests in Spain (28 sites, 544 trees) encompassing the whole biogeographical extent of the species. We determine if the basal area increment (BAI) trends are linked to climate warming and increased ca by focusing on region- and age-dependent responses. The largest improvement in BAI over the past six centuries occurred during the last 150 years affecting young trees and being driven by recent warming. Indeed, most studied regions and age classes presented BAI patterns mainly controlled by temperature trends, while growing-season precipitation was only relevant in the driest sites. Growth enhancement was linked to rising ca in mature (151-300 year-old trees) and old-mature trees (301-450 year-old trees) from the wettest sites only. This finding implies that any potential fertilization effect of elevated ca on forest growth is contingent on tree features that vary with ontogeny and it depends on site conditions (for instance water availability). Furthermore, we found widespread growth decline in drought-prone sites probably indicating that the rise in ca did not compensate for the reduction in water availability. Thus, warming-triggered drought stress may become a more important direct driver of growth than rising ca in similar subalpine forests. We argue that broad approaches in biogeographical and temporal terms are required to adequately evaluate any effect of rising ca on forest growth. © 2014 John Wiley & Sons Ltd., This study was supported by projects 012/2008 and 387/2011 (OAPN, Spain) and by ARAID (JJC) and a JAE-CSIC grant (JDG). We also acknowledge projects which contributed to build this dataset (FoRmat EU ENV4-CT97-0641, AMB95-0160 and CGL2011-26654). We are indebted to all people who helped us in the field. We thank the ESRL-NOAA for providing CO2 data to the public and the scientific community.

The study presents the results of an analysis of the pine tree growth increments (height increment, dbh increment, basal area increment and volume increment) for a 5-year period. The study involved Scots pine trees of Kraft’s class 1, 2 and 3 (dominant stand) in stands of different age classes (II, III, V) growing in fresh mixed coniferous (BMśw) and fresh coniferous (Bśw) forest habitats. The multivariate analysis of variance was performed to assess the statistical significance of age and dominance of trees within a stand on their increment. The dominance position was classified for each tree using Kraft’s criteria. The following characteristic were also measured: dbh of the trunk in two directions (N-S and W-E), and crown projection area on the basis of the characteristic tree crown points, projected using of a crown projector, characteristic points in tree crowns (7 to 14 on average). The actual height was determined after trees were felled. The following measurements of the single tree growing space were selected and determined: crown projection area - pk (m2), crown diameter - dk (m), Seebach’s growth space number - dk / d1.3, crown projection area to basal area ratio d 2 k / d 2 1.3, crown deflection coefficient dk / h, single tree space ppd = pk·h (m3). We assessed the strength of the relationships between tree growth parameters and tree growth space, crown length, relative crown length and slenderness. Both the age and dominance position of trees within the stand affected the growth increments. The strongest correlation among measured traits was between the 5-year volume increment and decreasing slenderness.

A historically unprecedented mountain pine beetle (MPB) outbreak affected western Montana during the past decade. We examined radial growth rates (AD 1860–2007/8) of co-occurring mature healthy and MPB-infected ponderosa pine trees collected at two sites (Cabin Gulch and Kitchen Gulch) in western Montana and: (1) compared basal area increment (BAI) values within populations and between sites; (2) used carbon isotope analysis to calculate intrinsic water-use efficiency (iWUE) at Cabin Gulch; and (3) compared climate-growth responses using a suite of monthly climatic variables. BAI values within populations and between sites were similar until the last 20–30 years, at which point the visually healthy populations had consistently higher BAI values (22–34%) than the MPB-infected trees. These results suggest that growth rates two–three decades prior to the current outbreak diverged between our selected populations, with the slower-growing trees being more vulnerable to beetle infestation. Both samples from Cabin Gulch experienced upward trends in iWUE, with significant regime shifts toward higher iWUE beginning in 1955–59 for the visually healthy trees and 1960–64 for the MPB-infected trees. Drought tolerance also varied between the two populations with the visually healthy trees having higher growth rates than MPB-infected trees prior to infection during a multi-decadal period of drying summertime conditions. Intrinsic water-use efficiency significantly increased for both populations during the past 150 years, but there were no significant differences between the visually healthy and MPB-infected chronologies.

An understanding of the interactions between climate change and forest structure on tree growth are needed for decision making in forest conservation and management. In this paper, we investigated the relative contribution of tree features and stand structure on Atlas cedar (Cedrus atlantica) radial growth in forests that have experienced heavy grazing and logging in the past. Dendrochronological methods were applied to quantify patterns in basal-area increment and drought sensitivity of Atlas cedar in the Middle Atlas, northern Morocco. We estimated the tree-to-tree competition intensity and quantified the structure in Atlas cedar stands with contrasting tree density, age, and decline symptoms. The relative contribution of tree age and size and stand structure to Atlas cedar growth decline was estimated by variance partitioning using partial-redundancy analyses. Recurrent drought events and temperature increases have been identified from local climate records since the 1970s. We detected consistent growth declines and increased drought sensitivity in Atlas cedar across all sites since the early 1980s. Specifically, we determined that previous growth rates and tree age were the strongest tree features, while Quercus rotundifolia basal area was the strongest stand structure measure related to Atlas cedar decline. As a result, we suggest that Atlas cedar forests that have experienced severe drought in combination with grazing and logging may be in the process of shifting dominance toward more drought-tolerant species such as Q. rotundifolia., J.C. Linares and L. Taïqui received financial support for this work from the Spanish Agency for International Cooperation and Develop (AECID), project A/024752/09. J.C. Linares is grateful to J. A. Carreira, at the University of Jaén, for providing additional support for this work. L. Taïqui is grateful to M. Jabrane at the University of Tetouan and M. Benzyane, ex-Director of the National Centre of Forest Research in Morocco, for providing the climatic data of Ifrane. J. J. Camarero is grateful for the support of ARAID and the Globimed network (http://www.globimed.net/). We also want to thank four anonymous reviewers for their helpful comments.

Studies on Fagus sylvatica show that growth in populations toward the southern limit of this species' distribution is limited strongly by drought. Warming temperatures in the Mediterranean region are expected to exacerbate drought where they are not accompanied by increases in precipitation. We studied levels of annual growth in mature F. sylvatica trees over the last half-century in the Montseny Mountains in Catalonia (northeast Spain). Our results show significantly lower growth of mature trees at the lower limit of this species' distribution when compared with trees at higher altitudes. Growth at the lower Fagus limit is characterized by a rapid recent decline starting in approximately 1975. By 2003, growth of mature trees had fallen by 49% when compared with predecline levels. This is not an age-related phenomenon, nor is it seen in comparable populations at higher altitudes. Analysis of climate-growth relationships suggests that the observed decline in growth is a result of warming temperatures and that, as precipitation in the region has not increased, precipitation is now insufficient to ameliorate the negative effects of increased temperatures on tree growth. As the climate-response of the studied forest is comparable with that of F. sylvatica forests in other southern European regions, it is possible that this growth decline is a more widespread phenomenon. Warming temperatures may lead to a rapid decline in the growth of range-edge populations and a consequent retreat of the species distribution in southern Europe. Assessment of long-term growth trends across the southern range edge of F. sylvatica therefore merits further attention.

Climate warming may enhance the negative effects of droughts on radial growth in areas with severe water deficit, such as Mediterranean mountains under semi-arid conditions. The impacts of drought on growth decline of Mediterranean pines have not been evaluated considering species with different vulnerability and areas with contrasting climates. Dendrochronological methods were used to assess the responses of basal area increment to drought in Pinus pinaster and P. halepensis plantations. We compared growth trends of trees with different defoliation degree in two sites in south-eastern Spain (Sierra de los Filabres and Sierra de Baza) with contrasting climatic conditions. In the more xeric area (Filabres) both pine species showed a sharp growth reduction in response to extreme droughts such as those observed in 1994-1995, 1999 and 2005. The radial growth of both species was enhanced by May and June precipitation of the year of tree-ring formation. P. pinaster showed higher defoliation in the xeric area (Filabres) than in the more mesic area (Baza) but needle loss was not linked to an abrupt growth reduction. Contrastingly, divergent radial growth patterns between trees showing high and low defoliation degrees were found for P. halepensis in the more xeric area, where a negative relationship between recent basal area increment and defoliation was found. Pine plantations in Mediterranean mountains under semi-arid conditions are highly vulnerable to warming-induced droughts. Such marginal stands constitute valuable monitoring systems to assess the negative impacts of drought on tree growth, and to test if management strategies as thinning can mitigate the negative impacts of climate warming on similar drought-stressed forests.

International audience; The effects of thinning and heavy stand density reduction was investigated in Turkey oak (Quercus cerris L.) forests of central Italy, to evaluate the physiological responses and the growth status of trees that survived a past coppice cut and thinning to convert the stand to high-forest.* The working hypothesis was that a strong decrease in stand density would cause a decreasing in canopy-intrinsic water-use efficiency (measured as the ratio of CO2 assimilation to stomatal conductance, A/g), thus an increase in tree-ring carbon isotopic discrimination (Δ13C).* The tree-ring Δ13C of the remaining trees ("survivors") was found to have significantly (P < 0.05) raised between year two and year seven since the coppice stand was thinned (high-forest conversion thinnings). This effect was mostly caused by a large decrease in tree-rings Δ13C at control site which was characterized by high density and competition by trees. An increase in survivors tree-rings Δ13C probably indicates an improved water availability, possibly induced by a decrease in competition and in stand density or a decrease in the precipitation intercepted by the canopy (i.e., a stronger increase in g over A since a decrease in A is highly unlikely). A change in foliar nitrogen, foliar Δ13C and content in chlorophylls was also recorded seven years after thinning.* Thinnings carried out to convert old abandoned coppices into high-forest stands induce short-term stimulation of Turkey oak growth by increasing light and water availability. We were able to make a detailed reconstruction of the impact of past silvicultural treatment on the stand using a tree-ring wood Δ13C time-series.; Les effets de l'éclaircie et de la réduction importante de la densité du peuplement ont été étudiés dans des forêts de chêne de Turquie (Quercus cerris L.) de l'Italie centrale, afin d'évaluer les réactions physiologiques et l'état de croissance des arbres qui ont survécu à une coupe de taillis et à une éclaircie pour la conversion du peuplement en futaie.* L'hypothèse de travail était qu'une forte diminution de la densité du peuplement entraînerait une baisse de l'efficience intrinsèque d'utilisation de l'eau de la canopée (mesurée par le rapport de l'assimilation de CO2 à la conductance stomatique, A/g), donc par une augmentation de la discrimination isotopique du carbone dans les cernes (Δ13C).* Les Δ13C des cernes des arbres restants ("survivants") ont été trouvés significativement (P < 0,05) augmentés entre deux ans et sept ans après que le peuplement de taillis a été éclairci (conversion en futaie). Cet effet a été principalement causé par une importante diminution du Δ13C des cernes dans le peuplement témoin qui se caractérise par une forte densité et par une forte concurrence entre les arbres. Une augmentation de Δ13C dans les cernes des arbres survivants indique probablement une disponibilité en eau améliorée, induite peut-être par une diminution de la concurrence et de la densité du peuplement ou une diminution des précipitations interceptées par la canopée (par exemple, une augmentation très forte de g au dessus de A puisque une diminution de A est hautement improbable). Un changement dans l'azote foliaire, le Δ13C foliaire et le contenu en chlorophylles ont également été enregistrés sept ans après l'éclaircie.* Les éclaircies effectuées pour convertir les anciens taillis abandonnés en futaies induisent une stimulation à court terme de la croissance du chêne de Turquie en augmentant la lumière et la disponibilité en eau. Nous avons été en mesure de faire une reconstitution minutieuse de l'impact des traitements sylvicoles passés en utilisant des séries chronologiques temporelles de Δ13C du bois des cernes.