Phenological plasticity will not help all species adapt to climate change

Concerns are rising about the capacity of species to adapt quickly enough to climate change. In long‐lived organisms such as trees, genetic adaptation is slow, and how much phenotypic plasticity can help them cope with climate change remains largely unknown. Here, we assess whether, where and when phenological plasticity is and will be adaptive in three major European tree species. We use a process‐based species distribution model, parameterized with extensive ecological data, and manipulate plasticity to suppress phenological variations due to interannual, geographical and trend climate variability, under current and projected climatic conditions. We show that phenological plasticity is not always adaptive and mostly affects fitness at the margins of the species' distribution and climatic niche. Under current climatic conditions, phenological plasticity constrains the northern range limit of oak and beech and the southern range limit of pine. Under future climatic conditions, phenological plasticity becomes strongly adaptive towards the trailing edges of beech and oak, but severely constrains the range and niche of pine. Our results call for caution when interpreting geographical variation in trait means as adaptive, and strongly point towards species distribution models explicitly taking phenotypic plasticity into account when forecasting species distribution under climate change scenarios.     

European beech in its northeasternmost stands in Europe: Varying climate-growth relationships among generations and diameter classes

Age, genetics and social status of trees affect their sensitivity to environmental factors, and information about such effects is needed for comprehensive assessment of growth potential. Climatic sensitivity of radial increment (i.e., tree-ring width) of introduced European beech (Fagus sylvatica L.) of different generations and social status, growing in its northeasternmost stands in Europe, was studied by dendroclimatological methods. At present, the studied stands occur outside of the natural distribution area of the species, providing opportunity to study adaptability and potential growth of beech in novel environments under changing climate. The sensitivity of radial growth to climatic factors was modulated by the generation and social status (size) of trees. The first generation trees, which were propagated from the material transferred from the northern Germany, were highly sensitive to climatic factors and showed wide spectrum of responses. The dominant trees were particularly sensitive to June precipitation, indicating sensitivity to water deficit in summer. The suppressed trees were mainly sensitive to temperature in the dormant period. Tree-ring width of the second generation trees, which were propagated from the first generation stands, was mainly affected by water deficit in summer, yet the local factors, modulated the mechanisms of response. In one stand, tree-ring width was affected by conditions during the formation of tree-ring, indicating direct influence of weather conditions on xylogenesis. In the other stand, tree-ring width was correlated to weather conditions in the preceding year, suggesting influence via carbohydrate reserves. The effect of social status on climatic sensitivity in the second generation stands was considerably weaker, likely due to the natural and anthropogenic selection of the material best adapted for local conditions. The effect of climatic factors on radial growth of beech has shifted during the 20th century. The effect of autumn temperature has weakened, likely due to warming; the effect of factors related to water deficit in summer has intensified that could be related to both, changes in climate and ageing. The observed climate-growth relationships suggested that conditions in winter have become suitable for beech, yet careful selection of sites/regions with appropriate hydrological conditions appear necessary to counteract the increasing effect of water deficit, hence to ensure productivity of future beech sites in Latvia.     

Patterns of Cross-Continental Variation in Tree Seed Mass in the Canadian Boreal Forest

Seed mass is an adaptive trait affecting species distribution, population dynamics and community structure. In widely distributed species, variation in seed mass may reflect both genetic adaptation to local environments and adaptive phenotypic plasticity. Acknowledging the difficulty in separating these two aspects, we examined the causal relationships determining seed mass variation to better understand adaptability and/or plasticity of selected tree species to spatial/climatic variation. A total of 504, 481 and 454 seed collections of black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb) across the Canadian Boreal Forest, respectively, were selected. Correlation analyses were used to determine how seed mass vary with latitude, longitude, and altitude. Structural Equation Modeling was used to examine how geographic and climatic variables influence seed mass. Climatic factors explained a large portion of the variation in seed mass (34, 14 and 29%, for black spruce, white spruce and jack pine, respectively), indicating species-specific adaptation to long term climate conditions. Higher annual mean temperature and winter precipitation caused greater seed mass in black spruce, but annual precipitation was the controlling factor for white spruce. The combination of factors such as growing season temperature and evapotranspiration, temperature seasonality and annual precipitation together determined seed mass of jack pine. Overall, sites with higher winter temperatures were correlated with larger seeds. Thus, long-term climatic conditions, at least in part, determined spatial variation in seed mass. Black spruce and Jack pine, species with relatively more specific habitat requirements and less plasticity, had more variation in seed mass explained by climate than did the more plastic species white spruce. As traits such as seed mass are related to seedling growth and survival, they potentially influence forest species composition in a changing climate and should be included in future modeling of vegetation shifts.     

Population differentiation in climate sensitivity of resin duct formation during growth resumption in Pinus pinaster

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

Climatic responses of Pinus brutia along the Black Sea coast of Crimea and the Caucasus

Pinus brutia var. pityusa (Steven) Silba (Calabrian pine) is considered a vulnerable species because of reductions in its population sizes linked to habitat decline in recent decades. Global warming alongside the collateral modification of precipitation regimes may markedly affect the distribution ranges of this species.In this dendroecological study, we identified the most influential climatic factors affecting the radial growth of P. brutia on the northern and eastern coasts of the Black Sea among the northern refugia of this species. Chronologies from five sites located on the Crimea Peninsula and the Caucasian coast and exposed to varying climatic conditions were used in this analysis. The study of environmental factors controlling the growth of P. brutia trees in the coastal populations of Crimea and the Caucasus revealed that within the longitudinal transect, which encompasses a specific range of climatic conditions, correlations between climate and the growth of P. brutia under analogous orographic conditions are similar.Aridisation of the dry Crimean climate in 1981–2012 led to an increase in the tree growth response. In the same period, populations of P. brutia trees growing in the subtropical climate of the Black Sea coast exhibited a weakened growth response to the point of disappearance. The northern populations of P. brutia, which are at the climatic limit of the species’ distribution, are exposed to a high risk of increasing climate aridisation. Our findings could provide useful information for further research on the effects of climate change on Black Sea coastal forest ecosystems.     

Water shortage affects the water and nitrogen balance in Central European beech forests

Whilst forest policy promotes cultivation and regeneration of beech dominated forest ecosystems, beech itself is a highly drought sensitive tree species likely to suffer from the climatic conditions prognosticated for the current century. Taking advantage of model ecosystems with cool-moist and warm-dry local climate, the latter assumed to be representative for future climatic conditions, the effects of climate and silvicultural treatment (different thinning regimes) on water status, nitrogen balance and growth parameters of adult beech trees and beech regeneration in the understorey were assessed. In addition, validation experiments with beech seedlings were carried out under controlled conditions, mainly in order to assess the effect of drought on the competitive abilities of beech. As measures of water availability xylem flow, shoot water potential, stomatal conductance as well as delta (13)C and delta (18)O in different tissues (leaves, phloem, wood) were analysed. For the assessment of nitrogen balance we determined the uptake of inorganic nitrogen by the roots as well as total N content and soluble N compounds in different tissues of adult and young trees. Retrospective and current analysis of delta (13)C, growth and meteorological parameters revealed that beech growing under warm-dry climatic conditions were impaired in growth and water balance during periods with low rain-fall. Thinning affected water, N balance and growth mostly of young beech, but in a different way under different local climatic conditions. Under cool, moist conditions, representative for the current climatic and edaphic conditions in beech forests of Central Europe, thinning improves nutrient and water status consistent to published literature and long-term experience of forest practitioners. However, beech regeneration was impaired as a result of thinning at higher temperatures and under reduced water availability, as expected in future climate.     

Balance of Competitive and Facilitative Effects of Exotic Trees on a Native Patagonian Grass

The balance between facilitation and competition in plants changes with species characteristics and environmental conditions. Facilitative effects are common in natural ecosystems, particularly in stressful environments or years. Contrarily, in artificial associations of plants, such as agroforestry systems, some authors have suggested that even when facilitative effects may occur, net balance of tree effects on grasses is usually negative, particularly in dry environments. The aim of this study was to determine the net effect of the exotic ponderosa pine on the native grass Festuca pallescens (St. Ives) Parodi in agroforestry systems in Patagonia. Soil water content, plant water status, and relative growth were measured in the grass growing in different treatments (determined by tree cover level) during two growing seasons with contrasting climatic conditions. Facilitative effects of trees over grass water status were recorded only when water availability was high. A net negative effect was detected on dates when soil water content was very low and evaporative demand was high. The strength of these negative effects depended on tree density and climatic conditions, being higher in treatments with lower tree canopy cover. These results indicate that the positive effect of trees could only be expected under relatively low stress conditions. However, relative growth of grasses was always similar in plants growing in forested plots than in open grassland. Differences in biomass allocation for grasses growing in shade and open habitats may reconcile these contrary results. Our results highlight the importance of the physiology of a species (relative drought and shade tolerance) in determining the response of a plant to a particular interacting species.     

Rhythmic growth fluctuations in forest trees of Central Europe and the Front Range in Colorado

Summary Growth ring sequences in conifers and broadleaved trees show abrupt growth reductions persisting for several years. The frequency and duration of such reductions in almost 10000 trees in forest stands of Central Europe, in particular Switzerland, and in the Front Range, Colorado, USA, is related to species, climate and weather, and geographical unit. The growth reductions in the populations investigated are concentrated in certain periods and, in all species examined, essentially related to periods of drought in the spring and summer months. During the years covered by the study (1850–1985), periods of growth reduction occur in Central Europe, the Front Range, Colorado, and also in the Hudson Valley, New York, at irregular intervals of 6–34 years, and on average every 13–14 years. The growth reduction periods normally do not show synchronism between the three areas investigated. Regionally valid growth periodicities can only be definitely determined through the examination of a very large amount of material comprising a number of species growing in different forest stands and on different sites within a major phytosociological unit. Findings from studies on trees in different climatic areas or on few samples scarcely allow reliable comparisons.     

Biomass partitioning and growth efficiency in four naturally regenerated forest tree species

Current forest growth models and yield tables are almost exclusively based on data from mature trees, reducing their applicability to young and developing stands. To address this gap, young European beech, sessile oak, Scots pine and Norway spruce trees approximately 0–10 yr old were destructively sampled in a range of naturally regenerated forest stands in Central Europe. Diameter at base and height was first measured in situ for up to 175 individuals per species. Subsequently, the trees were excavated and dry biomass of foliage, branches, stems and roots was measured. Allometric relations were then used to calculate biomass allocation coefficients (BAC) and growth efficiency (GE) patterns in young trees. We found large differences in BAC and GE between broadleaves and conifers, and also between species within these categories. Both BAC and GE are strongly age-specific in young trees, their rapidly changing values reflecting different growth strategies in the earliest stages of growth. We show that linear relationships describing biomass allocation in older trees are not applicable in young trees. To accurately predict forest biomass and carbon stocks, forest growth models need to include species and age-specific parameters of biomass allocation patterns.     

High-frequency variation of tree-ring width of some native and alien tree species in Latvia during the period 1965–2009

The plasticity of climate-growth relationships of trees is one of the main factors determining the climate-induced changes in forest productivity and composition. In this study, high-frequency variation of tree-ring width (TRW) of four native and three alien tree species and two hybrids of Populus L. growing in Latvia (hemiboreal zone) was compared using a principal component analysis based on TRW indices for the period 1965–2009. The effect of climatic factors was assessed using a bootstrapped correlation analysis. Influence of common climatic factors related to the length of the vegetation season, winter temperature, and water regime in summer was traced in the TRW of the studied species and hybrids. The combination and effect of the identified factors differed by species (and hybrids), to a certain extent explaining the diversity of TRW patterns. Nevertheless, some similarities among the species were also observed, suggesting the plasticity of growth response. Scots pine was generally sensitive to winter temperatures, but Norway spruce was mainly sensitive to summer water regime, while black alder was sensitive to winter temperatures and precipitation in spring. In contrast, silver birch showed the lowest sensitivity to the tested climatic factors (demonstrating sensitivity to winter precipitation in a few sites), suggesting tolerance to weather fluctuations. The TRW of the alien species was primarily sensitive to climatic factors related to water regime in the summer of the year preceding the formation of tree-ring, implying differences in mechanisms regulating wood increment. Nevertheless, temperature in the dormant period was significant for European larch in a few sites, suggesting sensitivity to cold damage. The variation of TRW of Populus hybrids diverged from others, as their growth was negatively correlated with the temperature in autumn, spring, and summer and positively correlated with water balance. Although the annual water balance in Latvia is positive, the effect of water deficit on tree growth was apparent.     

Climate impact on growth dynamic and intra-annual density fluctuations in Aleppo pine (Pinus halepensis) trees of different crown classes

Mediterranean environments are of special interest for the study of the relationships between climate, growth and anatomic features. Dendrochronological techniques were applied at eight sampling sites that were selected throughout the natural distribution area of Pinus halepensis in the Iberian Peninsula. The objectives of this paper were: (i) to identify relationships between radial growth and climate for different crown classes of Aleppo pine (P. halepensis Mill.); (ii) to quantify the presence of intra-annual density fluctuations (IADFs) according to crown class and cambial age; (iii) to establish the relationships between IADFs and climate. In the more mesic sites, dominant trees showed higher climatic sensitivity than suppressed trees, while in the more xeric sites suppressed trees showed higher sensitivity than dominant trees. Tree-ring growth of both crown classes correlated positively with precipitation during and prior to the growing season. IADFs were more frequent in young than in old stands without differences between crown classes. Precipitation in April and December was positively correlated to the occurrence of IADFs, while precipitation in July correlated negatively. A higher frequency in IADFs occurred in the last 50 years, which coincides with the increase in drought events in the Iberian Peninsula.     

Species-specific growth-climate responses of Dahurian larch (Larix gmelinii) and Mongolian pine (Pinus sylvestris var. mongolica) in the Greater Khingan Range,northeast China

Responses of tree growth to climate are usually spatially heterogeneous. Besides regionally varying external environments, species specificity is a crucial factor in determining said spatial heterogeneity. A better understanding of this species specificity would improve our estimations of the warming effects on forests. In this study, we selected two widely-distributed boreal conifers, Dahurian larch (Larix gmelinii) and Mongolian pine (Pinus sylvestris var. mongolica), to compare their growth-climate responses, including long-term growth-climate correlations and short-term growth resilience to drought. We sampled 160 trees and 481 tree-ring cores from the two species in two pure and two mixed forests, located in the Greater Khingan Range, northeast China. We found that Dahurian larch was generally positively correlated with spring temperature and negatively correlated with summer temperature. In contrast, Mongolian pine was more sensitive to summer moisture. Our results suggest that the main climatic limitations were low spring temperatures for Dahurian larch and summer moisture deficits for Mongolian pine. Dahurian larch represented higher growth resistance to drought, while Mongolia pine represented higher recovery. Based on this, we inferred that Dahurian larch was more vulnerable to extreme droughts, while Mongolian pine was more vulnerable to frequent droughts. We also demonstrated the effects of forest type on growth-climate responses. The negative effects of summer temperatures on Mongolian pine seemed to be more significant in mixed forests. As warming continued, Mongolian pine in this area would suffer severer moisture deficits, especially when coexisting with Dahurian larch. Our results suggest that Dahurian larch gained an advantage in the competition with Mongolian pine during high moisture stress. Driven by the warming trends, the species specificity in growth response would ultimately promote the separation of the two species in distribution. This study will help improve our estimations of the warming effects on forests and develop more species-targeted forest management practices.     

Ecophysiological response to severe drought in Pinus halepensis Mill. trees of two provenances

As a result of predicted regional climatic changes the need to select for the more drought-tolerant genotypes (ecotypes) among Mediterranean conifers has become clear. Aleppo pine (Pinus halepensisMill.) seems to be one of the most drought-tolerant pine species. Nevertheless, the existence of geographical trends in their genetic differentiation indicates potentially large differences in drought-tolerance among provenances. This assumption was verified by the finding of large variation among provenances in their internal water relations. Hence, the aim of this study was to compare the ecophysiological behaviour of several Aleppo pine provenances under contrasting climatic conditions. Growth parameters (height and diameter) and survival rate were measured in two provenance trials, one planted under sub-desertic conditions at the northern edge of the Negev desert, and the second under thermo-Mediterranean climatic conditions in the central coastal plains, Israel. Ecophysiological parameters such as: predawn needle water potential, sap flow in the xylem (i.e. transpiration), photosynthesis and water-use efficiency were measured in trees of selected provenances. The results suggest that it is not possible to predict provenance performance under harsh conditions from their performance under more favourable ones. Therefore, selection must be carried out under the exact conditions in which the trees from the resultant selection will be planted. The present study clearly emphasises the need for broad selection programs of P. halepensis.     

Vapor–pressure deficit and extreme climatic variables limit tree growth

Assessing the effect of global warming on forest growth requires a better understanding of species‐specific responses to climate change conditions. Norway spruce and European beech are among the dominant tree species in Europe and are largely used by the timber industry. Their sensitivity to changes in climate and extreme climatic events, however, endangers their future sustainability. Identifying the key climatic factors limiting their growth and survival is therefore crucial for assessing the responses of these two species to ongoing climate change. We studied the vulnerability of beech and spruce to warmer and drier conditions by transplanting saplings from the top to the bottom of an elevational gradient in the Jura Mountains in Switzerland. We (1) demonstrated that a longer growing season due to warming could not fully account for the positive growth responses, and the positive effect on sapling productivity was species‐dependent, (2) demonstrated that the contrasting growth responses of beech and spruce were mainly due to different sensitivities to elevated vapor–pressure deficits (VPD), (3) determined the species‐specific limits to VPD above which growth rate began to decline, and (4) demonstrated that models incorporating extreme climatic events could account for the response of growth to warming better than models using only average values. These results support that the sustainability of forest trees in the coming decades will depend on how extreme climatic events will change, irrespective of the overall warming trend.     

Sensitivity of French temperate coniferous forests to climate variability and extreme events (Abies alba,Picea abies and Pinus sylvestris)

Questions: (1) How do extreme climatic events and climate variability influence radial growth of conifers (silver fir, Norway spruce, Scots pine)? (2) How do elevation and soil water capacity (SWC) modulate sensitivity to climate? Location: The sampled conifer stands are in France, in western lowland and mountain forests, at elevations from 400 to 1700 m, and an SWC from 50 to 190 mm. Methods: We established stand chronologies for total ring width, earlywood and latewood width for the 33 studied stands (985 trees in total). Responses to climate were analysed using pointer years and bootstrapped response functions. Principal component analysis was applied to pointer years and response function coefficients in order to elucidate the ecological structure of the studied stands. Results: Extreme winter frosts are responsible for greater growth reductions in silver fir than in Norway spruce, especially at the upper elevation, while Scots pine was the least sensitive species. Exceptional spring droughts caused a notable growth decrease, especially when local conditions were dry (altitude<1000 m and SWC<100 mm for silver fir, western lowlands for Scots pine). Earlywood of silver fir depended on previous September and November and current‐year February temperature, after which current June and July water supply influenced latewood. Earlywood of Norway spruce was influenced by previous September temperature, after which current spring and summer droughts influenced both ring components. In Scots pine, earlywood and latewood depended on the current summer water balance. Local conditions mainly modulated latewood formation. Conclusions: If the climate becomes drier, low‐elevation dry stands or trees growing in western lowlands may face problems, as their growth is highly dependent on soil moisture availability.     

Drought response and changing mean sensitivity of European beech close to the dry distribution limit

European beech (Fagus sylvatica L.) covers a large area mainly in the colline and montane ranges in Europe, and a drier and warmer climate, as expected for the coming decades, is likely to alter its distribution. So far, an altitudinal shift has been projected using a variety of modelling approaches. However, we lack knowledge about the climatic and edaphic factors that control the growth and competitive behaviour of beech at its dry distribution limit. We applied and further developed dendroecological methods to study the drought response and sensitivity pattern of beech at sites with different moisture regimes. We compared three pairs of sites from different geographical regions near the dry distribution limit of beech in Switzerland, consisting of a dry and mesic site each. Radial growth differed between mesic and dry sites, in that average ring-width at mesic sites was around double the width at dry sites. For the whole study period (1930–2006), the sites with the lowest available soil water capacity (AWC) were found to respond most sensitively to drought. However, in recent years, sites with higher AWC have shown increasing drought sensitivity, i.e. they have responded even more strongly to drought than the dry sites. This change in sensitivity corresponds to a seasonal shift in drought response at mesic sites, with a change in the months showing significant drought response in all three studied regions compared with the past. Even though dry sites generally displayed a larger number of negative pointer years than mesic sites, it appears that the frequency of pointer years has increased at mesic sites, i.e. they have become more sensitive particularly in the last quarter of the twentieth century. Yet, the frequency of pointer years at the dry sites has remained fairly constant. These results indicate that beech trees near their dry distribution limit are adapted to extreme conditions already, while changes in the growth patterns of beech under mesic conditions have to be expected.     

Significant Mean and Extreme Climate Sensitivity of Norway Spruce and Silver Fir at Mid-Elevation Mesic Sites in the Alps

Climate forcing is the major abiotic driver for forest ecosystem functioning and thus significantly affects the role of forests within the global carbon cycle and related ecosystem services. Annual radial increments of trees are probably the most valuable source of information to link tree growth and climate at long-term time scales, and have been used in a wide variety of investigations worldwide. However, especially in mountainous areas, tree-ring studies have focused on extreme environments where the climate sensitivity is perhaps greatest but are necessarily a biased representation of the forests within a region. We used tree-ring analyses to study two of the most important tree species growing in the Alps: Norway spruce (Picea abies) and silver fir (Abies alba). We developed tree-ring chronologies from 13 mesic mid-elevation sites (203 trees) and then compared them to monthly temperature and precipitation data for the period 1846–1995. Correlation functions, principal component analysis and fuzzy C-means clustering were applied to 1) assess the climate/growth relationships and their stationarity and consistency over time, and 2) extract common modes of variability in the species responses to mean and extreme climate variability. Our results highlight a clear, time-stable, and species-specific response to mean climate conditions. However, during the previous-year''s growing season, which shows the strongest correlations, the primary difference between species is in their response to extreme events, not mean conditions. Mesic sites at mid-altitude are commonly underrepresented in tree-ring research; we showed that strong climatic controls of growth may exist even in those areas. Extreme climatic events may play a key role in defining the species-specific responses on climatic sensitivity and, with a global change perspective, specific divergent responses are likely to occur even where current conditions are less limited.     

Abiotic factors modulate post-drought growth resilience of Scots pine plantations and rear-edge Scots pine and oak forests

The proportion of planted forests in the Mediterranean Basin is one of the largest in the world. These plantations are dominated by pine species and present a series of characteristics such as low elevation, high competition or small tree size that make them more vulnerable to droughts. However, quantitative assessments of their post-drought growth resilience in accordance with species, site factors and tree characteristics are lacking. In this study we sampled 164 trees at four forest sites located in the drought-prone Sierra Nevada, southeastern Spain. We compared growth responsiveness to drought in rear-edge planted vs. relic natural Scots pine (Pinus sylvestris) and coexisting Pyrenean oak (Quercus pyrenaica) stands. Our objective was to characterize and compare the different growth responses to drought between species and sites and the effect of the main physiographic factors (altitude, aspect, and slope) on these responses since the influence of these factors on post-drought resistance and resilience has received little attention to date. Our results reveal that the planted pine sites with the lowest mean growth rates displayed greater resistance during drought, and that higher altitude was associated with improved resistance and/or resilience for all species and sites. Natural pine and Pyrenean oak stands were better adapted to the dry climatic conditions of the Mediterranean region where the study was undertaken, displaying greater resistance and/or resilience and lower influence of drought on growth in comparison to stands of planted pines. These results suggest that promoting the conservation of high-elevation pine plantations and enhancing the regeneration of natural pine and oak may improve the resistance and resilience of these drought-prone forest ecosystems.     

Climatic limits for the present distribution of beech (Fagus L.) species in the world

Aim Beech (Fagus L., Fagaceae) species are representative trees of temperate deciduous broadleaf forests in the Northern Hemisphere. We focus on the distributional limits of beech species, in particular on identifying climatic factors associated with their present range limits. Location Beech species occur in East Asia, Europe and West Asia, and North America. We collated information on both the southern and northern range limits and the lower and upper elevational limits for beech species in each region. Methods In total, 292 lower/southern limit and 310 upper/northern limit sites with available climatic data for all 11 extant beech species were collected by reviewing the literature, and 13 climatic variables were estimated for each site from climate normals at nearby stations. We used principal components analysis (PCA) to detect climatic variables most strongly associated with the distribution of beech species and to compare the climatic spaces for the different beech species. Results Statistics for thermal and moisture climatic conditions at the lower/southern and upper/northern limits of all world beech species are presented. The first two PCA components accounted for 70% and 68% of the overall variance in lower/southern and upper/northern range limits, respectively. The first PCA axis represented a thermal gradient, and the second a moisture gradient associated with the world‐wide distribution pattern of beech species. Among thermal variables, growing season warmth was most important for beech distribution, but winter low temperature (coldness and mean temperature for the coldest month) and climatic continentality were also coupled with beech occurrence. The moisture gradient, indicated by precipitation and moisture indices, showed regional differences. American beech had the widest thermal range, Japanese beeches the most narrow; European beeches occurred in the driest climate, Japanese beeches the most humid. Climatic spaces for Chinese beech species were between those of American and European species. Main conclusions The distributional limits of beech species were primarily associated with thermal factors, but moisture regime also played a role. There were some regional differences in the climatic correlates of distribution. The growing season temperature regime was most important in explaining distribution of Chinese beeches, whilst their northward distribution was mainly limited by shortage of precipitation. In Japan, distribution limits of beech species were correlated with summer temperature, but the local dominance of beech was likely to be dependent on snowfall and winter low temperature. High summer temperature was probably a limiting factor for southward extension of American beech, while growing season warmth seemed critical for its northward distribution. Although the present distribution of beech species corresponded well to the contemporary climate in most areas, climatic factors could not account for some distributions, e. g., that of F. mexicana compared to its close relative F. grandifolia. It is likely that historical factors play a secondary role in determining the present distribution of beech species. The lack of F. grandifolia on the island of Newfoundland, Canada, may be due to inadequate growing season warmth. Similarly, the northerly distribution of beech in Britain has not reached its potential limit, perhaps due to insufficient time since deglaciation to expand its range.     

Changes in diversity and storage function of ectomycorrhiza and soil organoprofile dynamics after introduction of beech into Scots pine forests

Diversity and storage function of mycorrhiza as well as soil organoprofile formation were investigated in a chronosequence of a pure Scots pine (Pinus sylvestris L.) stand, of Scots pine stands that were underplanted with beech (Fagus sylvatica L.) and in three pure beech stands of different age. Mycorrhiza diversity was higher in the pure beech stands compared to the pure pine stand. Beech and pine trees in the mixed stands had similar dominant mycorrhiza morphotypes. However, trees in two of the three pure beech stands were mycorrhized with other types. Mycorrhizal abundance and nutrient amounts of mycorrhizae associated with beech trees were higher in the mixed and in the pure beech stands compared to pine mycorrhizae indicating that nutrient uptake was higher in older beech than in older pine trees. Humus quality varied from pine to beech stands. Plant litter storage in the humus layer was highest in the youngest mixed stand and lowest in the oldest beech stand. Humus forms changed from moder grass-type in the pure Scots pine stand to mor-like moder and moder rich in fine humus with increasing age of beeches in the mixed stands. The older beech stands were characterised by oligomull and mull-like moder as the dominating humus forms. The ecologically favourable humus forms, i.e., nutrient rich humus forms in the older beech stands correlate well with the higher mycorrhizal diversity and abundance as well as the higher nutrient storage of their mycorrhizae in these stands. The results are also discussed with regard to the 'base-pump effect' of beech trees.