Tree rings indicate different drought resistance of a native (Abies alba Mill.) and a nonnative (Picea abies (L.) Karst.) species co-occurring at a dry site in Southern Italy

Climate changes induced by the anthropogenic alteration of the atmospheric radiative balance are expected to change the productivity and composition of forest ecosystems. In Europe, the Mediterranean is considered one of the most vulnerable regions according to climatic forecasts and simulations. However, although modifications in the inter-specific competition are envisaged, we still lack a clear understanding of the ability of the Mediterranean vegetation to adapt to climate changes. We investigated how two co-occurring tree species commonly used in afforestation programmes, the native Abies alba Mill. and the nonnative Picea abies L. Karst., adapt to climate change by assessing their growth performance and physiological responses in relation to past climate variability. Growth was addressed by analysing tree-ring width and carbon and oxygen stable isotopes. Statistical relationships between isotopic value and monthly climate data suggest that the two species underwent ecophysiological adaptation to Mediterranean climatic constraints. These adaptations are also expressed in the ring-width data. Based on the carbon isotope ratio reflecting the stomatal response to drought, we found that the precipitation in the first period of the growing season, i.e. early spring, is a major factor influencing the annual growth of A. alba, which although native, proved to be sensitive to drought. P. abies, on the other hand, showed a higher tolerance to summer drought stress. These findings should help define criteria for sustainability and effective forest conservation in the Mediterranean region.     

Photosynthetic characteristics of Fagus sylvatica and Quercus robur established for stand conversion from Picea abies

Efforts in Europe to convert Norway spruce (Picea abies) plantations to broadleaf or mixed broadleaf-conifer forests could be bolstered by an increased understanding of how artificial regeneration acclimates and functions under a range of Norway spruce stand conditions. We studied foliage characteristics and leaf-level photosynthesis on 7-year-old European beech (Fagus sylvatica) and pedunculate oak (Quercus robur) regeneration established in open patches and shelterwoods of a partially harvested Norway spruce plantation in southwestern Sweden. Both species exhibited morphological plasticity at the leaf level by developing leaf blades in patches with an average mass per unit area (LMA) 54% greater than of those in shelterwoods, and at the plant level by maintaining a leaf area ratio (LAR) in shelterwoods that was 78% greater than in patches. However, we observed interspecific differences in photosynthetic capacity relative to spruce canopy openness. Photosynthetic capacity (A₁₆₀₀, net photosynthesis at a photosynthetic photon flux density of 1600 μmol photons m⁻² s⁻¹) of beech in respect to the canopy gradient was best related to leaf mass, and declined substantially with increasing canopy openness primarily because leaf nitrogen (N) in this species decreased about 0.9 mg g⁻¹ with each 10% rise in canopy openness. In contrast, A₁₆₀₀ of oak showed a weak response to mass-based N, and furthermore the percentage of N remained constant in oak leaf tissues across the canopy gradient. Therefore, oak photosynthetic capacity along the canopy gradient was best related to leaf area, and increased as the spruce canopy thinned primarily because LMA rose 8.6 g m⁻² for each 10% increase in canopy openness. These findings support the premise that spruce stand structure regulates photosynthetic capacity of beech through processes that determine N status of this species; leaf N (mass basis) was greatest under relatively closed spruce canopies where leaves apparently acclimate by enhancing light harvesting mechanisms. Spruce stand structure regulates photosynthetic capacity of oak through processes that control LMA; LMA was greatest under open spruce canopies of high light availability where leaves apparently acclimate by enhancing CO₂ fixation mechanisms.     

Climate-growth variability in Quercus ilex L. west Iberian open woodlands of different stand density

? We present the longest tree-ring chronology (141 y) of Quercus ilex L. (holm oak), and discuss the species climate-growth relationships and the influence of stand density on tree sensitivity to climate.

? Similarly to Quercus suber L., the most influential climatic variables upon holm oak growth were late spring and early summer precipitation, which enhanced growth, and high temperatures in the previous August and current July, which negatively affected growth.

? High density stands responded to similar climatic factors as low density stands, but their response was generally weaker. Holm oak sensitivity to climate has increased in recent decades, which might be related to increasing temperatures in the region. Sensitivity was higher in low density stands. Additionally, the effect of summer stress on growth seems to have increased during the same period, similarly to other species in the Iberian Peninsula, suggesting that trees are more vulnerable to climatic changes.

? Stand density could buffer the response to climate by smoothing climatic extremes. Nevertheless, the effect of competition might reverse this positive effect at the individual tree level. Precautions should be taken before providing management guidelines regarding the effect of climate change and stand density on holm oak.

     

Signals of summer drought in crown condition data from the German Level I network

Crown transparency estimates of Scots pine, Norway spruce, common beech, pedunculate and sessile oak, annually surveyed between 1990 and 2004 within a grid over Germany, provide a suitable response variable to study drought effects on forest trees. Major climatic factors, available on a monthly basis as plot-specifically interpolated values and parameters of site and stand conditions, biotic and other relevant factors were used as predictors in different cross- and length-sectional, and longitudinal models. Stand age is a considerable and most constant driver of crown transparency in all species. Pine, spruce and beech responded—mainly with a delay of 1 year—with some foliar loss in areas where there was a surplus of temperature after the generally hot and dry summer of 2003. Parallel time-series analyses delivered species-specific geographic large-scale patterns with delayed or recent precipitation deficits or temperature surpluses. Even if beech is partly responding in current years with leaf loss towards precipitation surpluses, defoliation is especially high 1 year after hot summers, partly a result of high seed sets after such summers. Crown condition of oak responds in dry and warm areas according to the drought stress hypothesis, however, in cool and wet mountainous ranges oak responds after wet summers with higher defoliation. Longitudinal approaches revealed for all 4-tree species significant relationships between crown condition and deviations from the long-term means of temperature, precipitation but also global radiation and wind speed. Results do not always match the drought stress hypothesis, however, this is not to expect considering the heterogeneous site, stand and climatic conditions across Germany. Complex interactions of climatic and biotic factors also impede simple relationships. Soil-related clusters reveal higher sensitivity of spruce and beech towards climatic drought factors on more acid soils with thin humus layers. Also clusters constructed from plot-specific courses of defoliation reveal groups with rather closer relationships like a group of pine plots in the Oberpfalz, which seems to be especially sensitive to summer drought.     

Population differences in juvenile survival under increasing drought are mediated by seed size in cork oak (Quercus suber L.)

Many studies have focused on the physiological and morphological responses of Quercus suber to high temperatures and summer drought. Nevertheless, our understanding of the potential of this species to cope with climate change is incomplete. An increase in severity, length and frequency of summer droughts is expected in the Iberian Peninsula over the 21st century. We investigated the potential of cork oak to adapt to climate change in a 4-year study comparing seedling survival from thirteen Spanish populations in a common garden. Acorn size was evaluated as a possible adaptive trait enhancing stress resistance during establishment. Populations originating from sites with the driest summers exhibited the highest survival rates under dry conditions. These populations were characterized by bigger acorns, suggesting selection for this trait across sites experiencing drought. Our findings reveal that northern populations are not well adapted to cope with increasing drought but suggest that they might cope well with the moderate drought increase expected for these zones. However, continental populations are intermediately adapted to dry conditions, while drastic and fast increases in summer droughts are expected to occur in these regions. This extensive and quick change will provide scant chances to adapt making the populations of cork oak in these regions particularly vulnerable to the future climatic conditions.     

Modelling self-pruning and branch attributes for young Quercus robur L. and Fagus sylvatica L. trees

The aim of this study was to develop statistical models for first order branchiness in young planted forest stands of pedunculate oak (Quercus robur L.) and European beech (Fagus sylvatica L.), and to give an ecological and silvicultural interpretation to these models. The reported models focus on the lower most-valuable stem part (i.e. until 6 m height), and cover different tree development classes to capture the development of branchiness over time. For each species 30 study plots were selected spread over two nearby forests in Flanders (northern Belgium), minimising site and genetic variability. Branches were counted on a total of 399 oak and 376 beech trees. On a subsample of 30 trees per species (one tree per plot), detailed non-destructive branch measurements were performed, yielding data for 555 oak and 438 beech branches. For both species, models for tree self-pruning (i.e. total branch number and dead branch portion), branch mortality and branch architecture (i.e. branch diameter and branch insertion angle) were built. A generalised linear mixed modelling approach was adopted. The models for total branch number and dead branch portion may be interpreted in terms of four processes contributing to self-pruning: (1) stand and tree development, (2) tree competitive status, (3) stand density and (4) site humidity. The reported models reveal similar self-pruning rates in oak and beech, but with different driving factors: early branch dying and slow shedding for oak and the other way around for beech. Mortality of individual branches is further determined by branch position and branch dimension. Branch diameter and branch insertion angle of both species are mainly related to branch cord length and relative branch position. All modelled effects are consistent with known ecological and ecophysiological processes. Silvicultural implications for stand establishment and early tree selection are discussed. The reported models can be used to fine-tune operational silvicultural choices for quality timber production. This is a first step towards the integration of branchiness models for oak and beech into forest growth simulators.     

Driving factors for natural tree rejuvenation in anthropogenic pine (Pinus sylvestris L.) forests of NE Germany

The rejuvenation ecology of three main tree species in anthropogenic pine (Pinus sylvestris L.) forests is explored in our study. We focus on the scale of micro-plots, which provide the safe sites for tree rejuvenation. We thrive on the multi-factorial relationship of tree establishment and driving ecological factors using a large dataset from pine stands in NE Germany and applying multivariate analyses. The success of the establishment of the investigated focal tree species Fagus sylvatica L., Quercus petraea Liebl. and Pinus sylvestris L. is, on general, mostly affected by three factors, i.e. water balance of the upper soil layers, browsing pressure, and diaspore sources. Our investigations on the micro-plot scale revealed species-specific differences. For beech saplings <50 cm growth height, primarily the availability of water, indicated by available water capacity (AWC), thickness, quality, and structure of the organic layer, silt and humus content in the topsoil, and the lack of a dense competitive herb layer, were identified as most important factors. On the contrary, oak seems hardly be restricted by hydrologic and/or trophic deficits in the topsoil or humus layer. In conclusion and comparison to Fagus sylvatica L., we assume for Quercus petraea Liebl. advantages in natural regeneration processes under sub-continental climate conditions and thus under the scenarios of climate change. Pinus sylvestris L. regeneration in our investigation area occurs only in a narrow niche. We conclude with regard to future forest development and the objective of stand conversion with low management intensity that oak should be favoured within natural stand regeneration.     

Drought sensitivity of Norway spruce is higher than that of silver fir along an altitudinal gradient in southwestern Germany

Context

For Central Europe, climate projections foresee an increase in temperature combined with decreasing summer precipitation, resulting in drier conditions during the growing season. This might negatively affect forest growth, especially at sites that are already water-limited, i.e., at low elevation. At higher altitudes trees might profit from increasing temperatures.

Aims

We analyzed variations in radial growth of silver fir (Abies alba Mill.) and Norway spruce (Picea abies (L.) Karst.) along an altitudinal gradient from 400 until 1,140 m a.s.l. in the Black Forest, to assess climate responses with increasing elevation.

Methods

Climate–growth relationships were analyzed retrospectively using tree-ring and climate data. In total, we sampled stem discs of 135 trees to build 27 species- and site-specific chronologies (n _fir?=?13, n _spruce?=?14).

Results

Our results indicate distinct differences in climate–growth relations between fir and spruce along the gradient. Growth of high-altitude fir was positively related to temperature from January till March. Growth of low-altitude fir and spruce at all elevations was positively related to precipitation and negatively to temperature during the growing season, particularly in July. A self-calibrating Palmer drought severity index underlined summer drought sensitivity of these trees.

Conclusion

Overall, we found that climatic control of tree growth changes over altitude for fir. For spruce, a remarkable synchrony in growth variation and climate response was shown, which indicates that this species is drought sensitive at all studied elevations. In a future warmer climate, the growth of low-altitude fir and spruce along the entire studied gradient may be negatively affected in the Black Forest, if an increased evaporative demand cannot be compensated by increased water supply.     

我国栓皮栎分布及其生态学研究

栓皮栎作为广泛分布的树种之一,在全球气候变化的大环境下,成为研究树木生长应对气候变化的重要树种。文中分析了我国栓皮栎水平分布和垂直分布的特点及其与气候的关系,栓皮栎在不同地区的森林类型,主要包括栓皮栎纯林、松栎混交林、栎类混交林等类型;综述了我国对栓皮栎生态学、群落结构、更新等研究的最新进展和主要结论;提出今后开展栓皮栎研究的重点和方向,以期为栓皮栎生理生态学及其对气候变化响应研究提供参考。     

Growth–climate relationship of European beech at its northern distribution limit

In general, trees growing at or near their limit of distribution are more sensitive to climate than those growing at their ecological core. Here we examined the growth–climate relationship of European beech (Fagus sylvatica L.) close to its northern distribution limit in southern Sweden. Tree-ring width chronologies were developed from four well-separated sites where the species was dominant (Djupeåsen, DJ; Baldringe, BLD; Komperskulla, KSK and Ryssberget Nature Reserve, RYSS). The chronologies extended from 52 years (BLD) to 150 years (RYSS). Significant negative relationships were found between tree growth and previous summer (July and August) temperatures at three sites. July temperature of the year of growth had a negative relationship with beech growth at BLD and DJ. In contrast, current summer (July and August) precipitation was positively correlated with beech growth at DJ and KSK. This sensitivity of European beech to drought at its northern limit is in line with the previous research. However, following the exceptionally dry summer in southern Sweden in 1970, a marked growth decrease was noted as well as a shift in the relationship between beech growth and current growing-season temperature. Our results show that that the radial growth of European beech has become more sensitive to drought and precipitation than temperature at its northern distribution limit in the last several decades.     

栎属树种生长模型研究进展

栎属树种是亚热带常绿阔叶林和温带落叶阔叶林的主要建群树种之一,分布范围极为广泛,在国内外被广泛应用于城市园林绿化、水源涵养林、水土保持林,也是重要的珍贵用材树种,同时其果实、栓皮等具有重要的工业和药用价值.研究栎林的生长过程,对其经营抚育决策具有重要的参考意义.文中对近年来国内外关于栎属树种的生长过程,特别是栎属树种生长模型的研究进行了综述,包括栎属树种全林分生长模型、单木生长模型、径阶分布模型等;阐述了栎属树种生长模型的研究现状及发展趋势,以期为栎林的经营抚育决策提供参考.     

Dendroclimatic signals of pedunculate oak (Quercus robur L.) in Estonia

This study investigates the climate impact on the radial increment of pedunculate oak (Quercus robur L.) in Estonia at the species’ northern distribution limit. Tree-ring width series of 162 living oaks were compiled into three regional chronologies—western (1646–2008), northeastern (1736–2011), and southeastern Estonia (1912–2011). Although these regional growth patterns are similar to each other and even to the growth patterns in adjacent regions, spatial differences in growth responses to climate were established. Thus, oaks growing on shallow soil in western Estonia are positively influenced by summer (June–August) precipitation, and oaks on the deeper soil in northeastern Estonia are favoured by June temperature, while oaks in the southeastern part of the country depend on both July precipitation and temperature. These relationships are pronounced especially in pointer years. However, due to the impact of regional weather fluctuations on tree growth, there is a lack of correspondence between the local and the pan-European pointer years. In addition, our research presents the first tree-ring-based palaeoclimatic reconstruction for the country. Although the created model has relatively low predictive skill describing less than a quarter of the variance in actual summer precipitation in western Estonia, it has passable capacity of detecting past rainfall extremes.     

Seasonal and interannual ecophysiological responses of beech (Fagus sylvatica) at its south-eastern distribution limit in Europe

Due to its wide European distribution and its drought-susceptibility, beech (Fagus sylvatica L.) received intensive attention recently in the light of global warming. Contrary to central European beech ecosystems, little is known about the ecophysiology of beech at its south-eastern European distribution limit. Here we tested whether climatic fluctuations during a three-year period affected the ecophysiology of a beech site in Greece. Attention was paid at comparing our findings to the intense effects the 2003 extreme drought had on beech forests in central Europe.     

DNA sequence variation and development of SNP markers in beech (Fagus sylvatica L.)

European beech (Fagus sylvatica L.) is one of the most important deciduous tree species in Central Europe. The potential of beech to adapt to climate change, higher temperatures, and less precipitation in the summer months is still unknown. Most studies in beech used microsatellite, AFLP (amplified fragment length polymorphism), or isozyme markers, which have only a restricted potential to analyze adaptation. Only few studies investigated genes probably involved in the adaptation to drought stress and bud phenology in beech. In this study, SNP (single nucleotide polymorphisms) markers were developed in order to analyze adaptation and their technical advantages compared to microsatellites and AFLPs were discussed. Partial sequences of ten candidate genes probably involved in drought stress and/or bud phenology were identified at the genomic level, and SNPs and indels (insertions/deletions) in coding and non-coding regions were analyzed. Plant material was sampled along a precipitation gradient in Germany. In total, 8,145?bp were sequenced and analyzed, 4,038?bp were located in exon and 4,107?bp in intron regions. 63 SNPs and 11 indels were detected, which are differently distributed over the studied gene regions. The nucleotide diversity ranged from 0 to 6.62 (π?×?10^?3) and is comparable to other tree species, whereas the mean nucleotide diversity (2.64) for F. sylvatica is comparatively low. These results will help to investigate the genetic basis of drought stress and bud burst and to conduct association mapping in natural populations. Furthermore, the detected SNPs can also be used for population genetic studies.     

Effects of climatic conditions on tree-ring widths of three deciduous broad-leaved tree species at their northern distribution limit in Mont St. Hilaire,eastern Canada

This study examined the effects of climatic conditions on tree-ring widths of red oak (Quercus rubra), sugar maple (Acer saccharum) and American beech (Fagus grandifolia) at their northern distribution limit in Mont St. Hilaire, eastern Canada. A residual chronology of tree-ring width index was developed for each species. The tree-ring width of Q. rubra showed negative and positive correlations with May temperature and June precipitation in the current year, respectively. A. saccharum also showed similar patterns with Q. rubra, i.e., negative and positive correlations with June temperature and precipitation in the current year, respectively. F. grandifolia showed neither positive nor negative correlations with temperature and precipitation. The expressed population signals of tree-ring width chronologies of the three species indicated that climatic factors more greatly influenced the variations in tree-ring widths in the order Q. rubra > A. saccharum > F. grandifolia. Therefore, the radial growth of Q. rubra was most restricted by drought stress in early summer among the three species. Global warming is suggested to affect the radial growth of the three species differently by increasing drought stress at Mont St. Hilaire in eastern Canada.     

Productivity of mixed versus pure stands of oak (Quercus petraea (Matt.) Liebl. and Quercus robur L.) and European beech (Fagus sylvatica L.) along an ecological gradient

The mixture of beech (Fagus sylvatica L.) and oak (sessile oak, Quercus petraea (Matt.) Liebl., and pedunculate oak, Q. robur L.) is of considerable importance in Europe and will probably become even more important under climate change. Therefore, the performance of oak and beech in mixture was compared with the species’ growth in pure stands. Data from 37 long-term mixing experiments in Poland, Germany and Switzerland were pooled for analysis of mixing effects on stand productivity and possible interrelationships with mixing portions or site conditions. We found that on average, mixed stands of oak and beech exceeded biomass productivity in pure stands by 30 % or 1.7 t ha^?1 year^?1, as the growth of both species was benefitted by the mixture. However, that the interaction actually ranged from facilitation and overyielding on poor sites to underyielding on fertile sites triggered by competition. An empirically derived interaction model showed volume and dry mass growth changing in mixed stands from gains of 50 % to losses of 10 % depending on site conditions. It is concluded that the analysed mixture grows in accordance with the stress-gradient hypothesis and that our results suggest a site-specific relationship between species mixture and biomass productivity. As a consequence, an adequate species mix should result in increased productivity under steady state as well as climate change.     

Flying vs. climbing: Factors controlling arboreal seed removal in oak-beech forests

Nuts are heavy and nutritious seeds that need animals to be successfully dispersed. Most studies address nut removal by a single animal species once seeds fall onto the ground. However, nuts are also accessible before the seed drop and usually to a wide guild of seed foragers. This study examines the factors controlling arboreal seed removal in oak-beech forests within the whole guild of nut foragers. We found that seed-dispersing rodents (Apodemus sylvaticus) were the main acorn removers in the oaks (up to 3.75 m height), with a rapid seed encounter and a high removal rate. However, rodents did not climb the beech trees, probably due to their smoother bark in comparison to oak bark and/or the lower nutritional value of beechnuts with regard to acorns. Jays (Garrulus glandarius) were more abundant in oak stands (both dense and scattered) and clearly preferred acorns to beechnuts whereas nuthatches (Sitta europaea) were more abundant in beech stands and preferred beechnuts to acorns. Non-storing birds such as great tits (Parus major) also removed acorns and beechnuts, especially in the stands where oaks are dominant. Jays and rodents preferred sound seeds over insect-infested seeds but such a preference was not found for nuthatches. This study highlights that pure beech stands showed a reduced guild of arboreal nut foragers in comparison to oak stands. This different guild could probably affect the spatial patterns of seed dispersal, with a proportionally higher number of long dispersal events for acorns (mostly jay-dispersed) than for beechnuts (mostly nuthatch-dispersed). Long-distance dispersal of beechnuts (by jays) is determined by the presence of other preferred species (oaks) and their frequency of non-mast years. Seed location in different habitats strongly determines the contribution of different arboreal removers (including climbing rodents) and their removal speed, leading to a differential seed fate that will eventually affect tree regeneration. As nuthatches are sedentary birds, it is important to maintain old and dead trees where they can breed (crevices), forage (arthropods) and store seeds in order to favor beechnut dispersal and gene flow. By maintaining or favoring oak trees within beech stands we will ensure a wider guild of arboreal nut dispersers.     

Model-based analysis of the spatial variability and long-term trends of soil drought at Scots pine stands in northeastern Germany

Soil water availability determines the vitality of trees and forest stands to a large degree. Over the last decades, an increasing number of drought spells has been observed in several parts of Europe. Our study aims to estimate long-term trends of soil drought at Scots pine (Pinus sylvestris L.) stands along the prevailing climatic gradient in Mecklenburg-Western Pomerania, northeastern Germany. To this end, soil water balance simulations were carried out at 24 sites over the period from 1951 to 2009 with the physically based model LWF-BROOK90. As a threshold for soil water stress, we used 40% of relative extractable water (REW). The results indicated an increased number of drought days further east, together with declining totals of precipitation. However, specific site conditions had a large influence on the occurrence of soil drought, partly overriding the climatic differences across the study area. Soil drought has distinctly increased in the recent past, both in duration and in intensity, affecting the eastern sites more than the western sites. The increased soil dryness could be attributed to higher atmospheric evaporative demand due to higher temperatures, as well as slightly lower precipitation sums during the summer months. To mitigate the negative effects of future climate change, adaptation measures should preferably be conducted in the eastern parts of northeastern Germany.     

藏东南川滇高山栎群落物种多样性格局

通过样方调查,采用物种多样性指数和DCCA排序方法,并结合种间联结、种间协变和系统聚类分析,对藏东南川滇高山栎(Quercus aquifolioides)群落的物种多样性及其分布格局进行了研究。结果表明:1)川滇高山栎群落物种数(丰富度)随海拔增高而降低,一定程度的人为干扰(即中度干扰)、较大的林分郁闭度和较矮的林冠层有利于群落物种多样性的增加;另外干旱河谷现象对群落物种多样性格局也有影响。2)群落各层次间物种多样性呈现出草本层>灌木层>乔木层的特征。3)群落种间较高的正负关联比理论上说明川滇高山栎群落结构较为稳定,生态习性和分布差异造就了种间的联结和协变格局。海拔梯度和年均降水量是影响各种群空间分布的主要因素。4)结合种-环境DCCA排序结果、种间关系和聚类分析结果可将川滇高山栎群落中除川滇高山栎之外的48个主要物种划分为4个生态种组。     

坡位对灰木莲生长的影响

灰木莲(Manglietia glauca Blume)属木兰科(Magnoliaceae)常绿阔叶大乔木,树干通直,高大挺拔,材质优良,木材为散孔材,干材密度为0.611 g.cm-3,纹理细致,易加工,切面光滑美丽,干燥速度较