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.     

伊春地区红松和红皮云杉径向生长对气候变化的响应

树木生长-气候关系对准确评估气候变化对森林生态系统影响、预测森林生产力与植被动态及揭示树木对气候变化的响适应策略至关重要。在全球变暖背景下,升温可能会对树木的生长产生影响,从而改变区域森林生态系统的生产力或碳储量。本研究利用生长-气候响应函数、滑动相关分析等树木年轮学方法,探讨伊春地区阔叶红松林内红松和红皮云杉径向生长的主要限制因子及两者径向生长对快速升温(1980年后)响应的异同。结果表明:1980年前红松径向生长有明显加速的趋势,红皮云杉上升趋势较弱;而1980年后红松径向生长趋势显著下降,红皮云杉则下降不明显。红皮云杉径向生长与上一年9月及当年6月平均气温显著负相关,而红松径向生长与上一年12月及当年1月、4月和6月最低气温显著正相关。1980年快速升温后,高温对两树种生长的抑制作用增强,尤其是红松。生长季末(9月)降水对红松和红皮云杉的限制作用由升温前的负相关转变为升温后的显著正相关。温度是限制红松和红皮云杉径向生长的主要气候因子,降水影响相对较弱;其中红松径向生长对气候变化的响应比红皮云杉更敏感。快速升温后,红松和红皮云杉生长-气候关系的变化可能与升温导致的暖干旱化有关。若气...     

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.     

Critical forest age thresholds for the diversity of lichens,molluscs and birds in beech (Fagus sylvatica L.) dominated forests

Forest age is one of the most simple but ecologically effective key values that may be controlled by forest management. Young and mature but managed forests differ significantly from old-growth forests in species composition, structure and socio-ecological function. Human land-use has already caused the loss or dramatic reduction in occurrence of some entire species assemblages, especially of logging-sensitive species, in Central European forests. These general statements also apply to beech forests, beech (Fagus sylvatica) being the naturally dominating tree species in Central Europe. Based on data for breeding birds (from 258 sampling plots in a sub-montane and 228 plots in a montane area), molluscs (36 plots in the sub-montane and 79 plots in the montane area) and lichens (84 plots in the montane forest), this paper aims at identifying significant forest age threshold ranges for the occurrence of these old-growth sensitive taxa. The sampling plots in the sub-montane zone (420–520 m a.s.l.) are in beech-oak forests, plots in the montane zone (650–1150 m a.s.l.) are in beech-spruce-fir forests. Stand ages in both areas range up to around 350–400 years. Threshold values for the total number of species related to stand age were calculated by recursive partitioning.In all three taxonomic groups the number of species per plot significantly increases with forest age. The same analysis was run for red-listed lichen and mollusc species as well as hole-nesting bird species. The threshold values obtained are very similar to those for the whole species assemblages, except for molluscs where considerably lower threshold values are computed with red-listed species assemblages. Regarding the confidence intervals, the difference pattern between the whole species datasets and the more sensitive species subsets is inconsistent. Threshold values in sub-montane beech forests range from 100 to 170 years and in mixed montane forests from 160 to 220 years.These threshold levels are clearly incompatible with economic interests that aim on reducing the rotation period in beech stands to less than 140 years to avoid formation of red heartwood. It would therefore seem to be essential to establish a network of trees and stands that are never logged and may thus act as areas for retreat and dispersion for logging-sensitive species.     

Growth/climate response shift in a long subalpine spruce chronology

A new Norway spruce (Picea abies (L.) Karst.) tree-ring width chronology based on living and historic wood spanning the AD 1108–2003 period is developed. This composite record combines 208 high elevation samples from 3 Swiss subalpine valleys, i.e., Lötschental, Goms, and Engadine. To retain potential high- to low-frequency information in this dataset, individual spline detrending and the regional curve standardization are applied. For comparison, 22 high elevation and 6 low-elevation instrumental station records covering the greater Alpine area are used. Previous year August–September precipitation and current year May–July temperatures control spruce ring width back to ～1930. Decreasing (increasing) moving correlations with monthly mean temperatures (precipitation) indicate instable growth/climate response during the 1760–2002 period. Crucial June–August temperatures before ～1900 shift towards May-July temperature plus August precipitation sensitivity after ～1900. Numerous of comparable subalpine spruce chronologies confirm increased late-summer drought stress, coincidently with the recent warming trend. Comparison with regional-, and large-scale millennial-long temperature reconstructions reveal significant similarities prior to ～1900 (1300–1900 mean r=0.51); however, this study does not fully capture the commonly reported 20th century warming (1900–1980 mean r=?0.17). Due to instable growth/climate response of the new spruce chronology, further dendroclimatic reconstruction is not performed.     

Different responses of Korean pine (Pinus koraiensis) and Mongolia oak (Quercus mongolica) growth to recent climate warming in northeast China

Different tree species growing in the same area may have different, or even contrasting growth responses to climate change. Korean pine (Pinus koraiensis) and Mongolia oak (Quercus mongolica) are two crucial tree species in temperate forest ecosystems. Six tree-ring chronologies for Korean pine and Mongolia oak were developed by using the zero-signal method to explore their growth response to the recent climate warming in northeast China. Results showed that Mongolia oak radial growth was mainly limited by precipitation in the growing season, while Korean pine growth depended on temperature condition, especially monthly minimum temperature. With the latitude decrease, the relationships between Korean pine growth and monthly precipitation changed from negative to positive correlation, while the positive correlation with monthly temperature gradually weakened. In the contrary, Mongolia oak growth at the three sampling sites was significantly and positively correlated with precipitation in the growing season, while it was negatively correlated with temperature and this relationship decreased with the latitude decrease. The radial growth of Korean pine at different sites showed a clearly discrepant responses to the recent warming since 1980. Korean pine growth in the north site increased with the temperature increase, decreased in the midwest site, and almost unchanged in the southeast site. Conversely, Mongolia oak growth was less affected by the recent climate warming. Our finding suggested that tree species trait and sites are both key factors that affect the response of tree growth to climate change. In addition, the suitable distribution area of Korean pine may be moved northward with the continued global warming in the future, but Mongolia oak may not shift in the same way.     

The climatic drivers of primary Picea forest growth along the Carpathian arc are changing under rising temperatures

Climatic constraints on tree growth mediate an important link between terrestrial and atmospheric carbon pools. Tree rings provide valuable information on climate‐driven growth patterns, but existing data tend to be biased toward older trees on climatically extreme sites. Understanding climate change responses of biogeographic regions requires data that integrate spatial variability in growing conditions and forest structure. We analyzed both temporal (c. 1901–2010) and spatial variation in radial growth patterns in 9,876 trees from fragments of primary Picea abies forests spanning the latitudinal and altitudinal extent of the Carpathian arc. Growth was positively correlated with summer temperatures and spring moisture availability throughout the entire region. However, important seasonal variation in climate responses occurred along geospatial gradients. At northern sites, winter precipitation and October temperatures of the year preceding ring formation were positively correlated with ring width. In contrast, trees at the southern extent of the Carpathians responded negatively to warm and dry conditions in autumn of the year preceding ring formation. An assessment of regional synchronization in radial growth variability showed temporal fluctuations throughout the 20th century linked to the onset of moisture limitation in southern landscapes. Since the beginning of the study period, differences between high and low elevations in the temperature sensitivity of tree growth generally declined, while moisture sensitivity increased at lower elevations. Growth trend analyses demonstrated changes in absolute tree growth rates linked to climatic change, with basal area increments in northern landscapes and lower altitudes responding positively to recent warming. Tree growth has predominantly increased with rising temperatures in the Carpathians, accompanied by early indicators that portions of the mountain range are transitioning from temperature to moisture limitation. Continued warming will alleviate large‐scale temperature constraints on tree growth, giving increasing weight to local drivers that are more challenging to predict.     

Rapid warming induces the contrasting growth of Yezo spruce (Picea jezoensis var. microsperma) at two elevation gradient sites of northeast China

Accurately assessing the impact of climate changes on tree growth or forest productivity is vital to better understand global carbon cycles. Here, we carried out dendroclimatological research on Yezo spruce (Picea jezoensis var. microsperma) along an elevation gradient in two sites to investigate the effect of rapid warming on spruce growth in northeast China. Results indicated that trees at two low-elevation sites had significantly wider ring widths and higher basal area increment (BAI) compared with high-elevation sites. Ring widths and BAI of Yezo spruce at low elevations showed a clear growth increase during the 1940s–1970s followed by a significant decline after 1980. However, trees at high elevations showed a relatively stable growth during the 1940s–1970s followed by a significant increase after 1980. Rapid warming after 1980 increased the radial growth of Yezo spruce at high-elevation sites, but reduced tree growth at low-elevation sites. Winter precipitation and growing season temperature were positively correlated with radial growth of Yezo spruce at high elevations, but negatively correlated with tree growth at low elevations. A clear pattern of growth and growth-climate relationship changed in 1980. The temperature threshold for determining the impact of climate on Yezo spruce could change with latitude or site. Difference in drought caused by warming may be the main reason for the opposite response of tree growing at different altitudes in northeast China. The mechanism of rapid warming driving contrasting growth at different elevations should also be investigated in other tree species in NE Asia. In the context of future climate warming, our findings are of great significance for tree growth in assessing forest dynamics and carbon cycling.     

Summer drought exposure,stand structure,and soil properties jointly control the growth of European beech along a steep precipitation gradient in northern Germany

Increasing exposure to climate warming-related drought and heat threatens forest vitality in many regions on earth, with the trees' vulnerability likely depending on local climatic aridity, recent climate trends, edaphic conditions, and the drought acclimatization and adaptation of populations. Studies exploring tree species' vulnerability to climate change often have a local focus or model the species' entire distribution range, which hampers the separation of climatic and edaphic drivers of drought and heat vulnerability. We compared recent radial growth trends and the sensitivity of growth to drought and heat in central populations of a widespread and naturally dominant tree species in Europe, European beech (Fagus sylvatica), at 30 forest sites across a steep precipitation gradient (500–850 mm year⁻¹) of short length to assess the species' adaptive potential. Size-standardized basal area increment remained more constant during the period of accelerated warming since the early 1980s in populations with >360 mm growing season precipitation (April–September), while growth trends were negative at sites with <360 mm. Climatic drought in June appeared as the most influential climatic factor affecting radial growth, with a stronger effect at drier sites. A decadal decrease in the climatic water balance of the summer was identified as the most important factor leading to growth decline, which is amplified by higher stem densities. Inter-annual growth variability has increased since the early 1980s, and variability is generally higher at drier and sandier sites. Similarly, within-population growth synchrony is higher at sandier sites and has increased with a decrease in the June climatic water balance. Our results caution against predicting the drought vulnerability of trees solely from climate projections, as soil properties emerged as an important modulating factor. We conclude that beech is facing recent growth decline at drier sites in the centre of its distribution range, driven by climate change-related climate aridification.     

Climate‐diameter growth relationships of black spruce and jack pine trees in boreal Ontario,Canada

To predict the long‐term effects of climate change – global warming and changes in precipitation – on the diameter (radial) growth of jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] B.S.P.) trees in boreal Ontario, we modified an existing diameter growth model to include climate variables. Diameter chronologies of 927 jack pine and 1173 black spruce trees, growing in the area from 47°N to 50°N and 80°W to 92°W, were used to develop diameter growth models in a nonlinear mixed‐effects approach. Our results showed that the variables long‐term average of mean growing season temperature, precipitation during wettest quarter, and total precipitation during growing season were significant (alpha = 0.05) in explaining variation in diameter growth of the sample trees. Model results indicated that higher temperatures during the growing season would increase the diameter growth of jack pine trees, but decrease that of black spruce trees. More precipitation during the wettest quarter would favor the diameter growth of both species. On the other hand, a wetter growing season, which may decrease radiation inputs, increase nutrient leaching, and reduce the decomposition rate, would reduce the diameter growth of both species. Moreover, our results indicated that future (2041–2070) diameter growth rate may differ from current (1971–2000) growth rates for both species, with conditions being more favorable for jack pine than black spruce trees. Expected future changes in the growth rate of boreal trees need to be considered in forest management decisions. We recommend that knowledge of climate–growth relationships, as represented by models, be combined with learning from adaptive management to reduce the risks and uncertainties associated with forest management decisions.     

Warming induced growth decline of Himalayan birch at its lower range edge in a semi-arid region of Trans-Himalaya,central Nepal

Changes in the position of altitudinal treelines and timberlines are considered useful indicators of climatic changes on tree growth and forest dynamics. We sought to determine if recent warming is driving contrasting growth responses of Himalayan birch, at moist treeline (Lete Lekh) and semi-arid timberline (Chimang Lekh) sites in the Trans-Himalayan zone of central Nepal. We used dendrochronological techniques to measure tree ring width (TRW) and basal area increment (BAI) of birch trees from climatically contrasting but nearby sites. The TRW series were correlated with climate records from nearby meteorological stations, and BAI was compared between populations to explore growth trends over recent decades. We found contrasting precipitation trends between nearby sites such that the wet site (Lete) is getting warmer and wetter, and the dry site (Chimang) is getting warmer and drier in recent decades. The radial growth of birch in both moist and semi-arid sites are positively correlated to spring (March–May) rainfall, and negatively correlated to mean and maximum temperature for the same period. The growth climate analysis indicated that moisture availability in early growing season is crucial for birch growth at these locations. The BAI of birch is declining more rapidly at the dry timberline than at the moist treelines in the recent decades, indicating that climatic warming might negatively impact birch radial growth where warming interacts with increasing spring drought in the region. Our work highlights contrasting growth response of birch to climate change at moist and semi-arid forests indicating that local climatic variation must be accounted for when assessing and forecasting regional patterns of tree growth in topographically complex regions like Trans-Himalaya, in order to make accurate predictions of vegetation responses to climate change.     

Searching for thresholds in climate–radial growth relationships of Engelmann spruce and subalpine fir,Jasper National Park,Alberta, Canada

The relationship between monthly climate predictors and radial growth of Engelmann spruce (Picea engelmanni Parry) and subalpine fir (Abies lasiocarpa (Hook.) Nutt) were explored using both a standard dendroclimatological approach and a multiple adaptive regressions splines (MARS) framework. Consistent with previous research, the radial growth of fir and spruce was related to temperature variables over the time period of the instrumental record. We identify important temporal instability in the statistical relationships between climate variables and the radial growth of both subalpine fir and Engelmann spruce. Using a 30-year running window, only four of the climate variables related to the radial growth of either spruce or fir did not show a switch in the sign of the correlation. A multiple adaptive regressions spline method was then used to gain insight into thresholds that may relate to radial growth–climate instabilities. Using MARS, we were able to identify knots and non-monotonic relationships between radial growth and climate predictors that may be indicators of ecological thresholds. This combination of dendroclimatic methods provides valuable insight into the complex nonlinear responses that both subalpine fir and Engelmann spruce have been growing under in the past centuries.     

Climate signal shift under the influence of prevailing climate warming – Evidence from Quercus liaotungensis on Dongling Mountain,Beijing, China

Increasing climate warming is inducing drought stress and resulting in forest growth decline in many places around the world. The recent climate of northern China has shown trends of both warming and drying. In this study, we obtained tree ring width chronology of Quercus liaotungensis Koidz. from Dongling Mountain, Beijing, China. We divided the temperature series of the study area into cooling (1940–1969) and warming intervals (1970–2016). The climate–tree growth response analysis showed that temperature exerted a limiting impact on the annual radial growth of Q. liaotungensis during the cooling period, whereas the influence of temperature was lower during the warming period. The moving correlation analysis showed that the influence of summer temperature decreased with the warming climate since the 1970s, and that the influence of winter and spring temperatures decreased since the 2000s. The correlation values between the chronology and precipitation decreased during the cooling period, whereas spring and early summer precipitation correlations began to increase in the 1970s and reached significance (p < 0.05) in the 1990s. Our results show that the positive influence of temperature on radial growth of Q. liaotungensis in the study area has weakened, whereas precipitation has become the dominant regulator with climate warming. These findings suggest that forest growth on Dongling Mountain will decline if climate warming continues in the future.     

Contrasting resistance and resilience to extreme drought and late spring frost in five major European tree species

Extreme climate events (ECEs) such as severe droughts, heat waves, and late spring frosts are rare but exert a paramount role in shaping tree species distributions. The frequency of such ECEs is expected to increase with climate warming, threatening the sustainability of temperate forests. Here, we analyzed 2,844 tree‐ring width series of five dominant European tree species from 104 Swiss sites ranging from 400 to 2,200 m a.s.l. for the period 1930–2016. We found that (a) the broadleaved oak and beech are sensitive to late frosts that strongly reduce current year growth; however, tree growth is highly resilient and fully recovers within 2 years; (b) radial growth of the conifers larch and spruce is strongly and enduringly reduced by spring droughts—these species are the least resistant and resilient to droughts; (c) oak, silver fir, and to a lower extent beech, show higher resistance and resilience to spring droughts and seem therefore better adapted to the future climate. Our results allow a robust comparison of the tree growth responses to drought and spring frost across large climatic gradients and provide striking evidence that the growth of some of the most abundant and economically important European tree species will be increasingly limited by climate warming. These results could serve for supporting species selection to maintain the sustainability of forest ecosystem services under the expected increase in ECEs.     

长白山落叶松与鱼鳞云杉生长-气候关系的种间差异

为阐明不同树种间树木径向生长对气候变化的响应及其时间稳定性,本研究以长白山北坡高海拔处(1600～1750 m)落叶松和鱼鳞云杉为研究对象,运用年轮年代学方法探究树木径向生长与气候的关系.结果表明: 研究区落叶松生长与当年6月最高气温呈显著正相关,与当年6月降水呈负相关;鱼鳞云杉与当年5月最高温度呈显著正相关.冗余分析进一步表明,落叶松生长主要受夏季温度的影响,鱼鳞云杉生长主要受春季温度的制约.在1959—2014年,落叶松生长-夏季温度关系相对稳定;对于鱼鳞云杉,自1986年以来其与春季温度的相关性减弱,可能由于最高温度降低导致树木生长减慢.本研究结果可以为预测气候变化情景下长白山针叶树种生长的响应趋势提供数据支持和理论参考.     

The impact of the 2003 summer drought on the intra-annual growth pattern of beech (Fagus sylvatica L.) and oak (Quercus robur L.) on a dry site in the Netherlands

Climate change is expected to result in more extreme weather conditions over large parts of Europe, such as the prolonged drought of 2003. As water supply is critical for tree growth on many sites in North-Western Europe, such droughts will affect growth, species competition, and forest dynamics. To be able to assess the susceptibility of tree species to climate change, it is necessary to understand growth responses to climate, at a high temporal resolution. We therefore studied the intra-annual growth dynamics of three beech trees (Fagus sylvatica L.) and five oak trees (Quercus robur L.) growing on a sandy site in the east of the Netherlands for 2 years: 2003 (oak and beech) and 2004 (oak). Microcores were taken at 2-week intervals from the end of April until the end of October. Intra-annual tree-ring formation was compared with prior and contemporary records of precipitation and temperature from a nearby weather station.The results indicate that oak and beech reacted differently to the summer drought in 2003. During the drought, wood formation in both species ceased, but in beech, it recovered after the drought. The causes of species-specific differences in intra-annual wood formation are discussed in the context of susceptibility to drought.     

Recent climate warming forces contrasting growth responses of white spruce at treeline in Alaska through temperature thresholds

Northern and high‐latitude alpine treelines are generally thought to be limited by available warmth. Most studies of tree‐growth–climate interaction at treeline as well as climate reconstructions using dendrochronology report positive growth response of treeline trees to warmer temperatures. However, population‐wide responses of treeline trees to climate remain largely unexamined. We systematically sampled 1558 white spruce at 13 treeline sites in the Brooks Range and Alaska Range. Our findings of both positive and negative growth responses to climate warming at treeline challenge the widespread assumption that arctic treeline trees grow better with warming climate. High mean temperatures in July decreased the growth of 40% of white spruce at treeline areas in Alaska, whereas warm springs enhance growth of additional 36% of trees and 24% show no significant correlation with climate. Even though these opposing growth responses are present in all sampled sites, their relative proportion varies between sites and there is no overall clear relationship between growth response and landscape position within a site. Growth increases and decreases appear in our sample above specific temperature index values (temperature thresholds), which occurred more frequently in the late 20th century. Contrary to previous findings, temperature explained more variability in radial growth after 1950. Without accounting for these opposite responses and temperature thresholds, climate reconstructions based on ring width will miscalibrate past climate, and biogeochemical and dynamic vegetation models will overestimate carbon uptake and treeline advance under future warming scenarios.     

The potential of generalized additive modelling for the prediction of radial growth of Norway spruce from Central Germany

During the past decades managed forest ecosystems in Central Europe underwent vast changes, induced by extreme climate conditions and occasionally adverse forest management. Tree ring width patterns mirror these changes and thus have been widely examined as environmental archives and reliable empirical data sources in ‘tree growth modelling’. Dendrochronologists often suppose linear co-variation among the covariates, variable independence and homoscedasticity. Conventionally, these assumptions were achieved by eliminating biological age trends (detrending) and removing the autocorrelation from the time series (pre-whitening). Particularly detrending might be biased according to the scientific problem and sometimes inflexible age models. In this study, we tackle these issues and examine the suitability of a flexible Generalized Additive Model (GAM) on recently developed tree ring width time series of 30 Norway spruce stands (Picea abies [L.] H. Karst) from Central Germany.The model was established to simultaneously cope with the mentioned detrending issue, to unravel nonlinear climate-growth relationships and to predict mean ring width time series for spruce stands in the region. Particularly the latter was of primary interest, since recent forest planning relies on static yield tables that often underestimate the actual growth.The model reliably captured the empirical data, indicated by a small Generalized Cross Validation criterion (GCV = 0.045) and a deviance explained of 88.6 %. The flexible additive smoothers accounted for the social status of individual trees, captured low frequency variations of changing growth conditions adequately and displayed a rather flat biological age trend. The radial increment responded positively to summer season precipitation of the current and previous year. Positive temperature responses were found during the early vegetation period, whereas high summer season temperatures negatively affected the radial growth. The seasonal transition from spring to summer in June induced a shift in the climate response of the linear predictor, leading to a distinct negative effect of temperature and a no-role of precipitation on the linear predictor.Most important, utilizing the calibrated GAM for the purely climate-driven prediction of mean ring width time series from five independent spruce sites revealed proper coherencies. Herein, the mean ring width for sites located within the climatic-optimum for spruce growth were more exactly predicted than for sites with adverse spruce growth conditions. In addition, large mean ring widths were systematically underestimated, whereas small mean ring widths were precisely predicted. Overall, we strongly recommend GAMs as a powerful tool for the investigation of nonlinear climate-growth relationships and for the prediction of radial growth in managed forest ecosystems.     

阿尔泰山主要针叶树种树木径向生长及其对气候变化的响应

本研究以阿尔泰山富蕴地区的西伯利亚云杉和西伯利亚落叶松为对象,获取2个树种基部断面生长增量和树轮宽度年表与气候因子的相关系数,对比分析了相似生境下2个树种的径向生长特征及其对气候变化的响应。结果表明: 西伯利亚云杉基部断面生长增量总体高于西伯利亚落叶松,但西伯利亚落叶松的径向生长增加趋势更为显著。近60年来,上年快速生长期的高温对研究区内西伯利亚云杉的径向生长有限制作用,而当年6月较高的气温则有利于西伯利亚落叶松生长。西伯利亚落叶松的径向生长与当年1月气温呈负相关。分段相关分析显示,这种情况在1980年代中期气候变暖以后表现得更为明显。滑动相关分析表明,在气候变化背景下研究区内西伯利亚云杉和西伯利亚落叶松径向生长对气温和降水量的响应在近年来均有所增强。     

Shifts in the height‐related competitiveness of tree species following recent climate warming and implications for tree community composition: the case of common beech and sessile oak as predominant broadleaved species in Europe

Height growth is a trait that contributes to tree species fitness. How height growth responds to environmental changes may therefore provide indications on species ability to compete and maintain, and on changes in tree community composition. Common beech Fagus sylvatica and sessile oak Quercus petraea are the predominant late‐successional broadleaved species in Europe, and they differ in their shade‐tolerance. On common beech (a shade tolerant species), recent observations across Europe have shown a growth decline during recent climate warming. Because sessile oak is a warmth‐ and light‐demanding species, we therefore hypothesised that it may gain in competitiveness relative to common beech. We conducted analyses of historical height growth in several regions spanning the distributional range of the two species across a temperate‐continental gradient in France. Common beech and sessile oak were sampled in two and four regions, respectively, and were compared in two neighbouring regions. We documented the climatic and nutritional conditions of regional samples. Height growth of 408 trees of various ages was reconstituted from stem analyses. We estimated 20th‐century regional chronologies of height growth using a statistical modelling approach that filtered out the effects of ontogeny and site fertility. In regions where both species were sampled, modelled height trajectories were compared at different periods over the 20th century. Growth chronologies revealed 1) long‐term growth rate increases of a magnitude of 50–100% over 100 years in both species, more acute in the continental domain, 2) recurrent historical inversions in growth fluctuations between species, 3) a recent divergence, with growth decline in common beech versus a dramatic growth increase in sessile oak, more acute in colder regions. The analysis of height trajectories indicated a recent reduction in common beech competitiveness relative to sessile oak. In the face of future climate warming, we conclude that increased prevalence of beech–oak mixtures may arise.