Conifer Presence May Negatively Affect Sugar Maple’s Ability to Migrate into the Boreal Forest Through Reduced Foliar Nutritional Status

The discipline of ecology suffers from a lack of knowledge of non-climatic factors (for example, plant–soil, plant–plant and plant–insect interactions) to predict tree species range shifts under climate change. The next generation of simulation models of forest response to climate change must build upon local observations of species interactions and growth along climatic gradients. We examined whether sugar maple (Acer saccharum) seedlings were disadvantaged with respect to soil nutrient uptake under coniferous canopies, as this species would need to migrate northward into conifer-dominated forests in response to climate change. An experimental design was applied to 3 sites, forming the largest possible latitudinal/climatic gradient for sugar maple in Quebec (Canada) and isolating the effect of conifer presence on its seedling’s nutritional status. We tested whether: (1) both soil and climate and (2) presence of conifers affected foliar nutrient levels of sugar maple seedlings. Climate and soil (through pH) strongly affected nutrient availability for sugar maple seedlings and predicted 63.7% of their foliar nutrient variability. When controlling for site effects, we found a significant negative effect of conifers on foliar Ca and Mg levels of maple seedlings, which can adversely affect their overall health and vigour. When considering projected modifications of the forest environment due to climate change, we suggest that northward migration of sugar maple will be negatively affected by the presence of conifers through reduced foliar nutrition.     

Tree-ring growth of Gmelin larch under contrasting local conditions in the north of Central Siberia

While the forest-tundra zone in Siberia, Russia has been dendroclimatologically well-studied in recent decades, much less emphasis has been given to a wide belt of northern taiga larch forests located to the south. In this study, climate and local site conditions are explored to trace their influence on radial growth of Gmelin larch (Larix gmelinii (Rupr.) Rupr.) trees developed on permafrost soils in the northern taiga. Three dendrochronological sites characterized by great differences in thermo-hydrological regime of soils were established along a short (ca. 100 m long) transect: on a river bank (RB), at riparian zone of a stream (RZ) and on a terrace (TER). Comparative analysis of the rate and year-to-year dynamics of tree radial growth among sites revealed considerable difference in both raw and standardized tree-ring width (TRW) chronologies obtained for the RZ site, characterized by shallow soil active layer depth and saturated soils. Results of dendroclimatic analysis indicated that tree-ring growth at all the sites is mostly defined by climatic conditions of a previous year and precipitation has stronger effect on TRW chronologies in comparison to the air temperatures. Remarkably, a great difference in the climatic response of TRW chronologies has been obtained for trees growing within a very short distance from each other. The positive relation of tree-ring growth with precipitation, and negative to temperature was observed in the dry site RB. In contrary, precipitation negatively and temperature positively influenced tree radial growth of larch at the water saturated RZ. Thus, a complicate response of northern Siberian larch forest productivity to the possible climate changes is expected due to great mosaic of site conditions and variability of environmental factors controlling tree-ring growth at different sites. Our study demonstrates the new possibilities for the future dendroclimatic research in the region, as various climatic parameters can be reconstructed from tree-ring chronologies obtained for different sites.     

川西卧龙国家级自然保护区树木生长对气候响应的时间稳定性评估

根据川西卧龙地区岷江冷杉(Abies faxoniana)的年轮宽度资料, 分析了该地区树木生长特征及对气候响应在最近53年(1956-2008年)的异质性特征。结果表明, 在1956-1976年时段, 树木生长速率较快, 晚冬至早春(1月到4月)温度对树木生长有着明显的促进作用, 而春末5月份的高温对于树木生长有限制性影响, 而与日照时数关系不大; 在1977-2008年时段, 树轮生长主要受冬季(11月到1月)低温的限制, 另外, 日照时数对于树木生长的限制性影响明显增强。秋季到早冬(9-12月)降水在两个时段上对树木生长均有一定的限制性影响。树轮指数在1956-1976年时段与温度序列吻合较好, 而在1977-2008年时段树轮指数明显偏低, 与温度序列出现了明显的分离。1977-2008年时段内云层覆盖量增加导致太阳辐射量显著下降, 进而树木可利用的光合有效辐射也相应地降低, 这可能是树木生长速率在此时期明显较慢的主要原因。     

Growth responses to climate and drought at the southernmost European limit of Mediterranean Pinus pinaster forests

Climate warming and increasing aridity may negatively impact forest productivity across southern Europe. A better understanding of growth responses to climate and drought in southernmost populations could provide insight on the vulnerability of those forests to aridification. Here we investigate growth responses to climate and drought in nine Pinus pinaster (maritime pine) stands situated in Andalusia, southern Europe. The effect of climatic variables (temperatures and precipitation) and drought on radial growth was studied using dendrochronology along biogeographic and ecological gradients. We analyzed old native stands with non-tapped and resin-tapped trees mixed, showing their usefulness in dendroclimatic studies. Our results indicate a high plasticity in the growth responses of maritime pine to climate and drought, suggesting that site aridity modulated these responses. The positive growth responses to spring precipitation and the negative responses to summer drought were stronger in the more xeric inland sites than in wet coastal ones, in particular from the 1980s onwards. The characterization of tree species’ responses to climate at the southern or dry limits in relation to site conditions allows improving conservation strategies in drought-prone forest ecosystems.     

Millennium-Scale Crossdating and Inter-Annual Climate Sensitivities of Standing California Redwoods

Extremely decay-resistant wood and fire-resistant bark allow California’s redwoods to accumulate millennia of annual growth rings that can be useful in biological research. Whereas tree rings of Sequoiadendron giganteum (SEGI) helped formalize the study of dendrochronology and the principle of crossdating, those of Sequoia sempervirens (SESE) have proven much more difficult to decipher, greatly limiting dendroclimatic and other investigations of this species. We overcame these problems by climbing standing trees and coring trunks at multiple heights in 14 old-growth forest locations across California. Overall, we sampled 1,466 series with 483,712 annual rings from 120 trees and were able to crossdate 83% of SESE compared to 99% of SEGI rings. Standard and residual tree-ring chronologies spanning up to 1,685 years for SESE and 1,538 years for SEGI were created for each location to evaluate crossdating and to examine correlations between annual growth and climate. We used monthly values of temperature, precipitation, and drought severity as well as summer cloudiness to quantify potential drivers of inter-annual growth variation over century-long time series at each location. SESE chronologies exhibited a latitudinal gradient of climate sensitivities, contrasting cooler northern rainforests and warmer, drier southern forests. Radial growth increased with decreasing summer cloudiness in northern rainforests and a central SESE location. The strongest dendroclimatic relationship occurred in our southernmost SESE location, where radial growth correlated negatively with dry summer conditions and exhibited responses to historic fires. SEGI chronologies showed negative correlations with June temperature and positive correlations with previous October precipitation. More work is needed to understand quantitative relationships between SEGI radial growth and moisture availability, particularly snowmelt. Tree-ring chronologies developed here for both redwood species have numerous scientific applications, including determination of tree ages, accurate dating of fire-return intervals, archaeology, analyses of stable isotopes, long-term climate reconstructions, and quantifying rates of carbon sequestration.     

Climate Signals from Tree Ring Chronologies of the Upper and Lower Treelines in the Dulan Region of the Northeastern Qinghai-Tibetan Plateau

The radial growth of trees In mountainous areas is subject to environmental conditions associated with changes In elevation. To assess the sensitivity of tree-ring growth to climate variation over a wide range of elevations, we compared the chronological characteristics of Sabina przewalskii Kom. and their relationships with climatic variables at the upper and lower treellnes In the Dulan region of the northeastern Qlnghal-Tlbetan Plateau. It was found that the radial growth in this region was controlled primarily by precipitation in late spring and early summer （from May to June）. In addition, a higher temperature from April to June could Intensify drought stress and lead to narrow tree rings. The significant similarity In climate-tree growth relationships at both the upper and lower treellnes Indicated that tree rings of S. przewalskU In this region are able to provide common regional climate information. However, the chronologies at the lower forest limits showed a higher standard deviation and more significant correlations with climatic factors, suggesting that the radial growth there was more significantly Influenced by climate variation. The first principal component of the four chronologies showed a common growth response to local climate. The second principal component showed a contrasting growth response between different sampling sites. The third principal component revealed different growth patterns In response to altitudinal variation. Further analysis Indicated that the precipitation In late spring and early summer controlled the growth of S. przewalskii on a regional scale and that other factors, such as mlcroenvlronment at the sampling sites, also affected the strength of the climatic response of tree growth.     

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.     

Differential drought responses between saplings and adult trees in four co-occurring species of New England

Tree-ring characteristics in four species were examined to address whether co-occurring mature trees of different successional status respond differently to drought, and whether saplings of these species have a greater response to drought than mature trees. We examined saplings and mature trees of paper birch, yellow birch, red maple and sugar maple, which varied in successional status (shade-tolerance) and co-occurred at Harvard Forest, Petersham, Mass., USA. Three drought events in 1964–1966, 1981 and 1995 were identified using climate data. For mature trees, there was no significant interspecific difference in relative changes in ring-width index (RWI) during the 1964–1966 and 1995 drought events. However, the interspecific difference was significant in the 1981 drought event. Response function analysis for mature trees showed that the radial growth of sugar maple was mainly controlled by spring and summer precipitation, red maple by spring and summer precipitation and temperature, yellow birch by winter and summer precipitation, and spring and summer temperature, and paper birch by spring and summer precipitation and spring temperature. Saplings of sugar maple and yellow birch, but not red maple and paper birch, showed significant positive correlations between RWI and annual total precipitation. In the 1995 drought event, saplings and mature trees of red maple and paper birch differed significantly in drought responses, but this was not true in sugar maple and yellow birch. Our results do not support a generally greater response in saplings than in mature trees, nor an early- versus late successional difference in drought responses.     

滇西北石卡雪山2个针叶树种森林上限径向生长对温度和降水的响应

基于树木年轮学的理论和方法,建立滇西北高原石卡雪山森林上限丽江云杉(Picea likiangensis)和高山松(Pinus densata)差值年表,运用响应函数研究其与气候因子的关系,进而阐明影响滇西北高原针叶树种径向生长的主要气候因子,并利用冗余分析(RDA)进一步分析并验证树木生长与温度和降水的关系。研究结果表明:石卡雪山森林上限针叶树种径向生长主要受温度影响,温度和降水对树木生长有滞后效应,2个树种对气候响应存在差异。具体表现为(1)丽江云杉径向生长受温度和降水的共同作用,与上年10月平均最低温呈显著负相关,与上年11月平均最高温以及当年7月温度呈显著正相关,上年8月和当年5月降水抑制其生长;(2)高山松径向生长与上年10月平均温和平均最高温、11月平均温呈显著正相关,与当年7月平均温和平均最高温呈显著负相关,与降水未达到显著相关水平;(3)冗余分析与响应函数分析结果基本一致,进一步证明该方法能够有效量化树木径向生长与气候因子的关系。能够为气候变化背景下的滇西北高原森林生态系统管理与保护提供理论依据。     

Dynamic relationships between Picea crassifolia growth and climate at upper treeline in the Qilian Mts., Northeast Tibetan Plateau, China

Knowledge of the spatial pattern and temporal relationships between tree-growth and climatic factors are important not only for the projection of forest growth under varying climate but for dendroclimatology in general. Here, we systematically investigated tree-growth climate relationships of Picea crassifolia at upper treeline in the Qilian Mts., northwestern China. 297 trees from eleven sites, covering a large part of the natural range of this species, show increasing and partly divergent correlations with temperature in the most recent decades. The dominant signal at all sites was a strengthening of negative correlations of annual radial growth with summer temperature. In a subset of trees at six sites, a strengthening positive correlation with summer temperatures existed as well. Wetter and high altitude sites tended to show a higher percentage of trees that are positively correlated with warming temperatures, indicating that some individuals there may take advantage of warmer conditions. Divergent responses between the two sub-populations clustered by their response to climate factor were significantly stronger in the last 30 years compared to earlier time slices. In the same time frame, hydrothermal conditions of the investigation area changed to a drier and warmer combination. Drought conditions, most likely affecting the radial growth of most P. crassifolia, have been intensifying over time and expanding spatially from the middle Qilian Mts. to most of our study area during the last half century. While explanations such as methodological effects due to trend removal or human disturbance at the sampling sites might be able to explain the result at single sites, the spatial and temporal co-occurrence of large scale changes in climate and tree growth suggests a causal link between them.     

Spatiotemporal variation in the relationship between boreal forest productivity proxies and climate data

The impacts of climate change on high-latitude forest ecosystems are still uncertain. Divergent forest productivity trends have recently been reported both at the local and regional level challenging the projections of boreal tree growth dynamics. The present study investigated (i) the responses of different forest productivity proxies to monthly climate (temperature and precipitation) through space and time; and (ii) the local coherency between these proxies through time at four high-latitude boreal Scots pine sites (coastal and inland) in Norway. Forest productivity proxies consisted of two proxies representing stem growth dynamics (radial and height growth) and one proxy representing canopy dynamics (cumulative May-to-September Normalized Difference Vegetation Index (NDVI)). Between-proxy and climate-proxy correlations were computed over the 1982–2011 period and over two 15-yr sub-periods. Over the entire period, radial growth significantly correlated with current year July temperature, and height growth and cumulative NDVI significantly correlated with previous and current growing season temperatures. Significant climate responses were quite similar across sites, despite some higher sensitivity to non-growing season climate at inland sites. Significant climate-proxy correlations identified over the entire period were temporarily unstable. Local coherency between proxies was generally insignificant. The spatiotemporal instability in climate-proxy correlations observed for all proxies underlines evolving responses to climate and challenges the modelling of forest productivity. The general lack of local coherency between proxies at our four study sites suggests that forest productivity estimations based on a single proxy should be considered with great caution. The combined use of different forest growth metrics may help circumvent uncertainties in capturing responses of forest productivity to climate variability and improve estimations of carbon sequestration by forest ecosystems.     

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.     

黄土高原南北样带尺度人工刺槐林对气候响应的敏感性分析

根据黄土高原南北样带尺度的人工刺槐林(Robinia pseudoacacia)的年轮宽度资料,分析了该地区刺槐树木生长趋势,以及刺槐年表对气候响应随降雨梯度变化规律。研究结果表明延安以北的刺槐样点(绥德、神木)年轮指数近期趋于下降,树木有生长衰退现象;而延安以南刺槐样点(延安、富县、宜君、永寿)年轮指数近期趋于上升,树木无生长衰退现象。气候响应结果表明,刺槐年表对气候响应均以延安样点最为敏感,表现年表与温度的负相关关系,以及年表与降雨和干旱指数的正相关关系,而延安以北和以南刺槐样点对气候响应敏感性均较低。黄土高原中部延安地区地处森林草原过渡带,刺槐生长对外界环境变化最为敏感,年表中气候信号也较强;延安以南地区地处森林植被带,气候条件较为适宜刺槐林生长,因而年表中气候信号较弱;延安以北地区地处草原植被带,气候条件比较恶劣,刺槐生长对干旱气候已有一定适应性特征,因而年表中气候信号也较弱。     

Climatic signals in tree rings of <Emphasis Type="Italic">Burkea africana</Emphasis> and <Emphasis Type="Italic">Pterocarpus angolensis</Emphasis> from semiarid forests in Namibia

Tree-ring studies contribute worldwide to the understanding of climate and its relation to tree growth. Long tree-ring chronologies serve as climate proxies for the reconstruction of past, pre-instrument climate and its recent change. In tropical regions, the availability of exactly dated tree-ring chronologies is limited. The dendroclimatic potential of two dominant species from dry forests in northern Namibia was examined in the study presented in this paper. Both species (Burkea africana Hook and Pterocarpus angolensis DC) were sampled at two sites (ca. 900 km apart), and the response to several climatic variables, including ENSO indices, is studied. All specimens showed distinct growth rings and cross-dating between radii was successful for all trees. Species-specific mean curves were built for both sites. The mean curves of different species of the same site synchronised significantly, allowing the construction of a site-specific chronology. Synchronisation between sites was not possible, but spectral analysis of the chronologies implied that both show similar long-term (6.7 year) oscillation patterns. B. africana is more sensitive to rainfall variation than P. angolensis at both sites. Growth response to rainfall was positive, but a time-lag in the reaction occurred between the sites, corresponding to the time-lag of the beginning of the rainy season. Air temperature showed a negative correlation with stem increment at both sites. The response at the westernmost site to two ENSO indices indicates a tree growth decrease during El Niño years, which are generally dry in southern Africa.     

丽江老君山海拔上限长苞冷杉(Abies georgei)和云南铁杉(Tsuga dumosa)径向生长对气候变化的响应

基于树木年轮学方法,利用丽江老君山海拔上限长苞冷杉（Abies georgei）和云南铁杉（Tsuga dumosa）树轮宽度资料,构建差值年表,运用响应函数和滑动响应分析研究树木径向生长与气温和降水的相关关系及其稳定性,进而阐明影响该区域2个针叶树种径向生长的主要气候要素。结果表明：2个树种对降水累积效应的响应较为一致,对逐月气候因子的响应存在差异,相关关系较为稳定,具体表现为（1）上年11月平均温升高和当年生长季盛期（7-8月）降水增加有利于老君山海拔上限长苞冷杉生长;（2）云南铁杉径向生长与当年3月、树木休眠期（1-3月）、生长季盛期（7-8月）的降水表现为显著正相关关系,与上年7月与当年5月的气温及当年生长季末期（9-10月）降水呈显著负相关;（3）上述相关关系的稳定性较强,在全部或大部分分析时段（1951-2017）内达到显著相关,云南铁杉的稳定性更强。研究结果可为气候变化背景下滇西北高原树木生长的管理及森林生态系统的保护提供理论依据。     

Sugar maple (Acer saccharum Marsh.) establishment in boreal forest: results of a transplantation experiment

Aim To evaluate whether seedlings of sugar maple (Acer saccharum Marsh.) can establish beyond the species northern range limit in adjacent boreal forest. Location The hardwood–boreal forest transition zone on the north‐east shore of Lake Superior, Ontario, Canada. Methods Seed fall of sugar maple was monitored for 5 years in a stand of this species at its northern range limit, and seed from this stand was transplanted to five micro‐habitat types in an adjacent boreal forest. The establishment and survival of sugar maple seedlings there, and in the seed‐source stand, was monitored for the following 7–11 years. Soil‐surface light levels were measured in both forest types. Results Most seed fell in the final year of monitoring, when c. 250 seeds m^?2 were recorded. First‐year seedling establishment rates in the maple stand, deriving from this mast seed year, was approximately double that deriving from seed transplanted to the boreal forest sites; this is tentatively attributed to seed predator satiation in the maple stand. However, subsequent seedling survivorship in the boreal forest was greater than that in the maple stand, resulting in comparable seedling densities by the end of 6 years. This difference is tentatively attributed to better illumination in the boreal forest sites, and canopy‐opening disturbances appear to be especially facilitative of seedling survival. Main conclusions There is no fundamental impediment to sugar maple seedlings establishing in boreal forest communities if climate warming occurs and seed is available. If management intervention is needed to accelerate seed availability in a rapidly warming boreal forest, then diffuse seed application to disturbed boreal forest sites during mast years of local boreal tree species is recommended as the most effective way of avoiding seed predation and increasing seedling survival.     

Assessment of the potential role of metals in sugar maple (Acer saccharum Marsh) decline in Ontario, Canada

Spatial and temporal differences in the crown condition of sugar maple (Acer saccharum Marsh) in Ontario remain largely unexplained. In this study, the potential role of metals in sugar maple dieback was explored by measuring metal concentrations in foliage and forest floor (LFH) at 35 forest stands in south-central Ontario that exhibit varying levels of decline and span a climatic, soil acidity and acid deposition gradient. Foliar and forest floor metal concentrations varied among sites by between two and ten-fold, with acidic sites exhibiting the highest concentrations of many metals in the forest floor and foliage. Sites with moderate decline symptoms (decline index (DI)?>?10, averaged between 1986 and 2004) had significantly greater Cd, Zn, Cu, Pb and Mn concentrations and lower Ca concentrations in the forest floor compared with healthy sites (DI?<?10). Foliar concentrations of Cd, Sr and Mn were also significantly greater and Ca was significantly lower in sites with moderate decline symptoms compared with healthy sites. However the highest metal concentrations in foliage and the forest floor found in this study are lower than critical values reported in the literature. The notable exception is Mn where values at acidic sites may be high enough to negatively impact sugar maple.     

Variation in radial growth of Pinus cooperi in response to climatic signals across an elevational gradient

Climate change could modify the biogeography of many forest species. Elevational gradients have been documented as strategic sites to better understand tree growth response to regional climate variables. Pinus cooperi Blanco is one of the most important species in Northern Mexico. However, little is known concerning effects of climate responses on growth of this species. We used tree data records to compare the influence of precipitation and temperature on radial growth among P. cooperi populations across a mountain landscape at elevation gradient. Correlation and regression analysis of the regional growth–climate relationships showed that radial growth was correlated with previous winter conditions at most sites along the gradient. Wet and cold winters were positively associated with radial growth. Although our results showed significant climate influences on tree radial growth, other site factors also may have affected growth–climate responses. The results support the idea that climate change influences P. cooperi growth.     

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。若气候变暖持续或加剧,二者径向生长的气候限制因子也将由温度转变为水分;红松和红皮云杉会出现生长衰退,尤其是红松。     

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.