树木年轮揭示的东灵山主要树种间干旱耐受性差异

近年来北京地区的森林随极端干旱加剧表现出脆弱性特征,为了解气候变化下不同树种的干旱耐受性,选择北京东灵山森林内3个乔木树种(华北落叶松、油松和辽东栎),利用树木年轮生态学方法分析了径向生长与气候的关系,以及对极端干旱事件的抵抗力和弹性。结果表明: 华北落叶松和油松与5—6月气温呈显著负相关,辽东栎与5月气温呈显著负相关;华北落叶松与6月降水量、5—6月和8—9月相对湿度呈显著正相关,油松与6—8月降水量和相对湿度呈显著正相关,辽东栎与2月和5月降水量、5月相对湿度呈显著正相关;所有树种均与当年5—7月标准化降水蒸散指数(SPEI)呈显著正相关。华北落叶松是干旱耐受性最弱的树种,径向生长在所选极端干旱事件中(1994年、2001—2002年和2007年)下降幅度最大(46.6%～69.6%),抵抗力(0.534、0.304、0.530)和弹性(0.686、0.570、0.753)显著低于辽东栎和油松,辽东栎在2007年抵抗力显著高于油松,弹性无显著差异。生长季持续的高温或降水减少引起的极端干旱是树木径向生长下降的主要原因,树种间各异的生理生态策略是干旱耐受性差异的可能原因。研究结果可为未来造林树种选择和森林管护措施制定提供新依据,以在气候压力持续增加背景下维持森林生态系统功能和服务。     

Spatial and habitat variation in aphid,butterfly, moth and bird phenologies over the last half century

Global warming has advanced the timing of biological events, potentially leading to disruption across trophic levels. The potential importance of phenological change as a driver of population trends has been suggested. To fully understand the possible impacts, there is a need to quantify the scale of these changes spatially and according to habitat type. We studied the relationship between phenological trends, space and habitat type between 1965 and 2012 using an extensive UK dataset comprising 269 aphid, bird, butterfly and moth species. We modelled phenologies using generalized additive mixed models that included covariates for geographical (latitude, longitude, altitude), temporal (year, season) and habitat terms (woodland, scrub, grassland). Model selection showed that a baseline model with geographical and temporal components explained the variation in phenologies better than either a model in which space and time interacted or a habitat model without spatial terms. This baseline model showed strongly that phenologies shifted progressively earlier over time, that increasing altitude produced later phenologies and that a strong spatial component determined phenological timings, particularly latitude. The seasonal timing of a phenological event, in terms of whether it fell in the first or second half of the year, did not result in substantially different trends for butterflies. For moths, early season phenologies advanced more rapidly than those recorded later. Whilst temporal trends across all habitats resulted in earlier phenologies over time, agricultural habitats produced significantly later phenologies than most other habitats studied, probably because of nonclimatic drivers. A model with a significant habitat‐time interaction was the best‐fitting model for birds, moths and butterflies, emphasizing that the rates of phenological advance also differ among habitats for these groups. Our results suggest the presence of strong spatial gradients in mean seasonal timing and nonlinear trends towards earlier seasonal timing that varies in form and rate among habitat types.     

An ecoregion assessment of projected tree species vulnerabilities in western North America through the 21st century

Forest ecosystems across western North America will likely see shifts in both tree species dominance and composition over the rest of this century in response to climate change. Our objective in this study was to identify which ecological regions might expect the greatest changes to occur. We used the process‐based growth model 3‐PG, to provide estimates of tree species responses to changes in environmental conditions and to evaluate the extent that species are resilient to shifts in climate over the rest of this century. We assessed the vulnerability of 20 tree species in western North America using the Canadian global circulation model under three different emission scenarios. We provided detailed projections of species shifts by including soil maps that account for the spatial variation in soil water availability and soil fertility as well as by utilizing annual climate projections of monthly changes in air temperature, precipitation, solar radiation, vapor pressure deficit and frost at a spatial resolution of one km. Projected suitable areas for tree species were compared to their current ranges based on observations at >40 000 field survey plots. Tree species were classified as vulnerable if environmental conditions projected in the future appear outside that of their current distribution ≥70% of the time. We added a migration constraint that limits species dispersal to <200 m yr^?1 to provide more realistic projections on species distributions. Based on these combinations of constraints, we predicted the greatest changes in the distribution of dominant tree species to occur within the Northwest Forested Mountains and the highest number of tree species stressed will likely be in the North American Deserts. Projected climatic changes appear especially unfavorable for species in the subalpine zone, where major shifts in composition may lead to the emergence of new forest types.     

Tolerance to drought and flooding events provides a competitive advantage for an invasive over a native plant species

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近一世纪黄土高原区植物气孔密度变化规律

以黄土高原地区 4种典型 C3植物辽东栎 (Quercus liaotungensis)、虎榛子 (Ostryopsis davidiana)、酸枣 (Zizyphus jujubavar.spinosa)和狼牙刺 (Sophora viciifolia)植物腊叶样品标本为材料 ,利用数码图像显微镜处理系统 ,研究了从 2 0世纪 30年代至 2 0 0 2年中不同年代植物气孔密度的变化情况。结果表明 ,在近百年中 ,4种植物气孔密度随环境变化的演变规律不同 ,辽东栎气孔密度升高率为 1.31% ,几乎没有变化 ,虎榛子气孔密度降低率为 9.79% ,下降也不十分明显 ,而酸枣和狼牙刺的气孔密度降低率分别为 32 .35 %、4 6 .85 % ,下降非常明显。 4种植物气孔密度变化率比较 :狼牙刺 >酸枣 >虎榛子 >辽东栎。说明不同植物对气候环境因子的敏感性不同 ,具有不同的适应环境变化的策略 ,环境变化对气孔密度的影响 ,其效应因植物种类而异     

淮河流域暖季极端高温干旱复合事件的演变特征及其与气候和植被的关系

使用淮河流域1981年至2020年的149个气象站点的气温和相对湿度数据,分析了流域暖季极端高温干旱复合事件(Compound Drought and Heat Events,CDHEs)的时空演变特征,并通过趋势分析和相关分析法探讨了CDHEs与气候和植被的关系。结果表明:①CDHEs的发生日数在年代际尺度上呈现明显的增加趋势,并且范围扩大,频发区逐渐向淮河流域中西部移动;②在年际尺度上,CDHEs随时间序列呈显著的波动上升趋势,空间分布上以西北部为中心向四周递减。连续CDHEs事件呈年际变化,最大2至4天的连续事件存在波动,2019年达到高峰,并且在流域内零散或成片出现;③在月际尺度上,CDHEs的发生日数在6月最多,其次是5月、7月、9月和8月。淮河流域入汛前的旱情和入汛后的旱涝急转都容易导致CDHEs发生,而且随着月际变化向南移动;④CDHEs对水热条件和大气环流具有特别的敏感性。在850hPa反气旋和500hPa显著高压异常的控制下,高温、低湿、高蒸发和降水少的气候背景有利于淮河地区CDHEs的形成,尤其是在淮河中西部地区。因此,CDHEs的发生与气候变化密切相关;⑤CDHEs与植被生长也存在显著关系。CDHEs与GPP呈显著的负相关,而与NDVI呈显著的正相关,显著地区的土地类型以耕地和城乡、工矿、居民用地为主。GPP和NDVI的不同步可能是因为多种因素的非线性相互作用,而不仅仅是单一因素的影响。此外,对于GPP和NDVI来说,土壤含水量至关重要。总之,本文对淮河流域CDHEs的时空分布特征进行了深入研究,并探讨了其与气候和植被的关系。研究结果可以为该地区的气象灾害防御和生态环境保护提供科学依据和参考。     

Site‐adapted admixed tree species reduce drought susceptibility of mature European beech

Some forest‐related studies on possible effects of climate change conclude that growth potential of European beech (Fagus sylvatica L.) might be impaired by the predicted increase in future serious drought events during the growing season. Other recent research suggests that not only multiyear increment rates but also growth resistance and recovery of beech during, respectively, after dry years may differ between pure and mixed stands. Thus, we combined dendrochronological investigations and wood stable isotope measurements to further investigate the impact of neighborhood diversity on long‐term performance, short‐term drought response and soil water availability of European beech in three major geographic regions of Germany. During the last four decades, target trees whose competitive neighborhood consisted of co‐occurring species exhibited a superior growth performance compared to beeches in pure stands of the same investigation area. This general pattern was also found in exceptional dry years. Although the summer droughts of 1976 and 2003 predominantly caused stronger relative growth declines if target trees were exposed to interspecific competition, with few exceptions they still formed wider annual rings than beeches growing in close‐by monocultures. Within the same study region, recovery of standardized beech target tree radial growth was consistently slower in monospecific stands than in the neighborhood of other competitor species. These findings suggest an improved water availability of beech in mixtures what is in line with the results of the stable isotope analysis. Apparently, the magnitude of competitive complementarity determines the growth response of target beech trees in mixtures. Our investigation strongly suggest that the sensitivity of European beech to environmental constrains depends on neighborhood identity. Therefore, the systematic formation of mixed stands tends to be an appropriate silvicultural measure to mitigate the effects of global warming and droughts on growth patterns of Fagus sylvatica.     

Intra‐annual plasticity of growth mediates drought resilience over multiple years in tropical seedling communities

Precipitation patterns are changing across the globe causing more severe and frequent drought for many forest ecosystems. Although research has focused on the resistance of tree populations and communities to these novel precipitation regimes, resilience of forests is also contingent on recovery following drought, which remains poorly understood, especially in aseasonal tropical forests. We used rainfall exclusion shelters to manipulate the interannual frequency of drought for diverse seedling communities in a tropical forest and assessed resistance, recovery and resilience of seedling growth and mortality relative to everwet conditions. We found seedlings exposed to recurrent periods of drought altered their growth rates throughout the year relative to seedlings in everwet conditions. During drought periods, seedlings grew slower than seedlings in everwet conditions (i.e., resistance phase) while compensating with faster growth after drought (i.e., recovery phase). However, the response to frequent drought was species dependent as some species grew significantly slower with frequent drought relative to everwet conditions while others grew faster with frequent drought due to overcompensating growth during the recovery phase. In contrast, mortality was unrelated to rainfall conditions and instead correlated with differences in light. Intra‐annual plasticity of growth and increased annual growth of some species led to an overall maintenance of growth rates of tropical seedling communities in response to more frequent drought. These results suggest these communities can potentially adapt to predicted climate change scenarios and that plasticity in the growth of species, and not solely changes in mortality rates among species, may contribute to shifts in community composition under drought.     

小五台山青杨雌雄植株树轮生长特性及其对气候变化的响应差异

近年来逆境导致植物雌雄幼苗的生长出现差异被许多控制实验所证实, 而有关气候变化对雌雄异株植物成树生长的潜在影响尚未引起人们广泛的关注。为进一步揭示气候变化对雌雄植株树木径向和密度生长的不同影响, 该文通过树轮生态学的研究方法, 选择小五台山天然青杨(Populus cathayana)种群为研究对象, 对青杨雌雄植株近30年(1982-2011)的树轮生长特性及其与气候的相关性进行了分析。结果显示: 1)在近30年当地气温不断升高的气候条件下, 雌株的年轮最大密度和晚材平均密度均高于雄株(p < 0.05), 但雌雄植株的径向生长无显著差异; 2)雌雄植株年轮最大密度和宽度差值年表的变化趋势具有一致性, 但在年轮最大密度差值年表的变化上雄株波动幅度大于雌株; 3)青杨雌雄植株年轮密度差值年表对温度响应的月份明显不同。雌株年轮最大密度与当年8月的月平均最高气温显著正相关, 而雄株年轮最大密度与当年1月和4月的气温负相关; 4)生长季前的气候变化对青杨雌雄植株的径向生长均有明显的限制作用。此外, 当年6月的高温对于早材生长的限制作用特别明显。上述结果表明, 雌雄异株植物在树木年轮生长方面对全球气候变暖可能具有不同的响应机制, 雌株比雄株更侧重于密度生长。     

The role of climate,habitat, and species co‐occurrence as drivers of change in small mammal distributions over the past century

Species distribution models are commonly used to predict species responses to climate change. However, their usefulness in conservation planning and policy is controversial because they are difficult to validate across time and space. Here we capitalize on small mammal surveys repeated over a century in Yosemite National Park, USA, to assess accuracy of model predictions. Historical (1900–1940) climate, vegetation, and species occurrence data were used to develop single‐ and multi‐species multivariate adaptive regression spline distribution models for three species of chipmunk. Models were projected onto the current (1980–2007) environmental surface and then tested against modern field resurveys of each species. We evaluated models both within and between time periods and found that even with the inclusion of biotic predictors, climate alone is the dominant predictor explaining the distribution of the study species within a time period. However, climate was not consistently an adequate predictor of the distributional change observed in all three species across time. For two of the three species, climate alone or climate and vegetation models showed good predictive performance across time. The stability of the distribution from the past to present observed in the third species, however, was not predicted by our modeling approach. Our results demonstrate that correlative distribution models are useful in understanding species' potential responses to environmental change, but also show how changes in species‐environment correlations through time can limit the predictive performance of models.     

Size increase in high elevation ground squirrels over the last century

There is increasing evidence for morphological change in response to recent environmental change, but how this relates to fluctuations in geographic range remains unclear. We measured museum specimens from two time periods (1902–1950 and 2000–2008) that vary significantly in climate to assess if and how two high elevation contracting species of ground squirrels in the Sierra Nevada of California, Belding's ground squirrel (Urocitellus beldingi) and the golden‐mantled ground squirrel (Callospermophilus lateralis), and one lower elevation, stable species, the California ground squirrel (Otospermophilus beecheyi), have responded morphologically to changes over the last century. We measured skull length (condylobasal length), an ontogenetically more labile trait highly correlated with body size, and maxillary toothrow length, a more developmentally constrained trait predictive of skull shape. C. lateralis and U. beldingi, both obligate hibernators, have increased in body size, but have not changed in shape. In contrast, O. beecheyi, which only hibernates in parts of its range, has shown no significant change in either morphometric trait. The increase in body size in the higher elevation species, hypothesized to be a plastic effect due to a longer growing season and thus prolonged food availability, opposes the expected direction of selection for decreased body size under chronic warming. Our study supports that population contraction is related to physiological rather than nutritional constraints.     

欧洲典型树种展叶始期的时空变化及其对气候变化的响应

近年来,全球变暖对植物春季物候期产生了显著影响.很多研究报道了中国地区木本植物春季物候期变化的时空格局,但在同处于北半球温带地区的欧洲则相关研究较少.为了增进物候变化及其对气候变化响应规律的区域对比,本研究利用欧洲地区展叶始期(1980-2014年)数据和相应的气象数据,研究欧洲七叶树、垂枝桦、欧洲山毛榉和夏栎4种典型...     

Multiscale topoedaphic heterogeneity increases resilience and resistance of a dominant grassland species to extreme drought and climate change

It is argued that the inclusion of spatially heterogeneous environments in biodiversity reserves will be an effective means of encouraging ecosystem resilience and plant community conservation under climate change. However, the resilience and resistance of plant populations to global change, the specific life‐history traits involved and the spatial scale at which environmentally driven demographic variation is expressed remains largely unknown for most plant groups. Here we address these questions by reporting an empirical investigation into the impacts of an unprecedented 3‐year drought on the demography, population growth rates (λ) and biogeographical distribution of core populations of the perennial grassland species Austrostipa aristiglumis in semiarid Australia. We use life‐history analysis and periodic matrix population models to specifically test the hypothesis that patch‐ and habitat‐scale variation in vital life‐history parameters result in spatial differences in the resilience and resistance of A. aristiglumis populations to extreme drought. We show that the development of critical soil water deficits during drought resulted in collapse of adult A. aristiglumis populations (λ?1), rapid interhabitat phytosociological change and overall contraction towards mesic refugia where populations were both more resistant and resilient to perturbation. Population models, combined with climatic niche analysis, suggest that, even in core areas, a significant reduction in size and habitat range of A. aristiglumis populations is likely under climate change expected this century. Remarkably, however, we show that even minor topographic variation (0.2–3 m) can generate significant variation in demographic parameters that confer population‐level resilience and resistance to drought. Our findings support the hypothesis that extreme climatic events have the capacity to induce rapid, landscape‐level shifts in core plant populations, but that the protection of topographically heterogeneous environments, even at small spatial scales, may play a key role in conserving biodiversity under climate change in the coming century.     

Regional and local determinants of drought resilience in tropical forests

The increase in severity of droughts associated with greater mortality and reduced vegetation growth is one of the main threats to tropical forests. Drought resilience of tropical forests is affected by multiple biotic and abiotic factors varying at different scales. Identifying those factors can help understanding the resilience to ongoing and future climate change. Altitude leads to high climate variation and to different forest formations, principally moist or dry tropical forests with contrasted vegetation structure. Each tropical forest can show distinct responses to droughts. Locally, topography is also a key factor controlling biotic and abiotic factors related to drought resilience in each forest type. Here, we show that topography has key roles controlling biotic and abiotic factors in each forest type. The most important abiotic factors are soil nutrients, water availability, and microclimate. The most important biotic factors are leaf economic and hydraulic plant traits, and vegetation structure. Both dry tropical forests and ridges (steeper and drier habitats) are more sensitive to droughts than moist tropical forest and valleys (flatter and wetter habitats). The higher mortality in ridges suggests that conservative traits are not sufficient to protect plants from drought in drier steeper habitats. Our synthesis highlights that altitude and topography gradients are essential to understand mechanisms of tropical forest''s resilience to future drought events. We described important factors related to drought resilience, however, many important knowledge gaps remain. Filling those gaps will help improve future practices and studies about mitigation capacity, conservation, and restoration of tropical ecosystems.     

Persistent versus transient tree encroachment of temperate peat bogs: effects of climate warming and drought events

Peatlands store approximately 30% of global soil carbon, most in moss‐dominated bogs. Future climatic changes, such as changes in precipitation patterns and warming, are expected to affect peat bog vegetation composition and thereby its long‐term carbon sequestration capacity. Theoretical work suggests that an episode of rapid environmental change is more likely to trigger transitions to alternative ecosystem states than a gradual, but equally large, change in conditions. We used a dynamic vegetation model to explore the impacts of drought events and increased temperature on vegetation composition of temperate peat bogs. We analyzed the consequences of six patterns of summer drought events combined with five temperature scenarios to test whether an open peat bog dominated by moss (Sphagnum) could shift to a tree‐dominated state. Unexpectedly, neither a gradual decrease in the amount of summer precipitation nor the occurrence of a number of extremely dry summers in a row could shift the moss‐dominated peat bog permanently into a tree‐dominated peat bog. The increase in tree biomass during drought events was unable to trigger positive feedbacks that keep the ecosystem in a tree‐dominated state after a return to previous ‘normal’ rainfall conditions. In contrast, temperature increases from 1 °C onward already shifted peat bogs into tree‐dominated ecosystems. In our simulations, drought events facilitated tree establishment, but temperature determined how much tree biomass could develop. Our results suggest that under current climatic conditions, peat bog vegetation is rather resilient to drought events, but very sensitive to temperature increases, indicating that future warming is likely to trigger persistent vegetation shifts.     

Changes in plant species richness over the last century in the eastern Swiss Alps: elevational gradient, bedrock effects and migration rates

Areas of 2,800–3,000 m a.s.l. represent the alpine-nival ecotone in the Alps. This transition zone connecting the closed swards of the alpine belt and the scattered vegetation of the nival belt may show particularly strong climate warming driven fluctuations in plant species richness compared to the nival belt. To test this hypothesis, 12 summits within this range were investigated in the canton of Grisons, Switzerland in 2004. Complete lists of vascular plant species consisting of 5–70 species were collected on each summit and the elevation of the uppermost occurrence of each species was recorded. These data were compared to historical records over 120 years in age. Within this time, vascular plant species richness increased by 11% per decade on summits in the alpine-nival ecotone. Despite this considerable change, a comparison with nival summits did not support the hypothesis that species richness increase at the alpine-nival ecotone is higher than in the nival belt. A general trend of upward migration in the range of several metres per decade could be observed. Anemochorous species were more often found to be migrating than zoochorous or autochorous species and migration was higher on calcareous than on siliceous bedrock. A comparison between the summits with the adjacent slopes in our study revealed that changes in species number could be used as an indicator for climate-induced changes—if at all—only for the narrow summit areas.     

Land use and life history limit migration capacity of eastern tree species

Aim

Temperate tree species overwhelmingly responded to past climate change by migrating rather than adapting. However, past climate change did not have the modern human‐driven patterns of land use and fragmentation, raising questions of whether tree migration will still be able to keep pace with climate. Previous studies using coarse‐grained or randomized landscapes suggest that dispersal may be delayed but have not identified outright barriers to migration. Here, we use real‐world fragmented landscapes at the scale of forest stands to assess the migration capacity of eastern tree species.

Location

Eastern U.S.A.

Time period

Present day to 2100.

Major taxa studied

Eastern U.S. trees.

Methods

We simulated dispersal over 100 years for 15 species common to the mid‐Atlantic region and that are predicted to gain suitable habitat in the northeast. In contrast to previous studies, we incorporated greater realism with species‐specific life histories and real‐world spatial configurations of anthropogenic land use. We used simulation results to calculate dispersal rates for each species and related these to predicted rates of species habitat shift.

Results

Our simulations suggest that land use in the human‐dominated east‐coast corridor slows species dispersal rates by 12–40% and may prevent keeping pace with climate. Species most impacted by anthropogenic land use were often those with the highest predicted species habitat shifts. We identified two major dispersal barriers, the Washington DC metropolitan area and central NY, that severely impeded tree migration.

Main conclusions

Patterns of anthropogenic land use not only slowed migration but also resulted in effective barriers to dispersal. These impacts were exacerbated by tree life histories, such as long ages to maturity and narrow dispersal kernels. Without intervention, the migration lags predicted here may lead to loss in biodiversity and ecosystem functions as current forest species decline, and may contribute to formation of novel communities.     

基于树木年轮定量重建过去50年贵州典型森林优势树种的地上生物量与生产力变化

利用树木年轮宽度结合树木生物量方程,重建了贵州3个地区典型森林(2个常绿与落叶阔叶混交林和1个典型常绿阔叶林)6个优势树种(天龙山:化香树Platycarya strobilacea、安顺润楠Machilus cavaleriei;茂兰:化香树、马尾松Pinus massoniana;雷公山:华山松Pinus armandii、白梓树Pterostyrax psilophyllus)以树木个体为单元的地上生物量(AGB)与地上净初级生产力(ANPP);比较了喀斯特与非喀斯特地区树木AGB与ANPP的差异;并研究了近50年气候变化对ANPP的影响。结果显示,针叶树的平均年轮宽度大于阔叶树,喀斯特地区针叶树和阔叶树的平均树木年轮宽度,分别小于非喀斯特地区针叶树和阔叶树的平均树木年轮宽度。喀斯特地区树木的AGB及其变异幅度均小于非喀斯特地区树木。近50年来,喀斯特地区阔叶树与针叶树的ANPP平均分别为(2.4±1.2) kg a^-1株^-1和(4.6±4.1) kg a^-1株^-1,显著低于非喀斯特地区阔叶树...     

Decadal heat and drought drive body size of North American bison (Bison bison) along the Great Plains

Large grazers are visible and valuable indicators of the effects of projected changes in temperature and drought on grasslands. The grasslands of the Great Plains have supported the greatest number of bison (Bison bison; Linnaeus, 1758) since prehistoric times. We tested the hypothesis that body mass (BM, kg) and asymptotic body mass (ABM, kg) of Bison decline with rising temperature and increasing drought over both temporal and spatial scales along the Great Plains. Temporally, we modeled the relationship of annual measures of BM and height (H, m) of 5,781 Bison at Wind Cave National Park (WICA) from 1966 to 2015. We used Gompertz equations of BM against age to estimate ABM in decadal cohorts; both females and males decreased from the 1960s to the 2010s. Male ABM was variable but consistently larger (699 vs. 441 kg) than female ABM. We used local mean decadal temperature (MDT) and local mean decadal Palmer Drought Severity Index (dPDSI) to model the effects of climate on ABM. Drought decreased ABM temporally (?16 kg/local dPDSI) at WICA. Spatially, we used photogrammetry to measure body height (H_E) of 773 Bison to estimate BM_E in 19 herds from Saskatchewan to Texas, including WICA. Drought also decreased ABM spatially (?16 kg/local dPDSI) along the Great Plains. Temperature decreased ABM both temporally at WICA (?115 kg/°C local MDT) and spatially (?1 kg/°C local MDT) along the Great Plains. Our data indicate that temperature and drought drive Bison ABM presumably by affecting seasonal mass gain. Bison body size is likely to decline over the next five decades throughout the Great Plains due to projected increases in temperatures and both the frequency and intensity of drought.