Long‐term changes in the impacts of global warming on leaf phenology of four temperate tree species

Contrary to the generally advanced spring leaf unfolding under global warming, the effects of the climate warming on autumn leaf senescence are highly variable with advanced, delayed, and unchanged patterns being all reported. Using one million records of leaf phenology from four dominant temperate species in Europe, we investigated the temperature sensitivities of spring leaf unfolding and autumn leaf senescence (S_T, advanced or delayed days per degree Celsius). The S_T of spring phenology in all of the four examined species showed an increase and decrease during 1951–1980 and 1981–2013, respectively. The decrease in the S_T during 1981–2013 appears to be caused by reduced accumulation of chilling units. As with spring phenology, the S_T of leaf senescence of early successional and exotic species started to decline since 1980. In contrast, for late successional species, the S_T of autumn senescence showed an increase for the entire study period from 1951 to 2013. Moreover, the impacts of rising temperature associated with global warming on spring leaf unfolding were stronger than those on autumn leaf senescence. The timing of leaf senescence was positively correlated with the timing of leaf unfolding during 1951–1980. However, as climate warming continued, the differences in the responses between spring and autumn phenology gradually increased, so that the correlation was no more significant during 1981–2013. Our results further suggest that since 2000, due to the decreased temperature sensitivity of leaf unfolding the length of the growing season has not increased any more. These finding needs to be addressed in vegetation models used for assessing the effects of climate change.     

Temperature sensitivity of spring vegetation phenology correlates to within-spring warming speed over the Northern Hemisphere

The inter-annual shift of spring vegetation phenology relative to per unit change of preseason temperature, referred to as temperature sensitivity (days °C⁻¹), quantifies the response of spring phenology to temperature change. Temperature sensitivity was found to differ greatly among vegetation from different environmental conditions. Understanding the large-scale spatial pattern of temperature sensitivity and its underlying determinant will greatly improve our ability to predict spring phenology. In this study, we investigated the temperature sensitivity for natural ecosystems over the North Hemisphere (north of 30°N), based on the vegetation phenological date estimated from NDVI time-series data provided by the Advanced Very High Resolution Radiometer (AVHRR) and the corresponding climate dataset. We found a notable longitudinal change pattern with considerable increases of temperature sensitivity from inlands to most coastal areas and a less obvious latitudinal pattern with larger sensitivity in low latitude area. This general spatial variation in temperature sensitivity is most strongly associated with the within-spring warming speed (WWS; r = 0.35, p < 0.01), a variable describing the increase speed of daily mean temperature during spring within a year, compared with other factors including the mean spring temperature, spring precipitation and mean winter temperature. These findings suggest that the same magnitude of warming will less affect spring vegetation phenology in regions with higher WWS, which might partially reflect plants’ adaption to local climate that prevents plants from frost risk caused by the advance of spring phenology. WWS accounts for the spatial variation in temperature sensitivity and should be taken into account in forecasting spring phenology and in assessing carbon cycle under the projected climate warming.     

Latitudinal patterns in the phenological responses of leaf colouring and leaf fall to climate change in Japan

Aim  To estimate the potential effect of global climate change on the phenological responses of plants it is necessary to estimate spatial variations at larger scales. However, previous studies have not estimated latitudinal patterns in the phenological response directly. We hypothesized that the phenological response of plants varies with latitude, and estimated the phenological response to long-term climate change using autumn phenological events that have been delayed by recent climate change.
Location  Japan.
Methods  We used a 53-year data set to document the latitudinal patterns in the climate responses of the timing of autumn leaf colouring and fall for two tree species over a wide range of latitudes in Japan (31 to 44° N). We calculated single regression slopes for leaf phenological timing and air temperature across Japan and tested their latitudinal patterns using regression models. The effects of latitude, time and their interaction on the responses of the phenological timings were also estimated using generalized linear mixed models.
Results  Our results showed that single regression slopes of leaf phenological timing and air temperature in autumn were positive at most stations. Higher temperatures can delay the timing of leaf phenology. Negative relationships were found between the phenological response of leaves to temperature and latitude. Single regression slopes of the phenological responses at lower latitudes were larger than those at higher latitudes.
Main conclusions  We found negative relationships between leaf phenological responsiveness and latitude. These findings will be important for predicting phenological timing with global climate change.     

Passerines may be sufficiently plastic to track temperature‐mediated shifts in optimum lay date

Projecting the fates of populations under climate change is one of global change biology's foremost challenges. Here, we seek to identify the contributions that temperature‐mediated local adaptation and plasticity make to spatial variation in nesting phenology, a phenotypic trait showing strong responses to warming. We apply a mixed modeling framework to a Britain‐wide spatiotemporal dataset comprising >100 000 records of first egg dates from four single‐brooded passerine bird species. The average temperature during a specific time period (sliding window) strongly predicts spatiotemporal variation in lay date. All four species exhibit phenological plasticity, advancing lay date by 2–5 days °C^?1. The initiation of this sliding window is delayed further north, which may be a response to a photoperiod threshold. Using clinal trends in phenology and temperature, we are able to estimate the temperature sensitivity of selection on lay date (B), but our estimates are highly sensitive to the temporal position of the sliding window. If the sliding window is of fixed duration with a start date determined by photoperiod, we find B is tracked by phenotypic plasticity. If, instead, we allow the start and duration of the sliding window to change with latitude, we find plasticity does not track B, although in this case, at odds with theoretical expectations, our estimates of B differ across latitude vs. longitude. We argue that a model combining photoperiod and mean temperature is most consistent with current understanding of phenological cues in passerines, the results from which suggest that each species could respond to projected increases in spring temperatures through plasticity alone. However, our estimates of B require further validation.     

Phenological response to climate change in China: a meta‐analysis

The change in the phenology of plants or animals reflects the response of living systems to climate change. Numerous studies have reported a consistent earlier spring phenophases in many parts of middle and high latitudes reflecting increasing temperatures with the exception of China. A systematic analysis of Chinese phenological response could complement the assessment of climate change impact for the whole Northern Hemisphere. Here, we analyze 1263 phenological time series (1960–2011, with 20+ years data) of 112 species extracted from 48 studies across 145 sites in China. Taxonomic groups include trees, shrubs, herbs, birds, amphibians and insects. Results demonstrate that 90.8% of the spring/summer phenophases time series show earlier trends and 69.0% of the autumn phenophases records show later trends. For spring/summer phenophases, the mean advance across all the taxonomic groups was 2.75 days decade^?1 ranging between 2.11 and 6.11 days decade^?1 for insects and amphibians, respectively. Herbs and amphibians show significantly stronger advancement than trees, shrubs and insect. The response of phenophases of different taxonomic groups in autumn is more complex: trees, shrubs, herbs and insects show a delay between 1.93 and 4.84 days decade^?1, while other groups reveal an advancement ranging from 1.10 to 2.11 days decade^?1. For woody plants (including trees and shrubs), the stronger shifts toward earlier spring/summer were detected from the data series starting from more recent decades (1980s–2000s). The geographic factors (latitude, longitude and altitude) could only explain 9% and 3% of the overall variance in spring/summer and autumn phenological trends, respectively. The rate of change in spring/summer phenophase of woody plants (1960s–2000s) generally matches measured local warming across 49 sites in China (R = ?0.33, P < 0.05).     

Spring phenology at different altitudes is becoming more uniform under global warming in Europe

Under current global warming, high‐elevation regions are expected to experience faster warming than low‐elevation regions. However, due to the lack of studies based on long‐term large‐scale data, the relationship between tree spring phenology and the elevation‐dependent warming is unclear. Using 652k records of leaf unfolding of five temperate tree species monitored during 1951–2013 in situ in Europe, we discovered a nonlinear trend in the altitudinal sensitivity (S_A, shifted days per 100 m in altitude) in spring phenology. A delayed leaf unfolding (2.7 ± 0.6 days per decade) was observed at high elevations possibly due to decreased spring forcing between 1951 and 1980. The delayed leaf unfolding at high‐elevation regions was companied by a simultaneous advancing of leaf unfolding at low elevations. These divergent trends contributed to a significant increase in the S_A (0.36 ± 0.07 days 100/m per decade) during 1951–1980. Since 1980, the S_A started to decline with a rate of ?0.32 ± 0.07 days 100/m per decade, possibly due to reduced chilling at low elevations and improved efficiency of spring forcing in advancing the leaf unfolding at high elevations, the latter being caused by increased chilling. Our results suggest that due to both different temperature changes at the different altitudes, and the different tree responses to these changes, the tree phenology has shifted at different rates leading to a more uniform phenology at different altitudes during recent decades.     

拔节期干旱和复水对春玉米物候的影响及其生理生态机制

物候不仅是气候变化的指示指标,也是作物模型的关键参数。现有研究主要关注物候变化与气候环境因子的关系,关于植物物候变化的生理生态机制研究很少。基于春玉米拔节期干旱与不同时间(抽雄期和吐丝期)复水的田间模拟试验分析表明:(1)不同时间复水均使灌浆期延长,乳熟期推迟(9d),表明物候对前期水分胁迫存在记忆。(2)干旱条件下叶片净光合速率(P_n)、蒸腾速率(T_r)、气孔导度(G_s)和相对叶绿素含量(SPAD)均随物候进程呈先降后升再降趋势,且均在抽雄期达到极小值;不同时间复水均使P_n、T_r和G_s在吐丝期达到极大值,而SPAD则在灌浆期达到极大值;叶水势(LWP)随干旱进程整体呈下降趋势,不同时间复水均只是减缓了其下降速度,表明LWP可用于描述物候对前期水分胁迫的记忆。(3)通径分析和决策系数分析表明,P_n是最主要的物候影响因子,而影响LWP的土壤相对湿度(RSWC)则是物候的主要控制因子,物候的变化是由P_n的累积变化引起,表明存在P_n的物候触发阈值。研究结果为春玉米物候变化的准确预测提供了依据。     

Phenology model from surface meteorology does not capture satellite-based greenup estimations

Seasonal temperature change in temperate forests is known to trigger the start of spring growth, and both interannual and spatial variations in spring onset have been tied to climatic variability. Satellite dates are increasingly being used in phenology studies, but to date that has been little effort to link remotely sensed phenology to surface climate records. In this research, we use a two‐parameter spring warming phenology model to explore the relationship between climate and satellite‐based phenology. We employ daily air temperature records between 2000 and 2005 for 171 National Oceanographic and Atmospheric Administration weather stations located throughout New England to construct spring warming models predicting the onset of spring, as defined by the date of half‐maximum greenness (D₅₀) in deciduous forests as detected from Moderate Resolution Imaging Spectrometer. The best spring warming model starts accumulating temperatures after March 20th and when average daily temperatures exceed 5°C. The accumulated heat sums [heating degree day (HDD)] required to reach D₅₀ range from 150 to 300 degree days over New England, with the highest requirements to the south and in coastal regions. We test the ability of the spring warming model to predict phenology against a null photoperiod model (average date of onset). The spring warming model offers little improvement on the null model when predicting D₅₀. Differences between the efficacies of the two models are expressed as the ‘climate sensitivity ratio’ (CSR), which displays coherent spatial patterns. Our results suggest that northern (beech‐maple‐birch) and central (oak‐hickory) hardwood forests respond to climate differently, particularly with disparate requirements for the minimum temperature necessary to begin spring growth (3 and 6°C, respectively). We conclude that spatial location and species composition are critical factors for predicting the phenological response to climate change: satellite observations cannot be linked directly to temperature variability if species or community compositions are unknown.     

The shifting phenological landscape: Within‐ and between‐species variation in leaf emergence in a mixed‐deciduous woodland

Many organisms rely on synchronizing the timing of their life‐history events with those of other trophic levels—known as phenological matching—for survival or successful reproduction. In temperate deciduous forests, the extent of matching with the budburst date of key tree species is of particular relevance for many herbivorous insects and, in turn, insectivorous birds. In order to understand the ecological and evolutionary forces operating in these systems, we require knowledge of the factors influencing leaf emergence of tree communities. However, little is known about how phenology at the level of individual trees varies across landscapes, or how consistent this spatial variation is between different tree species. Here, we use field observations, collected over 2 years, to characterize within‐ and between‐species differences in spring phenology for 825 trees of six species (Quercus robur, Fraxinus excelsior, Fagus sylvatica, Betula pendula, Corylus avellana, and Acer pseudoplatanus) in a 385‐ha woodland. We explore environmental predictors of individual variation in budburst date and bud development rate and establish how these phenological traits vary over space. Trees of all species showed markedly consistent individual differences in their budburst timing. Bud development rate also varied considerably between individuals and was repeatable in oak, beech, and sycamore. We identified multiple predictors of budburst date including altitude, local temperature, and soil type, but none were universal across species. Furthermore, we found no evidence for interspecific covariance of phenology over space within the woodland. These analyses suggest that phenological landscapes are highly complex, varying over small spatial scales both within and between species. Such spatial variation in vegetation phenology is likely to influence patterns of selection on phenology within populations of consumers. Knowledge of the factors shaping the phenological environments experienced by animals is therefore likely to be key in understanding how these evolutionary processes operate.     

Urban environments provide new perspectives for forecasting vegetation phenology responses under climate warming

Given that already-observed temperature increase within cities far exceeds the projected global temperature rise by the end of the century, urban environments often offer a unique opportunity for studying ecosystem response to future warming. However, the validity of thermal gradients in space serving as a substitute for those in time is rarely tested. Here, we investigated vegetation phenology dynamics in China's 343 cities and empirically test whether phenological responses to spatial temperature rise in urban settings can substitute for those to temporal temperature rise in their natural counterparts based on satellite-derived vegetation phenology and land surface temperature from 2003 to 2018. We found prevalent advancing spring phenology with “high confidence” and delaying autumn phenology with “medium confidence” under the context of widespread urban warming. Furthermore, we showed that space cannot substitute for time in predicting phenological shifts under climate warming at the national scale and for most cities. The thresholds of ~11°C mean annual temperature and ~600 mm annual precipitation differentiated the magnitude of phenological sensitivity to temperature across space and through time. Below those thresholds, there existed stronger advanced spring phenology and delayed autumn phenology across the spatial urbanization gradients than through time, and vice versa. Despite the complex and diverse relationships between phenological sensitivities across space and through time, we found that the directions of the temperature changes across spatial gradients were converged (i.e., mostly increased), but divergent through temporal gradients (i.e., increased or decreased without a predominant direction). Similarly, vegetation phenology changes more uniformly over space than through time. These results suggested that the urban environments provide a real-world condition to understand vegetation phenology response under future warming.     

Forecasting phenology under global warming

As a consequence of warming temperatures around the world, spring and autumn phenologies have been shifting, with corresponding changes in the length of the growing season. Our understanding of the spatial and interspecific variation of these changes, however, is limited. Not all species are responding similarly, and there is significant spatial variation in responses even within species. This spatial and interspecific variation complicates efforts to predict phenological responses to ongoing climate change, but must be incorporated in order to build reliable forecasts. Here, we use a long-term dataset (1953–2005) of plant phenological events in spring (flowering and leaf out) and autumn (leaf colouring and leaf fall) throughout Japan and South Korea to build forecasts that account for these sources of variability. Specifically, we used hierarchical models to incorporate the spatial variability in phenological responses to temperature to then forecast species'' overall and site-specific responses to global warming. We found that for most species, spring phenology is advancing and autumn phenology is getting later, with the timing of events changing more quickly in autumn compared with the spring. Temporal trends and phenological responses to temperature in East Asia contrasted with results from comparable studies in Europe, where spring events are changing more rapidly than are autumn events. Our results emphasize the need to study multiple species at many sites to understand and forecast regional changes in phenology.     

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种典型木本植物展叶始期的时空变化格局,并识别影响物候变化的主要气候因子。结果表明: 1980—2014年,研究区4种植物的展叶始期以3.3～7.5 d·10 a^-1的趋势显著提前。展叶始期自南向北以每纬度2.03～3.19 d的速率推迟,自西向东以每经度0.19～0.80 d的速率推迟(除欧洲山毛榉外),海拔自低到高以2.25～3.44 d·100 m^-1的速率推迟。展叶始期的提前主要与春季温度的增高和冬春季降水量的增加有关,而秋冬季温度的升高对展叶始期有一定的推迟效应。     

Beyond the usual climate? Factors determining flowering and fruiting phenology across a genus over 117 years

Premise

Although changes in plant phenology are largely attributed to changes in climate, the roles of other factors such as genetic constraints, competition, and self-compatibility are underexplored.

Methods

We compiled >900 herbarium records spanning 117 years for all eight nominal species of the winter-annual genus Leavenworthia (Brassicaceae). We used linear regression to determine the rate of phenological change across years and phenological sensitivity to climate. Using a variance partitioning analysis, we assessed the relative influence of climatic and nonclimatic factors (self-compatibility, range overlap, latitude, and year) on Leavenworthia reproductive phenology.

Results

Flowering advanced by ~2.0 days and fruiting by ~1.3 days per decade. For every 1°C increase in spring temperature, flowering advanced ~2.3 days and fruiting ~3.3 days. For every 100 mm decrease in spring precipitation, each advanced ~6–7 days. The best models explained 35.4% of flowering variance and 33.9% of fruiting. Spring precipitation accounted for 51.3% of explained variance in flowering date and 44.6% in fruiting. Mean spring temperature accounted for 10.6% and 19.3%, respectively. Year accounted for 16.6% of flowering variance and 5.4% of fruiting, and latitude for 2.3% and 15.1%, respectively. Nonclimatic variables combined accounted for <11% of the variance across phenophases.

Conclusions

Spring precipitation and other climate-related factors were dominant predictors of phenological variance. Our results emphasize the strong effect of precipitation on phenology, especially in the moisture-limited habitats preferred by Leavenworthia. Among the many factors that determine phenology, climate is the dominant influence, indicating that the effects of climate change on phenology are expected to increase.     

近50年中国典型木本植物展叶始期温度敏感度变化及原因

展叶始期的温度敏感度是指气温每变化1℃,物候期变化的天数。展叶始期对温度响应更敏感的植物能够在生长季初期占据更多的资源从而在种间竞争中占据优势,因此研究展叶始期的温度敏感度变化有助于评估植物对气候变化的适应能力。选择1963-2014年10个站点163种植物的展叶始期资料,利用滑动分析法计算了每15a各植物的展叶始期温度敏感度。在此基础上,分析了温度敏感度的变化趋势及空间格局,并讨论了导致展叶始期温度敏感度变化的可能原因。主要结论为：在全部313条展叶始期时间序列中,60.1%的序列温度敏感度呈升高趋势,其中显著升高的占40.0%（P < 0.05）;39.9%的序列温度敏感度降低,其中显著降低的占28.4%。在空间分布上,温带地区的6个站点展叶始期温度敏感度平均呈升高趋势。其中,北京地区植物展叶始期温度敏感度升高最为普遍,显著升高的物种比例达到75.0%（P < 0.05）。而亚热带站点（除合肥外）的展叶始期温度敏感度主要呈降低趋势。其中,长沙植物展叶始期温度敏感度显著降低的物种比例最高,达68.4%。冬季冷激量和春季气温变率是影响植物展叶始期温度敏感度随时间变化的主要因素。冬季冷激量降低将导致植物展叶始期温度敏感度降低,而春季气温变率降低将导致植物展叶始期温度敏感度升高。     

Bergmann's rule in amphibians: combining demographic and ecological parameters to explain body size variation among populations in the common toad Bufo bufo

Large‐scale patterns of body size variation are described by well‐known generalizations such as Bergmann’s rule; the generality and underlying causes of these patterns have been much debated. Intraspecific extension of this rule was tested in various ectotherms, and evidence was found for both Bergmann and converse Bergmann clines. In this study, we explored spatial patterns of variation in a widespread amphibian, the Common toad (Bufo bufo), along a 2240 km latitudinal gradient across Europe. We tested for covariation of adult body size, age and growth parameters with latitude, altitude, length of activity period and mean temperature during this period using both original and literature data. We selected 13 European populations, representing a latitudinal range from 43 to 63°N and altitudinal range from 15 to 1850 m a.s.l. The length of activity period (12–33 weeks) and T_mean (6.6–15.6°C) significantly decreased as latitude and altitude of these populations increased. Mean body size decreased as latitude increased (not with altitude), and increased with T_mean (not with length of activity period). Mean and minimal adult age increased with latitude and altitude, longevity increased with altitude only. Age increased as length of activity period decreased (not with T_mean). The growth coefficient (0.32–0.92 in males, 0.18–0.74 in females, available for six populations) decreased as altitude increased, and increased as both length of activity period and T_mean increased; latitudinal trend was non‐significant. Our analysis shows that B. bufo clearly exhibited a converse Bergmann cline along latitudinal gradient, but not along altitudinal gradient; the main effect of elevation was on age. The effects of ecological conditions also differed: body size increased with T_mean, while age parameters were related to the length of activity period. This study highlights that, to identify causal factors underlying general ecogeographical rules, we have to take into account different phases of the life cycle, co‐variation among life history traits and ecological factors acting on each of these traits. In amphibians with complex life cycles, lack of appropriate demographical or ecological data may affect our understanding of the variety of observed body size patterns.     

The influence of local spring temperature variance on temperature sensitivity of spring phenology

The impact of climate warming on the advancement of plant spring phenology has been heavily investigated over the last decade and there exists great variability among plants in their phenological sensitivity to temperature. However, few studies have explicitly linked phenological sensitivity to local climate variance. Here, we set out to test the hypothesis that the strength of phenological sensitivity declines with increased local spring temperature variance, by synthesizing results across ground observations. We assemble ground‐based long‐term (20–50 years) spring phenology database (PEP725 database) and the corresponding climate dataset. We find a prevalent decline in the strength of phenological sensitivity with increasing local spring temperature variance at the species level from ground observations. It suggests that plants might be less likely to track climatic warming at locations with larger local spring temperature variance. This might be related to the possibility that the frost risk could be higher in a larger local spring temperature variance and plants adapt to avoid this risk by relying more on other cues (e.g., high chill requirements, photoperiod) for spring phenology, thus suppressing phenological responses to spring warming. This study illuminates that local spring temperature variance is an understudied source in the study of phenological sensitivity and highlight the necessity of incorporating this factor to improve the predictability of plant responses to anthropogenic climate change in future studies.     

Climate change and extension of the Ginkgo biloba L. growing season in Japan

To understand the effects of climate change on the growing season of plants in Japan, we conducted trend analysis of phenological phases and examined the relationship between phenology and air temperatures. We used phenological data for Ginkgo biloba L., collected from 1953 to 2000. We defined the beginning and the end of the growing season (BGS and EGS) as the dates of budding and leaf fall, respectively. Changes in the air temperature in the 45 days before the date of BGS affected annual variation in BGS. The annual variation in air temperature over the 85 days before EGS affected the date of EGS. The average annual air temperature in Japan has increased by 1.3°C over the last four decades (1961–2000), and this increase has caused changes in ginkgo phenology. In the last five decades (1953–2000), BGS has occurred approximately 4 days earlier than previously, and EGS has occurred about 8 days later. Consequently, since 1953 the length of the growing season (LGS) has been extended by 12 days. Since around 1970, LGS and air temperatures have shown increasing trends. Although many researchers have stated that phenological events are not affected by the air temperature in the fall, we found high correlations not only between budding dates and air temperatures in spring but also between leaf‐fall dates and air temperatures in autumn. If the mean annual air temperature increases by 1°C, LGS could be extended by 10 days. We also examined the spatial distribution of the rate of LGS extension, but we did not find an obvious relationship between LGS extension and latitude.     

西安4种落叶乔木物候期对气候变化的响应

以西安1979—2018年的气候资料和植物物候观测资料为基础,采用分段回归和趋势倾向率等方法,分析了毛白杨(Populus tomentosa)、杜梨(Pyrus betulifolia)、七叶树(Aesculus chinensis)和灯台树(Bothrocaryum controversum)4种落叶乔木展叶盛期和叶全变色期的生长趋势,使用偏相关分析探讨了气温、降水和日照时数与物候期的关系并通过偏最小二乘回归(Partial Least Squares, PLS)判断气候变量对物候期的综合影响。结果表明：(1)1979—2018年,4种乔木的生长季长度延长,整体表现为春季物候期提前,秋季物候期推迟;(2)展叶盛期物候指标与叶全变色期物候指标,转折均发生在1982年;转折后,物候特征变化显著,春季物候的提前速率和秋季物候的推迟速率加快,展叶盛期平均提前3.8d/10a,叶全变色期平均推迟4.7d/10a;(3)展叶盛期与春季气温表现为极显著负相关,叶变色期与秋季气温表现为显著正相关;降水对植物物候的影响不显著;春季物候与日照时数呈现极显著负相关关系,秋季物候期与日照时数呈不显著正相关...     

Shifts in the temperature‐sensitive periods for spring phenology in European beech and pedunculate oak clones across latitudes and over recent decades

Spring phenology of temperate trees has advanced worldwide in response to global warming. However, increasing temperatures may not necessarily lead to further phenological advance, especially in the warmer latitudes because of insufficient chilling and/or shorter day length. Determining the start of the forcing phase, that is, when buds are able to respond to warmer temperatures in spring, is therefore crucial to predict how phenology will change in the future. In this study, we used 4,056 leaf‐out date observations during the period 1969–2017 for clones of European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) planted in 63 sites covering a large latitudinal gradient (from Portugal ~41°N to Norway ~63°N) at the International Phenological Gardens in order to (a) evaluate how the sensitivity periods to forcing and chilling have changed with climate warming, and (b) test whether consistent patterns occur along biogeographical gradients, that is, from colder to warmer environments. Partial least squares regressions suggest that the length of the forcing period has been extended over the recent decades with climate warming in the colder latitudes but has been shortened in the warmer latitudes for both species, with a more pronounced shift for beech. We attribute the lengthening of the forcing period in the colder latitudes to earlier opportunities with temperatures that can promote bud development. In contrast, at warmer or oceanic climates, the beginning of the forcing period has been delayed, possibly due to insufficient chilling. However, in spite of a later beginning of the forcing period, spring phenology has continued to advance at these areas due to a faster satisfaction of heat requirements induced by climate warming. Overall, our results support that ongoing climate warming will have different effects on the spring phenology of forest trees across latitudes due to the interactions between chilling, forcing and photoperiod.     

气候变暖背景下青藏高原草本植物物候变化空间换时间预测

气候变暖背景下的植物物候变化广受关注, 然而常用的植物物候变化预测模型未充分考虑植物对环境的适应性, 给预测结果带来了较大的不确定性。该文基于2002-2011年青藏高原10个站点的地面物候观测资料以及年平均气温数据, 对空间换时间模型预测车前(Plantago asiatica)和蒲公英(Taraxacum mongolicum)各主要物候事件(展叶始期、开花始期和黄枯普遍期)变化的可行性及其在升温背景下的变化规律进行了分析。首先利用不同海拔高度的气温和物候事件分别与地理因子(经度、纬度和海拔)建立多元线性回归模型, 然后在此基础上剔除经度和纬度的影响, 单独考察海拔变化所引起的气温与植物物候变化, 最后以海拔高度作为桥梁来考察物候变化与温度变化的关系。结果表明, 采用各站点对应的海拔高度来模拟年平均气温空间差异的R²均大于0.89, 表明海拔梯度可以用来反映时间尺度下的年际温度变化; 车前和蒲公英各物候事件发生日期拟合值均与海拔高度变化关系显著, R²均大于0.70, 表明海拔变化是影响它们各物候事件变化的主要地理因子; 在物候事件发生日期拟合值和年平均气温拟合值的回归方程中, R²均大于0.93, 说明基于不同海拔高度模拟得到的年平均气温变化可以对时间尺度上车前和蒲公英的物候事件变化进行预测。空间换时间预测表明, 温度每升高1 ℃, 车前展叶始期和开花始期分别提前5.1和5.4 d, 而黄枯普遍期推迟4.8 d; 蒲公英展叶始期和开花始期分别提前6.5和7.8 d, 而黄枯普遍期推迟6.7 d。