Impact of climate change on plant phenology in Mediterranean ecosystems

Plant phenology is strongly controlled by climate and has consequently become one of the most reliable bioindicators of ongoing climate change. We used a dataset of more than 200 000 records for six phenological events of 29 perennial plant species monitored from 1943 to 2003 for a comprehensive assessment of plant phenological responses to climate change in the Mediterranean region. Temperature, precipitation and North Atlantic Oscillation (NAO) were studied together during a complete annual cycle before phenological events to determine their relative importance and potential seasonal carry‐over effects. Warm and dry springs under a positive phase of NAO advance flowering, leaf unfolding and fruiting dates and lengthen the growing season. Spatial variability of dates (range among sites) was also reduced during warm and dry years, especially for spring events. Climate during previous weeks to phenophases occurrence had the greatest impact on plants, although all events were also affected by climate conditions several months before. Immediate along with delayed climate effects suggest dual triggers in plant phenology. Climatic models accounted for more than 80% of variability in flowering and leaf unfolding dates, and in length of the growing season, but for lower proportions in fruiting and leaf falling. Most part of year‐to‐year changes in dates was accounted for temperature, while precipitation and NAO accounted for <10% of dates' variability. In the case of flowering, insect‐pollinated species were better modelled by climate than wind‐pollinated species. Differences in temporal responses of plant phenology to recent climate change are due to differences in the sensitivity to climate among events and species. Spring events are changing more than autumn events as they are more sensitive to climate and are also undergoing the greatest alterations of climate relative to other seasons. In conclusion, climate change has shifted plant phenology in the Mediterranean region.     

Responses of leaf unfolding and flowering to climate change in 12 tropical evergreen broadleaf tree species in Jianfengling,Hainan Island

为了探讨我国热带地区植物物候与气候变化的关系, 利用海南岛尖峰岭热带树木园12种热带常绿阔叶乔木植物2003-2011年物候观测资料结合同期月平均气温和降水数据, 运用积分回归分析方法, 筛选出影响海南岛12种乔木(8种本地种、4种引入种)展叶始期与开花始期的气象因素以及不同气象因素月值变化(月平均气温和月降水量)综合作用对这些树种物候期的动态影响, 最终建立积分回归-物候预测模型, 对气候变化背景下我国热带地区植物物候变化趋势进行了预测。结果表明: 海南岛12种热带常绿阔叶乔木展叶始期与开花始期均对气候变化做出较明显的响应, 几乎所有的树种展叶始期与开花始期的发生都受到气温和降水的共同影响。多数树种展叶始期受展叶前冬季及春季气温影响显著, 且在临近展叶始期的月份, 气温的影响更显著。上一年秋季月降水量对各树种开花始期的影响比其他时段显著, 这验证了降水的滞后性假说。本地种展叶始期对气候变化的响应比其开花始期对气候变化的响应更敏感, 引入种则相反。各树种展叶和开花在受气温和降水综合影响最明显的月份(假设其余11个月份月平均气温和月降水量不变), 月平均气温升高0.1 ℃、月降水量增加10 mm可使展叶始期和开花始期提前或推迟1-3天。积分回归分析方法为解释海南岛热带常绿阔叶乔木物候与气温和降水的动态关系提供了有效的途径, 基于气温和降水与物候资料建立的积分回归-物候预测模型具有对气温和降水变化影响下物候响应的解释率和预测精度高(R²≥ 0.943)的优点, 对于预测气候变化影响下的植物物候变化趋势有一定的适用性。     

海南岛尖峰岭12种热带常绿阔叶乔木展叶期与开花期对气候变化的响应

为了探讨我国热带地区植物物候与气候变化的关系, 利用海南岛尖峰岭热带树木园12种热带常绿阔叶乔木植物2003-2011年物候观测资料结合同期月平均气温和降水数据, 运用积分回归分析方法, 筛选出影响海南岛12种乔木(8种本地种、4种引入种)展叶始期与开花始期的气象因素以及不同气象因素月值变化(月平均气温和月降水量)综合作用对这些树种物候期的动态影响, 最终建立积分回归-物候预测模型, 对气候变化背景下我国热带地区植物物候变化趋势进行了预测。结果表明: 海南岛12种热带常绿阔叶乔木展叶始期与开花始期均对气候变化做出较明显的响应, 几乎所有的树种展叶始期与开花始期的发生都受到气温和降水的共同影响。多数树种展叶始期受展叶前冬季及春季气温影响显著, 且在临近展叶始期的月份, 气温的影响更显著。上一年秋季月降水量对各树种开花始期的影响比其他时段显著, 这验证了降水的滞后性假说。本地种展叶始期对气候变化的响应比其开花始期对气候变化的响应更敏感, 引入种则相反。各树种展叶和开花在受气温和降水综合影响最明显的月份(假设其余11个月份月平均气温和月降水量不变), 月平均气温升高0.1 ℃、月降水量增加10 mm可使展叶始期和开花始期提前或推迟1-3天。积分回归分析方法为解释海南岛热带常绿阔叶乔木物候与气温和降水的动态关系提供了有效的途径, 基于气温和降水与物候资料建立的积分回归-物候预测模型具有对气温和降水变化影响下物候响应的解释率和预测精度高(R²≥ 0.943)的优点, 对于预测气候变化影响下的植物物候变化趋势有一定的适用性。     

Long-term temporal changes in central European tree phenology (1946−2010) confirm the recent extension of growing seasons

One of the ways to assess the impacts of climate change on plants is analysing their long-term phenological data. We studied phenological records of 18 common tree species and their 8 phenological phases, spanning 65 years (1946?2010) and covering the area of the Czech Republic. For each species and phenophase, we assessed the changes in its annual means (for detecting shifts in the timing of the event) and standard deviations (for detecting changes in duration of the phenophases). The prevailing pattern across tree species was that since around the year 1976, there has been a consistent advancement of the onset of spring phenophases (leaf unfolding and flowering) and subsequent acceleration of fruit ripening, and a delay of autumn phenophases (leaf colouring and leaf falling). The most considerable shifts in the timing of spring phenophases were displayed by early-successional short-lived tree species. The most pronounced temporal shifts were found for the beginning of seed ripening in conifers with an advancement in this phenophase of up to 2.2 days year^?1 in Scots Pine (Pinus sylvestris). With regards to the change in duration of the phenophases, no consistent patterns were revealed. The growing season has extended on average by 23.8 days during the last 35 years. The most considerable prolongation was found in Pedunculate Oak (Quercus robur): 31.6 days (1976?2010). Extended growing season lengths do have the potential to increase growth and seed productivity, but unequal shifts among species might alter competitive relationships within ecosystems.     

Spatial and temporal variation of phenological growing season and climate change impacts in temperate eastern China

Using phenological and normalized difference vegetation index (NDVI) data from 1982 to 1993 at seven sample stations in temperate eastern China, we calculated the cumulative frequency of leaf unfolding and leaf coloration dates for deciduous species every 5 days throughout the study period. Then, we determined the growing season beginning and end dates by computing times when 50% of the species had undergone leaf unfolding and leaf coloration for each station year. Next, we used these beginning and end dates of the growing season as time markers to determine corresponding threshold NDVI values on NDVI curves for the pixels overlaying phenological stations. Based on a cluster analysis, we determined extrapolation areas for each phenological station in every year, and then implemented the spatial extrapolation of growing season parameters from the seven sample stations to all possible meteorological stations in the study area. Results show that spatial patterns of growing season beginning and end dates correlate significantly with spatial patterns of mean air temperatures in spring and autumn, respectively. Contrasting with results from similar studies in Europe and North America, our study suggests that there is a significant delay in leaf coloration dates, along with a less pronounced advance of leaf unfolding dates in different latitudinal zones and the whole area from 1982 to 1993. The growing season has been extended by 1.4–3.6 days per year in the northern zones and by 1.4 days per year across the entire study area on average. The apparent delay in growing season end dates is associated with regional cooling from late spring to summer, while the insignificant advancement in beginning dates corresponds to inconsistent temperature trend changes from late winter to spring. On an interannual basis, growing season beginning and end dates correlate negatively with mean air temperatures from February to April and from May to June, respectively.     

近30年北京自然历的主要物候期、物候季节变化及归因

根据中国物候观测网资料并结合气象观测数据, 重新编制了北京颐和园地区1981-2010年的自然历。通过与原自然历比较, 揭示了北京物候季节变化特征, 分析了1963年以来物候季节变化的可能原因。研究发现: 与原自然历相比, 1981-2010年北京的春、夏季开始时间分别提前了2天和5天, 秋、冬季开始时间分别推迟了1天和4天; 夏、秋季长度分别延长了6天和3天, 春、冬季长度则分别缩短了3天和6天; 各个物候期的平均日期、最早日期、最晚日期在春、夏季以提前为主, 在秋、冬季以推迟为主; 且春、秋、冬季节内部分物候期次序也出现了不同程度的变化。春、夏、冬季开始日期前的气温变化和秋季开始日期前的日照时数变化可能是北京颐和园地区物候季节变化的主要原因; 不同物种、不同物候期对气温变化的响应程度不同, 导致了物候季节内各种物候现象出现的先后顺序发生变化。     

中国东部温带植被生长季节的空间外推估计

利用地面植物物候和遥感归一化差值植被指数（NDVI）数据,以及一种物候-遥感外推方法,实现植被生长季节从少数站点到较多站点的空间外推。结果表明：（1）在1982～1993年期间,中国东部温带地区植被生长季节多年平均起讫日期的空间格局与春季和秋季平均气温的空间格局相关显著;（2）在不同纬度带和整个研究区域,植被生长季节结束日期呈显著推迟的趋势,而开始日期则呈不显著提前的趋势,这与欧洲和北美地区植被生长季节开始日期显著提前而结束日期不显著推迟的变化趋势完全不同;（3）北部纬度带的植被生长季节平均每年延长1．4～3．6d,全区的植被生长季节平均每年延长1．4d,与同期北半球和欧亚大陆植被生长季节延长的趋势数值相近;（4）植被生长季节结束日期的显著推迟与晚春至夏季的区域性降温有关,而植被生长季节开始日期的不显著提前则与晚冬至春季气温趋势的不稳定变化有关;（5）在年际变化方面,植被生长季节开始和结束日期分别与2～4月份平均气温和5～6月份平均气温呈负相关关系。     

气候波动对西安39种木本植物展叶始期及其积温需求的影响

过去几十年来暖春等异常气候事件发生的频次和强度显著增加, 使植物春季物候期发生了明显变化。但异常气候事件对植物春季物候积温需求的影响仍不清楚, 限制了对未来物候变化预测精度的提升。该研究利用西安植物园1963-2018年39种木本植物的展叶始期和相应气象数据, 首先根据3-4月平均气温划分了偏冷年、正常年和偏暖年, 对比了冷暖年相对于正常年的展叶始期变化。其次, 利用3种积温算法计算了各植物逐年的展叶始期积温需求, 比较了积温需求在冷暖年和正常年的差异。最后, 评估了传统积温模型在模拟偏冷或偏暖年展叶始期时的误差。结果表明, 所有植物的展叶始期在偏暖年比正常年平均早8.6天, 而在偏冷年平均晚8.2天。在偏暖年, 大多数物种展叶始期的积温需求(以5 ℃为阈值, 平均257.5度日)显著高于正常年(平均195.1度日); 在偏冷年的积温需求(平均168.0度日)低于正常年, 但在统计上差异不显著。就不同类群而言, 古老类群相对于年轻类群在偏冷年的推迟天数更多, 积温需求变化较小, 但在偏暖年无显著差异。不同生活型间物候与积温需求变化也无显著差异。造成偏暖年积温需求增加的可能原因是偏暖年冬季气温较高, 导致植物受到的冷激程度减轻, 从而抑制了后续的展叶。在正常年, 积温模型模拟木本植物展叶始期的平均误差仅为0.4-1.9天。在偏暖年和偏冷年, 模拟值分别比观测值平均早4.1天和晚3.0天。因此在预测未来物候变化时, 需要考虑气候波动条件下的积温需求变化。     

北京地区木本春季物候特征与生物学特性的关系

植物物候是植物生活史中的重要性状,也是指示气候与自然环境变化的重要指标,现已成为全球变化领域的研究热点之一。传统物候研究多假设物候由气候因素决定,如气温、降水、光照等,并主要从植物物候的年际变化角度探讨了气候因素对物候特征的影响。然而,不同物种的物候存在较大差异表明植物物候还与自身生物学特性（如系统发育和功能性状）有关,但植物生物学特性如何影响植物物候仍缺乏深入研究。基于北京地区44种木本植物1965-2018年的展叶始期和开花始期观测资料,以展叶始期和开花始期的3类物候特征（平均物候期、物候对温度的响应敏感度和物候期的积温需求）为例,探究植物物候特征与系统发育和功能性状的关系。首先,利用系统发育信号Blomberg’s K和进化模型检验植物物候特征是否具有系统发育保守性,并通过系统发育信号表征曲线直观表达植物物候特征的进化模式;之后,利用广义估计方程分析植物生活型、传粉型与物候特征的关系,以揭示不同植物的资源利用方式及生存策略的差异。研究发现：（1）除展叶始期的温度敏感度外,其余物候特征的进化均受随机遗传漂变和自然选择力的共同作用,可推断物候特征具有系统发育保守性,即亲缘关系越近的物种物候特征越相似。（2）开花始期的系统发育信号强度比展叶始期更大,表明繁殖物候的系统发育可能比生长物候更保守。（3）植物展叶始期及其积温需求与生活型密切相关。灌木比乔木的展叶时间早、积温需求少。植物开花始期与传粉型相关,风媒植物开花显著早于虫媒植物。研究成果有助于深入理解物候变化的生物学机制,对于丰富物候学的理论研究有重要意义,同时对植物保护也具有重要的指导价值。     

Spatial and temporal variability of the phenological seasons in Germany from 1951 to 1996

Various indications for shifts in plant and animal phenology resulting from climate change have been observed in Europe. This analysis of phenological seasons in Germany of more than four decades (1951–96) has several major advantages: (i) a wide and dense geographical coverage of data from the phenological network of the German Weather Service, (ii) the 16 phenophases analysed cover the whole annual cycle and, moreover, give a direct estimate of the length of the growing season for four deciduous tree species. After intensive data quality checks, two different methods – linear trend analyses and comparison of averages of subintervals – were applied in order to determine shifts in phenological seasons in the last 46 years. Results from both methods were similar and reveal a strong seasonal variation. There are clear advances in the key indicators of earliest and early spring (?0.18 to ?0.23 d y^?1) and notable advances in the succeeding spring phenophases such as leaf unfolding of deciduous trees (?0.16 to ?0.08 d y^?1). However, phenological changes are less strong during autumn (delayed by + 0.03 to + 0.10 d y^?1 on average). In general, the growing season has been lengthened by up to ?0.2 d y^?1 (mean linear trends) and the mean 1974–96 growing season was up to 5 days longer than in the 1951–73 period. The spatial variability of trends was analysed by statistical means and shown in maps, but these did not reveal any substantial regional differences. Although there is a high spatial variability, trends of phenological phases at single locations are mirrored by subsequent phases, but they are not necessarily identical. Results for changes in the biosphere with such a high resolution with respect to time and space can rarely be obtained by other methods such as analyses of satellite data.     

Effect of open-field experimental warming on the leaf phenology of oriental oak (Quercus variabilis) seedlings

Aims An open-field warming experiment enables us to test the effects of projected temperature increase on change in plant phenology with fewer confounding factors and to study phenological response to temperature ranges beyond natural variability. This study aims to (i) examine the effect of temperature increase on leaf unfolding and senescence of oriental oak (Quercus variabilis Blume) under experimental warming and (ii) measure temperature-related parameters used in estimating phenological response to temperature elevation.Methods Using an open-field warming system with infrared heaters, we increased the air temperature by ~3°C in the warmed plots compared with that of the control plots consistently for 2 years. Leaf unfolding and senescence dates of Q. variabilis seedlings were recorded and temperature-related phenological parameters were analysed.Important findings The timing of leaf unfolding was advanced by 3–8 days (1.1–3.0 days/°C) and the date of leaf senescence was delayed by 14–19 days (5.0–7.3 days/°C) under elevated air temperatures. However, the cumulative degree days (CDD) of leaf unfolding were not significantly changed by experimental warming, which suggest the applicability of a constant CDD value to estimate the change in spring leaf phenology under 3°C warming. Consistent ranges of advancement and temperature sensitivity in spring phenology and delayed autumn phenology and proposed temperature parameters from this study might be applied to predict future phenological change.     

Trends in phenological phases in Europe between 1951 and 1996

Increases in air temperature due to the anthropogenic greenhouse effect can be detected easily in the phenological data of Europe within the last four decades because spring phenological events are particularly sensitive to temperature. Our new analysis of observational data from the International Phenological Gardens in Europe for the 1959–1996 period revealed that spring events, such as leaf unfolding, have advanced on average by 6.3 days (–0.21 day/year), whereas autumn events, such as leaf colouring, have been delayed on average by 4.5 days (+0.15 day/year). Thus, the average annual growing season has lengthened on average by 10.8 days since the early 1960s. For autumn events, differences between mean trends of species could not be detected, but for spring events there were differences between species, with the higher trends for leaf unfolding and flowering of shrubs indicating that changes in events occurring in the early spring are more distinct. These observed trends in plant phenological events in the International Phenological Gardens and results of other phenological studies in Europe, summarised in this study, are consistent with AVHRR satellite measurements of the normalized difference vegetation index from 1981 to 1991 and with an analysis of long-term measurements of the annual cycle of CO₂ concentration in Hawaii and Alaska, also indicating a global lengthening of the growing season. Received: 21 October 1999 / Accepted: 2 March 2000     

Determining the growing season of land vegetation on the basis of plant phenology and satellite data in Northern China

The objectives of this study are to explore the relationships between plant phenology and satellite-sensor-derived measures of greenness, and to advance a new procedure for determining the growing season of land vegetation at the regional scale. Three phenological stations were selected as sample sites to represent different climatic zones and vegetation types in northern China. The mixed data set consists of occurrence dates of all observed phenophases for 50–70 kinds of trees and shrubs from 1983 to 1988. Using these data, we calculated the cumulative frequency of phenophases in every 5-day period (pentad) throughout each year, and also drew the cumulative frequency distribution curve for all station-years, in order to reveal the typical seasonal characteristics of these plant communities. The growing season was set as the time interval between 5% and 95% of the phenological cumulative frequency. Average lengths of the growing season varied between 188 days in the northern, to 259 days in the southern part of the research region. The beginning and end dates of the surface growing season were then applied each year as time thresholds, to determine the corresponding 10-day peak greenness values from normalized difference vegetation index curves for 8-km² pixels overlying the phenological stations. Our results show that, at the beginning of the growing season, the largest average greenness value occurs in the southern part, then in the northern, and finally the middle part of the research region. In contrast, at the end of the growing season, the largest average greenness value is measured in the northern part, next in the middle and lastly the southern part of the research region. In future studies, these derived NDVI thresholds can be applied to determine the growing season of similar plant communities at other sites, which lack surface phenological data. Received: 29 November 1999 / Revised: 14 March 2000 / Accepted: 15 March 2000     

Possible impacts of climate change on natural vegetation in Saxony (Germany)

Recent climate changes have had distinct impacts on plant development in many parts of the world. Higher air temperatures, mainly since the end of the 1980s, have led to advanced timing of phenological phases and consequently to an extension of the general growing season. For this reason it is interesting to know how plants will respond to future climate change. In this study simple phenological models have been developed to estimate the impact of climate change on the natural vegetation in Saxony. The estimations are based on a regional climate scenario for the state of Saxony. The results indicate that changes in the timing of phenophases could continue in the future. Due to distinct temperature changes in winter and in summer, mainly the spring and summer phases will be advanced. Spring phenophases, such as leafing or flowering, show the strongest trends. Depending on the species, the average timing of these phenophases could be advanced by 3–27 days by 2050. Phenophases in autumn show relatively small changes. Thus, the annual growth period of individual trees will be further extended, mainly because of the shift of spring phases. Frequent droughts in summer and in autumn can compensate for the earlier leafing of trees, because in this case leaf colouring and leaf fall would start some weeks earlier. In such cases, the growing period would not be really extended, but shifted to the beginning of the year.     

Changed plant and animal life cycles from 1952 to 2000 in the Mediterranean region

The available data on climate over the past century indicate that the earth is warming. Important biological effects, including changes of plant and animal life cycle events, have already been reported. However, evidence of such effects is still scarce and has been mostly limited to northern latitudes. Here we provide the first long‐term (1952–2000) evidence of altered life cycles for some of the most abundant Mediterranean plants and birds, and one butterfly species. Average annual temperatures in the study area (Cardedeu, NE Spain) have increased by 1.4 °C over the observation period while precipitation remained unchanged. A conservative linear treatment of the data shows that leaves unfold on average 16 days earlier, leaves fall on average 13 days later, and plants flower on average 6 days earlier than in 1952. Fruiting occurs on average 9 days earlier than in 1974. Butterflies appear 11 days earlier, but spring migratory birds arrive 15 days later than in 1952. The stronger changes both in temperature and in phenophases timing occurred in the last 25 years. There are no significant relationships among changes in phenophases and the average date for each phenophase and species. There are not either significant differences among species with different Raunkiaer life‐forms or different origin (native, exotic or agricultural). However, there is a wide range of phenological alterations among the different species, which may alter their competitive ability, and thus, their ecology and conservation, and the structure and functioning of ecosystems. Moreover, the lengthening of plant growing season in this and other northern hemisphere regions may contribute to a global increase in biospheric activity.     

An analysis of relationships among plant community phenology and seasonal metrics of Normalized Difference Vegetation Index in the northern part of the monsoon region of China

This study focuses on relationships between the phenological growing season of plant communities and the seasonal metrics of Normalized Difference Vegetation Index (NDVI) at sample stations and pixels overlying them, and explores the procedure for determining the growing season of terrestrial vegetation at the regional scale, using threshold NDVI values obtained by surface–satellite analysis at individual stations/pixels. The cumulative frequency of phenophases has been calculated for each plant community and each year in order to determine the growing season at the three sample stations from 1982 to 1993. The precise thresholds were arbitrarily set as the dates on which the phenological cumulative frequency reached 5% and 10% (for the beginning) and 90% and 95% (for the end). The beginning and end dates of the growing season were then applied each year as time thresholds, to determine the corresponding 10-day peak greenness values from NDVI curves for 8-km² pixels overlying the phenological stations. According to a trend analysis, a lengthening of the growing seasons and an increase of the integrated growing season NDVI have been detected in the central part of the research region. The correlation between the beginning dates of the growing season and the corresponding threshold NDVI values is very low, which indicates that the satellite-sensor-derived greenness is independent of the beginning time of the growing season of local plant communities. Other than in spring, the correlation between the end dates of the growing season and the corresponding threshold NDVI values is highly significant. The negative correlation shows that the earlier the growing season terminates, the larger the corresponding threshold NDVI value, and vice versa. In order to estimate the beginning and end dates of the growing season using the threshold NDVI values at sites without phenological data from 1982 to 1993, we calculated the spatial correlation coefficients between NDVI time-series at each sample station and other contiguous sites year by year. The results provide the spatial extrapolation area of the growing season for each sample station. Thus, we can use the threshold NDVI value obtained at one sample station/pixel for a year to determine the growing season at the extrapolation sites with a similar vegetation type for the same year. Received: 25 October 2000 / Revised: 19 June 2001 / Accepted: 19 June 2001     

Regional unified model‐based leaf unfolding prediction from 1960 to 2009 across northern China

Using first leaf unfolding data of Salix matsudana, Populus simonii, Ulmus pumila, and Prunus armeniaca, and daily mean temperature data during the 1981–2005 period at 136 stations in northern China, we fitted unified forcing and chilling phenology models and selected optimum models for each species at each station. Then, we examined performances of each optimum local species‐specific model in predicting leaf unfolding dates at all external stations within the corresponding climate region and selected 16 local species‐specific models with maximum effective predictions as the regional unified models in different climate regions. Furthermore, we validated the regional unified models using leaf unfolding and daily mean temperature data beyond the time period of model fitting. Finally, we substituted gridded daily mean temperature data into the regional unified models, and reconstructed spatial patterns of leaf unfolding dates of the four tree species across northern China during 1960–2009. At local scales, the unified forcing model shows higher simulation efficiency at 83% of data sets, whereas the unified chilling model indicates higher simulation efficiency at 17% of data sets. Thus, winter temperature increase so far has not yet significantly influenced dormancy and consequent leaf development of deciduous trees in most parts of northern China. Spatial and temporal validation confirmed capability and reliability of regional unified species‐specific models in predicting leaf unfolding dates in northern China. Reconstructed leaf unfolding dates of the four tree species show significant advancements by 1.4–1.6 days per decade during 1960–2009 across northern China, which are stronger for the earlier than the later leaf unfolding species. Our findings suggest that the principal characteristics of plant phenology and phenological responses to climate change at regional scales can be captured by phenological and climatic data sets at a few representative locations.     

Demography of an endangered endemic rupicolous cactus

The snow cover extent is an important factor for the structure and composition of arctic and alpine tundra communities. Over the last few decades, snowmelt in many arctic and alpine regions has advanced, causing the growing season to start earlier and last longer. In a field experiment in subarctic tundra in Interior Alaska, I manipulated the timing of snowmelt and measured the response in mortality, phenology, growth, and reproduction of the eight dominant plant species. I then tested whether the phenological development of these species was controlled by snowmelt date or by temperature (in particular growing degree days, GDD). In order to expand our understanding of plant sensitivity to snowmelt timing, I explored whether the response patterns can be generalized with regard to the temporal niche of each species. Differences in the phenology between treatments were only found for the first stages of the phenological development (=phenophases). The earlier the temporal niche (i.e., the sooner after snowmelt a species develops) the more its phenology was sensitive to snowmelt. Later phenophases were mostly controlled by GDD, especially in late-developing species. In no species did an earlier snowmelt and a longer growing season directly enhance plant fitness or fecundity, in spite of the changes in the timing of plant development. In conclusion, the temporal niche of a species’ phenological development could be a predictor of its response to snowmelt timing. However, only the first phenophases were susceptible to changes in snowmelt, and no short-term effects on plant fitness were found.     

Phytophenological trends in Switzerland

Nation-wide phenological observations have been made in Switzerland since 1951. In addition to these observation programmes, there are two very long phenological series in Switzerland: leaf bud burst of horse-chestnut trees has been observed in Geneva since 1808 and full flowering of cherry trees in Liestal since 1894. In addition to the presentation of these two long phenological series, trends for 896 phenological time series have been calculated with national data from 1951 to 1998. The earlier bud burst of horse-chestnut trees in Geneva can be attributed mainly to the city effect (warmth island). This phenomenon was not observed with the cherry tree flowering in Liestal. A clear trend towards earlier appearance dates in spring and a weak tendency towards later appearance dates in autumn could be shown with data from the national observation network. It must be noted that different phenophases and plant species react differently to various environmental influences. Received: 25 October 2000 / Revised: 9 May 2001 / Accepted: 4 June 2001