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1.
    
AimsSnow cover occupies large percentage of land surface in Tibetan Plateau. Snow cover duration (SCD) during non-growing seasons plays a critical role in regulating alpine vegetation’s phenology by affecting the energy budgets of land surface and soil moisture conditions. Different period’s snow cover during non-growing season may have distinct effect on the vegetation’s phenology. Start of season (SOS) has been observed advanced under the ongoing climate change in the plateau, but it still remains unclear how the SCD alters the SOS. This study attempts to answer the following questions: (i) What is the pattern of spatial and temporal variations for SCD and grassland SOS? (ii) Which period’s SCD plays a critical role in grassland’s SOS?  相似文献   

2.
    
Abstract Australian alpine ecosystems are expected to diminish in extent as global warming intensifies. Alpine vegetation patterns are influenced by the duration of snow cover including the presence of snowdrifts in summer, but there is little quantitative information on landscape‐scale relationships between vegetation patterns and the frequency of occurrence of persistent summer snowdrifts in the Australian alps. We mapped annual changes in summer snowdrifts in the Kosciuszko alpine region, Australia, from Landsat TM images and modelled the frequency of occurrence of persistent summer snowdrifts from long‐term records (1954–2003) of winter snow depth. We then compared vegetation composition and structure among four classes that differed in the frequency of occurrence of persistent summer snowdrifts. We found a curvilinear relationship between annual winter snow depth and the area occupied by persistent snowdrifts in the following summer (r2 = 0.9756). Only 21 ha (0.42% of study area) was predicted to have supported summer snowdrifts in 80% of the past 50 years, while 440 ha supported persistent summer snow in 10% of years. Mean cover and species richness of vascular plants declined significantly, and species composition varied significantly, as the frequency of summer snow persistence increased. Cushion plants and rushes were most abundant where summer snowdrifts occurred most frequently, and shrubs, grasses and sedges were most abundant in areas that did not support snowdrifts in summer. The results demonstrate strong regional relationships between vegetation composition and structure and the frequency of occurrence of persistent summer snowdrifts. Reductions in winter snow depth due to global warming are expected to lead to substantial reductions in the extent of persistent summer snowdrifts. As a consequence, shrubs, grasses and sedges are predicted to expand at the expense of cushion plants and rushes, reducing landscape vegetation diversity. Fortunately, few vascular plant species (e.g. Ranunculus niphophilus) appear to be totally restricted to areas where summer snow occurs most frequently. The results from this study highlight potential indicator species that could be monitored to assess the effects of global warming on Australian alpine environments.  相似文献   

3.
    
Satellite-based evaluations of change in vegetation phenology have been explored extensively but land cover-specific climate factors driving these anomalous changes are not fully understood in northern Sub-Saharan Africa. In this study, we identified the climatic factors controlling the start of the season (SOS) extracted from GIMMS NDVI from 1988 to 2013 with onset of rainy season (ORS), annual mean temperature (Temp) and precipitation (PP) through the stepwise regression analysis. The results showed that the SOS shifted towards a late onset in a northward direction with distinct earlier and later trends in grassland and cropland, respectively. The stepwise regression has successfully built a model between SOS and its drivers in 46.0% of the total pixels, where its primary factor differed regionally across land covers. The ORS explained the local anomalous SOS change primarily at 44.7% of the pixels where the model was built. Although the ORS was the primary dominant factor in savannah and cropland, the Temp and PP were leading in grassland and shrubland, respectively, and all factors contributed evenly in evergreen forest. The difference of land cover-specific primary factor implicates complex process in dependency of local vegetation phenology on physiological traits and climate regime across land cover in Sub-Saharan Africa.  相似文献   

4.
Changes in vegetative growing seasons are dominant indicators of the dynamic response of ecosystems to climate change. Therefore, knowledge of growing seasons over the past decades is essential to predict ecosystem changes. In this study, the long‐term changes in the growing seasons of temperate vegetation over the Northern Hemisphere were examined by analyzing satellite‐measured normalized difference vegetation index and reanalysis temperature during 1982–2008. Results showed that the length of the growing season (LOS) increased over the analysis period; however, the role of changes at the start of the growing season (SOS) and at the end of the growing season (EOS) differed depending on the time period. On a hemispheric scale, SOS advanced by 5.2 days in the early period (1982–1999) but advanced by only 0.2 days in the later period (2000–2008). EOS was delayed by 4.3 days in the early period, and it was further delayed by another 2.3 days in the later period. The difference between SOS and EOS in the later period was due to less warming during the preseason (January–April) before SOS compared with the magnitude of warming in the preseason (June–September) before EOS. At a regional scale, delayed EOS in later periods was shown. In North America, EOS was delayed by 8.1 days in the early period and delayed by another 1.3 days in the later period. In Europe, the delayed EOS by 8.2 days was more significant than the advanced SOS by 3.2 days in the later period. However, in East Asia, the overall increase in LOS during the early period was weakened in the later period. Admitting regional heterogeneity, changes in hemispheric features suggest that the longer‐lasting vegetation growth in recent decades can be attributed to extended leaf senescence in autumn rather than earlier spring leaf‐out.  相似文献   

5.
Sphagnum mosses form a major component of northern peatlands, which are expected to experience substantially higher increases in temperature and winter precipitation than the global average. Sphagnum may play an important role in the responses of the global carbon cycle to climate change. We investigated the responses of summer length growth, carpet structure and production in Sphagnum fuscum to experimentally induced changes in climate in a sub‐arctic bog. Thereto, we used open‐top chambers (OTCs) to create six climate scenarios including changes in summer temperatures, and changes in winter snow cover and spring temperatures. In winter, the OTCs doubled the snow thickness, resulting in 0.5–2.8°C higher average air temperatures. Spring air temperatures in OTCs increased by 1.0°C. Summer warming had a maximum effect of 0.9°C, while vapor pressure deficit was not affected. The climate manipulations had strong effects on S. fuscum. Summer warming enhanced the length increment by 42–62%, whereas bulk density decreased. This resulted in a trend (P<0.10) of enhanced biomass production. Winter snow addition enhanced dry matter production by 33%, despite the fact that the length growth and bulk density did not change significantly. The addition of spring warming to snow addition alone did not significantly enhance this effect, but we may have missed part of the early spring growth. There were no interactions between the manipulations in summer and those in winter/spring, indicating that the effects were additive. Summer warming may in the long term negatively affect productivity through the adverse effects of changes in Sphagnum structure on moisture holding and transporting capacity. Moreover, the strong length growth enhancement may affect interactions with other mosses and vascular plants. Because winter snow addition enhanced the production of S. fuscum without affecting its structure, it may increase the carbon balance of northern peatlands.  相似文献   

6.
7.
    
Shifts in plant phenology regulate ecosystem structure and function, which feeds back to the climate system. However, drivers for the peak of growing season (POS) in seasonal dynamics of terrestrial ecosystems remain unclear. Here, spatial–temporal patterns of POS dynamics were analyzed by solar-induced chlorophyll fluorescence (SIF) and vegetation index in the Northern Hemisphere over the past two decades from 2001 to 2020. Overall, a slow advanced POS was observed in the Northern Hemisphere, while a delayed POS distributed mainly in northeastern North America. Trends of POS were driven by the start of growing season (SOS) rather than pre-POS climate both at hemisphere and biome scale. The effect of SOS on the trends in POS was the strongest in shrublands while the weakest in evergreen broad-leaved forest. These findings highlight the crucial role of biological rhythms rather than climatic factors in exploring seasonal carbon dynamics and global carbon balance.  相似文献   

8.
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.  相似文献   

9.
内蒙古主要草原类型植物物候对气候波动的响应   总被引:2,自引:0,他引:2       下载免费PDF全文
苗百岭  梁存柱  韩芳  梁茂伟  张自国 《生态学报》2016,36(23):7689-7701
物候是气候变化的指示者,由于不同地区植被类型不同,导致其对气候波动的响应方式不同。利用2004—2013年内蒙古草原区生态监测站群落优势种物候观测资料和同时段的气象资料,分析了不同草原类型区优势种物候期变化及其与气候因子间的相互关系,结果表明:(1)2004—2013年内蒙古草原区各时段气候波动趋势均不显著,返青前以气温降低、降水增加趋势为主;黄枯前草甸草原、典型草原以气温降低、降水增加趋势为主,荒漠草原变化趋势相反。(2)2004—2013年典型草原植物返青期平均提前4.01 d,黄枯推后10.35 d,生长季延长14.36 d;草甸草原返青期提前2.04 d,黄枯期推后12.68 d,生长季延长14.72 d;荒漠草原物候变化趋势最小,返青期平均提前了1.32 d,黄枯期平均推后了9.58 d,生长季延长了10.90 d。(3)内蒙古草原区植物返青期主要受气温波动的影响,草甸草原返青期与前3个月平均气温的负相关最为显著,气温每升高1℃,返青期约提前1.123 d;典型草原、荒漠草原返青期与前2个月平均气温的负相关最为显著气,气温每升高1℃,返青期约提前1.137 d和1.743 d。(4)典型草原区植物黄枯期受前1—2月平均气温和累积降水的共同影响,与夏季平均气温和当月降水量的相关最为显著,夏季气温每升高1℃,黄枯期约提前2.250 d,当月降水每增加1 mm,黄枯期约推后0.119 d。草甸草原、荒漠草原植物黄枯期与各时段降水、气温的相关均不显著,影响黄枯机制比较复杂。  相似文献   

10.
Onset of spring starting earlier across the Northern Hemisphere   总被引:16,自引:0,他引:16  
Recent warming of Northern Hemisphere (NH) land is well documented and typically greater in winter/spring than other seasons. Physical environment responses to warming have been reported, but not details of large‐area temperate growing season impacts, or consequences for ecosystems and agriculture. To date, hemispheric‐scale measurements of biospheric changes have been confined to remote sensing. However, these studies did not provide detailed data needed for many investigations. Here, we show that a suite of modeled and derived measures (produced from daily maximum–minimum temperatures) linking plant development (phenology) with its basic climatic drivers provide a reliable and spatially extensive method for monitoring general impacts of global warming on the start of the growing season. Results are consistent with prior smaller area studies, confirming a nearly universal quicker onset of early spring warmth (spring indices (SI) first leaf date, ?1.2 days decade?1), late spring warmth (SI first bloom date, ?1.0 days decade?1; last spring day below 5°C, ?1.4 days decade?1), and last spring freeze date (?1.5 days decade?1) across most temperate NH land regions over the 1955–2002 period. However, dynamics differ among major continental areas with North American first leaf and last freeze date changes displaying a complex spatial relationship. Europe presents a spatial pattern of change, with western continental areas showing last freeze dates getting earlier faster, some central areas having last freeze and first leaf dates progressing at about the same pace, while in portions of Northern and Eastern Europe first leaf dates are getting earlier faster than last freeze dates. Across East Asia last freeze dates are getting earlier faster than first leaf dates.  相似文献   

11.
    
Climatic warming has lengthened the photosynthetically active season in recent decades, thus affecting the functioning and biogeochemistry of ecosystems, the global carbon cycle and climate. Temperature response of carbon uptake phenology varies spatially and temporally, even within species, and daily total intensity of radiation may play a role. We empirically modelled the thresholds of temperature and radiation under which daily carbon uptake is constrained in the temperate and cold regions of the Northern Hemisphere, which include temperate forests, boreal forests, alpine and tundra biomes. The two-dimensionality of the temperature-radiation constraint was reduced to one single variable, θ, which represents the angle in a polar coordinate system for the temperature-radiation observations during the start and end of the growing season. We found that radiation will constrain the trend towards longer growing seasons with future warming but differently during the start and end of season and depending on the biome type and region. We revealed that radiation is a major factor limiting photosynthetic activity that constrains the phenology response to temperature during the end-of-season. In contrast, the start of the carbon uptake is overall highly sensitive to temperature but not constrained by radiation at the hemispheric scale. This study thus revealed that while at the end-of-season the phenology response to warming is constrained at the hemispheric scale, at the start-of-season the advance of spring onset may continue, even if it is at a slower pace.  相似文献   

12.
    
  • 1 We reviewed worldwide spatial patterns in the food habits of the brown bear Ursus arctos in relation to geographical (latitude, longitude, altitude) and environmental (temperature, snow cover depth and duration, precipitation, primary productivity) variables.
  • 2 We collected data from 28 studies on brown bear diet based on faecal analysis, covering the entire geographical range of this widely distributed large carnivore. We analysed separately four data sets based on different methods of diet assessment.
  • 3 Temperature and snow conditions were the most important factors determining the composition of brown bear diet. Populations in locations with deeper snow cover, lower temperatures and lower productivity consumed significantly more vertebrates, fewer invertebrates and less mast. Trophic diversity was positively correlated with temperature, precipitation and productivity but negatively correlated with the duration of snow cover and snow depth. Brown bear populations from temperate forest biomes had the most diverse diet. In general, environmental factors were more explicative of diet than geographical variables.
  • 4 Dietary spatial patterns were best revealed by the relative biomass and energy content methods of diet analysis, whereas the frequency of occurrence and relative biomass methods were most appropriate for investigating variation in trophic diversity.
  • 5 Spatial variation in brown bear diet is the result of environmental conditions, especially climatic factors, which affect the nutritional and energetic requirements of brown bears as well as the local availability of food. The trade‐off between food availability on the one hand, and nutritional and energetic requirements on the other hand, determines brown bear foraging decisions. In hibernating species such as the brown bear, winter severity seems to play a role in determining foraging strategies. Large‐scale reviews of food habits should be based on several measures of diet composition, with special attention to those methods reflecting the energetic value of food.
  相似文献   

13.
14.
青藏高原1979-2007年间的积雪变化   总被引:4,自引:0,他引:4       下载免费PDF全文
利用雪深被动微波遥感数据产品,对青藏高原1979—2007年积雪深度、积雪日数的分布变化及其趋势进行了分析。结果表明:青藏高原积雪日数、积雪深度和海拔三者之间在空间上具有显著正相关;青藏高原积雪在1988年发生突变,该年前后积雪分布有显著不同,这与20世纪80年代中后期青藏高原由暖干时期进入暖湿时期有关;将青藏高原按夏季水汽来源不同将其分为南北两部分,发现29年来北部积雪日数变化与全国积雪变化相反呈极显著增加趋势(R2=0.39,P0.01),以1.40 d/a的趋势增加,主要原因是西北部地区冬季积雪日数增加;南部积雪深度与全国积雪变化一致呈极显著减少趋势(R2=0.24,P0.01),以-0.04 cm/a的趋势减少,主要原因是东南部春、夏、秋三季积雪深度减少。  相似文献   

15.
In terrestrial high‐latitude regions, observations indicate recent changes in snow cover, permafrost, and soil freeze–thaw transitions due to climate change. These modifications may result in temporal shifts in the growing season and the associated rates of terrestrial productivity. Changes in productivity will influence the ability of these ecosystems to sequester atmospheric CO2. We use the terrestrial ecosystem model (TEM), which simulates the soil thermal regime, in addition to terrestrial carbon (C), nitrogen and water dynamics, to explore these issues over the years 1960–2100 in extratropical regions (30–90°N). Our model simulations show decreases in snow cover and permafrost stability from 1960 to 2100. Decreases in snow cover agree well with National Oceanic and Atmospheric Administration satellite observations collected between the years 1972 and 2000, with Pearson rank correlation coefficients between 0.58 and 0.65. Model analyses also indicate a trend towards an earlier thaw date of frozen soils and the onset of the growing season in the spring by approximately 2–4 days from 1988 to 2000. Between 1988 and 2000, satellite records yield a slightly stronger trend in thaw and the onset of the growing season, averaging between 5 and 8 days earlier. In both, the TEM simulations and satellite records, trends in day of freeze in the autumn are weaker, such that overall increases in growing season length are due primarily to earlier thaw. Although regions with the longest snow cover duration displayed the greatest increase in growing season length, these regions maintained smaller increases in productivity and heterotrophic respiration than those regions with shorter duration of snow cover and less of an increase in growing season length. Concurrent with increases in growing season length, we found a reduction in soil C and increases in vegetation C, with greatest losses of soil C occurring in those areas with more vegetation, but simulations also suggest that this trend could reverse in the future. Our results reveal noteworthy changes in snow, permafrost, growing season length, productivity, and net C uptake, indicating that prediction of terrestrial C dynamics from one decade to the next will require that large‐scale models adequately take into account the corresponding changes in soil thermal regimes.  相似文献   

16.
气候变化引起的雪被变化会深刻地影响森林凋落物的分解过程.本研究采用人工控雪处理(对照、增雪、除雪)模拟研究雪被变化对两种温带树种——水曲柳和兴安落叶松凋落叶分解动态的影响. 为期一年的分解试验表明: 不同控雪处理下水曲柳和落叶松的凋落叶年分解率的变化范围分别为51.3%~57.4%和21.7%~31.4%;两者的分解系数(k)变化范围分别为0.048~0.057和0.022~0.030,其中增雪处理的k值最大、除雪处理的k值最小.与对照相比,增雪处理下水曲柳凋落叶50%和95%分解的时间分别缩短了1.1月和4.2月,落叶松则分别缩短了3.7月和15.5月;相反,除雪处理下相应的分解时间分别延长了1.8月和6.4月(水曲柳)及5.0月和21.1月(落叶松).此外,凋落叶分解率与树种、雪深、分解时间、土壤温度等密切相关,但其主要影响因子随分解阶段而异,表现为雪被期主要受土壤温度影响,而随后的无雪期主要受凋落叶初始质量的影响.本研究突显了雪被变化对凋落叶分解有显著的瞬时效应和延迟效应.  相似文献   

17.
Snow on land is an important component of the global climate system, but our knowledge about the effects of its changes on vegetation are limited, particularly in temperate regions. In this study, we use daily snow depth data from 279 meteorological stations across China to investigate the distribution of winter snow depth (December–February) from 1980 to 2005 and its impact on vegetation growth, here approximated by satellite‐derived vegetation greenness index observations [Normalized Difference Vegetation Index (NDVI)]. The snow depth trends show strong geographical heterogeneities. An increasing trend (>0.01 cm yr?1) in maximum and mean winter snow depth is found north of 40°N (e.g. Northeast China, Inner Mongolia, and Northwest China). A declining trend (?1) is observed south of 40°N, particularly over Central and East China. The effect of changes in snow depth on vegetation growth was examined for several ecosystem types. In deserts, mean winter snow depth is significantly and positively correlated with NDVI during both early (May and June) and mid‐growing seasons (July and August), suggesting that winter snow plays a critical role in regulating desert vegetation growth, most likely through persistent effects on soil moisture. In grasslands, there is also a significant positive correlation between winter snow depth and NDVI in the period May–June. However, in forests, shrublands, and alpine meadow and tundra, no such correlation is found. These ecosystem‐specific responses of vegetation growth to winter snow depth may be due to differences in growing environmental conditions such as temperature and rainfall.  相似文献   

18.
  总被引:20,自引:0,他引:20  
The relationship between vegetation phenology and climate is a crucial topic in global change research because it indicates dynamic responses of terrestrial ecosystems to climate changes. In this study, we investigate the possible impact of recent climate changes on growing season duration in the temperate vegetation of China, using the advanced very high resolution radiometer (AVHRR)/normalized difference vegetation index (NDVI) biweekly time-series data collected from January 1982 to December 1999 and concurrent mean temperature and precipitation data. The results show that over the study period, the growing season duration has lengthened by 1.16 days yr−1 in temperate region of China. The green-up of vegetation has advanced in spring by 0.79 days yr−1 and the dormancy delayed in autumn by 0.37 days yr−1. The dates of onset for phenological events are most significantly related with the mean temperature during the preceding 2–3 months. A warming in the early spring (March to early May) by 1°C could cause an earlier onset of green-up of 7.5 days, whereas the same increase of mean temperature during autumn (mid-August through early October) could lead to a delay of 3.8 days in vegetation dormancy. Variations in precipitation also influenced the duration of growing season, but such influence differed among vegetation types and phenological phases.  相似文献   

19.
    
Warming can lead to increased growth of plants or algae at the base of the food web, which may increase the overall complexity of habitat available for other organisms. Temperature and habitat complexity have both been shown to alter the structure and functioning of communities, but they may also have interactive effects, for example, if the shade provided by additional habitat negates the positive effect of temperature on understory plant or algal growth. This study explored the interactive effects of these two major environmental factors in a manipulative field experiment, by assessing changes in ecosystem functioning (primary production and decomposition) and community structure in the presence and absence of artificial plants along a natural stream temperature gradient of 5–18°C. There was no effect of temperature or habitat complexity on benthic primary production, but epiphytic production increased with temperature in the more complex habitat. Cellulose decomposition rate increased with temperature, but was unaffected by habitat complexity. Macroinvertebrate communities were less similar to each other as temperature increased, while habitat complexity only altered community composition in the coldest streams. There was also an overall increase in macroinvertebrate abundance, body mass, and biomass in the warmest streams, driven by increasing dominance of snails and blackfly larvae. Presence of habitat complexity, however, dampened the strength of this temperature effect on the abundance of macroinvertebrates in the benthos. The interactive effects that were observed suggest that habitat complexity can modify the effects of temperature on important ecosystem functions and community structure, which may alter energy flow through the food web. Given that warming is likely to increase habitat complexity, particularly at higher latitudes, more studies should investigate these two major environmental factors in combination to improve our ability to predict the impacts of future global change.  相似文献   

20.
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.  相似文献   

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