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1.
Impact of rainfall variability and grazing pressure on plant diversity in Mongolian grasslands 总被引：1，自引：0，他引：1
Climate and grazing are the main drivers of plant community composition and species richness in arid environments. This study aimed to examine the vegetation response to a spatial precipitation gradient, interannual rainfall variability, and grazing pressure in Mongolia. To examine the effect of a spatial precipitation gradient, we compared species richness among six sites. To investigate the effects of interannual rainfall variability and grazing pressure, we compared species richness for 2 years at two sites, in desert-steppe and steppe areas. The regional gradient in annual precipitation showed positive and negative relationships with grass richness and shrub richness, respectively, although total species richness did not vary significantly. The proportions of the different functional groups were affected by grazing pressure and rainfall variability in both zones. In the desert-steppe zone, species richness was lower in the drier year but did not vary with grazing pressure. In the steppe zone, species richness varied significantly with grazing pressure but did not vary between years. Precipitation would be more important than grazing pressure on vegetation changes in drier areas with high rainfall variability. 相似文献
2.
锡林郭勒草原生态恢复工程效果的评价 总被引：10，自引：1，他引：9
针对锡林郭勒草原的严重退化, 近年来启动了草原生态恢复工程, 但工程实施的效果由于范围广、时间短而很难予评价。利用锡林郭勒草原地区1999~2004 年的SPOT-VGT 10 天最大值合成NDVI 时间序列数据, 在求得各年NDVI 年最大值(NDVImax) 的基础上, 通过搜寻各像元邻域内NDVImax 的最大值以及与之相应的气候因子, 建立起了像元尺度上的气候-植被生长基准响应模型, 并以此为依据运用相对残差趋势法识别出了处于恢复阶段的草原区域。 最后, 将遥感监测结果与羊单位统计资料进行对比分析, 结果发现, 在县级行政区域尺度上的平均恢复趋势与基于羊单位和NPP 构建的放牧压力趋势具有较好的反比例关系, 初步证明了该方法在时间序列较短情况下的有效性。 相似文献
3.
Rangeland systems play an important role in ecological stabilization and the terrestrial carbon cycle in arid and semiarid regions. However, little is known about the vegetative carbon dynamics and climatic and topographical factors that affect vegetative carbon stock in these rangelands. Our goal was to assess vegetative carbon stock by examining meteorological data in conjunction with NDVI (normalized difference vegetation index) time series datasets from 2001-2012. An improved CASA (Carnegie Ames Stanford Approach) model was then applied to simulate the spatiotemporal dynamic variation of vegetative carbon stock, and analyze its response to climatic and topographical factors. We estimated the vegetative carbon stock of rangeland in Gansu province, China to be 4.4× 1014 gC, increasing linearly at an annual rate of 9.8×1011 gC. The mean vegetative carbon density of the whole rangeland was 136.5 gC m-2. Vegetative carbon density and total carbon varied temporally and spatially and were highly associated with temperature, precipitation and solar radiation. Vegetative carbon density reached the maximal value on elevation at 2500-3500 m, a slope of >30°and easterly aspect. The effect of precipitation, temperature and solar radiation on the vegetative carbon density of five rangeland types (desert and salinized meadow, steppe, alpine meadow, shrub and tussock, and marginal grassland in the forest) depends on the acquired quantity of water and heat for rangeland plants at all spatial scales. The results of this study provide new evidence for explaining spatiotemporal heterogeneity in vegetative carbon dynamics and responses to global change for rangeland vegetative carbon stock, and offer a theoretical and practical basis for grassland agriculture management in arid and semiarid regions. 相似文献
4.
Shrubs proliferated within a six-year exclosure in a temperate grassland—Spatiotemporal relationships between vegetation and soil variables 总被引：1，自引：0，他引：1
Overgrazing has been considered one of the maj or causes that trigger shrub encroachment of grassland. Proliferation of shrubs in grassland is recognized as an important indicator of grassland degradation and desertification. In China, various conservation measures, including enclosures to reduce livestock grazing, have been taken to reverse the trend of grassland desertification, yet shrubs have been reported to increase in the grasslands over the past decades. In late 2007, we set up a 400-m-by-50-m exclosure in a long-term overgrazed temperate grassland in Inner Mongolia, with the ob- jective to quantify the spatiotemporal relationship between vegetation dynamics, soil variables, and grazing exclusion. Soil moisture was continuously monitored within the exclosure, and cover and aboveground biomass of the shrubs were measured inside the exclosure in 2007, 2009, 2010, 2012, and 2013, and outside the exclosure in 2012 and 2013. We found the average shrub cover and biomass significantly increased in the six years by 103 % and 120%, respectively. The result supported the hypothesis that releasing grazing pressure following long-term overgrazing tends to trigger shrub invasion into grassland. Our results, limited to a single gradient, suggest that any conservation measures with quick release of overgrazing pressure by enclosure or other similar means might do just the opposite to accelerate shrub en- croachment in grassland. The changes in vegetation cover and biomass were regressed on the temporal average of the soil moisture content by means of the generalized least square technique to quantify the effect of the spatial autocor- relation. The result indicates that the grass cover and biomass significantly increased with the top, but decreased with the bottom layer soil moisture. The shrub cover and biomass, on the other hand, decreased with the top, but increased with bottom soil moisture, although the regression coefficients for the shrubs were not statistically significant. Hence this study supports the two-layered soil model which assumes grasses and shrubs use belowground resources in dif- ferent depths. 相似文献
5.
The isotope ratios in precipitation are associated with various meteorological processes and display obvious spatial and temporal
distributions, and thus can be used as important techniques in inversing atmospheric processes, tracing vapor sources, and reflecting
the local weather and climate conditions. The composition and distribution of stable isotopes in precipitation in China are
summarized and the factors that influence isotope ratios are elucidated. An overview of related research progress in China during
the past several decades is presented and the prospects for future work in this subject area are described. 相似文献
6.
Biological soil crusts exhibit a dynamic response to seasonal rain and release from grazing with implications for soil stability 总被引：2，自引：0，他引：2
A. Jimenez Aguilar E. Huber-Sannwald J. Belnap D.R. Smart J.T. Arredondo Moreno 《Journal of Arid Environments》2009,73(12):1158-1169
In Northern Mexico, long-term grazing has substantially degraded semiarid landscapes. In semiarid systems, ecological and hydrological processes are strongly coupled by patchy plant distribution and biological soil crust (BSC) cover in plant-free interspaces. In this study, we asked: 1) how responsive are BSC cover/composition to a drying/wetting cycle and two-year grazing removal, and 2) what are the implications for soil erosion? We characterized BSC morphotypes and their influence on soil stability under grazed/non-grazed conditions during a dry and wet season. Light- and dark-colored cyanobacteria were dominant at the plant tussock and community level. Cover changes in these two groups differed after a rainy season and in response to grazing removal. Lichens with continuous thalli were more vulnerable to grazing than those with semi-continuous/discontinuous thalli after the dry season. Microsites around tussocks facilitated BSC colonization compared to interspaces. Lichen and cyanobacteria morphotypes differentially enhanced resistance to soil erosion; consequently, surface soil stability depends on the spatial distribution of BSC morphotypes, suggesting soil stability may be as dynamic as changes in the type of BSC cover. Longer-term spatially detailed studies are necessary to elicit spatiotemporal dynamics of BSC communities and their functional role in biotically and abiotically variable environments. 相似文献
7.
Tea is an important cash crop for the economy in northeast India. It also supports the livelihoods of a large proportion of the population. At the same time, tea growth is sensitive to climatic conditions making it vulnerable to climate change and variability. Identifying the tea yield response to climatic variability in operational plantations, and identifying the most important climatic variables that impact tea yield is critical to assessing the vulnerability of the industry and informing adaptation. Here, we developed a garden level panel dataset and estimated statistical models to identify the causal effect of monthly temperature, monthly precipitation, drought intensity, and precipitation variability on tea yield. We found decreasing tea yield returns to warmer monthly average temperatures, and when monthly temperatures were above 26.6 °C warming had a negative effect. We found that drought intensity did not affect tea yield and that precipitation variability, and in particular precipitation intensity, negatively affect tea yield. An increase in average temperatures as expected with global warming will reduce the productivity of tea plantations, all else held equal. Further, interventions to reduce the sensitivity of tea plantations to warming and precipitation variability will have immediate pay-offs as well as providing climate change adaptation benefits. 相似文献
8.
ABSTRACTThis study quantified the temporal properties of precipitation and actual evapotranspiration (ETa) in the Zoige basin of the Yellow River source region, China during the 1967–2011 period, as well as their influence to the area reduction of peatland. We extracted areas of different land-use and land-cover (LULC) types and obtained daily precipitation data. Then, we calculated annual precipitation (AP) and specific cumulative precipitation (SCP), which is the sum of precipitation to the date when an image was taken, and showed that the peatland areas were strongly affected by SCP. Using a modified Penman–Monteith equation, we calculated ETa for each LULC type and the area-weighted ones to show that the area-weighted total ETa was mainly contributed from grassland and peatland, which was between 450 and 550 mm. Temporal trends of the ratio of SCP to evapotranspiration showed that precipitation was generally greater than evapotranspiration rate not only during the summer but also over the 1967–2011 period. This trend failed to completely explain the continuous decrease of peatland area in the Zoige basin in decades. The draining effect of artificial ditches and natural gullies might play an additional role in causing peatland degradation but requires further process-based studies. 相似文献
9.
基于逻辑回归模型的环北京地区土地退化态势分析 总被引：4，自引：0，他引：4
以环北京地区为研究区域,从土地利用类型变化和农用地质量下降两个方面分析了环北京地区土地退化状况,并利用逻辑回归模型分析了土地退化与气候、地貌、植被、土壤、人口、土地利用变化、社会经济因子之间关系,探讨土地退化的发展趋势。研究结果表明,风蚀土地是环北京地区土地退化的主要类型,主要分布在监测区内蒙古高原西北部、坝上高原北部及阴山北部地区,从监测区的西北到东南方向,土地退化数量逐渐减少;由牧草地退化而增加沙地是土地利用类型变化造成退化的重要类型,主要集中在浑善达克沙地监测区。基于建立的沙地增加、风蚀土地和水蚀土地逻辑回归模型,年均降雨量和土壤有机质对环北京地区沙地增加的影响最强,沙地增加最可能的区域将主要分布在浑善达克沙地的边缘地带和科尔沁沙地的东部区域;NDVI和土壤有机质对环北京地区风蚀土地影响最强,风蚀土地最可能发生的区域集中在浑善达克沙地南部;NDVI、坡度和土壤湿度对环北京地区水蚀土地影响最强,水蚀土地最可能发生的区域集中在监测区的东南部,并且所预测的最可能发生土地退化的区域与已存在的退化土地区域具有一定的相关性。通过以上分析,最后提出了环北京地区生态环境建设的建议。 相似文献
10.
树轮密度对气候的响应及重建研究进展 总被引：1，自引：0，他引：1
树轮密度是重建过去气候变化的重要代用指标。过去几十年,国内外学者针对树轮密度开展了大量的研究工作,取得了丰硕的成果。论文收集了国内外有关树轮密度的研究文献,从树轮密度对气候变化的响应和气候重建等方面进行了概述。尽管树轮密度对气候变化的响应可能受到样点的地理位置、地形(如海拔、坡向等)、树种等因素的影响,但湿冷地区树轮晚材最大密度能较好地反映生长季或生长季末期温度变化;而干旱地区的早材平均密度能揭示生长季早期的降水变化。因此,目前大多数研究以重建生长季或生长季末期温度为主,也有重建降水量、海平面气压变化的案例。此外,重建方程的方差解释量存在空间和树种间的差异,但这些差异需要更多的研究工作加以验证。最长的重建序列来自于欧洲,长达2018 a;国内基于树轮密度重建的最长温度序列来自于西南地区,长达449 a。另外,树轮密度序列在对温度响应的分异性问题以及评估强火山喷发的降温效应方面还存在争议。其争议源于树轮密度与温度关系还受到其他环境变量与人为因素的影响,因此今后研究还需关注树轮密度与降水、光照等其他气候变量的关系,同时也要注重树种、海拔、实验方法等非气候因子的影响。 相似文献
11.
Semi-arid and arid areas exhibit great temporal variability in water availability. In some of these regions, a one- or two-day rainfall is followed by intervening dry periods of variable length. In recent decades, many rivers of the semi-arid portion of the Jequitinhonha Basin have been undergoing a progressive discharge reduction, mainly of their base flow, the are presented herein. Satellite images, hydrometeorological and river discharge data were analyzed; mean and variance tests were conducted to determine temporal homogeneity.Historical pluviometric data analysis shows no corresponding precipitation reduction and temperature undergoes only a slight increase in the same period. On the other hand,evaporation is extremely high, higher than precipitation during most of the year, leaving alwaters of its tributaries are now occupied by a monoculture, Eucaliptus sp., used for paper production. Because of the decreased fluvial discharges, its lowlands, usually used for agriculture and pasture, are abandoned and partially eroded. 相似文献
12.
小型浮游动物在海洋食物网中扮演着重要的角色。2012年12月—2013年3月,利用稀释培养方法开展了南大洋及温带海域小型浮游动物对浮游植物的摄食实验研究。结果表明,浮游植物的生长率为0.04—0.89 d~(–1),小型浮游动物对浮游植物的摄食率为0.07—1.29 d~(–1)。浮游动物日摄食量占浮游植物现存量的6.4%—72.5%,对浮游植物初级生产力的摄食压力也较大,为14%—776.9%。尽管本实验中浮游动物的摄食率可能被高估,但在南大洋及温带海域生态系统中,小型浮游动物对浮游植物仍具有重要的调控作用。 相似文献
13.
围封对沙漠化草地土壤理化性质和固碳潜力恢复的影响 总被引：1，自引：0，他引：1
过度放牧是科尔沁沙地退化的主要原因,禁牧围封可以有效地控制牲畜对植被-土壤系统的破坏,促进退化生态系统的有效恢复。以过度放牧后的沙漠化草地为对象,调查了禁牧围封13年后沙漠化草地土壤理化性质的变化特征,并分析了围封对土壤固碳潜力的影响。结果表明：（1）沙漠化草地围封13年后,土壤砂粒含量减少、粉粒和黏粒含量增加,且粉粒增加最为明显,平均含量增加123%;土壤容重在不同土壤深度均呈下降趋势。（2）围封后土壤有机质、全氮、速效氮和速效钾含量呈增加趋势,分别增加了102%、97%、123%和24%,但土壤有效磷和缓效钾呈减少趋势;土壤pH显著升高,阳离子交换量呈现增加趋势。（3）除土壤有效铁外,其余有效微量元素包括有效铜、有效锰和有效锌平均含量均呈增加趋势,分别增加44%、30%和82%。（4）土壤有机质与pH值、阳离子交换量、全氮、速效氮、速效钾、有效铜、有效锰、有效锌含量呈显著正相关关系。（5）沙漠化草地围封13年后,100 cm深度土壤有机碳储量增加393.45 g·m-2,碳截存速率为30.27 gC·m-2·a-1。对于因持续过度放牧所导致的严重退化草地,禁牧围封可有效促进土壤有机质、养分和微量元素的增加,影响土壤质地及固碳潜力等的变化,但严重退化沙漠化草地的恢复需要一个长期的过程,土壤有机碳储量要恢复到科尔沁非沙漠化草地水平至少需要百年的时间尺度。 相似文献
14.
Cores of thick leaf spruce from the western Qilian Mountains were subjected to densitometric analysis to obtain data for seven tree-ring parameters (tree-ring width, earlywood width, latewood width, maximum density, minimum density, mean earlywood density and mean latewood density). The chronologies were analyzed individually and then compared with each other. Most of these variables show moderately high values of common variance and mean interseries correlation except latewood and maximum densities. The relationships between the different tree-ring parameters and climate data are also presented. The growth/climate response analyses reveal that the radial growth of thick leaf spruce is the mainly controlled by total annual precipitation (July-June). Herein the residual ring width chronology was used to reconstruct annual (July-June) precipitation of Jiuquan for the period 1768-2009 A.D., and it accounted for 45.0% of the precipitation variance. Multi-taper spectral analysis reveals the existence of significant 11.1-year, 4.9-year, and 2.0- to 3.4-year periods of variability. Spatial analysis shows that the precipitation of Jiuquan has strong common signals for the northern margin of the Tibetan Plateau and Hexi Corridor. Drought events in our reconstruction are compared to the historical archives and other moisture-sensitive tree ring width series in the Hexi Corridor. The results reveal common climatic extremes over much of the Hexi Corridor. Many of these events have had profound impacts on the peoples of the Hexi Corridor over the past several centuries. 相似文献
15.
Land managers need sound, evidence-based information about land degradation patterns and about the effectiveness of their management responses. Obtaining such information is particularly difficult in Mediterranean grazing lands and forests, where a long history of anthropogenic pressure, high topographical and climatic variability, and frequent disturbances combine to create a highly diverse and unstable environment.Our study aimed at designing a methodology to provide land managers in three data-scarce drylands in Spain, Greece, and Cyprus with spatially explicit, up-to-date information on the state of their land, the pressures driving land degradation, and the effectiveness of their management efforts using remotely sensed NDVI data. To translate NDVI values into a land degradation assessment, we analysed the variance of the annual average NDVI within different landscape units, which we identified based on land cover, aspect, and slope steepness parameters. After calibrating and validating the land degradation mapping methodology using field observations, we related the obtained land degradation patterns with spatial information about grazing and wildfire, as well as controlled grazing and afforestation practices.Our methodology proved useful to assess land degradation and management measures in dry, semi-natural ecosystems. It also provided insights into the role of landscape in modulating land degradation. Results indicate that grazing is a significant cause of land degradation even in partially abandoned areas; repeated fires have a negative impact; slope steepness increases the land's sensitivity to grazing; north- and east-facing slopes are less sensitive to fire in the long term than south- and west-facing slopes; and the effectiveness of responses to land degradation is substantially affected by land cover and topography.The methodology presented can be used to overcome the lack of spatially explicit information on the state of the land in drylands of the Mediterranean and beyond, or as a basis for more in-depth studies to plan restoration interventions. 相似文献
16.
Inter-annual variability and interaction of remote-sensed vegetation index and atmospheric precipitation in the Aral Sea region 总被引：10，自引：0，他引：10
The remotely sensed Normalized Difference Vegetation Index (AVHRR NDVI) and precipitation data were analysed in the Aral Sea region in Central Asia during two recent decades. Both variables exhibited pronounced seasonal variation, with maximum precipitation in March and maximum NDVI in May–June. The regions of synchronous seasonal and inter-annual variability between the vegetation index and precipitation were distinguished using the Empirical Orthogonal Functions (EOF) method and time-lagged correlations between EOF modes. At a seasonal scale, precipitation and the vegetation index were correlated with a time lag from 1 to 6 months in different regions with peak plant growth following precipitation maxima. 相似文献
17.
干旱半干旱地区草地碳循环关键过程对降雨变化的响应 总被引：2，自引：0，他引：2
未来全球气候变化背景下,全球或局部地区的降雨量及降雨时间分布将发生一定的变化.草地生态系统在全球碳收支中作用显著,对气候变化的反馈起着重要的作用.但由于草地多处于干旱半干旱地区,受到水分条件的限制,对降雨变化响应敏感,其碳源汇功能表现出很大的不确定性.为了更好地预测未来全球气候变化背景下草地的碳源汇功能及其对气候变化的进一步反馈,有必要深入研究决定草地碳源汇功能的两大碳循环关键过程--净初级生产力和土壤呼吸对降雨变化的响应特征及机制.本文对国内外有关草地生产力和土壤呼吸如何对降雨量、降雨强度、降雨频率和间隔时间进行响应的相关研究成果进行了综述,在此基础上指出了目前研究存在的不足,并对未来相关的重点研究方向进行了探讨和展望. 相似文献
18.
基于logistic回归模型的农牧交错区土地利用变化驱动力分析——以内蒙古翁牛特旗为例 总被引：29，自引：1，他引：28
本文以农牧交错带的典型区域——内蒙古翁牛特旗为例,考虑土地利用变化过程的空间变量,建立了不同土地利用变化过程的logistic回归模型。结果表明:模型中转为耕地的主要解释变量是到农村居民点的距离和农业气候区;转为草地的主要解释变量是到农村居民点的距离、土壤表层有机质含量和到乡镇中心的距离;转为林地的主要解释变量是到农村居民点的距离和海拔;空间异质性和土地利用变化过程的时间变量共同影响着使用logistic回归模型来解释土地利用变化驱动力的能力;通过对草地logistic回归模型的检验,得出空间统计模型能较好地揭示不同土地利用变化过程的主要驱动力及其作用机理。 相似文献
19.
气象站和卫星降雨资料估算降雨侵蚀力时存在无法反映空间异质性且精度差的问题,基于CLDAS多源融合降水,利用EI60模型从不同的时空尺度对中国的降雨侵蚀力进行评估,并结合降雨量、侵蚀性降雨次数、侵蚀密度等指标,探讨降雨对土壤侵蚀的潜在作用。结果表明：（1） CLDAS降雨侵蚀力与地面实测数据在不同的时间尺度均有良好的回归关系,相关系数达到0.8以上,与CMORPH降雨侵蚀力相比,其相对误差显著降低,可以准确反映全国范围的降雨侵蚀力季节性变异。（2） 在2001—2020年,不同雨量区的降雨侵蚀力、降雨量和侵蚀性降雨次数的变化趋势基本一致,高雨量区的年际变化波动剧烈,侵蚀性降雨次数和暴雨过程协同影响降雨侵蚀力的大小。（3） 空间上,中国的降雨侵蚀力值的特点为东南沿海地区高、西北内陆地区低。时间上,侵蚀性降雨集中在5—8月,夏、秋两季对土壤造成的侵蚀影响更大。（4） 通过对年降雨量、年侵蚀密度和年暴雨量进行分区定量分析,结果表明暴雨量与侵蚀密度成正相关关系,即年降雨量一定,暴雨事件越多,降雨侵蚀密度越大。 相似文献
20.
Analysis of vegetation changes and dominant factors on the Qinghai-Tibet Plateau,China 总被引：2，自引：0，他引：2
This research was undertaken to clarify the characteristics of vegetation change and its main influencing factors on the Qinghai-Tibet Plateau. Using the greenness rate of change(GRC) and correlation factors, we analyzed the trend of vegetation change and its dominant factors from 2000 to 2015. The results indicate that the vegetation tended to improve from 2000 to 2015 on the Qinghai-Tibet Plateau, with the improved area accounting for 39.93% of the total; and the degraded area accounting for 19.32%. The areas of degraded vegetation are mainly concentrated in the low-relief and intermediate-relief mountains of the high-altitude and extremely high-altitude areas on the Qinghai-Tibet Plateau, as the vegetation characteristics are impacted by the terrain. Temperature and precipitation have obvious response mechanisms to vegetation growth, but the effects of precipitation and temperature on vegetation degradation are not significant over a short time frame. Overgrazing and population growth are the dominant factors of vegetation degradation on the Qinghai-Tibet Plateau. 相似文献