2001-2015年天山北坡植被覆盖对干旱的响应——基于土地利用/土地覆盖分析

天山北坡生态系统脆弱,易受干旱影响,全球变暖和不合理的人类活动加剧了干旱的影响,评估植被覆盖对干旱的响应,为改善生态环境和减轻干旱影响提供科学参考。基于MODIS-NDVI遥感数据以及气象数据,计算了2001-2015年天山北坡多尺度标准化降水蒸散发指数（SPEI）和植被覆盖度,总结出植被覆盖度与多尺度SPEI时空动态变化规律,从土地利用/土地覆盖（LUCC）的角度分析了植被覆盖度对气候干旱的响应。结果表明：（1）天山北坡绝大部分区域呈湿润状态,中部（石河子、呼图壁）、西北部（克拉玛依市）呈轻度干旱。3个月、6个月、12个月时间尺度SPEI均表现出干旱化增强的年际变化趋势;（2）天山北坡植被覆盖度整体上属中低覆盖,总体呈南高北低,天山山区、城市绿洲内部高的分布特点。2001-2015年天山北坡植被覆盖度变化总体呈下降趋势;（3）年尺度天山北坡植被覆盖度与SPEI整体呈正相关关系。不同土地利用/土地覆盖的植被覆盖度与12个月时间尺度SPEI（SPEI 12）的相关性不同,大小依次为：草地 > 未利用地 > 城乡用地 > 林地 > 水域 > 耕地;（4）季节尺度夏季和春季干旱对植被覆盖度的影响最明显,不同季节干旱对不同土地利用/土地覆盖植被覆盖度影响程度不同。     

Abundance and distribution of the tsetse flies, Glossina austeni and G. brevipalpis, in different habitats in South Africa

The distribution and abundance of Glossina austeni Newstead and Glossina brevipalpis Newstead (Diptera: Glossinidae) were studied in the three main vegetation types in Zululand, KwaZulu-Natal, South Africa. During a period of 12 months, a trap transect consisting of 38 H-traps traversing the three vegetation types was monitored. The Index of Apparent Abundance (IAA) for G. brevipalpis was high in indigenous forest and open grassland but lower in exotic plantations. Glossina austeni, on the other hand, was captured mainly in or adjacent to indigenous forest. The seasonal trend in the IAA did not differ between vegetation types. The findings on the distribution of G. brevipalpis are in contrast with the historic records. Historically, this species was considered to be restricted to areas with a dense overhead canopy and high relative humidity. The repercussions of these findings for the epidemiology of livestock trypanosomiasis and the control of tsetse in Zululand are discussed.     

1982-2012年中亚植被变化及其对气候变化的响应

归一化植被指数(NDVI)能够反映植被生长状况, 被广泛应用于区域乃至全球的植被变化研究中。该文利用1982-2012年GIMMS-NDVI数据, 通过基于像元的线性趋势分析、偏相关分析, 基于场域的经验正交分解(EOF)、奇异值分解(SVD), 综合时间和空间两个维度上的信息, 研究了近31年来中亚植被的变化及其变化中的区域差异, 分析了植被对气候变化的响应关系。线性趋势分析发现, 34%的中亚植被NDVI显著增长(p < 0.05), 山区植被NDVI的增长速率可达到每年0.004。偏相关分析表明, 63%的中亚植被受到降水的显著影响(p < 0.05, 仅4%为负相关), 而32%的植被受到气温的显著影响(p < 0.05, 仅9%为正相关)。EOF分析发现, 中亚植被NDVI的变化表现出较大的空间差异: 山区及东北部的植被NDVI变化主要分为3个阶段, 即先增长(1982-1994年)、后波动(1994-2002年)、然后继续增长(2002-2012年); 而西北部平原区的植被NDVI变化主要表现为两个阶段, 即先增长(1982-1994年)而后减少(1994-2012年)。SVD分析表明: 1982-2012年间中亚植被受到降水和气温的共同影响, 植被NDVI的空间变化特征与降水的空间变化特征较为一致, 但西北部和山区的植被NDVI对气温的响应存在差异。     

1982—2015年新疆地区植被生长对气温的响应

基于1982-2015年归一化植被指数(NDVI)数据集、植被类型和气象数据,采用滑动偏相关分析、线性趋势分析和GIS空间分析方法,揭示了新疆地区生长季植被对气温响应的变化特征.结果表明:研究期间,在整个生长季,新疆地区植被活动对气温变化的响应强度呈现明显的降低趋势;季节尺度上,这种响应关系的变化趋势在夏、秋两季较为明显,春季植被活动对气温变化响应的变化趋势与之相反.在整个生长季,不同类型植被对气温变化的响应呈现减弱态势;在春季,草地和森林对气温变化的响应呈现显著增强趋势,而灌丛和荒漠对气温变化的响应趋势正好相反;在夏季,4种植被(草地、灌丛、荒漠、森林)对气温变化的响应均呈现显著降低趋势;在秋季,4种植被对气温变化的响应均没有显著的统计学特征.新疆地区生长季气温对植被的影响力减弱具有区域的普遍性特征,这可能与研究区降雨和太阳辐射活动变化的有关.     

Ground‐ and satellite‐based evidence of the biophysical mechanisms behind the greening Sahel

After a dry period with prolonged droughts in the 1970s and 1980s, recent scientific outcome suggests that the decades of abnormally dry conditions in the Sahel have been reversed by positive anomalies in rainfall. Various remote sensing studies observed a positive trend in vegetation greenness over the last decades which is known as the re‐greening of the Sahel. However, little investment has been made in including long‐term ground‐based data collections to evaluate and better understand the biophysical mechanisms behind these findings. Thus, deductions on a possible increment in biomass remain speculative. Our aim is to bridge these gaps and give specifics on the biophysical background factors of the re‐greening Sahel. Therefore, a trend analysis was applied on long time series (1987–2013) of satellite‐based vegetation and rainfall data, as well as on ground‐observations of leaf biomass of woody species, herb biomass, and woody species abundance in different ecosystems located in the Sahel zone of Senegal. We found that the positive trend observed in satellite vegetation time series (+36%) is caused by an increment of in situ measured biomass (+34%), which is highly controlled by precipitation (+40%). Whereas herb biomass shows large inter‐annual fluctuations rather than a clear trend, leaf biomass of woody species has doubled within 27 years (+103%). This increase in woody biomass did not reflect on biodiversity with 11 of 16 woody species declining in abundance over the period. We conclude that the observed greening in the Senegalese Sahel is primarily related to an increasing tree cover that caused satellite‐driven vegetation indices to increase with rainfall reversal.     

湖北省地区植被覆盖变化及其对气候因子的响应

归一化植被指数(NDVI)作为一个重要的遥感参数,能够准确地反映植被覆盖程度和植被生长状况、生物物理化学性质及生态系统参数的变化,其时序数据也已成为基于生物气候特征开展大区域植被和土地覆盖分类的基本手段。基于2001—2012年MODIS-NDVI数据,利用趋势分析法以及线性相关分析等方法对湖北省植被年际变化趋势、月变化趋势进行详细分析;并且研究该区植被覆盖时空变化及其与气温和降水的关系。结果表明近12年来,研究区大部分区域植被覆盖度良好,其中鄂西北及鄂南地区NDVI值较高为0.82,鄂中东部城市NDVI值较低为0.13;2001—2012年间年均NDVI整体呈增加趋势,增速1%/10a;植被覆盖度基本不变区域占研究区总面积的92.8%,大致符合我国中部地区植被覆盖变化趋势;分析NDVI与气候因子的相关关系可知,降水量对湖北植被NDVI年变化起有重要影响;逐月NDVI与月平均气温及月降水量的回归分析表明,降水和气温对生长季不同月份的植被NDVI影响明显不同,同时呈现一定的滞后性。     

Evaluating the impacts of climate and elevated carbon dioxide on tropical rainforests of the western Amazon basin using ecosystem models and satellite data

Forest inventories from the intact rainforests of the Amazon indicate increasing rates of carbon gain over the past three decades. However, such estimates have been questioned because of the poor spatial representation of the sampling plots and the incomplete understanding of purported mechanisms behind the increases in biomass. Ecosystem models, when used in conjunction with satellite data, are useful in examining the carbon budgets in regions where the observations of carbon flows are sparse. The purpose of this study is to explain observed trends in normalized difference vegetation index (NDVI) using climate observations and ecosystem models of varying complexity in the western Amazon basin for the period of 1984–2002. We first investigated trends in NDVI and found a positive trend during the study period, but the positive trend in NDVI was observed only in the months from August to December. Then, trends in various climate parameters were calculated, and of the climate variables considered, only shortwave radiation was found to have a corresponding significant positive trend. To compare the impact of each climate component, as well as increasing carbon dioxide (CO₂) concentrations, on evergreen forests in the Amazon, we ran three ecosystem models (CASA, Biome‐BGC, and LPJ), and calculated monthly net primary production by changing a climate component selected from the available climate datasets. As expected, CO₂ fertilization effects showed positive trends throughout the year and cannot explain the positive trend in NDVI, which was observed only for the months of August to December. Through these simulations, we demonstrated that the positive trend in shortwave radiation can explain the positive trend in NDVI observed for the period from August to December. We conclude that the positive trend in shortwave radiation is the most likely driver of the increasing trend in NDVI and the corresponding observed increases in forest biomass.     

1982-2012年中亚地区植被时空变化特征及其与气候变化的相关分析

干旱区植被生态系统对气候变化极为敏感,并且干旱区的植被变化研究对全球碳循环具有重要意义。然而近几十年来,中亚干旱区植被对气候变化的响应机制尚不甚明朗。利用归一化植被指数NDVI数据集和MERRA（Modern-Era Retrospective Analysis for Research and Applications）气象数据,采用经验正交函数（EOF,Empirical Orthogonal Function）和最小二乘法等方法系统分析了31a（1982-2012年）来中亚地区NDVI在不同时间尺度的时空变化特征。进一步分析和研究NDVI与气温和降水的相关性,结果表明：1982-2012年,中亚地区年NDVI总体呈现缓慢增长趋势,而1994年以后年NDVI呈现明显下降趋势,尤其在哈萨克斯坦北部草原地区下降趋势尤为突出。这可能是由于过去30年间,中亚地区降水累计量的持续减少造成的。NDVI的季节变化表明春季NDVI增长最为明显,冬季则显著下降。与平原区相比,中亚山区的NDVI值增长幅度最大,并且山区年NDVI与季节NDVI呈现显著增加趋势（P < 0.05）。中亚地区年NDVI与年降水量正相关,而年NDVI与气温变化存在弱负相关。年NDVI和气温的正相关中心在中亚南部地区,负相关中心则出现在哈萨克斯坦的西部和北部地区;NDVI和降水的相关性中心刚好与气温相反。此外,在近30年间的每年6月至9月,中亚地区NDVI与气温存在近一个月的时间延迟现象。本研究为中亚干旱区生态系统变化和中亚地区碳循环的估算提供科学依据。     

黄河流域植被时空变化及其对气候要素的响应

在气候变化和人类活动的双重作用下,黄河流域生态环境不断发生变化。探讨植被生长动态对于实施生态保护政策至关重要。利用Advanced Very High Resolution Radiometer(AVHRR) Leaf Area Index(LAI)遥感资料,结合气候要素数据,分析1981—2017年黄河流域植被覆盖的时空分布特征,探讨气候要素对其变化的影响及贡献率。研究结果表明：(1)时序上,黄河流域植被覆盖呈显著增长趋势,夏季植被覆盖的增长幅度和年际波动最大,冬季植被覆盖呈缓慢平稳增长,波动最小。(2)空间上,植被覆盖显著提高的区域占整个区域的52.1%,主要分布在中东部平原;显著降低的区域占4%,主要分布在北部和西部高原山地;生态脆弱的区域植被覆盖率大多有不同程度的提高,但生态环境良好的部分区域植被覆盖率降低。(3)时序上,黄河流域植被覆盖与气温具有显著的正相关关系。春夏冬三季的植被覆盖与气温呈显著正相关,与降水呈不显著关系;秋季的植被覆盖与气温和降水量均呈显著正相关;春秋冬三季的植被覆盖与太阳辐射呈不显著负相关,夏季的植被覆盖与太阳辐射呈不显著正相关。春夏秋冬四季的气温对植被覆...     

Vegetation coverage changes driven by a combination of climate change and human activities in Ethiopia, 2003–2018

Climate change often leads to the vulnerability of vegetation cover, while the impact of human activities on vegetation cover is undoubtedly more complex in this context, especially in Ethiopia. This paper analyzed the spatiotemporal dynamics of vegetation growth in Ethiopia from 2003 to 2018 by the enhanced vegetation index (EVI) based on different time scales and explored the coefficient of variation and driving factors of the fractional vegetation coverage (FVC). The results indicated that the EVI mainly presents a “double peak” pattern, with large spatiotemporal differences between quarters and months in Ethiopia. The FVC increased by 0.0005 per year, but vegetation showed a browning trend after 2013. The FVC degraded area accounted for 43.9% of the total area, of which the significantly degraded area accounted for 7.51% due to human activities, mainly in northern, central, and southern Ethiopia. The effects of precipitation and maximum temperature on vegetation differed on time scales. Spatially, the vegetation on the northwest side of the Main Ethiopian Rift Valley (MERV) was dominated by a combination of maximum temperature and precipitation, while vegetation on the southeast side of MERV was mainly influenced by precipitation. However, the spatial overlay analysis with degraded and healthy vegetation zones revealed that human activities were the key driver of vegetation cover change rather than climate change. This study provides support for further development of vegetation health conservation policies in Ethiopia and monitoring of vegetation dynamics in other countries around the world.     

Quantifying the impacts of opencast mining on vegetation dynamics over eastern India using the long-term Landsat-series satellite dataset

Enhanced spatio-temporal and up-to-date information on vegetation dynamics at various spatial scales are imperative in understanding the human, biosphere, and atmosphere interactions. Thus, the present study attempts to derive the vegetation greenness trends with the medium spatial resolution (30 m) satellite data at the regional scale with the support of Google Earth Engine (GEE) cloud platform. The long-term Landsat series satellite dataset was employed to characterize vegetation greenness trends using the Mann-Kendall test over the mining-dominated regions of Eastern India (Jharkhand and Odisha states) for two study periods, viz. earlier (1988–2004) and later (2000−2020). The key findings revealed that ∼1285 km² (2.97%) and 1688 km² (3.91%) areas over Jharkhand state and ∼ 5213 km² (5.68%) and 2940 km² (3.20%) areas over Odisha state showed the negative vegetation greenness trend (indicative of decreasing vegetation activity) during 1988–2004 and 2000–2020, respectively. It was observed that the major anthropogenic activities, particularly opencast mining, are the major factor for vegetation degradation in Jharkhand and Odisha states, contributing to ∼3–5.7% vegetation degradation during the study periods. The negative vegetation greenness trend patches were mainly observed in mining sites, settlement encroachments, construction sites, roadways, logging sites, etc. The drastic rise in the intensity of mining activities in the last two decades (2000–2020) has led to massive vegetation destruction compared to the earlier period (1988–2004). Furthermore, the key climatic parameters (i.e., precipitation, temperature, downward radiation, and soil moisture) have less control over the long-term vegetation greenness trends in the mining-dominated regions (∼ 27%) in contrast to forest regions (∼ 47%). The findings of the study shall be helpful to the policy-makers, stakeholders, environmentalists, and government bodies to formulate and implement various sustainable development programs in the mining-dominated regions to ensure ecological conservation and enhance ecological services.     

内蒙古植被枯黄期变化及其与气候和植被生产力的关系

基于2001—2018年MODIS NDVI数据,采用累计归一化植被指数(NDVI)的Logistic曲线曲率极值法,识别内蒙古植被枯黄期及其时空变化特征,并在生态区尺度上分析枯黄期对气候因子和NDVI的响应特征。结果表明: 研究期间,内蒙古植被平均枯黄期主要集中在第260～280天。森林生态区枯黄期为第270～280天,从南向北推迟;草原生态区枯黄期最早,介于第257～273天,从东北向西南逐渐推迟;荒漠生态区枯黄期为第270～283天,东北向西南呈推迟态势。2001—2018年间,3个生态区植被枯黄期均呈不显著推迟趋势。植被生产力从东北向西南逐渐降低,在时间上呈增加趋势的面积大于呈减小趋势的面积。全内蒙古和各生态区植被枯黄期受季前2～3个月降水量的正面影响较大,与季前平均温度、最高温度和最低温度均呈正相关关系。全内蒙古和各生态区,8和9月植被生产力的增加(或减少)将推迟(或提前)植被枯黄期,而6和7月植被生产力的增加(或减少)将提前(或推迟)草原和荒漠生态区植被枯黄期。     

2000—2016年云南地区植被覆盖时空变化及其对水热因子的响应

基于2000-2016年MODIS-NDVI数据,利用趋势分析法以及线性相关分析等方法对云南地区植被月变化趋势、年际变化趋势进行详细分析;探讨植被覆盖变化与主要气候水热因子的关系。结果表明：研究区大部分地区植被覆盖良好,年NDVI的平均值为0.55,其中NDVI较高值（> 0.8）区域主要分布于南部,而西北部和中部城市地区NDVI值较低;自2000年开始,研究区NDVI总体呈显著（P < 0.05）增加趋势,年NDVI的变化斜率为0.0036,植被覆盖呈增加趋势的区域占研究区总面积79.80%;不同季节（春、夏、秋、冬）和生长季的植被状况均呈良性发展趋势;湿润指数和水热综合因子在滇西北与NDVI多呈负相关,在滇中地区以正相关为主;春、夏、秋3个季节NDVI受降水影响较大,而冬季NDVI则受气温影响较大;受降水影响较大的区域主要分布在中部和南部,受气温影响较大区域主要分布在滇西北、滇东北地区;NDVI在不同月份对气候因子的滞后时间存在差异,NDVI与当月气温的相关性强于与当月降水的相关性,植被生长对气温的响应无明显滞后效应,对降水存在3个月的滞后期。     

国家生态保护重要区域植被长势遥感监测评估

国家生态保护重要区域植被长势对于维持区域生态系统结构和功能的稳定性至关重要.以国家重点生态功能区、国家重要生态功能区、国家生物多样性保护优先区和国家级自然保护区等四类生态保护重要区域为研究区,选取年累积NDVI作为指示因子,监测评估了1998-2007年间国家生态保护重要区域的植被长势特征.结果表明:(1)国家生态保护重要区域总面积为536.59万km2,占全国陆地国土面积的55.89％.国家生物多样性保护优先区与国家重点生态功能区、国家重要生态功能区的重叠面积较大,分别占到相应生态功能区总面积的53.36％和50.20％.国家级自然保护区与其他三种类型区域的空间叠加关系较好,尤其与国家重点生态功能区,重叠面积占国家级自然保护区总面积的75.10％.国家重点生态功能区和国家重要生态功能区的重叠面积分别占各自面积的63.73％和39.15％.(2)对于植被长势总体状况,国家生态保护重要区域中东部的植被状况好于西部.植被状况较差的区域面积为10.59％,植被状况一般的区域面积为29.59％,植被状况好的区域面积为23.44％,植被状况较好的区域面积为36.39％.国家级自然保护区和生物多样性保护优优先区的植被状况好于国家重要生态功能区和国家重点生态功能区.国家级自然保护区的空间分布差异最大.(3)对于植被长势变化趋势,国家生态保护重要区域的植被状况整体呈现出变好趋势.62.39％区域面积的植被状况较为稳定,22.69％区域面积的植被状况呈现出变好趋势,14.93％区域面积的植被状况呈现出变差趋势.国家重要生态功能区的植被变好趋势最为明显,其次为国家生物多样性保护优先区.国家生物多样性保护优先区的植被变化趋势空间差异最大,国家级自然保护区的植被变化趋势空间差异最小.     

Satellite‐based evidence for shrub and graminoid tundra expansion in northern Quebec from 1986 to 2010

Global vegetation models predict rapid poleward migration of tundra and boreal forest vegetation in response to climate warming. Local plot and air‐photo studies have documented recent changes in high‐latitude vegetation composition and structure, consistent with warming trends. To bridge these two scales of inference, we analyzed a 24‐year (1986–2010) Landsat time series in a latitudinal transect across the boreal forest‐tundra biome boundary in northern Quebec province, Canada. This region has experienced rapid warming during both winter and summer months during the last 40 years. Using a per‐pixel (30 m) trend analysis, 30% of the observable (cloud‐free) land area experienced a significant (P < 0.05) positive trend in the Normalized Difference Vegetation Index (NDVI). However, greening trends were not evenly split among cover types. Low shrub and graminoid tundra contributed preferentially to the greening trend, while forested areas were less likely to show significant trends in NDVI. These trends reflect increasing leaf area, rather than an increase in growing season length, because Landsat data were restricted to peak‐summer conditions. The average NDVI trend (0.007 yr^?1) corresponds to a leaf‐area index (LAI) increase of ~0.6 based on the regional relationship between LAI and NDVI from the Moderate Resolution Spectroradiometer. Across the entire transect, the area‐averaged LAI increase was ~0.2 during 1986–2010. A higher area‐averaged LAI change (~0.3) within the shrub‐tundra portion of the transect represents a 20–60% relative increase in LAI during the last two decades. Our Landsat‐based analysis subdivides the overall high‐latitude greening trend into changes in peak‐summer greenness by cover type. Different responses within and among shrub, graminoid, and tree‐dominated cover types in this study indicate important fine‐scale heterogeneity in vegetation growth. Although our findings are consistent with community shifts in low‐biomass vegetation types over multi‐decadal time scales, the response in tundra and forest ecosystems to recent warming was not uniform.     

Trend analysis of vegetation dynamics in Qinghai-Tibet Plateau using Hurst Exponent

As one of the most sensitive areas responding to global environmental change, especially global climate change, Qinghai-Tibet Plateau has been recognized as a hotspot for coupled studies on global terrestrial ecosystem change and global climate change. As an important component of terrestrial ecosystems, vegetation dynamic has become one of the key issues in global environmental change, and numerous case studies have been conducted on vegetation dynamic trend in different study periods. However, few are focused on the quantitative analysis of the consistency of vegetation dynamic trends after the study periods. In the study, taking Qinghai-Tibet Plateau as a case, vegetation dynamic trend during 1982-2003 were analyzed, with the application of the method of linear regression analysis. The results showed that, vegetation dynamics in Qinghai-Tibet Plateau experienced a significant increasing as a whole, with nearly 50% forest degradation in the study period. And among the 7 kinds of vegetation types, the change of forest was the most fluctuant with desert the least one. Furthermore, the consistency of vegetation dynamic trends after the study period, was quantified using Hurst Exponent and the method of R/S analysis. The results showed high consistency of future vegetation dynamic trends for the whole plateau, and inconsistent areas were mainly meadow and steppe distributed in the middle or east of the plateau. It was also convinced that, vegetation dynamic trends in the study area were significantly influenced by topography, especially the elevation.     

Effects of water dependence on the utilization pattern of woody vegetation by elephants in the Tembe Elephant Park, Maputaland, South Africa

The utilization of vegetation and particularly trees in enclosed small reserves where elephant populations are confined is a contentious conservation issue. In Tembe Elephant Park in Maputaland, the diverse Sand Forest is considered the most valuable feature to conserve; yet it is considered at risk from increasing elephant utilization of the park's vegetation in general. The mean canopy removal by elephants across the park was studied over two periods: a recent period including the twelve months before the study and an older period >12 months earlier. Age of utilization was determined from the degree of decay observed on woody fibres. The relationships between intensity of utilization, vegetation unit selection and distance to water were evaluated. Results show that utilization patterns have shifted in the recent drier period, during which elephants used vegetation communities closer to permanent water. Concurringly, a significant decrease in utilization intensity was correlated to an increasing distance from water points in the park during that period, while this effect was not observed during the wetter old period. We debate that active water availability management may be a way to limit elephant utilization in small fenced reserves.     

Vegetation dynamics and responses to recent climate change in Xinjiang using leaf area index as an indicator

There is a strong signal showing that the climate in Xinjiang, China has changed from warm-dry to warm-wet since the early 1980s, leading to an increase in vegetation cover. Based on a regression analysis and Hurst index method, this study investigated the spatial–temporal characteristics and interrelationships of the vegetation dynamics and climate variability in Xinjiang Province using the leaf area index (LAI) and a gridded meteorological dataset for the period 1982–2012. Further analysis focused on the discrimination between climatic change and human-induced effects on the vegetation dynamics, and several conclusions were drawn. (1) Vegetation dynamics differ in mountain and plains regions, with a significant increasing trend of vegetation cover in oases and decreasing trend of vegetation growth in the Tienshan and Altay Mountain. The Hurst exponent results indicated that the vegetation dynamic trend was consistent, with a sustainable area percentage of 51.18%, unsustainable area percentage of 4.04%, and stable and non-vegetated area ratio of 44.78%. (2) The warm-dry to warm-wet climatic pattern in Xinjiang Province since the 1980s mainly appeared in the western part of the Tienshan region and North Xinjiang. Temperatures increased in all seasons over the majority of Xinjiang, and precipitation showed a significant increasing trend in the mountainous regions in spring, summer and autumn, whereas the rate of precipitation change was higher in the plains region in winter compared with that in other seasons. (3) A correlation occurs between the climate variables (precipitation and temperature) and mean LAI, and this correlation varies at the seasonal and regional scales, with coniferous forest, meadow and grassland more correlated with precipitation in spring and summer and not correlated with temperature, which indicated that precipitation was the dominant factor affecting the growth of mountain vegetation. The mean LAI of vegetation in the plains exhibited significant correlation with precipitation in winter and temperature in spring and summer. (4) A residual analysis showed a human-induced change that was superimposed on the climate trend and exhibited two effects: vegetation regeneration in oases throughout Xinjiang and desertification in the meadow located in the mountainous area of the western Tienshan Mountains and Altay Mountains. (5) Grassland is the most sensitive vegetation type to short-term climatic fluctuations and is the land-use type that has been most severely degraded by human activity; thus, local governments should take full advantage of this climatic warm-wet shift and focus on protecting vegetation to improve this fragile arid environment.     

1982-2016年东北黑土区植被NDVI动态及其对气候变化的响应

植被是陆地生态系统的重要组成部分,在调节气候、水土保持等方面具有重要作用,因此,监测植被生长变化并探讨其与气候变化之间的关系,在全球变化研究中具有重要意义。基于MODIS NDVI和GIMMS NDVI数据集,并通过一致性检验,在区域和像元两个空间尺度上,利用一元线性回归模型,研究东北黑土区1982-2016年植被生长动态,分析植被生长对气温和降水量的响应程度。结果表明：区域尺度上,1982-2016年东北黑土区植被生长季NDVI变化分为3个阶段（先增加继而减少最后再增加）,区域植被的生长在气温、降水量的共同作用下,呈现出明显季节差异;像元尺度上,1982-2016年东北黑土区NDVI总体趋势为改善状态,主要改善植被类型为草原、森林和农业植被,鹤岗市、绥化市和长春市改善面积较大;多年平均NDVI值与同期气温和降水量具有一定的相关关系,平原地区植被NDVI与气温主要呈显著正相关关系,植被类型主要为耕地;平原地区边缘和山地地区的植被NDVI与降水量以显著正相关关系为主,主要植被类型为森林和草地。     

Analog‐based fire regime and vegetation shifts in mountainous regions of the western US

Climate change is expected to result in substantial ecological impacts across the globe. These impacts are uncertain but there is strong consensus that they will almost certainly affect fire regimes and vegetation. In this study, we evaluated how climate change may influence fire frequency, fire severity, and broad classes of vegetation in mountainous ecoregions of the contiguous western US for early, middle, and late 21st century (2025, 2055, and 2085, respectively). To do so, we employed the concept of a climate analog, whereby specific locations with the best climatic match between one time period and a different time period are identified. For each location (i.e. 1‐km² pixel), we evaluated potential changes by comparing the reference period fire regime and vegetation to that of the fire regime and vegetation of the nearest pixels representative of its future climate. For the mountainous regions we investigated, we found no universal increase or decrease in fire frequency or severity. Instead, potential changes depend on the bioclimatic domain. Specifically, wet and cold regions (i.e. mesic and cold forest) generally exhibited increased fire frequency but decreased fire severity, whereas drier, moisture‐limited regions (i.e. shrubland/grassland) displayed the opposite trend. Results also indicate the potential for substantial changes in the amount and distribution of some vegetation types, highlighting important interactions and feedbacks among climate, fire, and vegetation. Our findings also shed light on a potential threshold or tipping point at intermediate moisture conditions that suggest shifts in vegetation from forest to shrubland/grassland are possible as the climate becomes warmer and drier. However, our study assumes that fire and vegetation are in a state of equilibrium with climate, and, consequently, natural and human‐induced disequilibrium dynamics should be considered when interpreting our findings.