Spatial heterogeneity of tundra vegetation response to recent temperature changes

The spatial heterogeneity of recent decadal dynamics in vegetation greenness and biomass in response to changes in summer warmth index (SWI) was investigated along spatial gradients on the Arctic Slope of Alaska. Image spatial analysis was used to examine the spatial pattern of greenness dynamics from 1991 to 2000 as indicated by variations of the maximum normalized difference vegetation index (Peak NDVI) and time‐integrated NDVI (TI‐NDVI) along latitudinal gradients. Spatial gradients for both the means and temporal variances of the NDVI indices for 0.1° latitude intervals crossing three bioclimate subzones were analyzed along two north–south Arctic transects. NDVI indices were generally highly variable over the decade, with great heterogeneity across the transects. The greatest variance in TI‐NDVI was found in low shrub vegetation to the south (68.7–68.8°N) and corresponded to high fractional cover of shrub tundra and moist acidic tundra (MAT), while the greatest variance in Peak‐NDVI predominately occurred in areas dominated by wet tundra (WT) and moist nonacidic tundra (MNT). Relatively high NDVI temporal variances were also related to specific transitional areas between dominant vegetation types. The regional temporal variances of NDVI from 1991 to 2000 were largely driven by meso‐scale climate dynamics. The spatial heterogeneity of the NDVI variance was mostly explained by the fractional land cover composition, different responses of each vegetation type to climate change, and patterned ground features. Aboveground plant biomass exhibited similar spatial heterogeneity as TI‐NDVI; however, spatial patterns are slightly different from NDVI because of their nonlinear relationship.     

陕北长城沿线风沙区植被指数变化及其与气候的关系

陕北长城沿线风沙区位于毛乌素沙漠东南部边沿,属毛乌素沙地向东南移动的最活跃地段,生态环境十分脆弱。使用1981～2003年23a长时间序列的NOAA/AHRR NDVI数据、气候资料,分析了陕北长城沿线风沙区植被覆盖的历史演变及其与气候因子的关系。结果表明:(1)陕北长城沿线风沙区植被覆盖状况23a来尽管有波动起伏,但是整体在持续转好,年平均NDVI增加了10.62%。低覆盖率植被面积在减少,高覆盖率植被面积在增加。夏季的NDVI值最高、波动起伏最大,其次是秋季;春、夏、秋三季的NDVI具有明显的上升趋势,季平均NDVI年增长率夏季最大,秋季次之;夏、秋季NDVI与年NDVI具有很高的相关性,这两个季节的植被状况基本决定了全年的植被分布状况。NDVI年变化曲线为单峰型,春季NDVI缓慢增加,秋季NDVI降低速度比较快。(2)年平均NDVI与温度的年际变化相关不明显,各季节NDVI与温度相关也不明显。近年来长城沿线风沙区的年降水量没有明显增加,而年平均NDVI线性增加趋势显著,降水量是引起NDVI年际波动的主要因子,非气候因素是年平均NDVI线性增加的主要原因。降水量与NDVI存在着明显的年相关和隔季相关。年降水量与年NDVI的相关,冬季降水量与春季NDVI的相关,春季降水量与夏季NDVI的相关,夏季降水量与秋季NDVI的相关性都非常高。(3)非气候因素中生态保护和环境建设等人为措施,如植树造林、草原围栏封育等是导致植被显著增加的重要原因。     

陕西吴起植被动态及其与气候变化的关系

使用归一化植被指数(normalized difference vegetation index,NDVI)资料,分析了陕西省吴起县1982-2003年NDVI的演变情况及其与气候变化的关系。结果表明,22年来植被覆盖状况尽管有波动起伏,但整体在持续转好,表现在低覆盖率植被面积在减少,高覆盖率植被面积在增加;年平均NDVI与降水量呈正相关,植被覆盖的改善有利于减小风速;从季节平均值来看,春季降水量与夏季NDVI、夏季降水量与秋季NDVI的相关性均极显著(P<0.01),并且夏秋两季的降水量与年NDVI相关性也显著,说明降水量是影响吴起县植被分布状况的关键性因子;春夏季蒸发量与夏季的NDVI均呈极显著的负相关(P<0.01);春夏季相对湿度与夏季的NDVI呈极显著的正相关(P<0.01),冬季相对湿度与冬季的NDVI呈极显著的负相关(P<0.01)。     

Patterns of floristic richness in vegetation communities of California: regional scale analysis with multi-temporal NDVI

Aim Applying water‐energy dynamics and heterogeneity theory to explain species richness via remote sensing could allow for the regional characterization and monitoring of vegetation community assemblages and their environment. We assess the relationship of multi‐temporal normalized difference vegetation index (NDVI) to plant species richness in vegetation communities. Location California, USA. Methods Sub‐regions containing species inventories for chaparral, coastal sage scrub, foothill woodland, and yellow pine forest communities were intersected with a vegetation community map and an AVHRR NDVI time series for 1990, 1991, 1992, 1995 and 1996. Principal components analysis reduced the AVHRR data to three variables representing the sum and temporal trajectories of NDVI within each community. A fourth variable representing heterogeneity was tested using the standard deviation of the first component. Quadratic forms of these variables were also tested. Species richness was analysed by stepwise regression. Results Chaparral, coastal sage scrub, and yellow pine forest had the best relationships between species richness and NDVI. Richness of chaparral was related to NDVI heterogeneity and spring greenness (r² varied between 0.26 and 0.62 depending on year of NDVI data). Richness of coastal sage scrub was nonlinearly related to annual NDVI and heterogeneity (r² 0.63–0.81), with peak richness at intermediate values. Foothill woodland richness was related to heterogeneity in a monotonic curvilinear fashion (r² 0.28–0.35). Yellow pine forest richness was negatively related to spring greenness and positively related to heterogeneity (r² 0.40–0.46). Main Conclusions While NDVI's relationship to species richness varied, the selection of NDVI variables was generally consistent across years and indicated that spatial variability in NDVI may reflect important patterns in water‐energy use that affect plant species richness. The principal component axis that should correspond closely with annual mean NPP showed a less prominent role. We conclude that plant species richness for coarse vegetation associations can be characterized and monitored at a regional scale and over long periods of time using relatively coarse resolution NDVI data.     

The greening and browning of Alaska based on 1982–2003 satellite data

Aim To examine the trends of 1982–2003 satellite‐derived normalized difference vegetation index (NDVI) values at several spatial scales within tundra and boreal forest areas of Alaska. Location Arctic and subarctic Alaska. Methods Annual maximum NDVI data from the twice monthly Global Inventory Modelling and Mapping Studies (GIMMS) NDVI 1982–2003 data set with 64‐km² pixels were extracted from a spatial hierarchy including three large regions: ecoregion polygons within regions, ecozone polygons within boreal ecoregions and 100‐km climate station buffers. The 1982–2003 trends of mean annual maximum NDVI values within each area, and within individual pixels, were computed using simple linear regression. The relationship between NDVI and temperature and precipitation was investigated within climate station buffers. Results At the largest spatial scale of polar, boreal and maritime regions, the strongest trend was a negative trend in NDVI within the boreal region. At a finer scale of ecoregion polygons, there was a strong positive NDVI trend in cold arctic tundra areas, and a strong negative trend in interior boreal forest areas. Within boreal ecozone polygons, the weakest negative trends were from areas with a maritime climate or colder mountainous ecozones, while the strongest negative trends were from warmer basin ecozones. The trends from climate station buffers were similar to ecoregion trends, with no significant trends from Bering tundra buffers, significant increasing trends among arctic tundra buffers and significant decreasing trends among interior boreal forest buffers. The interannual variability of NDVI among the arctic tundra buffers was related to the previous summer warmth index. The spatial pattern of increasing tundra NDVI at the pixel level was related to the west‐to‐east spatial pattern in changing climate across arctic Alaska. There was no significant relationship between interannual NDVI and precipitation or temperature among the boreal forest buffers. The decreasing NDVI trend in interior boreal forests may be due to several factors including increased insect/disease infestations, reduced photosynthesis and a change in root/leaf carbon allocation in response to warmer and drier growing season climate. Main conclusions There was a contrast in trends of 1982–2003 annual maximum NDVI, with cold arctic tundra significantly increasing in NDVI and relatively warm and dry interior boreal forest areas consistently decreasing in NDVI. The annual maximum NDVI from arctic tundra areas was strongly related to a summer warmth index, while there were no significant relationships in boreal areas between annual maximum NDVI and precipitation or temperature. Annual maximum NDVI was not related to spring NDVI in either arctic tundra or boreal buffers.     

东北地区植被物候时序变化

植被与气候的关系非常密切,植被物候可作为气候变化的指示器。东北地区位于我国最北部,是气候变化的敏感区域,研究该区植被物候对气候变化的响应对阐明陆地生态体统碳循环具有重要意义。利用GIMMS AVHRR遥感数据集得到了东北地区阔叶林、针叶林、草原和草甸4种植被25a(1982—2006年)的物候时序变化,得出4种植被春季物候都表现出先提前后推迟的现象,秋季物候的变化则比较复杂,阔叶林和针叶林整体上呈现出秋季物候推迟的趋势,草原和草甸则表现为提前-推迟-提前的趋势。应用偏最小二乘(Partial Least Squares)回归分析了该区域植被物候与气候因子之间的关系,结果表明:春季温度与阔叶林、针叶林和草甸春季物候负相关,前一年冬季温度与草原春季物候正相关,降水与植被春季物候的关系有点复杂;4种植被秋季物候与夏季温度均呈正相关,除草原外,其余3种植被秋季物候均与夏季降水负相关。植被春季物候可能主要受温度影响,而秋季物候很可能主要受降水控制。     

Rangeland vegetation dynamics and moisture availability in Tunisia: an investigation using satellite and meteorological data

Improved knowledge of the interactions between regional climatic patterns and vegetation dynamics are necessary for predicting the future impacts of climate change on vegetation and biogeochemical processes. This paper describes how Normalized Difference Vegetation Index (NDVI) images generated from Advanced Very High Resolution Radiometer (AVHRR) satellite data were used to investigate the dynamics of rangeland vegetation in Tunisia. The NDVI images provided information about intra- and inter-annual variations in vegetation over nine growing seasons (1983–1992). Comparison of the NDVI data with field-collected ecological parameters for nine individual field sites indicated a strong relationship between the NDVI and percentage vegetation cover. The relationship between biomass measurements and NDVI was, however, less strong. Rainfall and NDVI data for each field site were compared, and significant relationships were found between the two. These indicated that there was a delay in the vegetation response to rainfall. In addition, the NDVI data showed that the vegetation at some of the field sites remained active throughout the summer although there was no rainfall during this period. TuMERT (Tunisian Model to Estimate Rangeland Transpiration), a simple water-balance model, was developed to estimate the amount of rainfall available for use by the vegetation during transpiration. The estimates of actual transpiration derived from TuMERT were found to be more strongly correlated with the AVHRR-NDVI measurements than the rainfall data.     

近30年新疆植被生长异常值时空变化及驱动因子

作为陆地生态系统的主体,植被的时空变化深刻地影响着景观格局和生态功能,深入理解植被动态及其对气候变化的响应,对于提高对生态过程的认识、加强生态管理具有重要意义。在一致性检验的基础上,利用中分辨率成像光谱仪(moderateresolution imaging Spectroradiometer,MODIS)的归一化植被指数(normalized Difference Vegetation Index,NDVI)数据集将新疆地区全球检测与模型研究组(Global Inventory Modeling and Mapping Studies,GIMMS)开发的NDVI数据集的时间序列拓展到2012年,探讨了生长季和各季节植被绿度、气候异常值的动态变化,分析了植被对气候变化的响应。研究结果显示,区域尺度和像元尺度GIMMS与MODIS NDVI之间的一致性较强。1982—2012年,研究区域生长季和各季节植被绿度呈显著增加趋势,但生长季存在明显阶段性:1998年前后分别呈显著增加和显著减少,夏季与秋季与生长季类似,而春季则不存在变化趋势的逆转。NDVI呈正异常值的面积比例与区域尺度NDVI的变化趋势一致;极端异常值、较大异常值多呈明显减少趋势,而一般异常值多呈增加趋势,NDVI的变化倾向于逐渐平稳。区域变暖趋势显著,降水量略有增加,潜在蒸散发显著提高,而湿润指数变化不明显。气温、潜在蒸散发主要在春季、秋季促进植被生长,而夏季降水量、湿润指数对植被生长的调节作用更为突出。     

1982-2015年黄土高原NDVI时空演变及其对气候变化的季节响应

基于GIMMS NDVI、温度和降水数据,利用集合经验模态分解(EEMD)、线性回归分析、偏相关分析等方法分析了1982-2015年黄土高原植被覆盖时空变化及其对气候变化的季节响应。结果表明:年际变化趋势上,1982-2015年黄土高原生长季、春、夏、秋季NDVI均呈显著增长趋势,且各个季节NDVI增加速率逐年升高,尤其以夏季增加速率的变化最为明显;空间上,生长季、春、夏、秋季NDVI均呈由西北向东南递增的趋势,且在大部分地区呈显著上升趋势;线性回归表明,生长季、春、夏、秋季温度均呈显著上升趋势;生长季、秋季降水呈增加趋势,春、夏季降水呈减少趋势。EEMD分析进一步表明,生长季、春、夏、秋季温度均先升高后降低,降水均呈先减少后增加的趋势;空间变化趋势上,温度在生长季、春、夏、秋季大部分地区呈显著上升趋势,降水仅秋季有部分区域呈显著上升趋势;NDVI与温度在黄土高原东北部及西南部地区呈显著正相关,与降水在黄土高原北部及西北部地区呈显著正相关。     

Feeding ecology of kererū (

The diet and food preferences of the kererū (Hemiphaga novaeseelandiae) were studied in Whirinaki Forest Park, central North Island, New Zealand, during February 2000 ? March 2001. The study was carried out in two areas of podocarp?hardwood forest, Oriuwaka (1750?ha) and Otupaka (1830?ha). Fruit dominated in the diet at both sites (65% in Oriuwaka, 87% in Otupaka), but there were seasonal changes. Foliage and flowers were more important in the diet in winter and spring, but the timing of the switch from fruit to foliage differed between the areas. The main fruit eaten also changed seasonally from tawa (Beilschmiedia tawa) in early summer to miro (Prumnopitys ferruginea) in late summer and autumn. Variation in diet partly reflected seasonal phenology of the plants and differences in vegetation between the two areas, but when food-type availability is considered, kererū showed selective preference for some food types at some times. Miro and tawa fruits were highly preferred food types in both areas. This study highlights the likely need of kererū to have access to various vegetation types in order to meet their seasonally changing nutritional requirements in a podocarp?hardwood forest where the availability of food, especially fruits, can differ markedly both in time and space. Thus, large forest blocks that contain a variety of habitat types, or landscapes containing patches of various habitat types, are needed for the long-term conservation of kererū populations.     

青藏高原草地植被覆盖变化及其与气候因子的关系

为揭示气候变化对青藏高原草地生态系统的影响及其生态适应机制,利用1982~1999年间的NOAA/AVHRR NDVI数据和对应的气候资料,研究了近20年来青藏高原草地植被覆盖变化及其与气候因子的关系。结果表明,18年来研究区生长季NDVI显著增加(p=0.015),其增加率和增加量分别为0.41% a^-1和0.001 0 a^-1。生长季提前和生长季生长加速是青藏高原草地植被生长季NDVI增加的主要原因。春季为NDVI增加率和增加量最大的季节,其增加率和增加量分别为0.92% a^-1和0.001 4 a^-1;夏季NDVI的增加对生长季NDVI增加的贡献相对较小,其增加率和增加量分别为0.37% a^-1和0.001 0 a^-1。3种草地(高寒草甸、高寒草原、温性草原)春季NDVI均显著增加(p<0.01;p=0.001; p=0.002); 高寒草甸夏季NDVI显著增加(p=0.027),而高寒草原和温性草原夏季NDVI呈增加趋势,但都不显著(p=0.106; p=0.087);3种草地秋季NDVI则没有明显的变化趋势(p=0.585; p=0.461; p=0.143)。3种草地春季NDVI的增加是由春季温度上升所致。高寒草地(高寒草甸和高寒草原)夏季NDVI的增加是夏季温度和春季降水共同作用的结果。温性草原夏季NDVI变化与气候因子并没有表现出显著的相关关系。高寒草地植被生长对气候变化的响应存在滞后效应。     

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。     

Primary producers in a Pampean stream: temporal variation and structuring role

Low current velocities, high nutrient levels, the lack of riparian forest vegetation, and the development of dense and rich macrophyte communities characterize Pampean streams. The objective of this study was to describe the main physical, chemical, and biological characteristics of a headwater Pampean stream as well as to analyze the role of macrophytes and phytobenthos. The study was conducted in a stream considered to be not much disturbed by human activities. Samples of water and organisms (macrophytes, benthic algae and invertebrates) were taken monthly for 14 months in two sampling stations, in fast flow and slow flow sites. Macrophyte biomass and diversity increased in spring and summer, and they decreased in autumn, when the plant community was greatly affected by an important flood. Phytobenthos biomass was lower in late summer, possibly due to the establishment of a dense cover of the floating macrophyte Lemna gibba L. Density of amphipods and gastropods greatly increases in spring and summer, jointly with the macrophyte development. Analysis of correlation showed that current velocity is the most important factor influencing macrophyte biomass and phytobenthos structure, while depth, nutrients, and herbivores are linked factors. Pampean streams could be considered systems dynamically fragile, because habitat heterogeneity is generated by aquatic vegetation, a substratum that varies along time.     

Dissecting NDVI–species richness relationships in Hawaiian dry forests

Aim A growing body of research has used the normalized difference vegetation index (NDVI) as a proxy for productivity to predict species richness. Yet the mechanisms that produce the relationship between NDVI and species richness remain unclear because of correlated biotic and abiotic factors that influence NDVI. In this study we investigated different biotic and abiotic effects that potentially drive plant species richness–productivity relationships. Location Hawaiian Islands, USA. Methods We quantified woody plant species richness, structure (density, basal area and canopy height), and species composition along a precipitation gradient of 14 Hawaiian dry forest plots. We then used structural equation models combined with 10 years of satellite data to disentangle the effects of precipitation, structure and NDVI‐estimated productivity on species richness. Results Underlying the simple correlation between NDVI and species richness was the indirect effect of precipitation and direct effect of forest structure. The best‐fit model showed there was no direct effect of NDVI on species richness. Main conclusions Our results demonstrate that complex relationships drive simple correlations between species richness and productivity. Considering the mechanisms and underlying factors driving NDVI–species richness relationships could improve predictions of species diversity as satellite measures of productivity have an increasingly important role in habitat mapping, species distribution modelling and predictions for global change.     

22年来西北不同类型植被NDVI变化与气候因子的关系

 为了研究气候变化对西北地区不同类型植被的影响,利用NASA GIMMS 1982～2003年逐月归一化植被指数（Normalized difference vegetation index, NDVI）数据集和西北地区138个气象站点同期的气温和降水资料,计算了各站22年月平均气温和降水与NDVI的相关系数。同时, 选西北 地区森林、草原、绿洲和雨养农业4类有代表性的植被类型为研究区,对各类植被NDVI与气温和降水的相关关系进行分析。研究结果表明：除无 植被的戈壁沙漠地区外,西北地区NDVI与气温和降水均有较好的相关性。除祁连山中部地区外,西北地区NDVI与气温的相关系数大于降水。天 山、阿尔泰山和秦岭的NDVI与气温相关系数最高,而青海东北部NDVI与降水相关系数最高。西北地区各种类型植被对气候变化反映敏感。其敏 感度因植被类型不同和同类植被所处的地理位置不同而有差异;纬度较高的新疆林区与温度相关性最高,高寒草甸次之。在植被生长最旺盛的 夏季（6～8月）,22年来西北地区各林区的NDVI均呈下降趋势。其中西北东部林区下降趋势显著,与这些地区的降水减少和气温增加有关。草 原区植被以上升趋势为主,高寒草甸和盐生草甸上升趋势最为显著,气温升高是这些地区植被生长加速的原因 之一。西北绿洲是NDVI增加极为 显著的地区,以新疆绿洲NDVI上升趋势最大。气候变暖是近年绿洲NDVI增加的主要驱动力之一,绿洲面积扩大、种植结构调整和种植品种变化 等人为因素对绿洲NDVI增加的作用不可忽视,这种作用在新疆表现的尤为突出。雨养农业区NDVI年际 间波动较大,各区域间变化不太一致。 NDVI的波动与降水变化有很好的正相关,与气温变化有很好的负相关,近年来西北东部气温升高和降水的减少是雨养农业区NDVI下降的原因, 农业措施的实施也改变了植被生长对气候条件的依赖性。     

Natural vegetation phenology assessment by ground spectral measurements in two semi-arid environments

Natural vegetation in semi-arid regions is characterized by three ground features, in addition to bare surfaces - biological soil crusts, annuals, and perennials. These three elements have distinguishable phenological cycles that can be detected by spectral ground measurements and by calculating the weighted normalized difference vegetation index (NDVI). The latter is the product of the derived NDVI of each ground feature and its respective areal cover. Each phenological cycle has the same basic elements - oscillation from null (or low) to full photosynthetic status and back to a stage of senescence. However, they vary in phase. The biological soil crusts show the earliest and highest weighted NDVI peak during the rainy season, and their weighted NDVI signal lasts longer than that of the annuals. The annuals are dominant in late winter and early spring while the perennials predominate in late spring and during the summer.     

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.     

Vegetation variation of mid-subtropical forest based on MODIS NDVI data — A case study of Jinggangshan City,Jiangxi Province

Vegetation variation is an important topic of global change research, which is of great significance to deeply understand the relationship between vegetation and global change or human activities, and to disclose regional environment evolution and transition. The dynamics of forest vegetation in the mid-subtropical zone have received little attention. Thus, this paper takes the typical distribution area of the subtropical forest ecosystem — Jinggangshan City in Jiangxi Province as a study area. The changes within the year, inter-annual changes trend and spatial variation of the mid-subtropical forest vegetation index during the recent 10 years are analyzed based on MODIS NDVI data from 2000–2011 with the spatial resolution of 250 m. The Savitzky–Golay filter is used to smooth the original MODIS NDVI data. The forest distribution data is taken as the mask to eliminate the impact of non-forest cover area. The results showed that: (1) The changes of forest vegetation index within the year present a single peak mode with the maximum value in July; in the past 10 years, the forest vegetation index fluctuated with a downward trend; NDVI values were high and stable in summer and autumn, but low and unstable in winter; (2) The distribution of NDVI values of forest vegetation had great spatial difference. The NDVI values were low in the area nearby non-forest area in the north, where the non-forest vegetation is widely distributed. The NDVI values were high in the northwestern and southeastern areas. The distribution of NDVI values are comparatively even in the middle area with the NDVI values of more than 0.7; (3) High NDVI values (>0.75) distributed most in the northwestern and southeastern areas with the altitude of 400–600 m. Low NDVI values (<0.65) distributed mostly in the northern areas with the altitude less than 400 m. As for different altitude zones, NDVI values are high in the area with altitude of 400–800 m and low in the area with altitude below 400 m or above 1200 m. There is an agreement between the spatial distribution of the NDVI value of forest vegetation and regional topography, because topography has great impacts on the distribution of forest types which are different in coverage; (4) The NDVI value of forest vegetation presents a downward trend in the northern area, but an increasing trend in the southern area. The vegetation coverage tends to decrease with high population density and intensive distribution of township and scenic spot.     

基于植被指数的海南岛霸王岭热带森林地上生物量空间分布模拟

热带森林在全球碳循环方面扮演着重要的角色, 预测其生物量分布可以加深对碳循环过程的理解。然而目前基于植被指数模拟技术进行热带森林生物量分布的研究报道较少。该文以海南岛霸王岭林区热带森林为研究对象, 在基于遥感影像和135个公里网格样地调查的基础上, 分别选取归一化差异植被指数(NDVI)、短红外湿度植被指数(MVI5)、中红外湿度植被指数(MVI7)和比值植被指数(RVI)与总物种生物量、顶极种生物量和先锋种生物量做相关分析, 并利用逐步线性回归分析分别构建了基于植被指数的生物量回归模型; 利用残差图对模型的有效性进行检验。结果表明, MVI7和MVI5与总物种和顶极种生物量关系显著, 而NDVI和RVI对先锋种生物量具有较好的指示作用; 总物种、顶极种和先锋种生物量预测精度较高的区域分别占总面积的69.24%、73.98%和88.08%, 表明3个生物量模型均具有较好的拟合精度; 模拟结果表明总物种和顶极种生物量主要集中于研究区中部、北部和西南部区域, 而先锋种生物量无明显的分布规律, 是不均衡地散布于整个研究区域, 反映了群落组成结构、干扰历史、地形及气候因素等的影响。     

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.