Consequences of Buffelgrass Pasture Development for Primary Productivity,Perennial Plant Richness,and Vegetation Structure in the Drylands of Sonora,Mexico

Abstract: In large parts of northern Mexico native plant communities are being converted to non‐native buffelgrass (Pennisetum ciliare) pastures, and this conversion could fundamentally alter primary productivity and species richness. In Sonora, Mexico land conversion is occurring at a regional scale along a rainfall‐driven gradient of primary productivity, across which native plant communities transition from desert scrub to thorn scrub. We used a paired sampling design to compare a satellite‐derived index of primary productivity, richness of perennial plant species, and canopy‐height profiles of native plant communities with buffelgrass pastures. We sampled species richness across a gradient of primary productivity in desert scrub and thorn scrub vegetation to examine the influence of site productivity on the outcomes of land conversion. We also examined the influence of pasture age on species richness of perennial plants. Index values of primary productivity were lower in buffelgrass pastures than in native vegetation, which suggests a reduction in primary productivity. Land conversion reduced species richness by approximately 50% at local and regional scales, reduced tree and shrub cover by 78%, and reduced canopy height. Land conversion disproportionately reduced shrub species richness, which reflects the common practice among Sonoran ranchers of conserving certain tree and cactus species. Site productivity did not affect the outcomes of land conversion. The age of a buffelgrass pasture was unrelated to species richness within the pasture, which suggests that passive recovery of species richness to preconversion levels is unlikely. Our findings demonstrate that land conversion can result in large losses of plant species richness at local and regional scales and in substantial changes to primary productivity and vegetation structure, which casts doubt on the feasibility of restoring native plant communities without active intervention on the part of land managers.     

2000~2014年黄土高原植被覆盖时空变化特征及其归因

基于MODIS-NDVI数据,辅以一元线性回归分析、Mann-Kendall检验、Hurst指数等方法,分析了2000~2014年黄土高原植被覆盖时空演变特征及其驱动因素.研究表明:近15年黄土高原NDVI呈显著增加趋势,增速为6.93%/10a(P<0.01);空间上,植被归一化指数,或归一化值被指数Normalized Difference Vegetation Index(NDVI)呈由东南向西北递减的分布格局,高值区主要分布在东南部的土石山区、河谷平原区;同时,500m以下和3500米左右的NDVI值最高;在趋势上,NDVI呈现增加和减小趋势的面积比重分别为88.24%和11.76%;Hurst指数表明研究区未来NDVI变化趋势呈持续性和反持续的比重分别为50.07%和49.93%,其中持续改善和由改善变为退化的面积分别占43.98%和44.28%;降水是影响NDVI变化的主要驱动因子,表现为NDVI随降水的增加而增加;人类活动也是影响NDVI的重要因素,且对NDVI有双重影响.     

基于MODIS时序NDVI主要农作物种植信息提取研究

农业在黄河三角洲地区占有重要地位,及时、准确地掌握该地区农作物分布信息对政府有关部门制定农业政策、指导农业生产具有十分重要的意义。时序植被指数能够反映农作物物候特征,帮助识别农作物类型,在农作物种植信息提取方面具有明显优势。论文选取2014年MOD09Q1时序遥感数据集,以黄河三角洲主要农作物为研究对象,利用Harmonic Analysis of NDVI Time-Series（Hants）滤波重构NDVI时序曲线,通过对比待分像元NDVI时序曲线与参考时序曲线的相似性,实现农作物种植信息提取。对分类结果进行面积统计和空间分布精度检验：冬小麦、棉花、玉米的面积提取精度分别达到96.8%、95.5%、85.1%,空间匹配总体精度达86.9%。结果表明该方法有效可行,能够为该地区农业监测提供技术基础。     

半干旱山区采矿扰动植被指数时空变化规律

选取潞安矿区7个生产矿井中的8个试验工作面,采用概率积分法预测开采沉陷值;对2004—2007年7个时相(分别为2004年7月8日、11月1日,2005年2月1日、8月26日,2006年5月22日,2007年4月9日和6月1日)的SPOT2/4卫星遥感数据进行大气校正及波段运算,提取工作面开采沉陷前后的NDVI(归一化植被指数)平均值,经离散傅立叶变换得到NDVI时间序列曲线,以研究采矿扰动区植被指数的时空变化规律. 结果表明:①试验工作面地表覆被NDVI变化与采矿扰动区具有空间相关性. 非采矿扰动区(伪不变特征区)森林冠层的NDVI最大值由2004年的0.619451增至2007年的0.739987,平均年净增加6.18%. 在采矿扰动区,虽然开采前地表NDVI最大值呈增加趋势,但开采当年却显著下降,年均降幅达11.91%. ②试验工作面地表NDVI变化与采矿扰动具有时间相关性. NDVI在开采前表现相对稳定,受开采扰动虽出现下降但却滞后4～6个月,并且持续1～2a,其后转入上升期. 常村矿的S1-1#、S3-2#、N1-4#,漳村矿的2101#、2102#、2201#,五阳矿的5100#,王庄矿的5210#等8个试验工作面NDVI最大值年均降幅分别为12.24%、27.81%、15.79%、19.19%、7.19%、21.48%、13.25%和1.66%,平均值为14.83%. 在气候、耕作、采矿扰动等诸多因素影响下,采矿扰动是半干旱山区采矿区地表NDVI变化的主要诱因.      

太湖流域下垫面改变与气候变化的响应关系

运用两种NDVI数据集(Pathfinder AVHRR和SPOT VEGETATION)和卫星遥感数据,采用3S技术,通过人机交互式目视方法解译出1979、1984、2000和2009年太湖流域的土地利用数据,结合1956-2007年太湖流域主要气象站点的气象资料,研究了太湖流域下垫面(NDVI和土地利用)变化与各主要气候因子的响应关系。结果表明:①近30 a太湖流域NDVI变化呈先增后减的趋势,空间上呈由东北向西南递增的趋势,浙江省区域植被覆盖较好,其次为苏锡常镇地区,上海植被较为稀少;②太湖流域耕地面积显著减少,城镇用地显著增加,林地与草地呈缓慢增长趋势,其中上海和苏州城市化进程速度最快,其次是无锡、常州,而杭州、嘉兴、湖州和镇江城市化进程较为缓慢;③20世纪80年代初期太湖流域出现显著的增温,并在近20 a增温幅度显著增加,平均相对湿度呈波动下降趋势,其下降速率为-1.25%/10 a,近50 a降水总量呈现小幅上升趋势,但近20 a降水量呈减少趋势,速率达到-37.31 mm/10 a,日照时数呈现下降趋势,其下降速率为-56.66 h/10 a;④与太湖流域NDVI变化响应最为显著的气候因子为气温,其次为平均相对湿度以及日照时数,降水总量与NDVI的相关性比较弱;⑤城市化进程迅速的地区相较于城市化缓慢的地区,其增温更快、相对湿度降幅更大、降水量增加更为缓慢,日照时数减少越快。     

内蒙古典型草原作物系数和实际蒸散量的时空分布特征

利用内蒙古典型草原21个气象站点的气象和牧草观测资料,结合潜在蒸散量和改进的作物系数计算方法,模拟计算了2009年草原植被作物系数和实际蒸散量.在GIS软件的支持下,分析了二者的时空分布特点,并通过反映牧草长势的NDVI变化趋势予以验证.结果表明:5-8月间随着月份的增加作物系数Kc_x最大值的变化趋势由0.6→1.2→1.4→1.4,平均值是0.28→0.36→0.40→0.38.4个时期的Kc_x值以0.2~0.6之间的区域占主体,为55%以上.实际蒸散量在时间变化和空间分布上与Kc_x值基本一致.随着月份的增加实际蒸散量低值级的区域面积逐渐缩小,相对应的高值级的面积逐渐增大,整个生长季以30~90 mm的蒸散量为主.5-8月牧草实际蒸散量和NDVI值的相关系数达到0.446,通过了0.01水平的显著性检验.     

贵州省NDVI变化及其与主要气候因子的相关性

运用全球检测与模型研究(GIMMS)组制作的取每隔15 d最大值合成的归一化差异植被指数(NDVI)数据集和贵州省84个气象站点提供的气候资料,分析1987-2003年贵州省植被变化状况以及NDVI与主要气候因子温度、降水的相互关系.结果表明: 17 a间贵州省年均NDVI呈现缓慢下降趋势,但春季NDVI出现了一定幅度的增长,年均NDVI下降主要是冬季NDVI大幅下降造成.植被变化在年际尺度上与温度和降水均无显著相关,但在季节尺度上与春季温度在α=0.05水平上显著相关.整体上看,春季NDVI与温度和降水的相关系数高于其他季节;温度与NDVI的同季相关高于滞后相关,而降水与NDVI的滞后相关却高于同季相关;与温度的相关性高于降水.     

Temporal-spatial dynamics of vegetation variation on non-point source nutrient pollution

The temporal-spatial interaction of land cover and non-point source (NPS) nutrient pollution were analyzed with the Soil and Water Assessment Tool (SWAT) to simulate the temporal-spatial features of NPS nutrient loading in the upper stream of the Yellow River catchment. The corresponding land cover data variance was expressed by the normalized difference vegetation index (NDVI) that was calculated from MODIS images. It was noted that the temporal variation of land cover NDVI was significantly correlated with NPS nutrient loading. The regression analysis indicated that vegetation not only detained NPS nutrient pollution transportation, but also contributed to sustainable loading. The temporal analysis also confirmed that regional NDVI was an effective index for monthly assessment of NPS nitrogen and phosphorus loading. The spatial variations of NPS nutrient loading can be classified with land cover status. The high loadings of NPS nitrogen in high NDVI subbasins indicated that forestry and farmland are the main critical loss areas. Farmland contributed sustainable soluble N, but the loading of soluble and organic N from grassland subbasins was much lower. Most P loading came from the areas covered with dense grassland and forestry, which cannot directly discharge to local water bodies. However, some NPS phosphorus from suburban farmland can directly discharge into adjacent water bodies. The interactions among nutrient loading, NDVI, and slope were also analyzed. This study confirmed that the integration of NPS modeling, geographic information systems, and remote sensing is needed to understand the interactive dynamics of NPS nutrient loading. Understanding the temporal-spatial variation of NPS nutrients and their correlations with land cover will help NPS pollution prevention and water quality management efforts. Therefore, the proposed method for evaluating NPS nutrient loading by land cover NDVI can be an effective tool for pollution evaluation and watersheds planning.     

新疆植被遥感绿度指数与水、热关系的动态相关分析

基于1982-2003年间GIMMS发布的NOAA /AVHRR遥感数据和新疆自治区53个地面国家标准站点的气象数据,研究新疆归一化植被指数(NDVI)动态变化及其与气候的时空关系.结果表明,22 a间新疆植被NDVI年际变化总体上呈显著增长趋势,年平均增长率为0.59%,显著增长区域位于准噶尔盆地南缘和塔里木盆地西南缘;生长季、夏季和秋季NDVI与同季降水相关显著,春季、秋季NDVI与同季温度相关显著;NDVI与温度呈显著正相关的区域主要分布于阿尔泰山、天山和昆仑山等山区,与降水呈显著正相关的区域分布于平原、低山带和绿洲.     

黄淮海地区冬小麦生产力时空变化及其驱动机制分析

黄淮海地区是我国重要的粮食生产基地,分析该区域粮食产量的时空变化特征及其变化机制,对我国粮食安全的评估有重要的现实意义。论文以AVH RR NDVI数据和逐日气象要素驱动土壤-植被-大气系统物质传输和作物生长的耦合模型,模拟分析1981-2000年黄淮海地区冬小麦产量的时空分布及其驱动机制。分析发现,从1981-1997年生物产量基本呈增加趋势,之后有所下降。但由于作物经济系数不断增加,整个时段冬小麦经济产量增加趋势明显,单位面积产量提高了一倍。化肥施用量的增加和优良品种的推广是增产的主要原因,而气候波动导致区域年际产量变化幅度为8.5%。黄淮海地区冬小麦产量的空间分布及其演变呈现显著的地域特性,与当地灌溉条件、土壤条件密切相关。