封育和放牧对高寒草甸植被群落特征和土壤特性的影响

为探究封育和放牧对高寒草甸植被群落和土壤特性的影响,本研究以封育13年和连续放牧高寒草甸为研究对象,采用野外群落调查和室内土壤分析相结合的方法,探究封育和放牧对植被群落状况和土壤特性的影响。结果表明：封育显著提高了群落的盖度和地上生物量（P<0.01）;封育显著提高了0~30 cm土壤总氮（Total nitrogen,TN）、速效氮（Available nitrogen,AN）、速效磷（Available phosphorus,AP）和速效钾（Available potassium,AK）（P<0.01）;封育显著降低了群落密度、物种丰富度指数、香农-维纳多样性指数和均匀度指数（P<0.01）。总之,封育虽增加了高寒草甸植物群落生物量和土壤养分,但在一定程度上导致草地植物群落多样性的下降,研究建议针对封育13年的高寒草甸进行适当的放牧以增加群落物种多样性和丰富度。     

鄂尔多斯高原北部沙区主要植被类型下土壤要素的空间分析

鄂尔多斯北部沙区存在着极为显著的风沙地貌,在此格局基础之上,特别是在植被与土壤的相互响应过程中,二者的相互关系逐渐密切,这种反馈作用使得该区域的植被与土壤要素形成的空间分布格局具有一定的耦合性。研究这种关系可以为该地区保护植被和合理利用土地资源提供科学依据。     

基于Landsat数据的条件植被温度指数升尺度转换方法

以陕西省关中平原为研究区域,应用点扩散函数、混合像素面积权重法和中值像素变异权重法将基于Landsat卫星遥感数据反演的分辨率为30 m的条件植被温度指数(VTCI)干旱监测结果上推至930 m的干旱监测结果,并与Aqua MODIS数据反演的分辨率为930 m的VTCI干旱监测结果进行对比分析,以期为两种空间尺度的干旱监测结果的综合应用提供技术支持。以MODIS数据反演的VTCI为参考,应用相关系数、均方根误差、半变异函数的估计值和图像纹理特征等对尺度上推的VTCI进行评价。结果表明,点扩散函数和混合像素面积权重法的尺度上推效果均较好,而中值像素变异权重法的尺度上推效果较差,说明点扩散函数和混合像素面积权重法均适用于研究区域VTCI干旱监测结果的尺度转换,且点扩散函数的数据处理过程更为简单。典型样点VTCI的尺度上推结果表明,空间异质性越小,尺度上推的结果越好。     

植被信息提取过程中ETM+遥感影像融合和分类试验

利用HIS、PCA、Brovey及小波变换4种图像融合方法对南京地区植被信息提取过程中ETM 遥感影像进行融合和分类试验。从信息量、高分辨率信息的融入度和分类精度三方面,对融合图像进行光谱质量和空间结构信息的定量评价。试验结果表明,Brovey变换更适合植被信息提取时的ETM 图像融合,并能够较明显提高影像的分类精度。     

军事医学科学院2006-2009年在CMCI收录期刊上发表的论文及其被引情况

对军事医学科学院2006-2009年在CMCI收录期刊发表的论文及其被引情况进行了分析,以期对该院未来的学科发展有所帮助。     

Soil nitrogen and denitrification potential as affected by land use and stand age following agricultural abandonment in a headwater catchment

Changes in vegetation and soil properties because of agricultural abandonment may affect soil nitrogen (N) and associated processes. We investigated soil N (total N: TN, inorganic N: NH₄–N and NO₃–N) and denitrification potential in cropland, pine plantations and abandoned agricultural land along a secondary succession sequence (grassland→shrubland→secondary forest) in a headwater catchment in the Qinling Mountains, northwest China. The results show that the soil denitrification potential differed significantly among the five land‐use types with the highest potential in the secondary forest, followed by grassland, shrubland, cropland and plantations. The denitrification potential of the 20‐ to 40‐cm layer was significantly lower compared with the topsoil (0–20 cm) across all land‐use types. TN, soil organic matter (SOM) and NH₄–N increased significantly with stand age, whereas there was an opposite trend in soil pH. However, the denitrification potential did not relate to stand age in a linear manner. We conclude that changes in soil TN, SOM and pH during vegetation succession following agricultural abandonment are critical controls on the denitrification potential.     

Postcards from the past: charting the landscape-scale conversion of tropical Australian savanna to closed forest during the 20th century

Repeated sequences of digitised and geo-referenced historical aerial photography provide a powerful means of understanding landscape change. We use this method to demonstrate a landscape wide expansion of closed forest (42% increase in total coverage) in the Australian monsoon tropics over the past five decades. Retrospective habitat suitability models (HSI) of closed forest derived using four landscape measures (drainage distance, slope angle, aspect and elevation) for imagery taken in 1947 correctly forecast the subsequent spatial distribution of the expansion, with topographic fire protection primarily determining the closed-forest distribution. The dynamics of the closed forest-savanna boundary were predicted accurately by generalised linear models, with closed-forest expansion in fire-protected sites along forest edges and regression in the more fire-prone areas. Two factors may plausibly explain the expansion of closed forests. First, eco-ethnographic records stress the skilful use of fire by Aboriginal people in protecting isolated and locally resource-rich closed-forest patches. Second, the recent global increase in atmospheric CO₂ may be changing the competitive balance between savanna and forest by enabling C₃ trees to grow fast enough to escape the fire trap presented by flammable C₄ grasses.     

Determining landscape extent for succession and disturbance simulation modeling

Dividing regions into manageable landscape units presents special problems in landscape ecology and land management. Ideally, a landscape should be large enough to capture a broad range of vegetation, environmental and disturbance dynamics, but small enough to be useful for focused management objectives. The purpose of this study was to determine the optimal landscape size to summarize ecological processes for two large land areas in the southwestern United States. We used a vegetation and disturbance dynamics model, LANDSUMv4, to simulate a set of nine scenarios involving systematically varied topography, map resolution, and model parameterizations of fire size and fire frequency. Spatial input data were supplied by the LANDscape FIRE Management Planning System (LANDFIRE) prototype project, an effort that will provide comprehensive and scientifically credible mid-scale data to support the National Fire Plan. We analyzed output from 2,000 year simulations to determine the thresholds of landscape condition based on the variability of burned area and dominant vegetation coverage. Results show that optimal landscape extent using burned area variability is approximately 100 km² depending on topography, map resolution, and model parameterization. Variability of dominant vegetation area is generally higher and the optimal landscape sizes are larger in comparison to those features determined from burned area. Using the LANDFIRE project as a case study, we determined landscape size and map resolution for a large mapping project, and showed that optimal landscape size depends upon geographical, ecological, and management context. This paper was written and prepared by U.S. Government employees on official time, and therefore is in the public domain and not subject to copyright. The use of trade or firm names in this paper is for reader information and does not imply endorsement by the U.S. Department of Agriculture of any product or service.     

Multi-scale study of bird species distribution and of their response to vegetation change: a Mediterranean example

Land use changes operate at different scales. They trigger a cascade of effects that simultaneously modify the composition or structure of the landscape and of the local vegetation. Mobil animals, and birds in particular, can respond quickly to such multi-scalar changes. We took advantage of a long term study on the response of songbirds to land-use changes on four Mediterranean islands in Corsica and Sardinia to explore the benefits of a multi-scale analysis of the relationships between songbird distribution, vegetation structure and landscape dynamics. Field data and aerial photographs were used to describe the vegetation at three different scales. Birds were censused by point counts. We used statistical variance decomposition to study how bird distribution and vegetation at various scales were linked. We analysed multi-scale vegetation changes (floristic composition, plot vegetation type, and landscape structure) and their consequences on bird distribution with multivariate and non-parametrical tests. The distribution of most species was linked to at least two spatial scales. The weight of a given scale was consistent with life-history traits for species whose biology was well-known. In the examples studied, vegetation composition, vegetation type and landscape changes that resulted from land abandonment negatively affected birds depending on open or heterogeneous areas. Our results emphasize that multi-scale analyses can greatly enhance our understanding of bird distribution and of their changes. Management of these populations should take into account measures at various spatial scales depending on the sensitivity of the species.     

草地植被盖度的近距离遥感测定

盖度或者覆盖度是植物群落结构的一个重要数量指标。通常的目视估测植物群落盖度方法不仅精度低,而且因人而异。本研究采用近距离遥感方法测定草地植物群落盖度,该方法主要包括数据获取、图像处理、像元数量提取和盖度计算4个部分。精度评价表明,该方法测定的绿色植被盖度误差很小,与目视估测方法比较,它具有客观、一致和精度高的优点。