The importance of plant root characteristics in controlling concentrated flow erosion rates

While it has been demonstrated in numerous studies that the aboveground characteristics of the vegetation are of particular importance with respect to soil erosion control, this study argues the importance of separating the influence of vegetation on soil erosion rates into two parts: the impact of leaves and stems (aboveground biomass) and the influence of roots (belowground biomass). Although both plant parameters form inseparable constituents of the total plant organism, most studies attribute the impact of vegetation on soil erosion rates mainly to the characteristics of the aboveground biomass. This triggers the question whether the belowground biomass is of no or negligible importance with respect to soil erosion by concentrated flow. This study tried to answer this question by comparing cross‐sectional areas of concentrated flow channels (rills and ephemeral gullies) in the Belgian Loess Belt for different cereal and grass plant densities. The results of these measurements highlighted the fact that both an increase in shoot density as well as an increase in root density resulted in an exponential decrease of concentrated flow erosion rates. Since protection of the soil surface in the early plant growth stages is crucial with respect to the reduction of water erosion rates, increasing the plant root density in the topsoil could be a viable erosion control strategy. Copyright © 2003 John Wiley & Sons, Ltd.     

A statistical approach to evaluating distance metrics and analog assignments for pollen records

The modern analog technique typically uses a distance metric to determine the dissimilarity between fossil and modern biological assemblages. Despite this quantitative approach, interpretation of distance metrics is usually qualitative and rules for selection of analogs tend to be ad hoc. We present a statistical tool, the receiver operating characteristic (ROC) curve, which provides a framework for identifying analogs from distance metrics. If modern assemblages are placed into groups (e.g., biomes), this method can (1) evaluate the ability of different distance metrics to distinguish among groups, (2) objectively identify thresholds of the distance metric for determining analogs, and (3) compute a likelihood ratio and a Bayesian probability that a modern group is an analog for an unknown (fossil) assemblage. Applied to a set of 1689 modern pollen assemblages from eastern North America classified into eight biomes, ROC analysis confirmed that the squared-chord distance (SCD) outperforms most other distance metrics. The optimal threshold increased when more dissimilar biomes were compared. The probability of an analog vs no-analog result (a likelihood ratio) increased sharply when SCD decreased below the optimal threshold, indicating a nonlinear relationship between SCD and the probability of analog. Probabilities of analog computed for a postglacial pollen record at Tannersville Bog (Pennsylvania, USA) identified transitions between biomes and periods of no analog.     

基于资源卫星图像对NDVI进行大气修正的一种简单方法

在遥感应用领域，植被指数己被广泛用来定性和定量表征植被覆盖度及其生长状况。由于大气变化的影响，使植被指数未能真实反映地表植被的真实分布状况，造成其应用的局限性。提出了一种简易方法，仅通过中巴资源卫星(CBERS：China Brazil Environment Resoure Satellite)图像的第3、第4波段中的水体，推算卫星接收到的大气程辐射，消除了大气对归一化植被指数(NDVI：Normalized Differece Vege—tation Index)的影响，减小植被指数所受的大气影响。应用结果表明，该方法能使植被指数较好地反映植被的生长及分布状况。     

气象卫星遥感预警福建省森林火灾

应用NOAA卫星遥感资料，研究森林防火期内森林植被的干燥指数的变化，结合分析相应的森林火灾的资料，做出福建省森林火险等级空间分布，应用福建省地理信息系统，根据高火险等级的地理位置，预警该地可能发生森林火灾。     

The Influence of Vegetation Cover on Summer Precipitation in China： a Statistical Analysis of NDVI and Climate Data

This study provides new evidence for the feedback effects of vegetation cover on summer precipitation in different regions of China by calculating immediate (same season), and one-and two-season lagged correlations between the normalized difference vegetation index (NDVI) and summer precipitation. The results show that the correlation coefficients between NDVI in spring and the previous winter and precipitation in summer are positive in most regions of China, and they show significant difference between regions. The stronger one-and two-season lagged correlations occur in the eastern arid/semi-arid region, Central China,and Southwest China out of the eight climatic regions of China, and this implies that vegetation cover change has more sensitive feedback effects on summer precipitation in the three regions. The three regions are defined as sensitive regions. Spatial analyses of correlations between spring NDVI averaged over each sensitive region and summer precipitation of 160 stations suggest that the vegetation cover strongly affects summer precipitation not only over the sensitive region itself but also over other regions, especially the downstream region.     

植被冠层多角度遥感研究进展

综述了近年来关于植被冠层多角度遥感研究的最新成果，分别讨论了二向性反射的正向模型和参量反演问题在理论和实际应用中的新进展。分析了卫星平台多角度遥感的应用前景及面临的困难，指出了未来多角度遥感研究的新方向。     

上海自然植被的特征、分区与保护

上海地区有种子植物约134科510属919种。种子植物的分区类型共15°个,其中泛热带分布、北温带和东亚分布各占总属数的27.8%、21.6%和11.9%.地带性植被以常绿阔叶林和常绿落叶阔叶混交林为主,其中红楠群落和青冈栎群落能较好地反映中亚热带的植被和环境特征。非地带性植被以潮间带植被和水生植被为主。上海自然植被的类型和分布规律反映了本区地处中亚热带向北亚热带过渡地带的气候特征以及濒江临海的环境特点。同时其现状也表明了上海的自然植被处于不断增长的压力之下所发生的变化,因此亟需加以保护。上海的植被区划可分为隶属于北亚热带常绿落叶阔叶林地带的河口沙洲植被区,碟缘高地植被区和东北淀泖低地植被区,以及隶属于中亚热带常绿阔叶林地带的西南丘陵、低地植被区等。     

RELATIONSHIP OF ECO-ENVIONMENTAL CHANGE WITH NATURAL EROSION AND ARTIFICIALLY ACCELERATED EROSION

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甘肃窑街寺湾沟－炭洞沟红层孢粉组合、地质时代与生态环境

对窑街寺湾沟－炭洞沟红层孢粉和地层层序及时代进行了系统分析与对比研究。在该剖面中划分出２个孢粉组合：①双束松粉属－无口器粉属－杉粉属－栎粉属－瘤面海金砂孢属组合，时代为早渐新世；②双束松粉属－拟桦粉属－栎粉属－藜粉属－瘤面海金沙孢属组合，属中渐新世。研究表明：窑街寺湾沟－炭洞沟红层剖面的层位位于朱儿庄剖面之上，整个窑街地区的红层剖面属始新统－中渐新统；窑街地区始新世孢粉组合与中国东、西部地区孢粉组合相似，均发育以亚热带和暖温带植物为主的亚热带型落叶阔叶林，气候炎热；始新世晚期至早渐新世则演变为以暖温带落叶阔叶树种为主的针阔叶混交林植被，气候温暖湿润；中渐新世为暖温带落叶阔叶林，气候较温暖湿润。区域对比分析表明，从渐新世早期中国东、西部植被开始出现差异并逐渐加大，该时期也许是中国新构造运动的一个重要时期。     

Dynamik der Schilfröhrichte am Bodensee unter dem Einfluss von Wasserstandsvariationen

On the basis of different sets of aerial photos the dynamics of the reed bed areas of Lake Constance were investigated in relation to the dynamics of the water levels. The objectives of the study were to quantify the changes of reed areas due to different flood events in the last decades and their recovery in the time periods between these events. The results should given information of the relevance of water level variations on reed bed dynamics and the regeneration times of reed beds after extreme disturbance events.Following the extreme flood at Lake Constance in 1999 the reed belts of Lake Constance lost approximately 30 ha (24%) of the lakeside reed beds. The loss is comparable to the situation in the late 1960s, when approximately 40 ha died back due to the extreme flood in 1965 and the high spring water levels in the subsequent years. In the time period between the extreme floods of 1965 and 1999, the reed areas expanded to nearly 85% of the area before 1965. The expansion rates increased with increasing distance to the flood event of 1965. Especially in periods with series of years of low spring water level the expansion rates were high.The damage degrees of the reed areas in the years 2000 and 2002 showed a clear relation to the elevation (i.e. average water level) of the stands. The damage degree increased with decreasing elevation. Furthermore the regeneration process of severely damaged stands was related to the elevation level of the stands. Whereas stands at high elevation regenerate fast, those at low elevation died off completely in the years after the extreme flood. This supports the hypothesis that the water level flutuations play a major role in the reed dynamics of Lake Constance.As a consequence of the climate change an increase in the frequency of high spring water levels is expected. Thus, it seems unlikely that reed stands will ever expand again to the same area as before 1965.