本文将生态脆弱性分为潜在脆弱性与现实脆弱性。根据南方丘陵易侵蚀退化脆弱区的脆弱因子分析,选择高度、坡度、土壤可蚀性K值、降雨量、暴雨量、多雨期降雨比重和少雨期干旱指数为潜在生态脆弱度指标;选取森林覆盖率和坡耕地指数作为现实脆弱度评估的人为修正指标,计算现实生态脆弱度。计算结果显示,衡阳盆地大部分的潜在生态脆弱性为轻度脆弱,其中盆地中部的衡南县脆弱度最大,衡阳县次之;无论1984年还是2000年的现实生态脆弱度,均以衡南县最大,祁东县次之;各县2000年的现实脆弱度均比1984年有所下降,其中下降幅度最大的是衡阳县,下降幅度最小的是衡南县。

The vulnerability assessment in this paper is based on the following points: 1) The vulnerable eco-environment is that with unstable structure,therefore it is sensitive to outside interfere factor sensitive and is easy to develop deterioration under external interference,and the self-restoring force of the eco-environment is worse.2) The type of vulnerability in the research area belongs to that being liable to be degradated caused by erosion,so the authors choose the key element and major indicator which are easy to cause erosion as the assessment indices.3) The vulnerability of ecosystem includes the potential vulnerability before influenced by human activity and the realistic vulnerability after influenced by human activity.This paper chooses altitude,gradient,soil erosion index K,annual rainfall,the proportion of rainfall in rainy period and the drought index of rainless period as an evaluation system of potential ecological vulnerability.In addition to the above factors,two other factors-forest coverage and sloping land index are added to denote the comprehensive effects of regional human-earth relation,economic development and managing level.The revised system indicates the realistic vulnerability. This paper takes Hengyang Basin as a case to study the evaluated potential vulnerability degree of the relevant counties and the realistic vulnerability degree of the same counties respectively in 1984 and 2000.The calculation results show that the potential environmental vulnerability in most parts of Hengyang Basin is at light degree,among them the vulnerable degree of Hengnan County in the central part of the basin is the biggest and Hengyang County comes second.Either in 1984 or 2000,the realistic ecological the vulnerability degree is the biggest in Hengnan County and Qidong County comes next.Comparing the realistic vulnerability degree in 1984 with that in 2000,the latter of all the counties reduces to various degree,among them,Hengyang County reduces the most and the least is Hengnan County.The assessment results show that the eco-logical vulnerability of Hengyang Basin is relatively low before the environment is destroyed by human activity,tending to be absolute degradation and relative restoration.Among all of the counties,the ecosystem of Hengnan County located in the middle part of the Hengyang Basin is most vulnerable,so the degradation here is serious and the restoration is very difficult.