喀斯特生态脆弱区桂西北土地变化特征

The characteristic of land changes in ecologically fragile Kast Areas:a case study in Northwest Guangxi,China

土地变化(LC)是当前国际全球变化研究的前沿和热点领域,喀斯特生态脆弱区的土地变化是国际LC研究中的薄弱环节。以典型喀斯特区域桂西北为例,通过详实的地面调查,以1985年、1990年和2000年的LandsatTM(ETM)影像为主要数据源,在3S集成技术支撑下,应用单一土地利用动态度、单一土地利用转入率和转出率、综合土地利用动态度、土地利用度以及土地变化空间指数等指标,定量研究了桂西北过去15a来的土地变化特征。研究表明:(1)研究区的土地类型主要以灌木、林地和稀疏地为主(在各个年份总比例分别为73.72%、74.14%和73.59%),居民建设用地少(3个年份分别为0.37%、0.37%和0.41%),石漠化地和稀疏地比例高(总比例分别为20.44%、22.84%和20.44%);(2)土地变化剧烈,各地类之间的变化幅度差别较大,旱地、石漠化地和林地等先减后增;水田、稀疏地和草地等先增后减;居民地持续增加型;(3)受降水量和生态移民影响,区域土地动态度先低后高(分别为63.54%和93.87%),石漠化地先减后增,生态环境向恶化方向发展;(4)伴随着土地类型转换的伸缩变化,各地类的平均分布高程和坡度也出现相应的变化。

Karst areas have usually poor geochemical conditions and fragile ecology, due to rocky desertification which is often induced by ineffective land uses and management. To understand land change in the Karst region over the past 20 years in North-western Guangxi, China, indexes of singe land change velocity, comprehensive land change velocity, land use degree, and spatial distribution were investigated by land surveys, and analyzed used information from remote sensed images of Landsat TM in 1985, 1990 and 2000, and RS, GIS and GPS techniques. The results show that shrub, woodland, and sparseness land were the main land types in the region （total ratios were 73.72%, 74.14% and 73.59% in the three years respectively）, where the proportions of rocky land and sparseness were high （total ratios were 20.44%, 22.84% and 20.44% in the three years respectively）. Land types in the study area have changed dramatically between 1985 and 2000. There were significant differences in land changes among different land types. Arable land, rocky land and woodland decreased in the early phase of the period, but increased afterwards, while paddy field, sparseness and grassland changed opposite, resident land increased continuously. Due to the influences of the precipitation and the environmental immigrant, the land change velocity and land use degree during the period from 1990 to 2000 were higher than those from 1985 to 1990 （93.87% and 63.54% respectively）. Since 1990, the rocky land increased and the ecological quality declined.