东江流域1989–2009年土地利用变化对生态承载力的影响

Impact of land use change during 1989–2009 on eco-capacity in Dongjiang watershed

探索流域生态承载力随土地利用类型及人口数量变化的时空变化格局对流域的可持续发展规划具有重要的生态意义。该研究通过对东江流域1989年、1994年、1999年、2004年、2009年5个时期Landsat-5 TM遥感影像的解译与分析,利用变化率、单一动态度、综合动态度等指标,探索了东江流域上、中、下游土地利用类型变化的时空格局。基于土地利用类型、东江流域人口数量、均衡因子、产量因子等数据,进一步计算了东江流域人均生态承载力和总生态承载力,并分析了影响生态承载力消长的因素。结果表明:(1)1989–2009年东江流域各类用地结构调整明显。在城镇化加剧的同时,森林植被也在改善,两者并非是消长关系。但是上、中、下游表现出不同的变化格局,上游和中游以园地向林地转移为主,下游以耕地向城镇用地转移为主。(2)在1989–2009年20年间东江流域人口持续增长的情况下,虽然流域人均生态承载力呈下降的趋势,但其下降的幅度低于人口的增长速度,总生态承载力仍呈增长的趋势,说明20年间土地利用类型在优化发展。从时间来看,"十年绿化广东"结束之后的10年间(1994–2004年),在人口增长的压力下,人均生态承载力趋于相对平稳的状态。而之前的5年(1989–1994年)和之后的5年间(2004–2009年),年人均生态承载力下降较明显,前者与改革开放初期的大量开发有关,后者与土地利用空间可优化的类型越来越少有关。流域内部不同区域的总生态承载力的变化趋势不尽相同,上游和中游表现为先减小后增加的趋势,下游表现为先增加后减小又恢复的趋势。综合来看,东江流域人口对城镇化需求增加的同时,并没有导致森林资源的恶化,一定程度上实现了两者的协调发展。因而,在人口增长对生态资源需求增长的情况下,可以通过优化土地利用类型和提高总体生态服务功能,来缓冲人均生态承载力下降的趋势。

Aims For sustainable watershed development planning, this study explores how ecological carrying capacity varies with changes in land use type and population. Methods Based on interpretation and analysis of five Landsat TM remote sensing images for 1989, 1994, 1999, 2004, and 2009, respectively, we examined the spatio-temporal patterns of land use change in the upper, middle, and lower reaches of Dongjiang watershed, using the total rate of change and single and integrated degree of land use dynamics as indicators. We calculated the total and per capita eco-capacity for the watershed in different years based on the population data, equivalence factors, and yield factors, in addition to the data of land use and land cover change, and further analyzed the factors determining the direction of changes in the eco-capacity. Important findings The results showed that：（1） there were apparent changes in the area for various land use types between 1989 and 2009. Despite the urban development, the coverage of forest vegetation increased, indicating lack of trade-off between urbanization and vegetation coverage. However, there were different patterns of change in land use among the upper, middle, and lower reaches. The land use type mainly varied from garden fields to forests in the upper and middle reaches of the watershed, while in the lower reach a change from arable land to build-up area dominated.（2） With the population growth along the Dongjiang watershed over the past two decades, although the per capita eco-capacity indicated a downward trend, its rate of decline lagged behind thepopulation growth rate, and the total eco-capacity still showed a trend of increase, implying an optimization of land use types during the 20-year period. With respect to the temporal patterns, in the decade（1994–2004） after the end of the ＂10-year greening of Guangdong Province＂, per capita eco-capacity tended to be relatively stable under the pressure of population growth, while it declined quickly in the periods of 1989–1994 and 2004–2009. The former period was probably associated with the development of reform and opening up policy, and the latter seemed to have less possibility on spatial optimization of land use types. The total eco-capacity showed different trends among the three regions; the upper and middle reaches exhibited an unstable trend（i.e., from decreasing to increasing）, while the lower reach indicated a pattern of increasing–decreasing–stable trend. In conclusion, the increasing population demand for urbanization did not lead to deterioration of the forest resources in the watershed. To some extent, we could thus achieve the coordinated development in both aspects. In spite of increasing demand on ecological resources with population growth, we could establish a better strategy in land use to improve ecological services, and to reduce the downward trend in the per capita eco-capacity.