区域生态系统重心指标的概念与应用

The concept and application of centroids in the spatial analysis of regional ecosystems

生态系统重心的变化可以反映生态系统整体的空间变化的特征和趋势,但是,目前生态系统重心这一指标只是简单作为指示社会经济变化的因子,或是作为辅助的角色用于探索生态景观格局的变化,其重要性一直未受到足够的重视。在阐述生态系统重心指标的概念及内涵,总结国内外有关重心应用研究成果的基础上,以川滇两省共同确立的泸沽湖生态保护区为例,运用重心理论分析了1990—2005年该流域生态系统重心的变化及影响因素。结果表明,泸沽湖流域农田、森林、草地、湿地和人居用地均具有相对独立且稳定的重心区间。相对来说,人居用地和农田重心的变化幅度明显大于其他用地,其重心均总体向东南方向偏移,不断靠近泸沽湖水体。2005年人居用地和农田重心均有所回撤,这主要是因为2003年泸沽湖景区进行调整,政策的强制干预导致其重心回撤。分析重心变化的影响因素发现,区域旅游业发展带来的人类干扰加剧及国家的生态保护政策主导重心变化。在总结前人研究和应用案例具体分析发现,由于重心理论假设区域背景为匀质平面,分析是基于二维空间进行,而不考虑海拔维度,这就限制了重心模型应用的深度和广度。但是在泸沽湖这样地形复杂多变的区域,地形因素在该区域生态系统变化过程中的作用不容忽视。因此,应尽快完善在垂直空间应用重心理论的研究方法并加强相关研究。

Analyzing the movement of an ecosystem＇s centroid has proven to be a powerful tool for assessing and monitoring its spatial variation. However,since centroid analysis is used as a simple indicator of change in economics or sociology,or as a minor part of studies of landscape pattern distribution and change,the importance of analyzing ecosystem centroids is often overlooked in the field of ecology. This study summarizes the applications of calculating ecosystem centroids from studies from around the world,in order to understand its global trends in correlation studies better,and to identify theapplication potential based on its basic concept and connotations. The centroid theory has been applied in various fields,for example in social and economic development,agriculture,ecological monitoring,and mapping. In this study,we applied the centroid theory to analyze the temporal and spatial distribution of the ecosystem centroid in Lugu Lake,where its distinct boundary was collectively determined by Yunnan Province and Sichuan Province,and its surrounding areas. We also determined how the centroids changed from 1990 to 2005（ e. g.,their positions,movement directions,and movement distances）. The results showed each ecosystem had a relatively independent and stable centroid in the region. This was caused by the effective conservation efforts of local governments and organizations and,particularly,the effective policies and measures that have been implemented in recent years. Compared with forest,grassland,and wetland ecosystems,builtup land and cropland ecosystems changed more profoundly. As for the extent and direction of centroid changes,the centroids of forest,grassland,and wetland ecosystems moved continuously back and forth in a relatively small area,indicating that these ecosystems were in a relatively dynamic equilibrium. The centroids of built-up land and cropland generally moved from northwest to southeast,and they continuously got closer to the water to utilize the water resource more conveniently. In addition,the centroids of built-up land and cropland to some extent move back in the opposite direction in 2005. The latter was caused by the government＇ s effective policy interventions in 2003,which regulate ecological patterns and coordinate conflicts between the environment and development. Furthermore, increased human-induced disturbances, especially tourism developments,can be a trigger for ecosystem centroids to move towards Lugu Lake,whereas national ecological protection policies lead to movements in the opposite direction of Lugu Lake. Additionally we found that currently,ecosystem centroid analyses are often conducted in two dimensions,without accounting for the third dimension of altitude due to the complexity of vertical space. However,in regions with complex terrain,like Lugu Lake,the terrain factors should not be ignored in the process of regional ecosystem changes. Therefore,the blank centroid theory in vertical dimension should be developed further,and the corresponding research methods completed urgently,in order to continuously expand and improve the applications of ecosystem centroids.