Present plant/forest communities are the result of long-term interactions between vegetation and site factors including man-made impacts. Thus, present vegetation deviates from its natural state, and even from its ideal state under present site conditions, to some extent. On the basis of the self-regulation theory of ecosystems and the assumptions that (1) increase in species diversity does not always mean optimization and evolution of the vegetation/ecosystem, and that (2) the invasion of exotic species results from the structural changes in site conditions, we developed a method, which is based on biodiversity assessments and estimates an index that combines the quantitative and qualitative differences between the present vegetation and its theoretic ideal stage at the given site. The index can also be used to compare present vegetation of different ecosystems or vegetation types.

地球上的土地是绝大多数植物赖以生存而植物又是人类赖以生存的最基本的物质基础，因此，自人类存在以来，人们便以各种方式对土地和植被进行利用干扰。所以，地球上现存的植物或森林群落都是植被与其环境长期适应，及人类长期影响的综合结果，也因此，现实的植被已被迫或多或少地离开了其天然状态，甚至离开了它们在当前立地条件下的理想状态。如何评估某一立地上的现实植被与其理想状态的差距，以实现生物多样性保护，生态恢复与重建，及最终实现生态平衡，乃作者撰写此文之目的。