Abstract: In July 7 th to 9th of 1983,a serious calamity from mountain torrents was happened in theupper sections of Liuyang River of Hunan province.Investigation shows that this calamity isrelated to landforms,topography,properties of rocks and soils,climate,vegetation and humanactivities.Among internal causes,forest vegetation is the main one,and among external causes——human activities.This calamity is also the result from cuantitative to qualitative changesof three great ecological crises——population explosion,forest exhausion and environmental deterioration.

Key words: Taxus chinensis var. mairei, Population, Spatial pattern, Dynamics