The dead wood of primeval Abies of Sejila Mountain in Southeastern Tibet was studied by the investigations of the permanent standard plot (100m×100m) and temporary sample plot (20m×30m) as a supplement. The results show that the dead wood is composed mainly of the standing die, the uprooted blown down, the breakage at trunk and the blown down. The main reasons for weakening trees are the old-age and rot disease of trees, and indirect factors to induce tree fallen include strong wind, rain, snow and human in...