Abstract: From altitude of 400 to 1000 m on the northern slope of Dahei Mountain,western Liaoning three sample belts were set with 100 m horizontal intervals and in every belt seven plots were investigated with an interval of 100 m to study the composition and biodiversity of forest communities and their variations along altitude.The results showed that the canopy density and average DBH obviously increased with the increasing elevation,as well as the basal area.The area over 800 m was covered by original mountainous vegetation as core area,while the area under 700 m was mainly covered by sparse woods and plantation.The composition of dominant tree species displayed a transitional tendency from complexity to simplicity with the increasing elevation.The Shannon diversity index of arbors and shrubs nearly linearly decreased with the increasing elevation,while their extents of dominance increased obviously with altitude.Compared with the layers of arbors and shrubs,the herbs have higher extent of dominance and lower diversity index variation with altitude.Horizontal β diversity decreased quickly with the increasing elevation,showing that low-elevation forests were not only locally more diverse,but also spatially more patchy.

Key words: Water stress, Phellodendron amurense, Cell protective enzyme, Lipid peroxidation