A preliminary probe into the secondary succession series of tropical forests in the big bend gorge of Yalu Tsangpo River in S.E. Tibet, E. Himalayas.
The characteristics of tropical forests and their secondary succession series in this region of Tibet [Xizhang] are described. The forests occur in the bottom of the gorge at an altitude of 600-1200 m, and are classified as low mountain semi-evergreen tropical rain forests. They include 3 main types: Altingia excelsa/Terminalia myriocarpa forest; Altingia excelsa/Lagerstroemia minuticarpa forest; and Altingia excelsa forest. The natural and artificial factors causing the destruction of the original semi-evergreen tropical rain forest are discussed. They have led to 2 secondary successional series. The first, caused by natural factors, went through about 6 stages: (1) Alnus nepalensis colonizing the area; (2) Alnus nepalensis forming relatively stable communities; (3) dominant trees of the original vegetation invading the Alnus nepalensis community; (4) dominant trees of the original vegetation developing and Alnus nepalensis declining; (5) the prevailing trees of the original vegetation gradually becoming dominant; and (6) a return to the original vegetation. The second successional series, caused by artificial factors, went through about 5 stages: (1) colonization and community formation by tropical high grasses; (2) invasion of the community by Musa balbisiana; (3) colonization and growth by heliophytes, shrubs and trees; (4) formation of a mixed tree community; and (5) a return to the original vegetation. Protection of the biodiversity of the region is urged.