STRUCTURE AND DYNAMICS OF SUB-ALPINE FORESTS IN THE WANG-LANG-NATURAL-RESERVE, SICHUAN, CHINA

Population structure (size, age, spatial patterns) and radial growth p atterns are used to analyze regeneration patterns of Abies faxoniana, Betula albosinensis, Betula utilis, Larix potaninii, Picea purpurea, a nd Sabina saltuaria and reconstruct disturbance history in 8 subalpine forest stands in Wang Lang Natural Reserve, Sichuan, China. In old-gr owth stands tree regeneration occurs in tree-fall gaps whereby A. faxo niana, Betula sp., P. purpurea, and S. saltuaria persist at stand scal es by gap-phase regeneration. Clump sizes of young populations are sim ilar to canopy gap sizes but clumps sizes vary among species. Young Be tula patches are larger than those of A. faxoniana suggesting that gap -partitioning by size contributes to species coexistence in mixed stan ds. Picea purpurea and S. saltuaria are longer lived than A. faxoniana which may compensate for lower recruitment and prevent their replacem ent by A. faxoniana. Tree regeneration and community structure are als o influenced by the understory bamboo Fargesia denudata. Seedlings, sa plings, and shrub density all decline with an increase in bamboo cover . Species that regenerate in old-growth forest also regenerate after f looding as do species that establish only on bare substrates (i.e. Lar ix potaninii, Prunus sp.). Structural and compositional patterns in Wa ng Lang forests are a reflection of disturbance history, canopy specie s life history attributes such as dispersal ability, shade tolerance, growth rates, and longevity, and competition of trees and shrubs with understory bamboos.