Abstract:

By adopting the concept of space as a substitute for time,we analyzed the dynamics of species composition and diversity of different restoration series(20,30,40 and 50 years)in two secondary forest types in western Sichuan,China,distributing in the north or north west aspect based on the 50 plots at the altitudes between 3 100～3 600 m,the forests came from natural regeneration in combination with reforestation of spruce when the old-growth bamboo-dark brown coniferous forests and moss-dark brown coniferous old growth forests were harvested and the similar old-growth dark brown coniferous forests with the ages of 160～200 years were selected as the reference forests for comparisons.We recorded 167 species of vascular plants from 44 families and 117 genera.There was no significant difference in terms of species number among secondary forests,but the importance value of dominant species varied with restoration processes.The dominant species in the secondary forests is Betula albo-sinensis,While Abies faxoniana is the dominant species in old-growth dark brown coniferous forests.Species richness increased significantly with restoration processes.It increased quickly in secondary forests during the period of 30～40 years,but decreased significantly in the old-growth dark brown coniferous forests.The species richness among growth forms varied as follows:herb layer>shrub layer>tree layer.The maximum value of evenness index occurred in secondary forests with age of 40 years,and remained relatively stable in bamboo-birch forests,but evenness index tended to decrease in moss-birch forests and slightly increased in the old-growth moss-dark brown coniferous forests.There was significant difference in evenness index between tree layer and shrub layer,and between tree layer and herb layer,respectively.But there was not significantly difference between shrub layer and herb layer.The value of Shannon index varied with an increasing trend with increasing restoration time.In bamboo-birch forests,the maximum value of Shannon index was 3.796 7,which recorded in the forest with age of 50 years.However,in moss-birch forest,the maximal value was 3.654 3,which recorded in the forest with age of 30 years.The value of Shannon index of old-growth dark coniferous forests was recorded between younger secondary and older secondary forests.The value of dominance index of communities varied in a increasing way firstly,and then in a decreasing way.The dominance index of tree layer had the similar trend with community dominance index,but with large variation.The minimum value of dominance index of tree layer which moss-birch forests reached ahead of 20 years earlier than that of bamboo-birch forests.There was significant difference among restoration series on α diversity except dominance index,but not significant difference between two secondary forest types.With increasing age,the value of Bray-Curtis index between secondary forest and old-growth dark brown coniferous forest had an increasing trend.

Key words: species composition, species diversity, degradation dark brown coniferous forests, forest restoration, sub-alpine, western Sichuan