Secondary succession in two subtropical forests

We studied secondary succession in two subtropical evergreen broad-leaved forests near Shanghai, China that had been harvested 2-60 years earlier. Shrubs were thinned in one of the forests to about 60% of their original density for the first 20 years after harvesting. The other was not disturbed after harvesting. Five stands were sampled in each forest. Species composition and richness varied little during succession. Biomass, soil organic matter, total soil nitrogen, and soil water all increased with time. Soil organic matter and total nitrogen were significantly less in thinned forest than in undisturbed forests, but soil moisture did not vary with shrub thinning. Total tree density did not change over time, suggesting that species replacements were not driven by self-thinning. The eventual replacement of shrubs by trees occurred because shrub density decreased whereas tree density remained constant and tree mass increased.