Microenvironment Characteristics and Dynamic Regeneration of Seedlings in Schima superba Forest Gaps

Forest gaps of small, medium and large gaps were selected to examine their impacts on microclimate, soil properties and seedling regeneration in Schima superba stand on Jianglang Mountain, Jiangshan City, Zhejiang Province. The results shows illumination intensity were significantly increased with the rise of gap size, whereas moisture showed the opposite trend; the lower the temperature, the greater the relative humidity. The regeneration density of S. superba was maximum in medium forest gaps and lowest in non-forest gaps. The density of medium forest gaps was 41.20%, 57.15% and 49.66% higher than small, large and non-forest gaps; the seedling height, sapling diameter and sapling height in medium forest gaps were higher than those in small and large forest gaps, suggesting suitable environmental conditions of the balance of humidity and illumination intensity for seedling growth in the medium forest gaps. Seedling height and seedling basal diameter were influenced by soil total N and hydrolyzable N, while saplings height and basal diameter were regulated by total P and available P. The influence of illumination and air temperature on seedlings with height < 50 cm was stronger than that of relative humidity and soil nutrients. Seedlings between 50 and 100 cm in height, soil organic matter and relative humidity had the strongest influence. Saplings with height > 100 cm were governed by soil nutrients, suggesting differences in resource utilization and competitiveness caused by the forest gap size. The effect of gap size on C, N and P cycles was correlated with regeneration density, indicating that the medium gap may be optimal from an ecosystem perspective.