Questions: How do frequent disturbances of varying intensity affect heterogeneity of canopy openness and resulting regenerating tree diversity in subtropical rain forests? How does canopy gap pattern and regeneration time of a forest experiencing frequent but unpredictable typhoon disturbance vary over 17 yr? How is the understorey light environment influenced by canopy gaps in a forest experiencing frequent defoliation? Compared to non-gap areas, do gaps provide unique niches reflected in different seedling communities? Location: Natural evergreen hardwood forest, northeastern Taiwan. Methods: We examined gap characteristics, light availability and variability, and seedling diversity in both gaps and non-gaps in a subtropical forest with frequent typhoon disturbance, and compared the results to a survey at the same site conducted in 1995 following six typhoons in 1994. Results: Gaps were smaller and covered a much smaller proportion of the forest in the 2012 survey (mean gap size 10 m2, 3.3% of the forest) than the 1995 survey (33 m2 and 10%). Canopy regeneration times estimated from the 2012 survey (200-400 yr) were much longer than those based on the 1995 survey (50-175 yr). Neither light availability nor variability differed between gaps and non-gaps, so gaps ostensibly did not provide a unique niche space. There were no seedling species occurring exclusively in gaps, and very high plant community similarity (>90%) between gaps and non-gaps. Conclusions: In ecosystems with small canopy gaps resulting from frequent disturbance, gaps play a neutral role in understorey light environment and thus provide no unique niches and play a neutral role in plant diversity. Our study also suggests that measures of gap area, occurrence and forest turnover should be taken multiple times, during years with varying background disturbance rates.
ASJC Scopus subject areas