Growth of dipterocarp seedlings in artificial gaps: An experiment in a logged-over rainforest in South Kalimantan, Indonesia

Background

Regeneration of dipterocarps following logging has become a crucial issue in tropical forest management. Secondary forest frequently and rapidly replaces dipterocarps in large logged-over patches. If unmanaged, these secondary forest patches are often composed of unmerchantable early-succession species. It has been hypothesized that dipterocarps grow most successfully in small gaps.

Research goals & methods

This study assesses the feasibility of artificial gap openings for dipterocarp regeneration, testing growth and survival rates of dipterocarp seedlings in small gaps compared to large gaps and closed-canopy areas. Five artificial gaps ranging from 406 m² to 1242 m² were opened in logged-over forest areas. Height and DBH were measured for all trees greater than 5 cm in diameter and for all dipterocarp seedlings at the start of the study period and annually for 3 years. Among dipterocarps, S. fallax and S. parvifolia were the most frequently occurring tree species. Other dipterocarps were not present across all gaps due to their relatively short dispersal distance.

Conclusions & takeaways

A negative relationship was found between gap size and height growth for dipterocarps. This has been hypothesized to be caused by competition by light-loving pioneer species in larger gaps, or seedling shock from sudden exposure to direct sunlight. This study suggests that artificial gaps may be successful in dipterocarp regeneration, especially when established in areas with abundant advance regeneration or adjacent to seed trees.