Effect of selective logging on canopy and stand structure and tree species composition in a lowland dipterocarp forest in peninsular Malaysia

Abstract

The authors compared tropical rain forest canopy structure and tree species composition in two forests southeast of Kuala Lumpur, Malaysia: a primary forest and a regenerating forest that was selectively logged in 1958. For each of the forests, the study plots were set out and all trees of ≥1 cm in DBH (diameter at breast height) were mapped and measured. Canopy heights were measured in the two study plots based upon aerial triangulation using aerial photographs taken over the forests in 1997. Using this data, digital elevation models of the canopy were then constructed. The mean canopy height was greater in the primary forest (27.4 m versus 24.8 m), as was the variance in height and the number of emergent canopy trees >40 m height. The mean canopy surface area in the primary forest was nearly 1.5 times the value in the regenerating forest, and the mean crown size of canopy layer trees in the primary forest was more than twice that in the regenerating forest. The species diversity index (Fisher’s α) differed for the two forests, indicating that tree species diversity had been affected by the logging. Both forests had the same five families with the greatest stem density (stems ha −1), but the 50 most abundant species, in terms of both stem density and basal area, differed greatly between the two forests. Stem densities and basal areas were similar, but the number of stems per hectare and the basal areas of medium-sized trees (10–30 cm in DBH) were distinctly higher in the regenerating forest. These results suggest that average basal area and stem density in the regenerating forest that had been selectively logged 41 years earlier had recovered to levels similar to those in the primary forest; however, the regenerating forest had a more monotonic canopy structure comprised of medium-sized trees growing at high density. These findings also imply that structural development takes a long time to manifest in a regenerating forest as a result of the time taken for the development of emergent and canopy trees and the formation of gaps; structural development might also be delayed by the high density of medium-sized trees in the canopy layer.