The Sabah Biodiversity Experiment: A Long-Term Test of the Role of Tree Diversity in Restoring Tropical Forest Structure and Functioning

background

This article details the initial stages of an experiment in Borneo which aims to study the relationship between tree diversity and lowland dipterocarp rainforest functioning during restoration after selective logging.

Research Goals & Methods

The area of the forest where the experiment is being conducted was selectively logged between 1984 and 1986. Over an area of 500 hectares, enrichment plantings of 16 different native dipterocarp seedlings were made along cleared lines into cuts of the pre-existing, selectively logged forest. The project comprised 124 plots of 4 hectares divided into 2 blocks; the core of the project is a set of 108 plots which include plots of all 16 species planted individually, as well as 16 different 4-species mixtures and plots of all 16 species combined, and 12 unplanted control plots; the remaining 16 plots form a sub-experiment to examine the effect of enhanced removal of climbing plants. Four identical transects of 10 x 250m were established in nearby primary forest and within the selectively logged area.

Conclusions & Takeaways

Logging did not affect alpha or beta diversity; however, a large dissimilarity in species composition was found between the unlogged and selectively logged sites. Forest structure was impacted by logging which was supported by the observations of a total stand basal area of 29.9+0.7 for the unlogged forest versus 25.0+0.8 s.e.m. m²ha^-1for the logged forest, and a relative contribution of 60% to total stand basal area of dipterocarps in the unlogged forest versus 30% in the logged forest. Differences in the total basal area between the logged and unlogged forests resulted from tree size not tree density which was similar in both forests; no trees greater than 90cm d.b.h. were found within the logged transects while trees up to 180cm d.b.h. were found within the unlogged transects. The results suggest that the above-ground biomass and carbon pools of the logged forest have been reduced by 40%, even 22 years after logging occurred. The authors note that the differences in forest structure between the logged and unlogged forests are significant, while also stressing that their results are most likely conservative given that the selectively logged area of study has only been logged once whereas many areas have been logged at least twice.