Spatial and topographic patterns of canopy gap formation in a mixed dipterocarp forest in Sarawak, Malaysia

Abstract

We observed spatial and topographic patterns of canopy gap formation in a mixed dipterocarp forest over 4 years (1993-1996) (new gaps) and before 1993 (old gaps) in a 24-ha plot in Sarawak, Malaysia. Results showed a much lower canopy gap-formation rate (0.63 gaps ha-1; mean gap area: 49.4 m2 ha-1, gap formation ratio: 0.067% year-1 for ≤2-m gaps) than the range reported for tropical forests in the Neotropics. The spatial aggregation of new canopy gaps and old large-scale gaps on steep back slopes suggests that canopy gaps are closely linked to topography, especially to landslides. Uprooted trees were concentrated on steeper and more concave slopes and at more intermediate elevations than expected by chance, and occasionally caused landslides. Broken trees, including standing dead trees, were distributed at higher altitudes and on more convex slopes than uprooted trees. A variety of species-specific modes of gap makers between the two types of treefall suggest a degree of predictability in the type of treefall that will be present at different topographic positions. The marked differences in frequency distributions of area ratios of ≤2-m gaps to ≤5-m gaps within each gap showed temporal and spatial heterogeneity of vegetation recovery between new and old gaps. Thus, a forest with low gap-formation rates and abundant and nonrandom distribution of small-scale disturbances suggests spatial heterogeneity of vegetation recovery and contributes to a variable distribution of habitat specialists in canopy gaps.