Sustaining rainforest remnants in plantation landscapes: degree of oil palm stand-induced edge effects on forest microclimate and regeneration

Abstract

Background: Amplified edge effects stemming from land use change interfere with the community dynamics of forests by altering abiotic conditions. However, the impact of oil palm plantation-induced edge effects on forest remnants is still not well-understood. This study investigated the edge influences of an oil palm plantation on adjoining rainforest remnants’ microclimates and regeneration, along with variations in the effects imposed by oil palm stands’ structural differences. Parallel transects were established perpendicular to the forest border in four forest patches. Distance and magnitude of edge influence (DEI and MEI, respectively) were calculated for each response variable, and PCA and ANOVA tests were used to examine variations among the variables. Results: DEIs did not extend beyond 60 m, while the number of influenced variables decreased with increasing oil palm stand shade. MEI values were generally low, except for light intensity and seedlings. Significant differences were mostly observed only for variables at the forest fringe, and the reduction in edge influence was most prominent only with a minimum stand height of 8.5 m. Invasive undergrowth species penetrated less into the forest interior with more shade. Tree regeneration, especially of old growth species, was low, and seedlings were dominated by fast-growing trees. Conclusion: Forest remnants benefit from edge effect-minimizing shade, but by the time this shade has formed, regeneration has already been impacted. Sustaining the ecosystem integrity of forest fragments consequently requires continuous shade from adjacent ecosystems coupled with intervention to boost old growth forest species’regeneration in low-shade areas.