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 timethis 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.

摘要
背景：土地利用变化引发的增强型边缘效应，通过改变非生物环境条件干扰森林群落动态。然而，油棕种植园带来的边缘效应对森林残存斑块的影响仍未得到充分阐明。
本研究针对油棕种植园毗邻的热带雨林残存斑块的微气候与更新过程开展了边缘效应调查，同时探究了油棕林分结构差异所带来的效应变化。研究在4处森林斑块中设置了垂直于林缘的平行样带，针对各响应变量计算了边缘影响距离（Distance of Edge Influence, DEI）与边缘影响强度（Magnitude of Edge Influence, MEI），并通过主成分分析（Principal Component Analysis, PCA）与方差分析（Analysis of Variance, ANOVA）检验变量间的差异。
结果显示：边缘影响距离未超过60米，受影响的变量数量随油棕林分遮光度提升而减少；边缘影响强度整体偏低，仅光照强度与幼苗相关变量除外。显著差异主要仅见于林缘处的变量，且仅当林分最小高度达到8.5米时，边缘影响的减弱效果最为显著。遮光度更高的林分下，入侵性林下植被向森林内部的渗透程度更低。林木更新（尤其是原生老龄树种）整体水平偏低，幼苗群落以速生树种为主。
结论：森林残存斑块可受益于可弱化边缘效应的林分遮荫，但当该遮荫环境形成时，森林更新已受到负面影响。因此，维持森林片段的生态系统完整性，需要相邻生态系统提供持续的遮荫保护，同时辅以人工干预以提升低遮荫区域内老龄森林树种的更新效率。