From town to national park: Understanding the long-term effects of hunting and logging on tree communities in Central Africa

Anthropogenic disturbances are changing the structure and composition of tropical forests worldwide. Multiple disturbances often occur simultaneously in forests: for example, hunting and logging are within-forest disturbances that impact vast areas of seemingly intact rainforests. Despite recent work on the individual effects of these disturbances, our understanding of how they interact to influence tree communities is still limited. In northern Republic of Congo, we explored the effects of hunting and logging on tree communities. Over an 8-year period, we monitored 12,552 tree stems (≥ 10 cm diameter-at-breast height) spread over 30 1-ha plots along a gradient of human disturbance to compare the tree diversity between hunted and logged forest, once-logged forest, and protected forest free of both disturbances. Tree density, species richness, and community composition were affected by both hunting and logging. Forest close to human settlements was richer, more heterogenous, and more dynamic in species composition across censuses. In hunted and logged forest, fast-growing secondary species with low shade tolerance replaced old growth species. Comparatively, the once-logged forest had the greatest stem density and intermediate species richness with a density increase of shade-bearing species over time. Both tree species spatial turnover and tree recruitment were greatly affected by proximity to human settlements. A shift towards abiotically dispersed trees and increasing seed predation by rodents near villages can partly explain the differences in tree recruitment across the forest types. The combination of hunting and logging seems to have a greater impact on tree communities than either single disturbance, especially with nearness to villages.

全球范围内的人为干扰正持续改变热带森林的结构与组成。森林生态系统中常存在多重干扰叠加的现象：例如狩猎与采伐均属于林内干扰，它们会对看似完好的热带雨林大片区域造成影响。尽管目前已有针对这类干扰单一效应的研究成果，但我们对这类干扰如何协同作用进而影响树木群落的认知仍较为有限。在刚果共和国北部，我们探究了狩猎与采伐对树木群落的影响。本研究在8年的监测周期内，对沿人为干扰梯度布设的30块1公顷样地中的12552株胸径（diameter-at-breast height）≥10厘米的树木个体开展了监测，以此对比狩猎-采伐干扰林、择伐林以及无任何干扰的保护林之间的树木多样性差异。树木密度、物种丰富度与群落组成均会受到狩猎与采伐的共同影响。距人类聚居区较近的森林，其物种丰富度更高、群落组成异质性更强，且历次普查间的物种组成动态变化也更为显著。在狩猎-采伐干扰林中，生长迅速、耐阴性弱的次生树种逐步取代了原始林物种。相较而言，择伐林的树木个体密度最高，物种丰富度处于中等水平，且其耐阴树种的密度随时间推移呈上升趋势。树种空间周转与树木更新均会显著受到距人类聚居区远近的影响。聚居区附近森林中向非生物传播树种的群落转变，以及啮齿动物对种子捕食压力的加剧，可在一定程度上解释不同林型间树木更新的差异。狩猎与采伐的叠加干扰似乎比单一干扰对树木群落造成的影响更大，且这种影响在距村庄较近的区域更为显著。