SummaryAfrican forests are under increasing pressure to supply local, regional, and international demand for timber. Much of this trade is unregulated, such that there is increasing concern regarding the ecological sustainability of this resource use. However, there is a lack of studies investigating the ecological impact of informal timber harvesting in African forests. While forest species have adapted to natural canopy gap dynamics, harvesting may alter natural disturbance regimes, with adverse effects on biodiversity. Information regarding harvest gaps, and concomitant impacts on habitat and biodiversity is thus essential to inform sustainable management. This study compared the frequency and nature of harvest gaps and natural gaps in a coastal forest in the Eastern Cape, South Africa, where informal selective timber harvesting occurs. Habitat condition and bird species richness and composition were compared across intact forest, natural gaps, and harvest gaps. Harvest-created gaps increased the number of canopy gaps by 30%, but were comparable with natural gaps in size. Habitat conditions in harvest gaps represented an intermediate state between intact forest and natural gaps, thereby increasing forest-scale habitat heterogeneity. While bird species richness was not affected, species composition differed across intact forest, harvest gaps and natural gaps, driven by changes in habitat condition, and mediated by species’ feeding and nesting traits. Specifically, insectivores, cavity- and ground-nesting species, and hawking and arboreal probing species were negatively affected by the habitat gradient from intact sites to canopy gap conditions, while nectarivores, omnivores and ball/cup nesting species were positively affected. Thus, while the single-tree selective harvesting method used by informal harvesters largely emulated natural canopy disturbances, the harvest-mediated increase in the frequency of canopy gaps may reduce the abundance of certain bird species sensitive to canopy gap conditions and reduce forest-scale beta-diversity.

中文翻译：

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非正式木材采伐对南非东开普省沿海森林栖息地结构和鸟类群落的影响

摘要非洲森林在满足当地、区域和国际木材需求方面面临越来越大的压力。这种贸易的大部分是不受监管的，因此人们越来越关注这种资源使用的生态可持续性。然而，缺乏调查非洲森林非正式木材采伐对生态影响的研究。虽然森林物种已经适应了自然树冠间隙动态，但采伐可能会改变自然干扰机制，对生物多样性产生不利影响。因此，有关收获差距以及对栖息地和生物多样性的伴随影响的信息对于为可持续管理提供信息至关重要。这项研究比较了南非东开普省沿海森林中采伐间隙和自然间隙的频率和性质，那里发生了非正式的选择性木材采伐。对完整森林、自然间隙和收获间隙的栖息地条件和鸟类物种的丰富度和组成进行了比较。收获造成的间隙使树冠间隙的数量增加了 30%，但与自然间隙的大小相当。收获间隙中的栖息地条件代表了完整森林和自然间隙之间的中间状态，从而增加了森林规模的栖息地异质性。虽然鸟类物种的丰富度没有受到影响，但由于栖息地条件的变化以及物种的摄食和筑巢特征的调节，完整森林、收获间隙和自然间隙的物种组成存在差异。具体来说，食虫动物、洞穴和地面筑巢物种以及小贩和树栖探测物种受到从完整地点到冠层间隙条件的栖息地梯度的负面影响，而食蜜动物，杂食动物和球/杯筑巢物种受到积极影响。因此，虽然非正式采伐者使用的单树选择性采伐方法在很大程度上模仿了自然树冠干扰，但采伐介导的树冠间隙频率增加可能会减少某些对树冠间隙条件敏感的鸟类的丰度，并降低森林规模的贝塔系数。 -多样性。