Recurrent fruit harvesting reduces seedling density but increases the frequency of clonal reproduction in a tropical tree

Studies on the ecological impacts of non-timber forest products (NTFP) harvest reveal that plants are often more resilient to fruit and seed harvest than to bark and root harvest. Several studies indicate that sustainable fruit harvesting limits can be set very high (>80% fruit harvesting intensity). For species with clonal and sexual reproduction, understanding how fruit harvest affects clonal reproduction can shed light on the genetic risks and sustainability of NTFP harvest. We studied 18 populations of a gallery forest tree, Pentadesma butyracea (Clusiaceae), to test the impact of fruits harvest, climate and habitat size (gallery forest width) on the frequency of sexual or clonal recruitment in Benin, West Africa. We sampled populations in two ecological regions (Sudanian and Sudano-Guinean) and in each region, we selected sites with low, moderate and high fruit harvesting intensities. These populations were selected in gallery forests with varying width to sample the natural variation in P. butyracea habitat size. Heavily harvested populations produced significantly less seedlings but had the highest density and proportion of clonal offspring. Our study suggests that for plant species with dual reproductive strategy (via seeds and clonal), fruit harvesting and associated disturbances that come with it can lead to an increase in the proportion of clonal offspring. This raises the issue that excessive fruit harvest by increasing the proportion of clonal offspring to the detriment of seed originated offspring may lead to a reduction in genetic diversity with consequence on harvested species capability to withstand environmental stochasticity.

有关非木材林产品（non-timber forest products, NTFP）采收的生态影响研究显示，植物通常对果实和种子采收的耐受性高于对树皮和根系采收的耐受性。多项研究表明，可持续果实采收阈值可设置得相当高（果实采收强度超过80%）。对于兼具无性与有性生殖的物种而言，解析果实采收如何影响无性生殖，有助于阐明非木材林产品采收的遗传风险与可持续性。

我们以西非贝宁的18个廊道森林树种Pentadesma butyracea（藤黄科，Clusiaceae）种群为研究对象，探究果实采收、气候与栖息地规模（廊道森林宽度）对有性或无性更新频率的影响。我们在苏丹生态区与苏丹-几内亚过渡生态区两个生态区域内开展种群采样，并在每个区域内选取果实采收强度低、中、高的样地。这些种群均选自宽度各异的廊道森林，以覆盖Pentadesma butyracea栖息地规模的自然变异范围。

高强度采收的种群产生的幼苗数量显著更少，但无性后代的密度与占比最高。本研究表明，对于兼具种子与无性双重生殖策略的植物物种而言，果实采收及其伴随的干扰可能会提升无性后代的占比。这一结果引出了一个问题：过度采收果实会通过增加无性后代占比、牺牲有性种子起源后代，导致遗传多样性下降，进而影响采收物种抵御环境随机性的能力。