Ribeiro Elâine M S, Santos Bráulio A, Arroyo-Rodríguez Víctor, Tabarelli Marcelo, Souza Gustavo, Leal Inara R
Ecology. 2016 Jun;97(6):1583-92. doi: 10.1890/15-1122.1.
Chronic disturbances, such as selective logging, firewood extraction and extensive grazing, may lead to the taxonomic and phylogenetic impoverishment of remaining old-growth forest communities worldwide; however, the empirical evidence on this topic is limited. We tested this hypothesis in the Caatinga vegetation--a seasonally dry tropical forest restricted to northeast Brazil. We sampled 11,653 individuals (adults, saplings, and seedlings) from 51 species in 29 plots distributed along a gradient of chronic disturbance. The gradient was assessed using a chronic disturbance index (CDI) based on five recognized indicators of chronic disturbances: proximity to urban center, houses and roads and the density of both people and livestock. We used linear models to test if mean effective number of lineages, mean phylogenetic distance and phylogenetic dispersion decreased with CDI and if such relationships differed among ontogenetic stages. As expected, the mean effective number of lineages and the mean phylogenetic distance were negatively related to CDI, and such diversity losses occurred irrespective of ontogeny. Yet the increase in phylogenetic clustering in more disturbed plots was only evident in seedlings and saplings, mostly because clades with more descendent taxa than expected by chance (e.g., Euphorbiaceae) thrived in more disturbed plots. This novel study indicates that chronic human disturbances are promoting the phylogenetic impoverishment of the irreplaceable woody flora of the Brazilian Caatinga forest. The highest impoverishment was observed in seedlings and saplings, indicating that if current chronic disturbances remain, they will result in increasingly poorer phylogenetically forests. This loss of evolutionary history will potentially limit the capacity of this ecosystem to respond to human disturbances (i.e., lower ecological resilience) and particularly their ability to adapt to rapid climatic changes in the region.
诸如选择性采伐、薪柴砍伐和过度放牧等长期干扰，可能会导致全球范围内现存老龄森林群落的分类学和系统发育多样性丧失；然而，关于这一主题的实证证据有限。我们在巴西东北部的季节性干旱热带森林——卡廷加植被中验证了这一假设。我们沿着长期干扰梯度，在29个样地中对51个物种的11653个个体（成体、幼树和幼苗）进行了采样。该梯度是使用基于五个公认的长期干扰指标的长期干扰指数（CDI）来评估的：与城市中心、房屋和道路的距离以及人口和牲畜的密度。我们使用线性模型来检验谱系的平均有效数量、平均系统发育距离和系统发育离散度是否随CDI降低，以及这些关系在个体发育阶段之间是否存在差异。正如预期的那样，谱系的平均有效数量和平均系统发育距离与CDI呈负相关，并且这种多样性丧失与个体发育无关。然而，在受干扰更严重的样地中，系统发育聚类的增加仅在幼苗和幼树中明显，主要是因为具有比预期更多后代分类群的分支（如大戟科）在受干扰更严重的样地中茁壮成长。这项新研究表明，长期的人类干扰正在促使巴西卡廷加森林中不可替代的木本植物群落在系统发育上变得贫瘠。在幼苗和幼树中观察到的贫瘠程度最高，这表明如果当前的长期干扰持续存在，它们将导致系统发育上越来越贫瘠的森林。这种进化历史的丧失可能会限制这个生态系统应对人类干扰的能力（即较低的生态恢复力），特别是其适应该地区快速气候变化的能力。
