Data from: Chronic anthropogenic disturbance drives the biological impoverishment of the Brazilian Caatinga vegetation

1. In addition to acute transformations of ecosystems caused by deforestation, old-growth forests worldwide are being increasingly altered by low-intensity but chronic human disturbance. Overgrazing and the continuous extraction of forest products are important drivers of chronic disturbance, which can lead to the gradual local extinction of species and the alteration of vegetation structure.
2. We tested this hypothesis in the Brazilian Caatinga vegetation, one of the most species-rich and populated semi-arid regions of the world. Using a multi-model averaging approach we examined the impact of five recognized indicators of chronic disturbance (i.e. proximity to urban centre, houses, roads, density of people and livestock) on the diversity, abundance and evenness of 30 woody plant communities. We separately tested the response of seedlings, saplings, and adults to identify the ontogenetic stages that are most susceptible to chronic disturbance.
3. We recorded over 11 000 individuals belonging to 51 plant species. As expected, most indicators of chronic disturbance were negatively related to species diversity and stem abundance, with a variable effect on community evenness. The density of people and livestock were the main factors driving changes in plant communities, with a stronger negative impact on seedling and sapling diversities. Species composition also varied significantly with disturbance indicators, irrespective of ontogeny.
4. Our results show the potential negative impact that chronic disturbance can have on Caatinga plant assemblages and highlight the fact that disturbance resulting from an extractivism-based and subsistence economy are probably driving old-growth forest stands towards shrub-dominated secondary stands.
5. Synthesis and applications. These findings indicate that chronic disturbance should not continue to be neglected and we argue for (1) research and rural programs able to support better practices in terms of land use and sustainable exploitation of forest resources, (2) improved governance and law enforcement to shift extractivism towards sustainable standards, and (3) expanding the coverage and effective implementation of strictly protected areas.

1. 除森林砍伐引发的生态系统突发性转变之外，全球范围内的原始老龄林（old-growth forests）正日益受到低强度但持续性人为干扰的影响而发生改变。过度放牧与森林产品的持续采伐是引发这类持续性干扰的重要驱动因素，其可逐步导致物种的局部灭绝，并改变植被结构。
2. 本研究以全球物种多样性最为丰富、人类活动最为密集的半干旱区域之一——巴西卡廷加植被（Caatinga vegetation）为研究对象，对该假说展开验证。我们采用多模型平均（multi-model averaging）方法，探究了5种公认的持续性干扰指标（即距城市中心、住宅、道路的距离，以及人口与牲畜密度）对30个木本植物群落的多样性、多度与均匀度的影响。此外，我们分别检验了幼苗、幼树与成树的响应特征，以明确最易受持续性干扰影响的个体发育阶段。
3. 本研究共记录到隶属于51个植物物种的11000余株个体。正如预期，多数持续性干扰指标与物种多样性及茎干多度呈显著负相关，而对群落均匀度的影响则存在差异。人口与牲畜密度是驱动植物群落变化的主要因素，其对幼苗和幼树多样性的负面影响更为显著。无论个体发育阶段如何，物种组成均随干扰指标发生显著变化。
4. 本研究结果证实了持续性干扰对卡廷加植物群落的潜在负面影响，并指出：基于采掘型经济（extractivism）与自给生计经济产生的干扰，可能正推动原始老龄林林分向以灌木为主的次生林分转变。
5. 总结与应用启示。本研究结果表明，持续性干扰不应再被忽视，我们呼吁：（1）开展相关研究并推行乡村发展项目，以优化土地利用模式与森林资源的可持续开发利用；（2）完善治理体系与执法力度，推动采掘型活动向可持续标准转型；（3）扩大严格保护地的覆盖范围并切实落实其保护成效。