School of Forestry and Environmental Studies, Yale University, 195 Prospect Street, New Haven, Connecticut, 06511, USA.
Hennur Cross, Bengaluru, Karnataka, 560096, India.
Ecol Appl. 2019 Dec;29(8):e01996. doi: 10.1002/eap.1996. Epub 2019 Oct 15.
Edge effects can alter the spatial organization of diversity in fragmented habitats. For tropical forests, however, there has been large variation in the strength and direction of such effects reported by different studies. For long-lived organisms like trees, one reason for inconsistent patterns might be due to most studies having examined patterns of diversity and compositional variation in older life stages that bear the legacy of a forest past. Younger life stages can reveal ongoing processes of assembly, but multi-stage examinations are rare. For seedling, sapling, and adult life stages of trees in a human-modified wet tropical forest in the Western Ghats Biodiversity Hotspot (India), we examined how proximity to forest edges (edge influence) modified the spatial organization of diversity. Specifically, for each life stage we tested whether edge influence led to loss of α- and γ-diversity and decreased β-diversity in this landscape. We found lower α- and γ-diversity closer to forest edges, but only for seedlings. Seedling composition at 90-100 m from forest edges diverged from composition of sites within 60 m, suggesting that edge influence restricted the recruitment of some species to interior sites. In contrast, β-diversity was greater near edges than interior forest for all life stages and most prominently for seedlings. Furthermore, β-diversity at edges was primarily driven by species turnover, suggesting either marked species-environment associations or dispersal limitation. Low turnover at 90-100 m implies that β-diversity arose from stochastic fluctuations in occurrences and abundances of the same species set. Overall, we find that high β-diversity structured spatial patterns of diversity near edges, but recruitment bottlenecks are likely to reduce alpha diversity of forest fragments. Our results also corroborate the need to maintain sufficiently large areas of tropical forest free from edge effects to avoid the loss of interior forest species. To improve landscape-scale diversity of fragmented landscapes, restoration efforts should focus on recovery of species that are unable to regenerate near forest edges.
边缘效应会改变破碎生境中多样性的空间组织。然而，对于热带森林，不同研究报告的这种效应的强度和方向有很大差异。对于像树木这样的长寿命生物，不一致模式的一个原因可能是由于大多数研究仅检查了处于衰老阶段的多样性和组成变化模式，而这些模式带有森林过去的特征。年轻阶段可以揭示正在进行的组装过程，但多阶段检查很少见。在印度西高止山脉生物多样性热点地区的一个人为干扰的湿润热带森林中，我们研究了树木的幼苗、幼树和成年阶段的生命阶段，考察了接近森林边缘（边缘影响）如何改变多样性的空间组织。具体来说，对于每个生命阶段，我们都测试了边缘影响是否导致了该景观中 α-和 γ-多样性的丧失以及 β-多样性的降低。我们发现，靠近森林边缘的幼苗的 α-和 γ-多样性较低，但仅对幼苗如此。距离森林边缘 90-100 米处的幼苗组成与 60 米以内的地点的组成不同，这表明边缘影响限制了某些物种向内部地点的繁殖。相比之下，对于所有生命阶段，边缘附近的 β-多样性大于内部森林，而对于幼苗最为显著。此外，边缘的 β-多样性主要由物种更替驱动，这表明存在明显的物种-环境关联或扩散限制。90-100 米处的低更替率意味着 β-多样性是由相同物种集的出现和丰度的随机波动引起的。总体而言，我们发现，高 β-多样性使边缘附近的多样性空间模式结构复杂化，但招募瓶颈可能会降低森林碎片的 α 多样性。我们的结果也证实了需要维持足够大的无边缘效应的热带森林面积，以避免内部森林物种的丧失。为了提高破碎景观的景观尺度多样性，恢复工作应集中于恢复那些无法在森林边缘附近再生的物种。
