Data from: Forest trees in human modified landscapes: ecological and genetic drivers of recruitment failure in Dysoxylum malabaricum (Meliaceae)

Tropical agro-forest landscapes are global priority areas for biodiversity conservation. Little is known about the ability of these landscapes to sustain large late successional forest trees upon which much forest biodiversity depends. These landscapes are subject to fragmentation and additional habitat degradation which may limit tree recruitment and thus compromise numerous ecosystem services including carbon storage and timber production. Dysoxylum malabaricum is a large canopy tree species in the Meliaceae, a family including many important tropical timber trees. This species is found in highly fragmented forest patches within a complex agro-forest landscape of the Western Ghats biodiversity hot spot, South India. In this paper we combined a molecular assessment of inbreeding with ecological and demographic data to explore the multiple threats to recruitment of this tree species. An evaluation of inbreeding, using eleven microsatellite loci in 297 nursery-reared seedlings collected form low and high density forest patches embedded in an agro-forest matrix, shows that mating between related individuals in low density patches leads to reduced seedling performance. By quantifying habitat degradation and tree recruitment within these forest patches we show that increasing canopy openness and the increased abundance of pioneer tree species lead to a general decline in the suitability of forest patches for the recruitment of D. malabaricum. We conclude that elevated inbreeding due to reduced adult tree density coupled with increased degradation of forest patches, limit the recruitment of this rare late successional tree species. Management strategies which maintain canopy cover and enhance local densities of adult trees in agro-forest mosaics will be required to ensure D. malabaricum persists in these landscapes. Our study highlights the need for a holistic understanding of the incipient processes that threaten populations of many important and rare tropical tree species in human dominated agro-forest landscapes.

热带农林复合景观是全球生物多样性保护的优先重点区域。目前学界对这类景观维持大型后期演替林木的能力知之甚少，而此类林木正是诸多森林生物多样性赖以存续的核心基础。这类景观易遭受生境片段化干扰，同时伴随额外的生境退化，这可能会限制林木更新，进而损害包括碳储存、木材生产在内的诸多生态系统服务功能。马拉巴尔坚木（Dysoxylum malabaricum）是楝科（Meliaceae）的大型冠层树种，该科包含诸多重要的热带用材树种。该物种分布于印度南部西高止山脉（Western Ghats）生物多样性热点区域的复杂农林复合景观中，栖息于高度片段化的森林斑块内。本研究结合近交繁殖的分子评估数据与生态学、种群统计学数据，探究了该树种更新面临的多重威胁。研究团队利用11个微卫星位点（microsatellite loci），对采自嵌入农林复合基质中的低密度与高密度森林斑块的297株苗圃培育幼苗开展近交繁殖评估，结果显示，低密度斑块内的近亲交配会降低幼苗的生长表现。通过量化这些森林斑块内的生境退化程度与林木更新情况，研究发现冠层开阔度提升以及先锋树种丰度增加，会普遍降低森林斑块对马拉巴尔坚木更新的适宜性。研究结论表明，成年林木密度降低引发的近交繁殖加剧，加之森林斑块退化加重，共同限制了这一稀有后期演替树种的更新。若要确保马拉巴尔坚木在这类景观中持续存续，需制定维持冠层覆盖、提升农林复合景观镶嵌体中成年林木本地种群密度的管理策略。本研究强调，需全面理解人类主导的农林复合景观中，诸多重要且稀有热带树种种群所面临的潜在威胁进程。