Abstract

In the neotropical region, seasonally dry tropical forests (SDTF) are commonly associated with scatterly distributed limestone outcrops, known for harbouring high numbers of endemic species and genera. In the context of lacking knowledge on fine-scale vegetation and environmental heterogeneity of these geoecosystems and having a limestone outcrop in eastern Brazil as a case study, we address the question: how important are limestone outcrops for SDTF tree community composition, structure, function and evolution? We distinguished five habitats related to position and distance to the outcrop, and within each of 25 sampled plots (five per habitat), we identified and measured the diameter of all living tree individuals and collected soil samples for chemical and textural analyses. We investigated taxonomic and phylogenetic substitution across the habitats and fitted linear models to test the effects of habitat type, soil fertility and texture on taxonomic/structural, functional and phylogenetic parameters. We found striking taxonomic and phylogenetic differentiation among the habitats, especially related to recent diversification, with soil fertility and texture largely accounting for variations in all analysed parameters. Given the predominant roles of vicariance and in situ diversification believed to have given rise to the current patterns of endemism and diversity of eastern Brazil SDTF, we argue that the conditions presented by limestone outcrops, including aridity and high fertility, may have favoured the persistence of SDTF lineages during the Quaternary environmental changes, highlighting their role as litho-refugia. In order to complete this biogeographic puzzle, we encourage other fine-scale assessments of outcrop-associated SDTF from the phylogenetic viewpoint.

中文翻译：

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对于干燥的林木世系，能否将石灰岩露头的小规模栖息地视为平整岩石？

摘要

在新热带地区，季节性干燥的热带森林（SDTF）通常与散布的石灰岩露头有关，而石灰岩露头则以大量的特有物种和属而闻名。在缺乏对这些地质生态系统的小规模植被和环境异质性的了解的情况下，并以巴西东部的石灰岩露头为案例研究，我们要解决的问题是：石灰岩露头对SDTF树群落的组成，结构，功能和重要性有多重要？演化？我们在25个采样区中每个区划了5个与露头位置和距离相关的栖息地（每个区5个）栖息地），我们确定并测量了所有活树个体的直径，并收集了土壤样本进行化学和质地分析。我们调查了整个生境的分类学和系统发育替代，并拟合了线性模型以测试生境类型，土壤肥力和质地对分类学/结构，功能和系统发育参数的影响。我们发现生境之间惊人的分类学和系统发育差异，特别是与最近的多样化有关，土壤肥力和质地在很大程度上解释了所有分析参数的变化。考虑到传情和就地多样化的主要作用被认为导致了巴西东部SDTF当前的地方性和多样性模式，我们认为石灰石露头带来的条件，包括干旱和高生育力在内，可能有利于SDTF世系在第四纪环境变化中的持久性，从而突出了它们作为光刻避难所的作用。为了完成这一生物地理难题，我们建议从系统发育的角度对露头相关SDTF进行其他精细评估。