Sabatini Francesco Maria, Burrascano Sabina, Tuomisto Hanna, Blasi Carlo
Department of Environmental Biology, Sapienza, University of Rome, Rome, Italy.
Department of Biology, University of Turku, Turku, Finland.
PLoS One. 2014 Apr 18;9(4):e95244. doi: 10.1371/journal.pone.0095244. eCollection 2014.
Different assembly processes may simultaneously affect local-scale variation of species composition in temperate old-growth forests. Ground layer species diversity reflects chance colonization and persistence of low-dispersal species, as well as fine-scale environmental heterogeneity. The latter depends on both purely abiotic factors, such as soil properties and topography, and factors primarily determined by overstorey structure, such as light availability. Understanding the degree to which plant diversity in old-growth forests is associated with structural heterogeneity and/or to dispersal limitation will help assessing the effectiveness of silvicultural practices that recreate old-growth patterns and structures for the conservation or restoration of plant diversity. We used a nested sampling design to assess fine-scale species turnover, i.e. the proportion of species composition that changes among sampling units, across 11 beech-dominated old-growth forests in Southern Europe. For each stand, we also measured a wide range of environmental and structural variables that might explain ground layer species turnover. Our aim was to quantify the relative importance of dispersal limitation in comparison to that of stand structural heterogeneity while controlling for other sources of environmental heterogeneity. For this purpose, we used multiple regression on distance matrices at the within-stand extent, and mixed effect models at the extent of the whole dataset. Species turnover was best predicted by structural and environmental heterogeneity, especially by differences in light availability and in topsoil nutrient concentration and texture. Spatial distances were significant only in four out of eleven stands with a relatively low explanatory power. This suggests that structural heterogeneity is a more important driver of local-scale ground layer species turnover than dispersal limitation in southern European old-growth beech forests.
不同的组装过程可能同时影响温带原始森林中物种组成的局部尺度变化。地被层物种多样性反映了低扩散物种的偶然定居和持续存在，以及精细尺度的环境异质性。后者既取决于纯粹的非生物因素，如土壤性质和地形，也取决于主要由上层结构决定的因素，如光照可用性。了解原始森林中的植物多样性与结构异质性和/或扩散限制相关的程度，将有助于评估为保护或恢复植物多样性而重建原始森林模式和结构的造林实践的有效性。我们采用嵌套抽样设计来评估南欧11片以山毛榉为主的原始森林中精细尺度的物种周转率，即采样单元之间物种组成变化的比例。对于每个林分，我们还测量了一系列可能解释地被层物种周转率的环境和结构变量。我们的目标是在控制其他环境异质性来源的同时，量化扩散限制与林分结构异质性相比的相对重要性。为此，我们在林分内尺度上使用距离矩阵的多元回归，在整个数据集尺度上使用混合效应模型。物种周转率最好由结构和环境异质性预测，特别是光照可用性以及表土养分浓度和质地的差异。在11个林分中，只有4个林分的空间距离具有显著意义，且解释力相对较低。这表明，在南欧原始山毛榉森林中，结构异质性是局部尺度地被层物种周转率比扩散限制更重要的驱动因素。
