Shrubs in pastures are expected to adversely affect plant species diversity and community composition at various spatial scales. We recorded vegetation composition as well as light conditions and other environmental variables in 105 1 m² plots nested in 35 sampling sites in shrubby pastures in Romanian Banat. We used generalized linear models, generalized linear mixed-effects models, and linear regression to find determinants of species turnover and richness at patch and community level. We expected shrubs to negatively influence species richness on the patch level but to introduce spatial heterogeneity to the light availability resulting in a unimodal relationship of light availability with species richness on the community level. Species turnover was significantly influenced by light conditions, grazing variability, and distance between the plots. We found a unimodal relationship between light availability and species richness consistently across the two spatial scales in grazed sites. However, the same relationship changed its shape from linear to unimodal in non-grazed sites. Shrubs in pastures may not be considered as a threat to plant species diversity. Instead, they contribute significantly to plant species diversity and vegetation heterogeneity.

中文翻译：

---

光照和放牧之间的相互作用增强了罗马尼亚灌木牧场中维管植物的物种丰富度和周转率

牧场中的灌木有望在各种空间尺度上对植物物种多样性和群落组成产生不利影响。我们记录了105 1 m ^2中的植被组成以及光照条件和其他环境变量地块嵌套在罗马尼亚巴纳特（Romanian Banat）灌木丛牧场的35个采样点中。我们使用广义线性模型，广义线性混合效应模型和线性回归来找出斑块和群落水平上物种更新和丰富度的决定因素。我们预计灌木会在斑块级别上对物种丰富度产生负面影响，但会在光利用率上引入空间异质性，从而在社区级别上导致光利用率与物种丰富度的单峰关系。物种的周转受到光照条件，放牧变异性和地块间距离的显着影响。我们发现放牧站点中两个空间尺度上的光利用率和物种丰富度之间始终存在单峰关系。但是，相同的关系在非磨砂部位将其形状从线性变为单峰。牧场中的灌木可能不被视为对植物物种多样性的威胁。相反，它们极大地促进了植物物种多样性和植被异质性。