Abandonment of pastures and successional shrub expansion are widespread in European mountain regions. Moderate shrub encroachment is perceived beneficial for plant diversity by adding new species without outcompeting existing ones, yet systematic evidence is missing. We surveyed vegetation along 24 transects from open pasture into shrubland across the Swiss Alps using a new protocol distinguishing different spatial scales, shrub cover of each plot (2 × 2 m) and larger-scale zonal cover along the transect. Data were analysed using generalized linear models of shrub cover, shrub species and environmental conditions, such as geology, aspect or soil. Most shrub communities were dominated by Alnus viridis (62% of transects) and Pinus mugo (25%), and the rest by other shrub species (13%). These dominant shrub species explained vegetation response to shrub cover well, without need of environmental variables in the model. Compared to open pasture, A. viridis resulted in an immediate linear decline in plant species richness and a marginal increase in beta-diversity (maximally + 10% at 35% cover). Dense A. viridis hosted 62% less species than open pasture. In P. mugo, species richness remained stable until 40% shrub cover and dropped thereafter; beta-diversity peaked at 35% cover. Hence, scattered P. mugo increases beta-diversity without impairing species richness. In transects dominated by other shrubs, species richness and beta-diversity peaked at 40–60% shrub cover (+ 23% both). A. viridis reduced species richness in a larger area around the shrubs than P. mugo. Therefore, effects of shrub encroachment on plant diversity cannot be generalized and depend on dominant shrub species.

在欧洲山区，草场的废弃和灌木丛的不断扩张。通过增加新物种而不与现有物种竞争，人们认为适度的灌木入侵对植物多样性有利，但缺少系统的证据。我们使用一种区分不同空间尺度，每个样地的灌木覆盖度（2×2 m）和沿该样带的较大比例带覆盖的新协议，调查了横跨瑞士阿尔卑斯山的从开放牧场到灌丛的24个样带的植被。使用灌木覆盖率，灌木种类和环境条件（例如地质，地形或土壤）的广义线性模型分析数据。大多数灌木群落以绿nu木（占横断面的62％）和mug松为主。（25％），其余由其他灌木种类（13％）决定。这些优势灌木物种很好地解释了植被对灌木覆盖的响应，而无需模型中的环境变量。与开放式牧场相比，A。viridis导致植物物种丰富度立即线性下降，β多样性略有增加（覆盖率达到35％时最大增加+ 10％）。密集的草假单胞菌的物种数量比露天牧场少62％。在P. mugo，物种丰富度保持稳定，直到灌木覆盖率达到40％，此后下降。beta多样性达到35％的覆盖率峰值。因此，散落的P.在不损害物种丰富度的情况下增加了β多样性。在以其他灌木为主的样带中，物种丰富度和β多样性在灌木覆盖率达到40％至60％时达到峰值（两者均为+ 23％）。绿假孢菌在灌木周围的面积减少的物种丰富度比蒲冈假单胞菌高。因此，灌木入侵对植物多样性的影响不能一概而论，而取决于优势灌木种。