Biodiversity time series reveal global losses and accelerated redistributions of species, but no net loss in local species richness. To better understand how these patterns are linked, we quantify how individual species trajectories scale up to diversity changes using data from 68 vegetation resurvey studies of seminatural forests in Europe. Herb-layer species with small geographic ranges are being replaced by more widely distributed species, and our results suggest that this is due less to species abundances than to species nitrogen niches. Nitrogen deposition accelerates the extinctions of small-ranged, nitrogen-efficient plants and colonization by broadly distributed, nitrogen-demanding plants (including non-natives). Despite no net change in species richness at the spatial scale of a study site, the losses of small-ranged species reduce biome-scale (gamma) diversity. These results provide one mechanism to explain the directional replacement of small-ranged species within sites and thus explain patterns of biodiversity change across spatial scales.

生物多样性时间序列揭示了全球损失和物种加速重新分配，但当地物种丰富度没有净损失。为了更好地了解这些模式之间的联系，我们使用来自欧洲半天然林的68个植被调查研究中的数据，量化了单个物种的轨迹如何扩展至多样性变化。地理范围较小的草本层物种正被分布更广泛的物种所取代，我们的结果表明，这是由于物种丰度而不是物种氮ni引起的。氮的沉积加速了小范围，高氮效率植物的灭绝，并导致了广泛分布的需氮植物（包括非本地植物）的定植。尽管在研究地点的空间范围内物种丰富度没有净变化，小型物种的丧失减少了生物群落规模（γ）的多样性。这些结果提供了一种机制来解释站点内小范围物种的定向替换，从而解释了整个空间尺度上生物多样性的变化模式。