Abstract Although many grassland species may exist within agricultural landscapes, some are still absent from individual grassland patches. Understanding which processes limit plant biodiversity within these landscapes is important, and may be better understood if we consider local diversity relative to its species pool size (community completeness). Here we test how habitat availability, dispersal limitation, grassland age, and local environmental conditions (productivity, fine scale heterogeneity) affect the completeness of grassland plant communities at two spatial scales in an agricultural region in Southeast Estonia, Northern Europe. We additionally test how species dispersal and persistence traits (seed production, potential dispersal distance, and clonal ability) depend on the landscape and local environmental factors. We collected vascular plant data from 31 grassland patches and used species co-occurrences to estimate which species from the surrounding region were suitable, but absent for each grassland site (dark diversity). We partitioned dark diversity for each site into species that were found within the surrounding 10 ha area (landscape scale) or species found only at other visited grassland sites (regional scale), and used these estimates to calculate completeness for each site at the landscape and regional scale. Environmental data (various soil characteristics, light availability, plant biomass) was collected to characterize productivity and fine scale heterogeneity of the sites. We found that community completeness was limited by seed production ability, dispersal distances, and grassland availability at the regional scale, whereas local environmental conditions (productivity) limited completeness at the landscape scale. Species dispersing long distances were more often present in areas historically bordered by more grasslands, whereas potential dispersal limitation was reduced in older grasslands with heterogeneous and sparse vegetation. We conclude that dispersal limitation, habitat availability, and local environmental conditions all determine completeness of grassland patches; however, their relative importance is scale dependent. Nevertheless, the presence of good dispersers in isolated grasslands is likely a disappearing legacy of historical landscapes. To support high taxonomic and functional diversity in agricultural landscapes, it is therefore crucial to increase the area and connectivity of grassland patches and maintain their moderate management by mowing or grazing.

中文翻译：

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植物群落完整性的驱动因素在区域和景观尺度上有所不同

摘要 尽管农业景观中可能存在许多草原物种，但个别草原斑块中仍不存在一些草原物种。了解哪些过程限制了这些景观中的植物生物多样性很重要，如果我们考虑相对于物种库规模（群落完整性）的当地多样性，可能会更好地理解。在这里，我们测试了栖息地可用性、扩散限制、草地年龄和当地环境条件（生产力、精细尺度异质性）如何影响北欧爱沙尼亚东南部农业区两个空间尺度上草地植物群落的完整性。我们还测试了物种传播和持久性特征（种子生产、潜在传播距离和克隆能力）如何取决于景观和当地环境因素。我们从 31 个草原斑块中收集了维管植物数据，并使用物种共现来估计周围地区的哪些物种是合适的，但每个草原地点都没有（黑暗多样性）。我们将每个地点的暗多样性划分为在周围 10 公顷区域内发现的物种（景观尺度）或仅在其他访问过的草原地点（区域尺度）发现的物种，并使用这些估计来计算每个地点在景观和区域规模。收集环境数据（各种土壤特征、光照、植物生物量）以表征场地的生产力和精细尺度异质性。我们发现社区完整性受到区域尺度上种子生产能力、传播距离和草地可用性的限制，而当地的环境条件（生产力）限制了景观尺度的完整性。远距离传播的物种更常出现在历史上与更多草原接壤的地区，而在植被异质和稀疏的老草原中，潜在的传播限制减少了。我们得出结论，扩散限制、栖息地可用性和当地环境条件都决定了草地斑块的完整性；然而，它们的相对重要性取决于规模。尽管如此，在偏远草原上存在良好的传播者很可能是历史景观的消失遗产。为了支持农业景观的高度分类和功能多样性，