Fire may mediate effects of landscape connectivity on plant community richness in prairie remnants

摘要

Following the predictions of island biogeography and metapopulation theory, efforts to understand and maintain plant communities have focused on spatial attributes such as patch size and connectivity. However, despite a large body of literature, the effects of these spatial attributes remain uncertain, and accumulating evidence suggests that they may interact with local patch characteristics. Here, we assess the role of spatial attributes (patch size and connectivity at two time periods) and of patch quality (indicated by number of years since last fire, as this is a fire-dependent system) in determining plant species richness at 63 remnant prairie sites in Wisconsin, USA. Our results demonstrate significant main effects of patch size, with larger patches being richer than small patches, and of fire, with recent-fire sites being richer than fire-excluded sites. We also report a novel interaction between number of years since fire and patch connectivity. Historical (1950) connectivity was negatively related to species richness at recent-fire sites, but positively related to species richness at fire-excluded sites, while current (2000) connectivity and species richness were positively correlated at recent-fire sites, but unrelated at fire-excluded sites. Our findings indicate that measures of patch quality such as time since last fire can alter the association between spatial attributes such as patch size or connectivity and species richness.