We used a landscape-scale experiment at the Savannah River Site (SC) to understand at which scales two important landscape features – habitat corridors and habitat edge-to-area ratio – influence species-area relationships for plants. We sampled plant species richness within nested plots ranging in area from 0.01 m² to 10,000 m² within open habitats (“patches”) surrounded by a matrix of mature pine forest. Patches were of equal area (~1 ha) and either connected by a corridor or isolated. Isolated patches were of two types and, relative to connected patches plus the corridor, either had a similar edge-to-area ratio (“high-edge patches”) or lower edge-to-area ratio (“low-edge patches”).
We found that corridors had no impact on species richness at small scales, as all three patch types had similar richness in 0.01 m² - 10 m² plots. Richness was higher in connected patches and high-edge unconnected patches in 100 m² plots, suggesting that corridors increase richness at this intermediate scale by increasing the edginess of a patch. At larger scales, there was a notable upturn in the species-area relationship in connected patches, resulting in higher richness values in 1000 and 10,000 m² plots, relative to both high- and low-edge unconnected patches. Thus, corridors increase species richness at larger scales because of the connectivity they provide. This work has important implications for conservation reserve design and points to the need to assess connectivity effects on biodiversity across spatial scales. Our work suggests that habitat fragmentation may have profound effects on species-area relationships; however, corridors may reconcile these effects by preventing species loss at larger scales.