Farmland bird responses to intersecting replanted areas

Abstract

Despite increasing revegetation of cleared landscapes around the world, there is limited research on the implications of different types of plantings for birdlife. We examined the "intersection effect", whereby species richness is higher at the intersection of "corridors" or vegetation strips for birds inhabiting replanted areas. We also examined individual species responses. Replicated sites at the intersections of plantings were compared with "internal controls" (located in the same plantings ∼100 m from intersections), "external controls"(sites in isolated linear plantings), and block plantings. We surveyed the 39 sites in our experimental design repeatedly - on different days by different observers and in different seasons. We found no significant difference in species richness between intersections and block plantings, but intersections had higher species richness than isolated linear strips and the internal controls. Similar results were found for bird assemblage scores derived by correspondence analysis. We found evidence of extra-variation at the farm-level for species richness and derived assemblage scores, suggesting a farm-scale response. This suggests the importance of other (often unmeasured) factors at the farm level (e.g. baiting for feral animals). Our results suggest that replanting programs aimed at maximizing bird species richness may benefit from consideration of planting geometry. In particular, linking strip plantings to create intersections and/or establishing block plantings appear to be superior to isolated strips for aggregate species richness.