Powerline easements: ecological impacts and contribution to habitat fragmentation from linear features

Abstract

The ecological effects of roads on plant and animal populations are well recognized. However, very little is known about the magnitude of the effects created by powerline easements. Like roads, powerline easements are ubiquitous in many landscapes, including reserves such as National Parks, which have restricted human activities. Regular mowing of the easements to manage vegetation regrowth creates a stark discontinuity with adjacent natural vegetation. Abrupt transitions such as these contribute to habitat fragmentation and are associated with movement and dispersal inhibition of fauna. We used GIS to estimate the area of direct and indirect effects of powerline easements in a 5735 km² area of coastal New South Wales, focusing on the potential reduction of habitat area both within and outside reserves. While the area directly replaced by these features is a small percentage of the total landscape (<1%), the upper estimates of direct and indirect effects combined amounted to a substantial portion of habitat (10 103 ha). Further, roads and powerlines combined may affect up to 33 780 ha (8%) of habitat in the study area. Although the overall ecological impact of powerline easements could be reduced by concentrating them in regions of pre-existing fragmentation, in our study area powerlines rarely occurred adjacent to paved roads. For example, in National Parks, only 3% of the habitat area affected by powerlines overlapped with that affected by roads. This study highlights the potential for powerline easements to make a significant contribution to habitat fragmentation, even in the presence of dense road networks, thus calling for greater attention to their ecological impacts and to improved management strategies.