Collocating pipelines to minimize fragmentation: evaluating ecological costs of a shale gas mitigation practice

Abstract

AbstractShale gas development occurs in forests of the Appalachian Basin within breeding habitat for forest songbirds. Development requires linear infrastructure (e.g., pipelines, gas access roads) that fragments habitat and reduces core forest. Collocation is a mitigation practice that sites new pipelines adjacent to existing surface disturbance such as forest roads; it reduces core forest loss but may have associated ecological costs, defined as negative effects on native species and ecosystems. We conducted a paired sampling design between forest roads and collocated pipelines (expanded gas access roads collocated with pipelines) to evaluate ecological costs to forest songbirds in 2013 in Pennsylvania, USA. We surveyed 4 focal songbird species: 3 territorial species that varied in habitat requirements and the non‐territorial brown‐headed cowbird (Molothrus ater), an obligate brood parasite. We used spot mapping to survey focal species within linear corridors and the adjacent mature forest. Territory density of forest interior ovenbirds (Seiurus aurocapilla) was significantly lower on collocated pipelines (5.1 fewer territories per 10 ha) compared to forest road sites. We found no effect of collocation on territory density for the early successional species, eastern towhee (Pipilo erythrophthalmus) and chestnut‐sided warbler (Setophaga pensylvanica). Territories of all 3 territorial focal species crossed collocated pipeline sites less frequently than forest roads (ovenbird: 16%, eastern towhee: 14%, chestnut‐sided warbler: 31%) and the barrier effect increased with increasing corridor width. In contrast, brown‐headed cowbird abundance was 15 times greater at collocated pipelines compared to forest roads, suggesting that wider gas corridors provide enhanced access routes for cowbirds. Our study indicates the expansion of forest roads to collocated pipelines exacerbates the negative ecological effects already present with the existing road including increased edge avoidance by a forest interior species, greater barrier effects for all 3 territorial forest songbirds, and increased access for brown‐headed cowbirds into core forest. We support collocation as a mitigation strategy but emphasize restricting overall corridor width to reduce the additional ecological costs associated with this practice.