Erecting dead trees and utility poles to offset the loss of mature trees

Abstract

Mature trees are declining faster than they are being replaced in landscapes managed for agriculture, wood production and residential development. Population bottlenecks are therefore predicted for biota that depends on mature trees. We erected five utility poles and five large dead trees to evaluate whether artificial structures can offset the loss of living mature trees from a residential development. We implemented the study as a before-after-control-impact (BACI) experiment that included five control sites with no trees and five sites with living mature trees—sampled before and soon after the artificial structures were erected. Bird species richness increased significantly where utility poles or dead trees were erected with no significant change at control sites or at living mature trees. Erecting dead trees provided the greatest gain in bird species richness and was also more cost-effective than erecting utility poles or planting seedlings and waiting for them to mature. However, dead trees did not support as many native bird species as living mature trees and 37% of the species observed in our study occurred exclusively at living mature trees indicating that erecting dead trees or utility poles is only a partial solution for offsetting the loss of mature trees. Our results suggest that conserving all birds where mature trees are declining requires a complementary strategy of: (a) protecting as many living mature trees as possible, (b) recruiting a new cohort of future mature trees by establishing seedlings; and (c) erecting artificial structures to provide suitable habitat until these seedlings reach maturity.