Winter bird use of harvest residues in clearcuts and the implications of forest bioenergy harvest in the southeastern United States

Abstract

Increased market viability of harvest residues gleaned for forest bioenergy feedstocks may intensify downed wood removal, particularly in intensively managed forests of the Southeast. Downed wood provides food and cover for many wildlife species, including birds, yet we are aware of no study that has examined winter bird response to experimentally manipulated, operational-scale woody biomass harvests. Further, little research has investigated avian use of downed wood following timber harvests. As such, our objectives were to: (1) evaluate effects of varying intensities of woody biomass harvest on the winter bird community and (2) document spatial associations between winter bird species and available habitat structure, including downed wood, in regenerating stands. In January and February of 2012–2014, we surveyed birds using a modified version of spot-mapping in six woody biomass removal treatments in North Carolina, USA (n=4 regenerating stands). Treatments included clearcut harvest followed by: (1) traditional woody biomass harvest with no biomass harvesting guidelines; (2) 15% retention with harvest residues dispersed; (3) 15% retention with harvest residues clustered; (4) 30% retention with harvest residues dispersed; (5) 30% retention with harvest residues clustered; and (6) no woody biomass harvest (i.e., reference). We tested for treatment-level effects on avian relative abundance (overall and individual species), species diversity and richness, and counts of winter birds detected near (∼1m from pile), in, or on branches of downed wood piles and calculated proportional avian habitat use of harvest residues and vegetation in regenerating stands. In 69 visits over three winters, we observed 3352 birds in treatments. In 2013, counts of birds detected in piles were greater in the no biomass harvest and 30% clustered treatments than the no biomass harvesting guidelines treatment. In 2012 and 2013 combined, mourning dove (Zenaida macroura) had greater relative abundance in the no biomass harvest treatment compared to the 15% dispersed treatment and was more often detected within 1m of downed wood piles than in vegetation. We counted more winter birds in and near adjacent forest edge than in treatment interiors each year. Overall, we detected minimal treatment effects on winter bird relative abundance and no effects on species diversity and richness. Relative abundance of winter birds increased over time as vegetative cover established in regenerating stands. Our results suggest woody biomass harvests in intensively managed pine forests had no effect on the winter bird community, but winter birds used harvest residues. Further, vegetation structure and composition, rather than availability of harvest residues, primarily influenced winter bird use of regenerating stands.