Paper addresses winter bird response to harvest of logging residues

Increased interest in renewable energy sources could lead to greater use of logging or harvest residues as a bioenergy feedstock. Because many forests in the southeastern US are intensively managed, the region is likely to be an important producer of bioenergy feedstocks. However, reductions of downed wood via woody biomass harvests could affect forest ecosystems including wildlife communities.

Questions about potential effects of woody biomass harvests on forest ecosystems and sustainability have led to development of non-regulatory biomass harvesting guidelines in several forested regions of the United States.  These guidelines specify target volumes of downed wood to be retained on harvested sites to maintain biological diversity and site productivity, but biomass harvesting guidelines have limited technical underpinnings due to a paucity of empirical support.

Winter birds are a sometimes overlooked component of the biological community but could be affected by woody biomass harvests. Some winter birds are known to use downed wood which can trap seeds, harbor insects, and provide thermal and escape cover. However, few studies have addressed use of retained logging residues by winter birds, response to different amounts or patterns of retained harvest residues, or winter bird use of young loblolly pine forests regenerating following clearcut harvest.

To fill these information gaps, NCASI recently supported a study in North Carolina 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 loblolly pine stands. The study was conducted on sites managed by Weyerhaeuser Company.

A paper recently published in the journal Forest Ecology and Management reports results from the study. Authors include Steven M. Grodsky, Christopher E. Moorman, Sarah R. Fritts, and Dennis W. Hazel of North Carolina State University; Jessica A. Homyack of Weyerhaeuser Company; Steven B. Castleberry of the University of Georgia; and T. Bently Wigley of NCASI. The abstract for the paper follows.

“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 (∼1 m 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 1 m 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.”



Grodsky, S.M., C.E. Moorman, S.R. Fritts, D.W. Hazel, J.A. Homyack, S.B. Castleberry, and T.B. Wigley. 2016. Winter bird use of harvest residues in clearcuts and the implications of forest bioenergy harvest in the southeastern United States. Forest Ecology and Management 379:91-101.