Breeding, Early-Successional Bird Response to Forest Harvests for Bioenergy.

Steven M Grodsky,T Bently Wigley,Christopher E Moorman,Sarah R Fritts,Steven B Castleberry,Bi-Song Yue

doi:10.1371/journal.pone.0165070

Abstract

Forest regeneration following timber harvest is a principal source of habitat for early-successional birds and characterized by influxes of early-successional vegetation and residual downed woody material. Early-successional birds may use harvest residues for communication, cover, foraging, and nesting. Yet, increased market viability of woody biomass as bioenergy feedstock may intensify harvest residue removal. Our objectives were to: 1) evaluate effects of varying intensities of woody biomass harvest on the early-successional bird community; and (2) document early-successional bird use of harvest residues in regenerating stands. We spot-mapped birds from 15 April– 15 July, 2012–2014, in six woody biomass removal treatments within regenerating stands in North Carolina (n = 4) and Georgia (n = 4), USA. Treatments included clearcut harvest followed by: (1) traditional woody biomass harvest with no specific retention target; (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 site). We tested for treatment-level effects on breeding bird species diversity and richness, early-successional focal species territory density (combined and individual species), counts of breeding birds detected near, in, or on branches of harvest piles/windrows, counts of breeding bird behaviors, and vegetation composition and structure. Pooled across three breeding seasons, we delineated 536 and 654 territories and detected 2,489 and 4,204 birds in the North Carolina and Georgia treatments, respectively. Woody biomass harvest had limited or short-lived effects on the early-successional, breeding bird community. The successional trajectory of vegetation structure, rather than availability of harvest residues, primarily drove avian use of regenerating stands. However, many breeding bird species used downed wood in addition to vegetation, indicating that harvest residues initially may provide food and cover resources for early-successional birds in regenerating stands prior to vegetation regrowth.

Highlights

Early-successional vegetation structure ephemerally occurs during forest succession and is precipitously declining in North America due to changes in natural and anthropogenic disturbance regimes [1]
Harvest residue removal on North Carolina (NC) sites either had no effect on the early-successional bird community or effects lasted for only one year, and early-successional birds were unaffected by distribution of harvest residues (Table 1)
Our results suggest that the successional trajectory of vegetation structure and composition rather than volume or distribution of harvest residues following timber harvest is the primary driver of breeding, early-successional bird use of regenerating stands

Summary

Introduction

Early-successional vegetation structure ephemerally occurs during forest succession and is precipitously declining in North America due to changes in natural and anthropogenic disturbance regimes [1]. Conservation of disturbance-dependent plant and animal species adapted to early-successional vegetation has grown in priority [2, 3, 4, 5]. Early-successional birds are adapted to open-canopy conditions created by increasingly uncommon natural and anthropogenic disturbances [1, 7, 8] and presently rank among the highest conservation priority avian habitat specialists [2, 9]. Forest regeneration following timber harvest is a principal source of habitat for early-successional birds [1], especially in regions supporting forest industry like the southeastern United States [9]. The positive relationship between vegetation structure and diversity following clearcutting and early-successional birds has been well studied, and young, intensively managed forests have been shown to provide habitat for early-successional birds prior to canopy closure [9, 17, 18, 19]

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Discussion

Conclusion