Timber management and forest songbirds

This project explores the impacts of timber stand improvement (TSI) on forest breeding songbirds in Vermont. TSI harvests are currently being promoted by the Vermont Natural Resource Conservation Service (USDA) as a means of creating habitat for some early successional species without negatively impacting most mature forest species. This recommendation is based on a program created by Audubon Vermont.  However, neither Audubon nor NRCS has collected empirical data showing that the program investment on private lands actually supports the targeted species.  My work, along with my graduate student David Rankin, tests this management model.  We published these results in:

Rankin, D.R., and N.G. Perlut. 2015. The effects of forest stand improvement practices on occupancy and abundance of breeding songbirds. Forest Ecology and Management. 335:99-107.

 

Abstract:

Silviculture can play an important role in managing avian habitat. In 2010 the Vermont Natural Resource
Conservation Service, in conjunction with Audubon Vermont, implemented a Forest Stand Improvement
initiative designed to improve timber quality while increasing habitat diversity for forest breeding songbirds.
To evaluate the effectiveness of this program in improving avian habitat, we conducted point count
surveys of breeding birds in harvested and control sites in 2012 and 2013, 1–3 years post-harvest.
Harvesting resulted in mean decreases of 18% in basal area, 10% in canopy cover, and 10% in canopy tree
density while piles of woody debris per ha increased by 402%. Occupancy and abundance estimates for 24
and 18 bird species respectively were derived using Program MARK. Compared to controls, occupancy
rates of four songbird species were greater on harvested sites – rose-breasted grosbeak (Pheucticus ludovicianus),
yellow-bellied sapsucker (Sphyrapicus varius), chestnut-sided warbler (Setophaga pensylvanica),
and mourning warbler (Geothlypis philadelphia)—while occupancy of one species—black-and-white warbler
(S. fusca)—was significantly lower. Two species were significantly more abundant at harvested sites—
rose-breasted grosbeak and yellow-bellied sapsucker—while two species were less abundant—hermit
thrush (Catharus guttatus) and black-and-white warbler. Piles of woody debris left after harvests were
negatively associated with site occupancy for 3 out of 10 understory species. Overall, our results suggest
that this program retains all interior forest species and has a slight positive impact on gap and early successional
species abundance and occupancy in the first 1–3 years post-harvest. This study provides the
first quantitative examination of the impact that Vermont NRCS’s Forest Stand Improvement program
has had on forest breeding birds.