Changes in breeding bird abundance and species composition over a 20 year chronosequence following shelterwood harvests in oak-hardwood forests

Abstract

Birds play an integral ecological, functional, and cultural role in New England forests and timber harvesting is known to affect their diversity and abundance. While much is known about bird communities immediately following a harvest (one to about three years), less is known about how communities shift through stand development. This study examines breeding-bird species diversity and composition in the 22years following shelterwood harvest of second-growth oak-hardwood forests in southern New England. We documented bird species richness, Shannon diversity, abundance, and evenness in 28 regenerating shelterwood harvests and compared them with eight mature forest stands. Early-successional regenerating stands (<12years since harvest) had higher bird abundance than regenerating stands 13–22years old and mature stands (80–100years old). Species richness and Shannon diversity were greater in regenerating shelterwoods compared to mature stands. Within the regenerating shelterwoods, species richness, Shannon diversity, and total bird abundance generally decreased with time since harvest. Species community composition differed between stands <12years old and older regenerating and mature stands. Abundances of forest dwelling, ground-nesting species increased steadily with time since harvest, while early-successional, shrub-nesting species decreased with time since harvest. Specifically, we observed higher abundances of shrub-nesting species such as chestnut-sided warbler (Setophaga pensylvanica) and indigo bunting (Passerina cyanea) in early stand-initiation (0–7years). Ground-nesting birds, such as ovenbirds (Seiurus aurocapilla), are present and abundant as early as 13years following a harvest and are not obligate to closed-canopied forest conditions. Indeed, abundances of species considered ‘late-successional’ were as high in early stem exclusion (13–22years) as in mature stands and were present in moderate numbers in stands considered late initiation (8–12years). Contrastingly, we found many early-successional species confined to stand initiation (<13years). In summary, bird communities in shelterwood harvests are highly dynamic in the 22years following harvesting and our understanding cannot be distilled to a single diversity number such as species richness. Our findings convey that bird abundance, richness, diversity and species composition change following a harvest, suggesting that natural resource managers in New England hoping to promote diverse and abundant bird populations should create forests composed of mosaics of differently aged managed stands, and mature forest reserves.