Shelterwood harvests promote high breeding bird diversity and shrubland species for less than 10 years in hardwood forests

Abstract

We compared forest structure and breeding bird communities between shelterwood harvests (SW; n = 15) and mature upland hardwood forests (M; n = 16) over 17 years (Y). Both were relatively static throughout the study period in M. In contrast, heavy canopy reduction and increased light after timber harvests in SW initiated rapid increases in small tree stem densities and shrub cover driven primarily by blackberry (Rubus spp.) - a clonal shrub that “pioneers” recently disturbed, high-light environments. This open-canopy forest structure with low, dense vegetation was short-lived; young trees reached canopy closure within 10 years, with concomitant reductions in blackberry cover and stem density. Total abundance, species richness, and diversity of breeding birds was greater in SW than M, especially the first several years post-harvest; in Y6 these metrics were more than twice as high in SW as in M. Higher abundance, richness, and diversity in SW was driven by an influx of shrubland associates (indigo buntings (Passerina cyanea), chestnut-sided warblers (Setophaga pensylvanica), Eastern towhees (Pipilo erythrophthalmus)) and positive or neutral responses by most other species; only ovenbirds (Seiurus aurocapilla) were more abundant in M. Abundances of shrubland bird species in particular tracked temporal changes in SW forest structure but each differed slightly in their patterns of increase, peak (with 15–26 times more in SW than M), and decline. By Y10 breeding bird communities in SW resembled those in M, although total abundance, species richness, and diversity remained slightly higher in SW throughout the study period. Total abundance, species richness, diversity, and abundance of shrubland bird species were positively- and ovenbird was negatively correlated with blackberry cover, indicating that it is a suitable stand-alone predictor of post-disturbance young forest and changes in breeding bird communities as forests mature. Our results show that young hardwood forests provide habitat for shrubland bird species and promote high breeding bird diversity for <10 years.