| Popis: |
During presettlement times, many Eastern deciduous forests in North America are thought to have been open park-like woodlands rather than the closed-canopy, second-growth forest encountered today. Changes in forest structure are of special concern given that oaks (Quercus spp.) cannot regenerate effectively in closed-canopy stands. Partial-harvesting is one management technique used to simulate historic disturbance regimes and restore a more open forest structure. I studied forest songbirds in shelterwoods recently harvested to 50% stocking and reference upland mixed-oak stands in the same landscape context. My research was conducted at four state forests in southern Ohio from 2007–2009. I focused on canopy songbirds as one late-successional group that could benefit from partial-harvesting. Specifically I examined the extent to which (1) canopy species select particular canopy features and (2) canopy structure affects reproductive success. Distance-based line-transect surveys showed that shelterwood harvesting shifted the bird community from midstory and ground-nesting species to shrub and canopy-nesting species. The declining Cerulean Warbler (Dendroica cerulea) favored northeast facing slopes with abundant grapevine. Nesting success of canopy species was comparable between partially-harvested and reference stands, although generally low (15–36%) even in a predominantly forested landscape. Canopy structure was important and overall species nested in areas with fewer medium trees (23–38 cm dbh). In addition, species selected white oaks and avoided red oaks which were negatively associated with nesting success. Management implications from this study include prioritization of areas for protection, and recommendations on size and species of trees retained in partial-harvests. Results suggest that shelterwood harvesting can provide suitable breeding habitat for canopy songbirds in the short-term, although long-term management options should be considered. |
