Breeding Birds of the Cornish Hardwood Management Area: Aitkin County, Minnesota

Abstract

The Cornish Hardwood management area (CHMA), located in northeast Aitkin County is managed by Aitkin County forestry department and Minnesota Department of Natural Resources in an uneven-aged format. The forestry goals for this area are to provide wood resources for local industry and to promote regeneration and growth of high value hardwood trees by maintaining this forest type throughout each rotation. Northern hardwood forests provide habitat for a variety of breeding bird species, including several long-distant migrants. Although, response of breeding birds to successional forest stages from clearcut to mature stand ages are relatively well known and predictable for northern Minnesota forests, breeding bird response to uneven-aged management in northern hardwoods has not been studied in Minnesota. Our objectives were to: 1) establish a long-term breeding bird monitoring program in the CHMA to detect annual changes in species abundances, 2) determine whether bird community composition and species abundances are affected by uneven-aged management, and 3) compare bird community in the CHMA with other northern hardwood stands in northern Minnesota. Twenty-six individual stands that were greater than 40 acres were selected for monitoring. Eight stands were harvested within the past 10 years (managed), eight stands are in the management area, but have not been recently managed (unmanaged), and ten sites were located in Savannah Portage State Park. One breeding bird survey was conducted at each point with an unlimited radius 10 minute count point count. A total of 25 bird species were observed in 26 stands (52 points). On average, we observed about 22 individuals and 7 to 8 species in each stand (total of two point counts). No differences were detected in bird communities among management types. Two of the 15 species tested with analysis of variance indicated a significant difference (P < 0.05) in abundance among management types. The Chestnut-sided Warbler and Winter Wren were more abundant in the managed than in the unmanaged or reference sites. Both of these species are associated with habitat features that occur shortly after forest management activities (shrubs or slash piles). A cluster analysis with bird species showed that bird community composition was not different among management types. Overall bird communities in all stands sampled regardless of management history were similar. This result indicates that uneven-aged management such as the type that has been lone at CHMA does not result in a forest structure that is different than what currently exists in other northern hardwood stands in this region. This result is similar to what we have found previously for other “old-growth” northern hardwood stands in the State. A species that was absent in northern hardwood stands in this region was the Black-throated Blue Warbler. This species is rarely found in northern hardwoods in north central Minnesota but occurs in selected northern hardwood stands in northeast Minnesota, primarily in the Lake Superior highlands. A study on the Black-throated Blue Warbler in northeast Minnesota in 1998 found that the species prefers northern hardwood stands with a shrub understory. In areas where there are few shrubs, the species was primarily associated with small gaps (in the range of 0.05 to 0.10 ha) in the canopy that have resulted from blowdowns. The natural disturbance regime for northern hardwoods in this region was windstorms which occur every few decades and create small forest gaps by blowing down senescent or weak and hollow trees. It is possible that the Black-throated Blue Warbler historically responded to habitat that was created by these gaps and moved across the landscape as new patches were created and old patches became unsuitable. It may be possible maintain the objectives for forest management in the CHMA by completing harvests that would result in the creation of small gaps. Another recommendation would be to chose harvest equipment that would have less impact on the understory vegetation (e.g., result in less skidding of trees). These management suggestions will not only provide more suitable habitat for avian species that require shrubs and saplings, but also a population of seedlings and saplings for future recruitment into the canopy.