U.S. Forest Service scientists recently published the results of one of the longest studies conducted on the effects of multiple forest harvest methods on early successional bird species. Published online in Forest Ecology and Management, the article by Forest Service Southern Research Station research wildlife biologist Roger Perry and retired scientist Ron Thill presents findings from an 18-year study in pine-dominated stands on federal lands in Arkansas and Oklahoma.
Early successional bird species—those that breed in young, disturbed, often shrubby forests—are consistently declining across the eastern United States due to loss of habitat. Over the past 50 years, various factors—fire suppression, farm abandonment, land development, and recolonization by second-growth forests—have shrunk the area of early successional habitat, squeezing out the species that rely on it.
By opening gaps, timber harvesting creates favorable conditions for bird species that prefer early successional habitat. In the past, clearcutting served as the primary method for regenerating forests, and previous research shows that clearcutting provides excellent habitat for early successional, shrub-adapted birds. The long-term study confirmed that clearcutting may still be the best option for maximizing densities of many early successional bird species.
Clearcutting is unpopular with the public, and public opposition to the practice led the U.S. Forest Service to limit the use of the method on many federal lands, relying more on a range of other even- and uneven-aged management practices to harvest and restart forests. Much less research has been conducted on the effects of these alternative systems on early successional bird populations, especially in pine-dominated forests of the Southeast.
The researchers conducted the study in the Ouachita and Ozark-St. Francis National Forests in Arkansas and Oklahoma. “We evaluated the long-term responses of 12 disturbance-associated bird species to four different forest regeneration methods—clearcut, shelterwood, single-tree selection, and group selection,” says Perry. “We compared these treatments with unharvested controls for 2 years prior to harvest and at various intervals for 16 years after harvest.” (Read explanations of the different silviculture systems used in the study.)
Bird species studied included:
- the 9 most abundant species associated with clearcuts: American goldfinch, blue grosbeak, common yellowthroat, indigo bunting, prairie warbler, northern bobwhite, yellow-breasted chat, field sparrow, and white-eyed vireo;
- three species associated with less intense disturbances that generally retain some mature trees: northern cardinal, Kentucky warbler, and hooded warbler; and
- the brown-headed cowbird, a significant nest parasite of shrub-nesting birds.
Multiple bird surveys took place and data on vegetation structure in each of the experimental plots was collected each year. In the article, the researchers provide findings for each bird species studied. In general they found that many bird species were found for longer periods of time in clearcuts than in other treatments.
“For some early successional species, it appears that clearcutting may still be the best option for maximizing densities,” says Perry. “Shelterwood treatments offer the closest approximation to clearcuts given the amount of trees that are removed during harvesting. In addition, shelterwood and single-tree selection treatments provide habitat to species that prefer stands with some mature trees and abundant shrubs, such as Kentucky warbler and hooded warbler, which were rare in both unharvested control stands and clearcuts.”
For more information, email Roger Perry at email@example.com .