PARENT SESSION
Contributed Oral Session 135: Invasive Species: Plant - Soil Feedbacks; Invasion Success
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 518 A, Level 5, Palais des congrès de Montréal
Forest management, deer herbivory, and exotic earthworm activity contribute to Pennsylvania sedge mat formation in northern hardwood forests.
Powers, Matthew*,1, Nagel, Linda2, 1 School of Forest Resources and Environmental Science, Houghton, Michigan, USA2 Ecosystem Science Center, Houghton, Michigan, USA
ABSTRACT- Pennsylvania sedge (Carex pensylvanica Lam.) is an aggressive native species that forms dense, monotypic mats in the understories of some northern forests. Natural resource professionals have expressed increasing concern that these sedge mats may limit tree regeneration and understory diversity, particularly in highly productive northern hardwood forests. We examined the relationship between management history, deer density, exotic earthworm density, and Pennsylvania sedge cover in 18 hardwood stands in northeastern Wisconsin to test the hypothesis that interactions between intensive management, heavy deer browsing, and exotic earthworm activity increase sedge cover. Stands were selected based on a gradient of management history (even-aged, uneven-aged, and unharvested second growth) and deer density (moderate density, 10 to 20 deer/km2, or high density, >20 deer/km2). We used ANCOVA to test for differences in sedge cover between combinations of management history and deer density. Even-aged stands with high deer densities were associated with greater sedge cover than even-aged stands or unharvested stands with moderate deer densities (p = 0.0012 and p = 0.0048, respectively). A regression model incorporating interactions between management history, deer density, and exotic earthworm density provided a good fit to observed sedge cover data (R2 = 0.91). Individual regression lines predicting sedge cover based on epigeic earthworm density for even-aged stands with both moderate and high deer densities, uneven-aged stands with moderate deer densities, and unharvested stands had positive slopes, although the line for uneven-aged stands with high deer densities had a negative slope. These preliminary findings indicate interactions between intensive management, overabundant deer populations, and exotic earthworms contribute to Pennsylvania sedge mat formation in northeastern Wisconsin. This suggests altered disturbance regimes and novel disturbances associated with biological invasions can interact to produce atypical vegetation dynamics in northern forests.
Key words: sedge mats, exotic earthworms, herbivory, northern hardwoods