PARENT SESSION
Poster Session #41: Plant Demography.
Thursday, August 9, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
56
Evidence for the role of canopy disturbance in the spatial distribution of eastern leatherwood (Dirca palustris).
Jones, Cynthia1, Schulz, Kurt1, Manar, Katherine1, Marriage, Tara1, Zasada, John2, 1 2
ABSTRACT- Eastern leatherwood is a small (< 3 m), persistent understory shrub of Acer saccharum-Tsuga canadensis-Betula lutea communites in the western Great Lakes Region. Its occurrence is sporadic both across the landscape and within stands. We conducted a series of related studies in the Ottawa NF, MI to identify causes for patchy distribution at the two scales. Leatherwood fruits are small drupes containing proportionately large seeds, with a thin, dry mesocarp. The fruits are not taken by birds, although rodents voraciously consume the ripe seeds. Most small leatherwood seedlings (< 25 cm) are found beneath the canopy of established individuals. A census of mature individuals (> 50 cm tall) reveals a disproportionate number became established on pit/mound complexes. Leatherwood populations are strongly aggregated in 100 m2 plots spaced 15-50 m apart. Virgin stands with canopy disturbances or managed second growth stands show higher population densities than stands with homogeneous canopies. Increased light stimulates vegetative growth and fruit production. We interpret the data to show that leatherwood is reliant on canopy disturbance for establishment, but has little capacity to disperse between disturbance patches. Single leatherwood individuals apparently persist in the forest understory until an overhead canopy gap stimulates growth and reproduction. We hypothesize that large leatherwood populations seen in ostensibly old gaps are largely the progeny of a few founders.
KEY WORDS: Dirca palustis, patch dynamics, spatial pattern, light gaps