PARENT SESSION
Oral Session #62: Vegetation change: Succession, recovery, facilitation. Presiding: S. Franklin.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas G.
Threshold time of conversion from oak-hickory to mesophytic forest in the Illinois Ozark Hills.
Fralish, James1, Helmig, Lisa2, 1 2
ABSTRACT- Published community ecology studies from the central states universally have reported the development of an understory of sugar maple, American beech and other shade tolerant mesophytic species in oak-hickory dominated forest. To estimate the time of conversion to mesophytic species in the mature undisturbed oak-hickory ecosystem of the Illinois Ozark Hills, tree, sapling, and seedling stem data were collected from 46 permanently marked nested plots located within the Ozark Hills Nature Preserve, and from an additional 48 unmarked nested plots systematically located on forested section and quarter-section corners distributed throughout the region. Stand table projection was used to develop density estimates by species and diameter class for the years 2024 (30 years hence), 2054 (60 years hence) and 2084 (90 years hence). Projections were based on the stem growth and mortality within the present population of trees, saplings and seedlings. Seedling and sapling diameter growth rates for sugar maple, American beech and red maple were obtained from increment cores and leader growth rates from bud scale scars. Tree diameter growth rates were taken from TWIGS, a projection program developed for species of the central states forest by the North Central Forest Experiment Station Mortality rate varied from 1-5 %/yr depending on species, with higher rates applied to young and old stems. To constrain the model, maximum stand basal area was set as 35 m2 ha-1, the highest value known to occur in central states forest communities. At the end of each projection period, density was calculated for the tree stratum. In 1994, the small tree density of mesophytic species was substantially higher than that of the large overstory oak and hickory trees. Basal area, a parameter directly related to biomass, indicated that mesophytic hardwoods, primarily sugar maple, will exceed that of oak and hickory between the years 2045 to 2050, the threshold time of conversion.
KEY WORDS: oak-hickory conversion, quercus-carya conversion, community ecology, Illinois Ozark Hills