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Abstract
In the mature oak-hickory ecosystem of the Illinois Ozark Hills, forest community composition, dynamics, and structure were studied to examine the extent of conversion to mesophytic species and eventually predict the broad threshold time of complete conversion. Tree, sapling, and seedling data were collected from 87 plots distributed throughout the region. Data for the tree stratum and for the seedling and sapling strata were analyzed by Ecological Land Type (ELT): south slope, ridgetop, north slope, and stream terrace. To compare the vegetation among ELTs and between stand strata, importance values (relative basal area for trees; relative density for seedlings and saplings) were calculated and a composition index [CI = Σ(Species Importance Value x Adaptation Value)] developed for each stratum. On south slope and ridgetop ELTs, CI values near 600 were typical of an oak-hickory dominated overstory (Adaptation Values [AVs] = 4-6.5). Dominant species were white and black oak. On the more mesic north slope ELT, a CI of 774 indicated a mixed overstory dominated by northern red oak, white oak, yellow-poplar, and black oak. The Terrace ELT was dominated by yellow-poplar and a mixture of upland and bottomland species; overstory CI was 747. For all ELTs, sapling CI ranged between 852 and 958, while seedling CI varied between 772 and 921. These CI values indicated an understory moderately to strongly dominated by mesophytes, primarily sugar maple, American beech, and red maple (AVs = 9.1, 9.6, and 10, respectively). Given the universal and extensive development of the understory, the Illinois Ozark Hills seem destined to be the fi rst major ecosystem to convert from a forest dominated by oak-hickory to one dominated by maple-beech.
Parent Publication
Citation
Helmig, Lisa M.; Fralish, James S. 2011. Composition, structure, and dynamics of the Illinois Ozark Hills Forest. In: Fei, Songlin; Lhotka, John M.; Stringer, Jeffrey W.; Gottschalk, Kurt W.; Miller, Gary W., eds. Proceedings, 17th central hardwood forest conference; 2010 April 5-7; Lexington, KY; Gen. Tech. Rep. NRS-P-78. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 109-127.
