Composition and structure of an old-growth floodplain forest of the lower Kaskaskia River

Compositional and structural properties of canopy, shrub/sapling, and ground-cover strata were measured within an old-growth floodplain forest bordering the lower Kaskaskia River in southwestern Illinois. Basal area for trees was estimated at 31.8 m(2)/ha, tree density was 398 trees/ha with 27 species recorded in the canopy stratum. The dominant tree species were Acer saccharinum, A. negundo, Carya laciniosa, Ulmus rubra, and Quercus macrocarpa. Presently, there appears to be insufficient recruitment to maintain A. saccharinum at current abundance levels in the canopy. Total sapling/shrub density, including woody vines, was estimated to be 7,440 stems/ha and 24 species were recorded. Dominant species were Toxicodendron radicans, Campsis radicans, Ulmus rubra, Celtis occidentalis, and Ilex decidua. Ground-cover vegetation was characterized by species density (species per 1/4-m(2) quadrat) of 4.88, with 81 species (in 240 quadrats), and 80.8 percent cover. Dominant species were Laportea canadensis, Toxicodendron radicans, Ranunculus septentrionalis, Viola pratincola, and Galium aparine. The floodplain is a mosaic of intergrading wet, wet-mesic, and mesic floodplain forest natural communities.