Summary of vegetation sampling for selected transects of La Grange Peitzmeier-Romano, S., K. D. Blodgett, and R. E. Sparks. 1992. Summary of vegetation sampling for selected transects of La Grange Pool, Illinois River, 1990. Report by the Illinois Natural History Survey, Havana, Illinois, for the U.S. Fish and Wildlife Service, Environmental Management Technical Center, Onalaska, Wisconsin, November 1992. EMTC 92-S007. 34 pp. (NTIS #PB94-109477) ABSTRACT Physical and chemical impacts of human activities have influenced the abundance and diversity of wetland and aquatic plants in the Upper Mississippi River System (UMRS). In 1990, the Long Term Resource Monitoring Program (LTRMP) vegetation component conducted a baseline study that will enable us to document successional changes in the UMRS during the next decade. Five LTRMP stations conducted vegetation studies; this report represents the study at La Grange Pool, Illinois River, during 1990. To obtain a representative sample of the pool, five transects transversing several plant communities were chosen. Transects were chosen according to criteria listed in the LTRMP Procedures Manual, Chapter 6 (Davies 1989). Each transect was divided into plant community types. Floodplain forest, shrub-carr, deep marsh, shallow marsh, seasonally flooded basins, and non-vegetated aquatic areas were the most common community types of La Grange Pool, Illinois River, in 1990. Sample sites were stratified within distinct communities by selecting an initial distance using a random numbers chart. The initial distance was measured from the edge of the community and subsequent sites were sampled 50 m apart along a predetermined compass bearing. Edge and emergent plant communities were rare during 1990, possibly due to the extreme water level fluctuations throughout the year. Within the resident floodplain forest, Acer saccharinum occurred at the highest frequency and is botanically the most important tree species of the floodplain forest in La Grange Pool at this time. Vitis spp. was the most frequent vine in the floodplain forest, followed by Sicyos angulatus, Toxicodendron radicans, Campsis radicans, and Ampelamus albidus. The herbaceous community of the forest was dominated by Aster simplex during 1990; this late-blooming species blankets the forest floor. Alluvial mudflats were populated by homogeneous stands of Salix spp. Salix nigra was the major constituent of shrub-carr communities within La Grange Pool. During 1990, one floating aquatic species common in La Grange Pool and associated backwaters was the very adaptable Polygonum natans. Other aquatic species, such as Nelumbo lutea, Nymphaea odorata, Myriophyllum spicatum, and Ceratophyllum demersum, were found in backwaters isolated from the river where water levels were more stable and turbidity lower. Baseline data to study vegetation dynamics have been collected and the methodology for the study of wetland and aquatic vegetation was developed during 1990. Our intense effort to understand the ecosystem of the UMRS has inspired further questioning and research in the area of vegetation and river ecology of La Grange Pool. KEYWORDS La Grange Pool, Illinois River, Upper Mississippi River System, plant communities, vegetation, inventory, wetland