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.
