PLANT COMMUNITIES IN RIPARIAN WETLAND MEADOWS DOMINATED BY REED CANARY GRASS 

Robin W. Tyser 1,2, Eileen M. Kirsh2, and Melissa S. Meier2   
1River Studies Center, University of Wisconsin-La Crosse, La Crosse, WI 54601. 
2U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, 
WI 54602.

Reed canary grass (Phalaris arundinacea) is known to aggressively invade and 
alter the composition of vegetation in wetland communities in the Upper Midwest.  
However, plant species that can tolerate reed canary grass dominance and 
environmental factors potentially associated with greater reed canary grass 
dominance are not well known.  Our primary objective was to describe plant 
species associations in wet meadows with a range of reed canary grass dominance.  
In addition, we examined whether certain environmental nutrients were associated 
with occurrence of reed canary grass in these communities.  Thirteen riparian 
wet meadows sites (4.5-16.5-ha) located within 75-km of La Crosse, WI were 
sampled in early to mid-August 2002, and aerial cover of plant species at points 
within each site (n=33-89) was estimated.  Concentrations of selected soil 
nutrients (NO3, NO4, total nitrogen, and available phosphorus) were sampled at 
three to nine randomly selected points at each site (ca. one sample per 1.5 ha).  
Vegetation and nutrient data were analyzed using non-metric multidimensional 
scaling, which is a multivariate ordination technique commonly used to explore 
relationships between community composition and environmental gradients.  A 2-
axis ordination accounted for most of the variation in the plant species data 
(cumulative r2 > 0.90) and separted sites into two distinct clusters.  Cluster 1 
sites were characterized by relatively high coverage of RCG and taxa (e.g., 
Sagittaria latifolia and Sparganium eurycarpum) with relatively strong wetland 
indicator status (classified as obligate wetland or facultative wetland 
species).  Cluster 2 sites were characterized by relatively low coverage of reed 
canary grass and taxa (e.g., Amphicarpaea bracteata, Eupatorium perfoliatum, and 
Baptisia alba) with lower wetland indicator status (classified as facultative 
wetland, facultative, or facultative upland species).  In addition, ordination 
axes show generally weak associations with individual soil nutrients (r2 < 
0.20).  Our results show that RCG greatly affects wetland vegetation patterns, 
but also that several species, e.g., Polygonum amphibium, Sagittaria latifolia, 
and Sparganium eurycarpum, may be capable of attaining relatively high coverages 
in sites dominated by RCG.  This study also suggests that the abundance of RCG 
is positively correlated with a moisture gradient and that soil nutrients may 
not be not strongly associated with vegetation patterns in these study sites.

Keywords: Phalaris arundinacea, upper Mississippi River, non-metric 
multidimensional scaling, wet meadow, soil nutrients