Effects of a Highway on Plant Species Composition and Diversity of a Southwestern Michigan Wetland
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Human interactions with the environment are diverse and ubiquitous. One of the most notable of these interactions comes in the form of roads. Because of the widespread nature of roadways in the US (approximately 6.2 million km of public roads), the potential for marked ecological effects is high. Roads have been implicated in damage to vegetation, reduction of regional biodiversity and facilitation of alien species invasions. Yet, road effects on vegetation diversity and composition are poorly studied to date. Accordingly, a study of the effects of a state highway (M-43) was taken on an adjacent wetland community in the Lillian Anderson Arboretum in Kalamazoo County, Michigan. Six transects were established perpendicular to M-43 within a one hectare area of the wetland. Plant species composition and frequency were sampled at six points along each transect and on the roadbank above the wetland using 0.5 m2 plots. Groundwater pH, conductivity and osmolarity of a subset of the 35 sample points were measured. We found that groundwater conductivity within the wetland was four times greater near the highway. Wetland vegetation also changed with distance from road, with Typha sp. (cat-tail) dominating near the road and species density increasing linearly with distance from road. The percentage of introduced species was nearly ten times greater on the roadbank than in the wetland. There are substantial road effects on plant species composition in this wetland, which appear to be directly correlated to groundwater conductivity. The dominance of Typha sp. seems to facilitate loss of biodiversity, which can lead to long-term sustainability difficulties for the wetland.