Initiating a long-term monitoring program of aquatic and terrestrial invasive species in Kenosha County, Wisconsin

Background/Question/Methods   Approximately 50,000 species have been introduced to the United States. Although the majority of these species remain harmless, others are problematic because they become invasive and outcompete native species. Riparian areas are particularly vulnerable to invasion due to high natural and anthropogenic disturbance, which promotes the spread of invasives. In Wisconsin, common invaders include aquatic species such as Myriophyllum spicatum (Eurasian water milfoil) and Potamogeton crispus (curly-leaf pondweed) and terrestrial species such as Lythrum salicaria (purple loosestrife). Long-term monitoring is crucial for increasing our overall understanding of invasives, and simultaneous monitoring of aquatic and terrestrial species could reveal important links between the spread and impact of terrestrial and aquatic organisms. In this initial phase of a long-term study, diversity and abundance of terrestrial and aquatic plant species were measured at two connected pairs of lakes in Kenosha County, Wisconsin. It was expected that larger lakes would have lower richness of terrestrial and aquatic species than smaller lakes due to increased opportunities for transport and dispersal of invasive species.

Results/Conclusions   Our hypothesis was partially supported. Aquatic species richness per sample was the highest at the smallest lake that was sampled (p<0.05); however, at this same lake, terrestrial species richness was the lowest (p<0.05). The finding that terrestrial and aquatic species richness exhibited opposing trends is potentially due to variation in dispersal mechanisms between land and aquatic species. The other three lakes did not demonstrate the hypothesized inverse relationship between lake size and species richness. This may be due to the fact that at all lakes, for both terrestrial and aquatic species, invasive species appear to be at early stages of establishment – though both aquatic and terrestrial invasive species were present at all sites, they did not dominate any of the lakes. Continued long-term monitoring will be important for ensuring that appropriate management techniques are implemented should these species continue to establish and increase in their dominance.