PARENT SESSION
Organized Oral Session 17: Coastal indicators of ecological condition: Integration of spatial scales
Organizer(s): GJ Niemi, H Paerl, and B Levinson
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 516 A, Level 5, Palais des congrès de Montréal

Understanding a biotic indicator: Scaling down from regional patterns to local mechanisms of cattail dominance and plant species density.

Vaccaro, Lynn^*,1, Johnston, Carol², Bedford, Barbara ¹, ¹ Cornell University, Ithaca, NY² South Dakota State University, Brookings, SD

ABSTRACT- Invasive species could be used as indicators of wetland condition if their abundance reflected the degree to which anthropogenic activities negatively impact the native community. Many wetlands of the Great Lakes region are increasingly dominated by invasive species of cattails, Typha angustifolia L. and Typha X glauca Godr. This study first examined regional and lake-wide patterns of cattail distribution to evaluate the relationship between cattails and watershed development. In collaboration with the Great Lakes Environmental Indicators project, we surveyed the vegetation of 90 wetlands around the Great Lakes and related characteristics of the plant community to watershed characteristics. In contrast to five co-occurring native species, the presence of invasive Typha species was associated with lower species density (7.1 vs. 8.6- 9.7 spp/m² for natives). Unlike that of the native species, relative cover of invasive Typha species was positively related to human population density (p=0.015) and an index of agricultural intensity (p=0.003) within the wetland watershed. This suggests that anthropogenic activities may affect wetland species diversity by promoting the growth of invasive cattails. However, the abundance of invasive Typha varied among ecological provinces and lakes, indicating that factors such as climate and lake-level management also may influence its cover. We then evaluated one mechanism of dominance at the wetland scale by experimentally manipulating the amount of cattail litter and measuring its effect on the plant community. We found that cattail litter negatively influenced the survival of a phytometer seedling (p=0.046) and overall plant species density (p=0.0005). Therefore, factors affecting cattail production (e.g., agriculture) and litter decomposition (e.g., lake water levels) could have important implications for both cattail dominance and species diversity in Great Lakes wetlands. Thus, the abundance of invasive Typha species seems to indicate a wetland response to human activity. An understanding of the geographic variability and the processes promoting dominance of these invasive species should guide monitoring efforts.

Key words: Invasive species, Biotic indicators, Great Lakes, Typha angustifolia