Optimum Water Depth and Flooding Duration for Native and Exotic Plant Species in Lake Ontario Shoreline Wetlands

Objective

To review extensive literature on range and ideal water depth and flooding duration associated with native and exotic plant species in Lake Ontario shoreline wetlands.

Justification

The colonization and growth responses of wetland plant species in northeastern North American wetlands relative to water depth and flooding duration have been investigated by numerous scientists. These basic parameters determine whether any plant species can colonize and dominate a site, and are essential to compile to assess the effects of changes in Lake Ontario water levels relative to plant species abundance, richness, and diversity. On-site studies of water levels relative to plant species composition and structure do not necessarily indicate optimum water depth and flooding duration for each plant species in the year of field sampling. While water levels may widely differ from one year to the next, many plant species can not immediately respond to favorable or unfavorable growing conditions. For example, vegetation may be flooded during one high water year but not show any adverse effects of the high water until following years.

Although one approach might gather this information only for a few species of concern, e.g., cattails (Typha spp.) or purple loosestrife (Lythrum salicaria), gathering this information for the hundreds of plant species found in wetlands of Lake Ontario shorelines would allow for predictions about plant species richness and diversity for specific water depths and flooding duration. Since fish and wildlife utilize specific plant communities, the use of various wetlands by fish and wildlife species can be inferred from predictions about wetland plant species composition and structure generated from this proposed research. This information on “plant performance” relative to water depth and flooding duration can also be applied to models that could predict success of wetland restoration efforts along the shoreline of Lake Ontario.

Project Description

Vegetation of shallow to deep, freshwater wetlands is largely a product of water depth and flooding duration, although certainly profoundly influenced locally by herbivores (especially muskrats) and a few, highly competitive plant species. We will synthesize the vast amount of data collected by numerous researchers, that has examined plant species distribution and abundance relative to water depth and flooding duration. We will try to gather this information for all vascular plant species that occur in Lake Ontario and St Lawrence River shoreline wetlands (shallow to deep water habitats).

The first task will be to establish a list of these plant species based on regional, state, and provincial floras, scientific journal publications, and unpublished documents and theses. The relationship between water depth and flooding duration is strongly documented for some species and sparsely documented for others. We will attempt to qualify this information in terms of establishing a confidence rating for each species, based on how strongly relationships are supported by the literature. Additionally, we will incorporate data on plant species relative to site fertility and disturbance gradients when such data are available. With the published data we plan to develop simple graphic models that show the relationship between plant species and water depths and flooding duration. Because many wetland species germinate from the seed bank only during drawdown conditions, we will develop these models to show plant response to a water level gradient from draw down to very deep water over very short (seasonal) to very long (two to three years) periods of flooding.

Project Leader and First Contact:
Donald J. Leopold
Distinguished Teaching Professor
SUNY-ESF
Syracuse, NY, 13210
email: dendro@mailbox.syr.edu

Sponsor:
International Joint Commission (USA/Canada)
Environmental Working Group of the Lake Ontario - St. Lawrence River Study