To develop the model we collected data on the distribution and spread of Japanese stiltgrass at several sites in south central Indiana from 2007 - 2010.
We used high-accuracy portable GPS units to map all patches of Japanese stiltgrass at a site. For each stiltgrass patch, we recorded the diameter, density, and plant height. We also took digital photographs of the canopy using a hemispherical lens to estimate canopy cover and understory light levels.
Laboratory Data Collection for Biomass and Seed Production
To estimate seed production, we harvest plants from a 25 x 25 cm plot in the field. Back in the lab, we sort the plants by species, and sort out all the stiltgrass seeds.
Stiltgrass seeds are numerous. Some fall from the plant into vegetation and soil and others remain in stems. To count all the seeds, we separated seeds from plant material, dissecting stems, and isolateed seeds from soil.
There is a strong relationship between plant mass (size) and seed production. This allows us to use plant size and density as a proxy for seed production in the model.
We are using these data to analyze stiltgrass spread with geographic information system (GIS) software. This will help to determine what environmental factors make the best habitat and how stiltgrass spreads across the landscape, and hopefully help us better understand how to contain its spread.
