PARENT SESSION
Poster Session #57: Invasive Species Ecology: Grasslands.
Thursday, August 8. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Variability in tansy ragwort (Senecio jacobaea) population dynamics in a range of environments.

Trainor, Meghan^*,1, Maxwell, Bruce¹, Markin, George², ¹ Montana State University, Bozeman, MT² USDA Forestry Sciences Lab, Bozeman, MT

ABSTRACT- Tansy ragwort colonized burned areas in northwestern Montana following a 1994 wildfire. Invasive populations were previously thought to be in maritime environments in North America. Intermountain West wildfires of 2000 and 2001 have produced large areas with potential for colonization by tansy ragwort. Therefore, it is important to examine the biotic and abiotic factors that influence tansy ragwort colonization and population dynamics in burned and unburned areas. We conducted a population viability analysis including construction of a life history model for tansy ragwort over a range of environmental conditions: 1) burned by wildfire, 2) burned and then salvage-logged, and 3) undisturbed forest and undisturbed meadow. Natural-occurring plant populations were mapped in 1-m² plots. Life history stages (seedling, rosette, flowering, seed produced) were recorded in spring and fall. Measurements allowed calculation of transition rates, which were incorporated into a transition matrix model. Vital rates compared across environments indicate variability. The model was used to compare stable stage distributions and growth rates of populations in the different environments including populations in the Pacific coast region (McEvoy and Coombs 1999). Vulnerable life stages were identified. Tansy ragwort populations were most invasive in burned and logged environments and found to have growth rates less than one in undisturbed meadows. Assessing population growth rate differences with a density-independent model provides a first approximation comparison to estimate invasiveness of weeds in different environments.

KEY WORDS: Senecio jacobaea, population dynamics, fire effects, life history model