Propagule Pressure, Disturbance, and Invasion Dynamics

Martha Hoopes (Biological Sciences, Mount Holyoke College)

Increasing forest cover has accompanied a decline in agriculture in New England since about 1930. As forests have increased, grasslands and meadows and their associated species have decreased with the result that a large portion of Massachusetts’s rare and threatened species are grassland habitat specialists. Management to maintain grasslands often involves disturbance (e.g., logging, mowing) that may introduce novel conditions and non-native species into habitats with rare species. Species composition in a local habitat reflects the regional species pool and any transport and disturbance mechanisms that disperse species between local patches to colonize new sites. This project examines plant community composition in wet and dry meadows in areas open to logging and recreational use or closed to the public in the Quabbin watershed and Harvard Forest. Previously collected data offer baseline regional species pools, and current research will link those data with dispersal trials and new species diversity assessments to disentangle the effects of dispersal, propagule pressure (a measure of the number of individuals and introduced and the number of times that introductions occur), disturbance, and abiotic environmental factors on invasion dynamics in grassland environments. Student projects will include dispersal trials, plant community data collection, and models that combine dispersal and population growth. Mathematical approaches include mixed effects statistical models, robust methods for variable selection and clustering for multivariate responses, and integrodifference equations. Field work will take place at the Quabbin and Harvard Forest in Petersham, MA.