Earthworm composition and abundance
The fallen leaves of buckthorn have unusually high concentrations of nitrogen, which makes them a preferred food for many soil invertebrates including invasive European earthworms that are present in nearly all forested sites across Minnesota. As a result, buckthorn invasion is also associated with invasion of exotic earthworms, which can have further influences on nitrogen cycling. To understand how earthworms and buckthorn interact to influence soil nitrogen recycling and potential nitrogen exports into ground water and the atmosphere, we sampled the same plots at Warner Nature Center described above for soil nitrogen to investigate the relationship between buckthorn and earthworm abundance. In the early and later summer of 2012 and 2013, we sampled earthworm communities four times to quantify their abundance and community composition. Preliminary analysis indicates that earthworms were more diverse and abundant in silty versus sandy soil. Also, total earthworm biomass increased with increasing buckthorn. An ecological model that included buckthorn abundance light levels, soil moisture, and pH as predictors of earthworm abundance indicated that buckthorn facilitates worms through increased soil moisture.
We prepared a pamphlet, "Preventing and managing common buckthorn invasion: recent research and recommendations" (.pdf) that included all aspects of the research, as it pertains to the invasion of buckthorn. The pamphlet also provides suggestions for pre-invasion management to reduce invasibility, the main focus of the "Healthy Forests" research project.