Alliaria petiolata is an invasive, biennial herb that has become problematic in mesic forests throughout the Northeastern and Midwestern United States. A. petiolata may compete with native plants for light, space, and soil resources, or may suppress natives through allelopathic effects. In an ongoing study, we are exploring the population dynamics of A. petiolata in two forested nature preserves in central Ohio, one that has a large A. petiolata population (the invaded preserve) and one where this species is still relatively rare (the uninvaded preserve). We established twenty-three fifty meter transects (fourteen in the invaded preserve and nine in the uninvaded preserve) with up to eight 2x2 meter plots at five meter intervals along each transect. A. petiolata rosettes and mature plants present in each plot were recorded each summer from 2004 through 2007, and the number of siliques and seeds per plot were also estimated in 2005 and 2007. Ground cover and plant stem counts were recorded in a 1x1 meter area of each plot for all species in summer 2005 and 2007. 

Results/Conclusions

Populations of A. petiolata rosettes in both preserves fluctuated from year to year, but overall the mean number of rosettes per plot almost doubled between 2004 and 2007 in the invaded preserve, while rosettes remained rare in the uninvaded site in 2007.  A. petiolata was the second most abundant understory species as measured by stem counts in the invaded site, but because the rosettes are small, they represented less than 1% of the ground cover.  Seed rain per plot in the invaded preserve was found to be significantly greater in 2007 than in 2005 (P < 0.05), and this was due to a tendency for mature plants to produce greater numbers of siliques, since numbers of mature plants per plot declined slightly over time.  These data suggest that while the A. petiolata population fluctuates significantly from year to year, this population is expanding in the invaded preserve, and has the potential for continued increase due to the high seed rain observed in 2007.  In contrast, the population in the uninvaded preserve has remained small and stable during this observation period.