Indirect effects of white-tailed deer on Microstegium vimineum abundance in a post-agricultural woodland

Background/Question/Methods

Microstegium vimineum is a non-native annual grass that negatively impacts the understory flora of eastern broadleaf forests. For small scale invasions, late-season hand-weeding of Microstegium is an effective management strategy for eradication, if repeated for approximately five years. Our goal was to create a plan to decrease the time needed to eradicate Microstegium. We predicted that: 1) hand-weeding Microstegium three times during each growing season would hasten eradication, 2) deer exclusion would reduce Microstegium and increase native species cover, and 3) the combination of multiple removals and deer exclusion would be the most effective treatment combination. We established one set of paired 1m² quadrats in each of eight 100m² plots during June 2013. Half of all plots excluded deer. Each quadrat within a pair was assigned to receive either one or three weeding events of Microstegium per growing season. We quantified abundance (% cover) of all understory species after one year (June 2014) and evaluated the efficacy of the treatments using a split-plot ANOVA. 

Results/Conclusions

After one season of treatments, our results do not support our predictions. Multiple hand-weeding events did not reduce Microstegium cover or promote native cover. Total plant cover (F_1,6 = 8.721, p= 0.0255) and Microstegium cover (F_1,6 = 4.805, p= 0.071) increased when deer were excluded. Cover of the native annual Persicaria pensylvanica, however, decreased when deer were absent (F_1,6 = 9.93, p= 0.012). Combined with observations of high Persicaria cover in deer trails and beds and a strong correlation between Microstegium and Persicaria abundance, we hypothesize that the indirect effects of soil disturbance by deer are reducing Microstegium productivity by facilitating a strong competitor, Persicaria. We are currently attempting to validate this hypothesis with field experiments.