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2003: Assessing the Impact of Deer on Forest Growth in Wetlands

Ian Cornell (Biology) College Of William and Mary

In the William and Mary College Woods, some areas show very little evidence of new forest growth, namely young, woody saplings between 50 cm and 2 m tall. Last summer (2002), an unusually high number of white-tailed deer (Odocoileus virginianus) was noticed in the College Creek riparian wetlands off Compton Drive. This occurrence can most likely be attributed to the drought conditions experienced last year, but it prompted a question to be asked: Is deer grazing pressure the cause for the lack of saplings in the riparian forest? During summer 2003, three deer exclosures, each ten meters by ten meters, were constructed and paired with control plots. Seedling densities of all woody species were monitored via sampling in early June, and then again six weeks later. Sampling is proposed to continue for several years. I hypothesize that, owing to the absence of deer grazing in exclosure plots, higher densities of seedlings will occur.

Results from this first summer of sampling indicate no significant difference between deer exclosure plots and control plots. However, this summer has also been wet, with plenty of water available for deer, thus not confining them to watering areas within the College Creek riparian wetlands. Baseline values for the Index of Dominance ranged from 0.247 to 0.444 in June and from 0.244 to 0.536 in July, the greatest change being from 0.387 to 0.536. Coefficient of Community values varied little (0.67 and 0.73) in June and then diverged in July (.25 and 0.89) as seedlings of certain species of trees failed and seedling diversity was lost. The overall composition of the plots did not change substantially as Community Similarity values remained relatively constant.

To date, the most important environmental factor affecting seedling distribution and abundance is flooding that physically swept seedlings out of some plots. This impact, however, was observed in both control and experimental plots. The current results document conditions prior to exclusion of deer, and I expect the impact of deer on forest growth will be observed in the coming years.

For additional documentation Ian Cornell provided a PowerPoint Presentation entitled " Assessing the Impact of Deer on Forest Growth in Wetlands " provided here in PDF form.