Floristic Change Spanning 45 Years of Global Change in the College Woods, Williamsburg, Va

• Main Author: Cyrus, Caitlin
• Format: Others
• Language: English
• Published: W&M ScholarWorks 2016
• Subjects: Biology
• Online Access: https://scholarworks.wm.edu/etd/1477068006; https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=1038&context=etd

The College Woods, located in Williamsburg, VA, is a natural preserve of approximately 960 acres owned by the College of William & Mary. The Woods supports a relatively diverse flora in a mature coastal-plain forest which has been under long-term biological study by members of the College. This thesis contributes to the ongoing investigation of the Woods by documenting floristic and vegetation changes that have occurred over the last 45 years amidst a rising and uncontrolled white-tailed deer population. Three main research questions are addressed: (1) How has floristic diversity, composition, and species abundance changed since the last floristic survey in 1989? (2) Under the assumption of chronic browse by white-tailed deer, are there species-specific plant traits that associate with a suite of declining species? and (3) What is the estimated forest successional trajectory indicated by a 2015 quantitative analysis of the diversity, composition, importance, and browse rates in 19 long-term permanent plots? For the floristic analysis, 297% more effort was required in 2015 to find 7% fewer species than in the last floristic survey of 1989, indicating a decline in the abundance of populations, making their rediscovery more difficult. Over the last 45 years, 745 vascular plant species have been documented in the Woods. One hundred and twenty-six species were newly reported in 2015, while 196 previously-reported species were not relocated. The turnover of species is consistent with the species-time relationship and was especially prominent in early successional open habitats. Assessments of changes in relative abundance showed that 46% of the species had declined in abundance. This appears to be driven by an overabundant white-tailed deer population, but no plant trait previously hypothesized to confer vulnerability to browse by white-tailed deer showed a signficant association with the set of declining species. It is hypothesized that because the deer population has been overabundant for 20 years, any trait-based associations that may have once existed would have become obscured over time as browse intolerant species were reduced and deer switched to less-preffered plant material. Deer-browse data on less preferred plants such as Fagus grandifolia, Polystichum acrosticoides and Ilex americana supports this hypothesis. Nineteen permanent plots erected in 2003 were sampled for vegetation analysis immediately after Hurricane Isabel in 2004 and then resampled in 2015. Analysis showed little change in the large tree and small tree size classes, but there was significant change in the sapling size class. In the sapling size class, average stem density and species diversity significantly decreased between 2004 and 2015, or did not show the expected regeneration patterns in areas severely hit by the hurricane. An analysis of deer browse in these plots showed that nearly 60% of all vegetation was browsed. This is expected to slow down the rate of succession and alter forest composition, possibly resulting in a beech-dominated forest with very little understory. A management plan designed to allow the flora of the College Woods to recover from chronic deer browse was written and recommends controlling the white-tailed deer population through yearly managed hunts.