Assessment of vegetation in six long-term deer exclosure investigations at Morristown National Historical Park: Data synthesis & management recommendations

Epiphan, Jean; Handel, Steven

Countless habitats in the Northeast region of the United States are being threatened by stresses that lower native biodiversity and natural resource quality. The main stressors near developed areas are waves of invasive plants and the overabundance of white-tailed deer (Odocoileus virginianus). One common solution to protecting native plants is the exclosure fence, which eliminates deer herbivory and potentially the spread of some introduced plants. Twenty-four long-term deer exclosures have been established in Morristown National Historical Park for six differing research purposes. The long-term data from these exclosures, collected for over thirty years, provide a wealth of information to the National Park Service as well as other professionals in conservation management. The goals of this study were to synthesize the long-term data sets and reveal the dynamics and successes of these exclosures as tools in ecological conservation. As built structures in a changing landscape, how have these exclosures performed as protection tools over time? How successful have they been in protecting native vegetation for up to thirty years and with limited funding? The lessons learned here can inform managers and professionals throughout parks where deer herbivory and invasive plants pose serious concerns. We found that the majority of exclosures have been able to preserve native species (herbaceous and woody shrubs and trees) that have important ecological services. Location within MNHP played an important role in their success. Exclosures within intact mid- to late succession mixed oak-beech-birch forests had more native species and higher floristic quality than those in tulip-ash or black locust successional forests or areas near field edges. The smaller exclosures (3.7 x 3.7 m) were less likely to break open and provide deer access, even if damaged. Larger exclosures, such as the two-acre exclosure or the 10 x 10 m exclosures, had higher risk of tree limb fall and subsequent failure. This is due to the greater chance of damage because of larger ground coverage. (Any fence damage opens up the entire exclosure to deer herbivory). Distance from high density introduced species invasions was correlated with success. Exclosures intentionally placed in or adjacent to invasive plant colonies were more likely to be infiltrated by invasive plants in comparison to exclosures placed intentionally in areas free of invasive plants. The invaded exclosures provided insights on introduced species dynamics. In particular, woody invasive plants dominated in specific locations that were previously dominated by Japanese stiltgrass (Microstegium vimineum). This has implications for management and control strategies into the future as these populations of invasive plants demonstrate a novel form of succession. We recommend that with limited resources, investments should be directed to exclosures located in high quality forest sites as they are most beneficial to native habitat conservation over time. Exclosure fences must have a continual repair management protocol to be effective, such as regularly scheduled and frequent visits, especially after storms. The care needed to maintain the exclosures is much more time intensive than was expected over the years and cannot be managed by just one devoted employee as in the past. If funding does not allow for more people-hours devoted to exclosure maintenance, we recommend focus on small exclosures (such as 3.7 x 3.7 m) that require less frequent and costly maintenance and experience less frequent damage. Although fewer acres would be protected, the success of more secure exclosures overtime would be improved.

Assessment of vegetation in six long-term deer exclosure investigations at Morristown National Historical Park: Data synthesis & management recommendations

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