Abstract Detail

Interactions of White-Tailed Deer and Invasive Plants in Forests of Eastern North America

Gorchov, David L [1], Martinod, Kylie [2].

Are white-tailed deer responsible for apparent competition between the invasive shrub, Lonicera maackii, and native plants?

Apparent competition is an indirect interaction where one species negatively impacts another through a shared enemy. Some invasive plants are hypothesized to impact native plants by increasing the abundance, or altering the foraging, of shared herbivores. White-tailed deer are generalist herbivores that occur at densities much higher than pre-settlement in many areas of North negative effects on native plants. While deer avoid some invasives, they browse on others, including bush honeysuckles (Lonicera spp.) that are prevalent in many deciduous forests in eastern U.S. In our study site, the Miami University Natural Areas in southwest Ohio, deer browse is sufficient to reduce Lonicera maackii cover and basal area growth. We explored whether this herbivory is sufficient to sustain higher deer populations.
We estimated the contribution of L. maackii to annual food consumption by deer by dividing the estimated mass of L. maackii twigs consumed by deer by the estimated total mass of food required by deer. The numerator was estimated by multiplying the estimated number of browsed twigs (obtained by monthly census of marked twigs in 100 0.25 x 0.25 m² quadrats in each of three habitats) by the estimated mass of browsed twigs (obtained by allometric relationships of twig mass with diameter and length of unbrowsed portions of twigs). The denominator was the product of the estimated abundance of deer (from distance sampling of fecal pellet groups) and daily consumption estimates from the literature.
Depending on which estimate of food consumption we used, our overall estimate for the contribution of L. maackii to deer diet was 40% or greater. Though surprisingly high, we note that L. maackii comprised the majority of woody browse within the height range accessible to deer (0.3 - 2.1 m) in each of the three habitats (deciduous forest, Juniperus virginiana-dominated successional forest, and forest-field edge). The low frequencies of other woody species may be due to decades of high deer browse in these areas, perhaps worsened by shading from L. maackii. Similar invasive-dominated understories are common in eastern North American forests, and our findings suggest these invasive shrubs sustain large deer populations that in turn reduce preferred species of native plants.
We are investigating the importance of L. maackii‘s extended leaf phenology in this interaction, particularly whether deer browse is most intense in the early spring, when the leafy twigs of L. maackii provide more nutritious browse than the leafless twigs of native deciduous plants.

1 - Miami University, Biology, 212 Pearson Hall, Oxford, OH, 45056, USA
2 - Miami University, Biology, 212 Pearson Hall, Oxford, OH, 45056, United States

Keywords:
indirect effects
Herbivory
invasive plants
phenology.

Presentation Type: Colloquium Presentations
Session: C1, Interactions of white-tailed deer and invasive plants in forests of eastern North America
Location: Chatham Ballroom - C/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 4:30 PM
Number: C1011
Abstract ID:162
Candidate for Awards:None