Individual- and population-level effects of Odocoileus virginianus herbivory on the rare forest herb Scutellaria montana

Abstract

Odocoileus virginianus (white-tailed deer) grazing can impact rare plant species dramatically given their risk for local extirpation and extinction. To determine if O. virginianus management could aid conservation of federally threatened Scutellaria montana (large-flowered skullcap), we conducted an exclosure experiment across a large occurrence of this rare species in Catoosa County, Georgia, USA. We aimed to: (1) quantify the effects of O. virginianus grazing on S. montana individuals, and (2) evaluate the potential of O. virginianus to influence S. montana populations. A lesser percentage of S. montana individuals protected from O. virginianus were grazed than plants accessible to grazers and additional protection from smaller grazers did not reduce grazing, suggesting that O. virginianus primarily do graze S. montana. But grazing did not significantly influence S. montana individuals as evidenced by changes in stem height or the number of leaves per plant assessed during two single growing seasons or across those growing seasons. At the population-level, grazing impacts were buffered by a lack of grazer preferences for specific plant life stages. Although mostly not significant, our findings are biologically interesting given the numerous ecological concerns associated with O. virginianus abundance, including their demonstrated and proposed impact on rare plants.

Keywords

• Grazing
• Herbivory
• Odocoileus virginianus
• Scutellaria montana
• Rare species
• White-tailed deer