Does Supplemental Feeding of White-tailed Deer Alter Response of Palatable Shrubs to Browsing?

Abstract

The impact on palatable shrubs when herbivores have access to high-quality food is unclear. We determined if providing high-quality food and increasing white-tailed deer (Odocoileus virginianus) density reduced growth and altered nutritional quality of two palatable shrub species. We maintained target densities of 13, 31, or 50 deer km−2 in six 81-ha−1 enclosures on each of two ranches. We provided nutritious, dry feed ad libitum in one of each pair of enclosures with similar densities on each ranch. We measured height and width of Texas kidneywood (Eysenhardtia texana Scheele) and spiny hackberry (Celtis ehrenbergiana [Klotzsch] Liebm), measured hackberry thorns, and estimated crude protein. Plants were protected from browsing with wire exclosures in 2005; a similar-sized unprotected plant was paired with each protected plant. We estimated density of shrub species using twenty 3 × 50 m belt transects/enclosure June 2005, 2007−2012. Growth of protected and unprotected kidneywood was similar (P ≥ 0.88) at 13 deer km−2, but growth was reduced (P ≤ 0.05) by higher deer densities. Protection from browsing and increasing deer density did not influence (P ≥ 0.25) size of spiny hackberry. Browsed kidneywood plants had a 34% lower crude protein (P ≤ 0.01) compared with protected plants when deer did not have access to feed. Spiny hackberry protein was greater (P ≤ 0.05) in unprotected plants compared with protected plants at 50 deer km−2. Response of Texas kidneywood density at > 1.5-m tall to deer density depended on year (P = 0.04), with no effect of deer density (P ≥ 0.10) on spiny hackberry density. Density of both shrubs was similar (P > 0.14) with and without supplement. Access to feed does not alter effects of browsing on these sympatric shrubs; however, responses to increasing herbivore density contrast. Texas kidneywood is less tolerant of herbivory than spiny hackberry.