The hispid cotton rat (Sigmodon hispidus) is a common field rodent in the southeastern United States, where volunteer loblolly pine trees (Pinus taeda) rapidly invade open space and accelerate ecological succession from field to pine forest. While using capture-mark-recapture methods in studies of small mammal populations, we observed dead pine trees in late summer, all killed by girdling, prompting us to determine the extent of damage on a 1.26 ha grid in a 5 y old successional pine forest in southeastern Virginia. We recorded damage to 65% of >15,000 trees, of which 2064 were killed by rodents. Areas with a high density of trees 11–40 mm in diameter (3–5 y old) were most actively damaged during late winter and early spring, following autumnal population peaks of cotton rats. Old field habitats undergoing succession to loblolly pine forest may briefly offer optimal habitat for cotton rats, and girdling by cotton rats may regulate the rate of succession depending on densities of trees and rodents.