Effects of forest treatments on nutritional carrying capacity for white‐tailed deer in mid‐rotation loblolly pine stands

Abstract Landowners and managers are interested in improving habitat quality for white‐tailed deer ( Odocoileus virginianus ; hereinafter, deer) in loblolly pine ( Pinus taeda ) forests in the southeastern United States. Commercial thinning, prescribed fire, and herbicides can increase forage quality and quantity for deer at mid‐rotation, but past studies have generally been limited to stands thinned to ≥15 m 2 ha −1 or have not evaluated the effects of herbicide mixtures on forage availability for deer. We evaluated the effects of thinning, prescribed fire, and herbicide use on forage biomass (kg/ha) and nutritional carrying capacity (NCC) for deer in 5 loblolly pine stands in central Georgia, USA. We divided each stand into 3 equally sized plots and randomly assigned a thinning treatment of 9, 14, or 18 m 2 ha −1 . We thinned stands in spring 2017, applied prescribed fire to half of each plot in spring 2018 and 2020, and applied herbicide (imazapyr + metsulfuron methyl) to half of each subplot in fall 2019. Our design resulted in 3 treatment combinations (fire only, herbicide only, fire + herbicide), plus a control (thinning only), within each level of thinning. We sampled and estimated forage availability and NCC in June 2020 and 2021 using fixed nutritional constraints of 6% (maintenance) and 14% (lactation) crude protein (CP). Nutritional carrying capacity was greatest in the low basal‐area treatment but did not differ between the medium and high basal‐area treatments. Herbicide and fire, applied separately or together, reduced NCC by 52–97% under 6% CP requirements. In contrast, NCC at 14% CP was ~160% greater in the fire and fire + herbicide treatments compared to the control by the 2nd growing season post‐treatment. On average, across years, NCC at 6 and 14% CP constraints was greatest in untreated controls. However, NCC declined from 2020 to 2021 in untreated controls, likely due to additional height growth and maturation of woody plants, suggesting repeated disturbance is required to maintain NCC at high levels by promoting the optimal mix of woody plants and forbs while maintaining forage within reach. In our study, prescribed fire was the least costly treatment for accomplishing the objective of maintaining high NCC.