Effects of hurricane canopy gaps on longleaf pine and upland oak sapling growth

Abstract

Longleaf pine forests and woodlands are an ecologically important ecosystem that once dominated much of the southeastern U.S. Frequent fire is well-known to be a driver of forest dynamics in these systems, but far less is known about how wind disturbance may reorganize plant communities. To gain a better understanding of how hurricane impacts may alter dynamics in a second-growth longleaf pine woodland, we investigated growth response of saplings from three competing upland species (Pinus palustris, Quercus falcata, Q. margaretta) following Hurricane Michael (2018) in southwest Georgia, United States. We used maximum likelihood to model height and radial growth of saplings as species-specific Michaelis-Menten functions of light availability and examined the effect of sapling size, soil water holding capacity, and annual precipitation using a model comparison approach. The best model for both height and radial growth included species-specific growth rates, a power function for sapling size, and an effect of 2-year lagged precipitation. Overall, we found that height growth rate increased with irradiance for all species, but asymptotic height growth rate for all species was approached at low irradiance. Rates of radial growth also increased with irradiance and were more strongly differentiated among species. Radial growth in longleaf pine and southern red oak responded most strongly to increasing irradiance. Our findings suggest that increases in light availability from hurricanes has direct effects on altering growth dynamics of saplings. Further, because stem radius is a strong predictor of survival from surface fires, hurricane damage may also have an indirect effect on sapling dynamics, by altering survival in future fires. Our results suggest that hurricanes can reinforce the dominance of longleaf pine and potentially play a role in stabilizing community structure. Understanding the effects of common disturbances like wind and fire—together and individually—can reveal important mechanisms that shape the structure and function of fire-prone ecosystems.