Soil Physical Effects on Longleaf Pine Performance in the West Gulf Coastal Plain

-We summarize 8 years of soil physical property responses to herbicide manipulation of the understory in two young longleaf pine stands growing on either Ruston fine sandy loam or Beauregard silt loam soils. We also describe relationships between pine sapling vigor and the soil physical environment across a 3-year period on the Ruston soil and a 2-year period on the Beauregard soil. It is hypothesized that understory control affects soil porosity, bulk density, and the ability to store plant-available water by a change in the amount and distribution of non-pine roots. Furthermore, Pinus vigor may be reduced when the inherent physical nature of a soil limits pine root elongation. We observed temporal changes in soil porosity fractions and bulk densities, possibly representing natural soil recovery after disturbance. Near the surface of the soil, soil perturbation by grass roots may have aided pine vigor by increasing the water-holding capacity of soil micropores. In the subsoil, pine vigor was correlated with bulk density and microporosity. Relationships between pine vigor and subsoil physical properties were different between the two soil types. Clay illuviation and sand content in the two soil types may have played a role in these relationships. Our results provide insight regarding soil variables that impart some degree of control on pine root system expansion and tree vigor on the West Gulf Coastal Plain.