Effects of Herbaceous Weeds on Fourth Year Water Relations and Gas Exchange of Loblolly Pine

Stands of four-year-old loblolly pines grown with and without herbaceous competition were compared to determine whether early increases in soil moisture and plant water status had been maintained throughout the first four years. Non-weeded stands tended to have greater soil moisture than weeded stands, although these differences were never statistically significant (P > 0.05). Plant water potential was remarkably similar between treatments, as were photosynthesis and stomatal conductance. The increase due to weed control in foliage production early in stand development apparently caused a depletion in available soil moisture to levels similar to nonweeded stands. Therefore, the direct benefit of increased soil resources with weed control is short lived.