MODIFICATION OF TEXAS CLEAR-CUT ENVIRONMENTS WITH LOBLOLLY-PINE SHELTERWOODS

The near-surface (within 0.30 m of the surface) environments of a clea r-cut and a loblolly pine (Pinus taeda L.) shelterwood in east Texas w ere instrumented to determine treatment effects on the radiation, ther mal, humidity and wind components of microclimate. The shelterwood pro duced lower net radiation and photosynthetically-active radiation load s, lower daytime air temperatures, the same or slightly lower daytime vapor pressures and lower wind speeds than the clear cut. Although sun fleck incidence in the shelterwood allowed net radiation and photosynt hetically-active radiation (PAR) to increase briefly to levels similar to those measured in the clear cut, seedlings within the shelterwood were subjected to sunflecks for only a short period of time before the sunfleck dissipated and shade returned. Air temperature differences b etween treatments were not great and soil temperature differences were negligible. The influence of the shelterwood on all environmental fac tors was primarily due to the partial overstory canopy, which dissipat ed incident radiation before it reached the near-surface environment w here it could significantly alter the microclimate.