Gap soil moisture at the Coweeta Hydrologic Laboratory from 1993 to 1996

Small canopy openings often alter understory microclimate, leading to changes in forest structure and composition. It is generally accepted that physical changes in the understory (i.e., microclimatic) due to canopy removal drive changes in basic forest processes, particularly seedling recruitment which is intrinsically linked to soil moisture availability, light and, to a lesser extent, temperature. We examined the impact of small canopy gaps of the type (snags) and size (~300 m2) most frequently observed in the southern Appalachians on the understory microclimate. We created artificial canopy gaps at two elevations (a.m.s.l.) by girdling trees in areas with and without a Rhododendron maximum L. (rosebay rhododendron) understory. Soil and air temperature (degrees C), photosynthetically active radiation (PAR; mmol m-2s-1), and volumetric soil water content (WC%) in the upper 15 cm of soil were measured along transects generally running north to south through each gap. Overall, PAR was substantially less in rhododendron gaps than in non-rhododendron gaps.