COMPLEX EDGE EFFECTS ON SOIL-MOISTURE AND MICROCLIMATE IN CENTRAL AMAZONIAN FOREST

We investigated the influence of a four-year-old forest edge near Mana us, Brazil, on soil moisture and vertical profiles of air vapour press ure deficit (VPD) within the forest. Soil moisture was measured (with a neutron probe) 0, 5, 10, 20, 40, 60, 80, 100, 150 and 200 m into the forest from the edge, in undisturbed control areas, and in the pastur e. Control soil moisture was better explained by rainfall in the previ ous 2 or 10 days than by longer-term totals. Soil water potentials les s-than-or-equal-to - 1.5 MPa occurred at some forest locations during the driest period. The variation in soil moisture with distance from t he forest edge was complex, with higher values just inside the edge an d depleted zones at the edge and 40-80 m inside it. At a given height, VPD (standardized relative to measurements in the open) was not relat ed to distance from the edge, but VPD increased more with height near the edge than in control areas. The complexity of the edge's influence and the contrast with earlier data from the same edge can be explaine d by the changing vegetation structure near the edge. Regrowth 'seals' the edge with more leaves that transpire and deplete soil moisture, w hile protecting the understorey just inside the edge from desiccating conditions. A mosaic of gaps of differing ages develops behind the edg e, increasing the variation in microclimatic conditions near the groun d and consequently in evapotranspiration and soil moisture.