Some effects of growing season soil moisture and microclimate on redwood seedlings in a forest edge and gap environment

This study was conducted to capture the effects of solar radiation, as estimated from hemispherical photographs, on soil moisture status and factors potentially influencing soil moisture status in a small meadow and across the edge between a small clearcut and an uncut section of second-growth redwood forest during the 2001 growing season in Humboldt County, California. In addition, potential edge effects and edge zone dimensions were measured for soil moisture, soil temperature, air temperature, and relative humidity across a west-facing forest edge. Redwood seedling survival was then analyzed with respect to variability in the solar regimes, soil moisture regimes, microclimate, and vegetative competition across the tested plots. Gravimetric soil moisture was depleted more rapidly and measurements had significantly and consistently less water in clearcut plots than in meadow or uncut forested plots. Soil moisture depletion showed a stronger correlation with increasing soil temperatures and the density of grasses than with estimates of direct solar radiation. Edge zones were found for each of the measured variables. These zones were fairly abrupt, extending less than 40 meters into the uncut stand and out less than 40 meters into the clearcut, but were unique in size to each of the measured variables. Seedling survival rates were best within the Meadow Study, where comparatively elevated soil moisture status and moderate soil temperatures were measured, relative to the clearcut plots. Seedling mortality was highest under the canopy of the second-growth redwood forest, where very little solar radiation reached the study plots.