Aspect Induced Differences in Vegetation, Soil, and Microclimatic Characteristics of an Appalachian Watershed

Abstract

This study evaluates and quantifies the variation in vegetation, plant nutrients, and microclimate across four topographic aspects in an Appalachian watershed (39°39′43′′N, 79°45′28′′W). The study found that the north and east aspects were 27–50% more productive than the west and southwest aspects. Species groups that showed strong aspect preference included yellow poplar (Liriodendron tulipifera), black cherry (Prunus serotina), chestnut oak (Quercus prinus), and white oak (Quercus alba); the former two being dominant on the north and east aspects while the latter two dominate the west and southwest aspects. Red oak (Quercus rubra) and red maple (Acer rubrum) showed mild aspect preference indicating their broad ecological amplitude. Although the north and east aspects had greater biomass, the west and southwest aspects had about 23% more stems per hectare.There were large differences in microclimate among the four aspects. Air temperature during midday period averaged 25.2°C, 24.9°C, 30.5°C, and 29.4°C for the north, east, west and southwest aspects respectively. The maximum temperature difference between the mesic (north and east aspects) and xeric (west and southwest aspects) sites was 5.55°C and was observed at noon. The relative humidity at the xeric site was about 25% lower than that at the mesic site during midday periods. Plant water stress as measured by vapor pressure difference was about 37% higher on west and southwest aspects than on north and east aspects. Plant nutrients only showed minor differences with concentrations being higher on the north and east aspects except for phosphorus, which was higher on the west and southwest aspects.