Soil and plant water stress in an Appalachian oak forest: its relationship to topography and forest site quality

Abstract

A forest site quality index (FSQI) based on topographic parameters of aspect, slope inclination and slope position was used to investigate soil moisture and plant water stress relationships on the southeast face of Potts mountain in Craig County, Virginia. Topographical effects on available water are especially pronounced during low late season rainfall levels encountered in the Ridge and Valley physiographic province of Virginia. The soil moisture trends and plant water potentials demonstrated that for all forest site quality index values representing the topographically derived moisture gradient, available soil moisture and plant stress levels probably seriously decrease or inhibit tree growth from the middle of July to the end of the growing season.

The Forest Site Quality Index (FSQI) delineated the soil moisture gradient within the study area most successfully in the more xeric areas, supporting its use for predicting relative site quality on those sites where soil moisture has been demonstrated as being the limiting factor of tree growth. The FSQI is a rapid and easy measure based on topographic parameters for evaluating relative site quality but is restricted in use to areas where rainfall is critical to plant growth during the growing season.