Understory Density Characteristics in Several Midlatitude Temperature Forests

Understory density can have impacts on such military activities as cross-country mobility, bivouac, cover and concealment, and line of sight Airborne sensors provide a fairly good mechanism for measuring the overstory: crown diameter and tree height. The nature and characteristics of the understory, however, must be subjectively estimated by the analyst. This current work focused on the development of a model to predict understory plant densities from measurable overstory characteristics. Over 7,200 overstory and understory woody plants were measured in a series of 30 forestry transects conducted at six sites in central Virginia. Measurements included overstory height, mean crown diameter, diameter at breast height (d.b.h.), and species. Understory species and d.b.h. were gathered. For both overstory and understory, x-,y-location within the transect was also determined. Ancillary variables such as soils, slope, aspect, canopy closure, ground cover, and surface drainage were also measured or noted. The best-fit equation for estimating understory plant density was a simple linear model with overstory mean height being the most statistically significant relationship between the maximum understory density and the range in densities along the transect. Species diversity indices also were computed but showed no relationship to understory density. Understory mortality rates were noted with special interest given to the threatened flowering dogwood (Cornus florida).