GRS is the designer and manufacturer of the GRS Densitometer (TM), a tool for the estimation of vegetation cover. The GRS Densitometer, when used with line-point transect sampling, combines horizontal and vertical vegetation sampling, thereby enabling the collection of resource information across the landscape (horizontally) at different canopy levels (vertically). This techniquedensitometere provides estimates of cover for any element in a forested environment such as: trees, shrubs, herbs, downed-woody material, fuels, and snags. This method of sampling has been shown to be accurate, objective, and repeatable be tween observers.
The difference between the GRS Densitometer and a spherical densiometer - Using the GRS Densitometer one estimates canopy cover and frequency of occurrence; using a spherical densiometer one estimates canopy closure. Canopy cover is a vertical measure of the canopy as would be seen on an aerial photograph or reflected on a satellite image, whereas canopy closure is based on estimating the oblique coverage of the canopy as indicated by the number of covered squares counted on the mirror at a single location(Jennings, Brown, and Sheil, 1999).
As a result, estimates using a spherical densiometer are generally higher than those developed using a vertical sighting device and will tend to overestimate canopy cover levels, if used for that purpose rather than for the estimation of canopy closure (Robards, Berbach, Cafferata, and Valentine, 2000). In addition, the GRS Densitometer when used with the line-point transect sampling methodology enables one to easily develop percent cover estimates by species, size classes, and canopy position, as well as for landscape features such as the ground surface condition; such detailed and comprehensive estimates are virtually impossible, or would be far too impractical, time consuming, and inaccurate to estimate using a spherical densiometer.