What is a GRS Densitometer ?The GRS Densitometer™ is a handheld sampling tool that can be used to develop estimates of vegetation/landscape-feature cover. The GRS Densitometer™, when used with either line-point or line-intercept transect sampling, combines horizontal and vertical vegetation sampling, thereby enabling the collection of comprehensive natural resource information across the landscape (horizontally) at different canopy levels (vertically). This technique
provides estimates of cover for any element of any ecosystem including trees, shrubs, herbs, graminoids, non-vascular plants, down-woody debris, fuels, snags, and different ground surface conditions.
"... most accurate, least expensive, and most easily applied..." - The line-point transect method of sampling has been shown to be accurate, objective, and repeatable be tween observers. Just recently, the Food and Agriculture Organization of the United Nations concluded in a research study of four different methods of assessing canopy cover characteristics that the line-point transect was the "most accurate, least expensive, and most easily applied among the four methods tests. This method is scientifically accurate and records forest canopy and floor cover as a set. The instrument used in this method, the GRS Densitometer™, is small, light and easy to carry and comparatively cost efficient."
The difference between the GRS Densitometer™ and a spherical densiometer - Using the GRS Densitometer™ one estimates canopy cover and abundance within an individual sample area sampled by a transect; using a spherical densiometer one estimates what many now consider canopy closure at a single location (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 (in a non-photointerpretive meaning) 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 linear transect sampling methodologies 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.
The GRS Densitometer™ has also been found to be useful in the estimation of visual obstruction, based on the amount of horizontal cover observed surrounding a feature, such as a Northern Bobwhite nest. By sighting horizontally (backwards through the densitometer) in different directions radiating outward from the nest (feature), a measure of visual obstruction was developed that used to relate nesting success to the vegetation present in the vicinity of the nest (feature) (Moore, S., 2010)
Please note that as of April of 2008, GRS began the production of the newer version of the GRS Densitometer™, as show in the picture above.
TransIn is a program written specifically for GRS Densitometer™ transect data entry. Visit our TransIn page to download a FREE demonstration copy.
Visit/join our GRS Densitometer Users Group.
