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GRS Densitometer

Stock #:1DEGE-DENS04
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The GRS densitometer, when used with line-point transect sampling, combineshorizontal and vertical vegetation sampling thereby enabling the collection ofresource information across the landscape (horizontally) at different canopylevels (vertically). This technique provides estimates of cover for any elementin a vegetated environment such as: trees, shrubs, herbaceous, down woodymaterial, fuels, snags etc. This method of sampling has been shown to beaccurate, objective, and repeatable between observers.

The cover estimates generated using the GRS densitometer are based on anevaluation of cover data collected at sample points evenly spaced alongtransects. For example, trees are determined to be "cover" trees bysighting through the densitometer and determining whether any portion of a treecrown intersects the vertical line of sight through the densitometer. Thevertical line of sight is obtained by levelling both of the densitometer'sbubble-levels and then sighting through the instruments so that the sightingmarks are aligned. The GRS Densitometer can be oriented to sight either up ordown, to provide canopy and/or ground sample.

Transects of several different forms and lengths may be used, depending onthe characteristics of the sample area. If the sample area is too small toeffectively place a straight-line transect within, then a diamond-shaped ortriangular shaped intersect can be used. The transect layout should avoid anypotential bias and error that may result from the systematic orientation of thetransect with respect to physiographic (terrain) features.

The point-transect sampling methodology provides estimates of the covercontribution of the different characteristics measured at each point along thetransect. Estimated distributions of species composition, tree size, age, crowndiameter, and any other sampled characteristics are easily generated by dividingthe number of points tallied for each recorded characteristic by the totalnumber of sample points. For example, if 100 points are sampled along thetransect and 29 of the sample points are covered by Douglas-fir trees, then theestimated cover of Douglas-fir is 29 percent. If 17 of the 100 sample pointsindicate cover is provided by trees equal to or greater than 36" dbh thenthe estimated cover of the 36" + size class is 17 percent. If 74 samplepoints indicate conifer cover and 9 points indicate hardwood cover then thetotal tree cover estimate is 83 percent ((74+9)/100) and the estimated percentconifer composition is 89.2 percent (74/83).


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