Agenda - 09-29-1999 - 9e - Laserfiche WebLink

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INTRINSIC RATING (IR) OF A TRACT OF FOREST The IR provides a measure of the value of a tract of forest for wildlife based solely on the features of the forest itself. To obtain a simple yet reasonable index, we have focused on six features of a forest important for wildlife, as described previously and in Table 2.. For each feature, we have assigned a numerical weight or value to each possible condition. For instance, one important feature of a forest is its maturity. The forest maps show four stages of maturity: forests that are mostly pine (more than 50% of the canopy); forests that are mostly but not entirely hardwoods (50 -90% of the canopy); and forests that are almost entirely or entirely hardwoods (more than 90% of the canopy). These three types of forest are rated 1, 2, and 3, respectively, for maturity. Areas with no tall forest receive a rating of 0 for this feature. See Table 2 for our methods of scoring five other features of forests. The Intrinsic Rating (IR) of a tract of forest is obtained by multiplying the six numbers together: IR= AxMxDxExSxI with A = acreage, M = maturity, D = distur- bance, E = edginess, S = stream, I = inventoried natural area. Each number is explained further in Table 2 and in the following paragraphs. In calculating the IR, the basic feature of a forest is its area or acreage (A). As we have seen the size of a forest is the primary determinant of how many individuals of each species it can contain. The other five numbers serve to adjust the rating based on the acreage. For instance, mature forests (almost entirely hardwoods) have three times the rating of predominantly pine forests (M). Forests with no human disturbance of the canopy have twice the rating of those with a lot of disturbance (D). Forests with a high propor- tion of edge to area have ratings that are decreased proportionately (E). Forests that overlap areas with inventoried natural areas (I) of regional or state -wide significance '(as classified by the N. C. Natural Heritage Program) have ratings 2 and 3 times as high, respectively, as otherwise comparable areas with special signifi- cance. Forests that include streams or other known bodies of water (S) have ratings that are twice as high as areas without those features. A large, mature, undisturbed, compact forest that includes a stream and an inventoried natural area has a very high rating. The highest IR for a single tract of forest in Orange County is 48,260. In contrast, a small disturbed patch of pines with an irregular shape and no water or inventoried natural area has a very low rating. The Intrinsic Ratings of tracts of forest in Orange County in 1988 appear in Map 1. Bobcats