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Forest Health Information Management

Estimating the Number of Red Trees Within Suppression Beetle Management Units

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The numbers of red trees is estimated using the data provided from the Provincial Aerial Overview Survey.

The bark beetle information is provided in two formats: Spots (points) and Polygons.  Spots are small infestations comprised of 2 to 50 trees.  Polygons usually consist of entire stands or contiguous areas within a stand containing red trees.  The percentage of mortality within the polygon is assigned a severity class of Light (1 to 10%), Moderate (11 to 29%) and Severe (30+%).  

SPOT DATA:  It is easy to obtain the total number of red trees from the spot data because the field NUM_SPOT contains the number of red trees recorded by the surveyors within in each spot.  By doing a spatial query of the IBM spot data that fall within the boundaries of the suppression BMUs, a total number of red trees can be summed.

POLYGON DATA:  The polygonal overview data can be queried similarly to the spot data.  However, to estimate the number of red trees, the area of the infested polygon must be converted using an infestation severity (Trace = 0.5%, Light = 5%, Moderate = 15%, Severe = 40% and Very Severe = 75%) and an average stem/ha (default 250 sph).

POLY AREA X SEVERITY (%) X AVG SPH = Numbers of red trees [repeat for each severity class]