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Impact of the National Algorithm for Stocking, Stand Size Class, and Forest Type Determination. Study Across a Three-State Region. Mark Hansen Northern Research Station St. Paul, MN. Outline. Background Stocking Current Methods Past Methods Results. Background.

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  1. Impact of the National Algorithm for Stocking, Stand Size Class, and Forest Type Determination. Study Across a Three-State Region.Mark HansenNorthern Research StationSt. Paul, MN

  2. Outline • Background • Stocking • Current Methods • Past Methods • Results

  3. Background • Minnesota 1990, Michigan 1993, and Wisconsin 1996 periodic inventories • States double and triple the inventory effort • 1999-2005 Annual inventories • Some forest type changes did not agree with what was expected

  4. Stocking • Expression of stand density • Absolute measures of stocking • Basal area • Crown closure • Volume per acre • Number of trees per acre • Relative stocking • Implies a standard • Accounts for stage of stand development and species composition • Portion of the available space (or other limiting attribute) is occupied by “crop trees”.

  5. Relative Stocking • At full stocking growth is maximized because the growing space is fully occupied. • Increasing the relative stocking of under-stocked stands will increase growth. • Decreasing the relative stocking of over-stocked stands will increase growth. • A forest (by definition) must have (or previously had) some minimum stocking level.

  6. FIA approach to stocking • All live tally trees (including seedlings) are assigned stocking values = the tree’s contribution the total stocking of the stand. • Total stocking is the sum of the stocking values.

  7. A-line of stocking charts S = (100/TPA) = b0 D b1 D = ave. stand diameter TPA = trees per acre at max. density with mean diameter D. 100 = reference level of a stand of max. competition. b0 and b1 are species/forest type dependent

  8. The Current Algorithm • Future diameter – Stocking of stands < 5” is based on a 5” stand. • Reduction for non-stockable inclusions • Limit the total stocking on each subplot • 5” and larger trees get full stocking (up to the subplot max), remainder goes to seedlings and saplings. • Open grown, dominant and codominant trees get full stocking. • Intermediate trees get 50% stocking. • Overtopped trees get 10% stocking.

  9. Forest type • Each tree is assigned to an initial type group based on species. • Stocking values are summed for each initial type group. • Initial type group stockings are summed into combined type groups. • A decision tree is used to combine and compare stocking values until a final type is reached.

  10. Decision tree (2 of 5 pages)

  11. The Previous Algorithm • Trees were sampled proportional to BA. • All stocking trees received equal stocking values (stocking = b*BA). • Field crews limited the total stocking on each subplot by excluding trees from stocking. • Trees < 5” were only included in stocking if needed to meet full stocking.

  12. More work • Oak/gum/cypress is a problem • Mich and Wisc would like a northern pin oak forest type added • 1977-1986 inventories need to be reclassified.

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