Calculations

Examp1e:

1. Ponderosa pine, west of continental divide. Nineteen inches of annual precipitation. Forage condition good.
2. Current stand spacing D+2. Site index (SI) 80
3. Desired spacing for SI 80 from guides: D+5
4. Canopy at D+2 = 70 percent
5. Canopy at D+9 = 30 percent

Using the stocking guide in "Technician's Guide to Grazable Woodland Ponderosa Pine West of Continental Divide - Montana" (aum = animal unit month):

Stocking at (30 percent canopy = .35 aum per acre) - (70 percent canopy = 10 aum per acre) = (.25 aum per acre) = future forage value if stand is thinned to D+9 spacing.

For canopy densities more than 70 percent, one can estimate (for excellent forage condition) using the curve in figure two or estimate from measurements or observation.

Using the curve in figure two, for a ponderosa pine stand with 85 percent canopy (D+1 spacing) herbage production is about 150 pounds per acre. Consider 80 percent of this forage of which 50 percent can be consumed; we can utilize then, 40 percent of the herbage production or 60 pounds per acre.

Assume 7001 of forage per cow month.
60 pounds per acre divided by 700 pounds per cow month = .085 aum per acre.

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Last Modified: 07/05/2007