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Missouri Silviculture

Uneven Size Distribution Calculations

by
David Larsen
The School of Natural Resources, University of Missouri
and
Ed Loewenstein
North Central Forest Experiment Station, USDA Forest Service
Q spreadsheet

The above spreadsheet can help you determine the number of trees needed in each size class to sustain an uneven-size structure in your Missouri Oak forests. If trees are to continue to grow, they need sufficient light for tree growth. Small trees in the dense shade will not grow yet can live for many years. If you want the your cutting practice to be sustainable you need to maintain enough space for trees to grow up through the different size classes. A tree surviving in dense shade for a long time will not start to grow again even if you provide growing space.

The shape of an uneven sized forest can be described with a measure called a q-value. The q-value is the relationship of the number of trees in a diameter class to the number in the next smaller diameter class. Through examining many uneven-sized managed forests in the Ozarks, we have found that a typical q-value for two-inch diameter classes to be 1.7. This q-value would mean the each smaller 2? diameter class would have 59% more trees than the one above.

Another measure of a forest is the basal area or the cross-sectional area of all the tree stems on an acre. This is typical measure used by foresters in managing stands and is easy to estimate.

With basal area and a q-value you can determine the number of trees needed in each 2-inch diameter class needed to allow some trees enough growing space to grow up to be a canopy dominants. We recommend you use a q-value of 1.7 and a residual basal area of 55 square feet per acre.

To get a copy of the above spreadsheet, go to Q-value.


Created:: December 15, 1998
Last Updated: March 23, 2009