Theoretical Growth and Yield of Hypothetical Ponderosa Pine Stands under Different Thinning Regimes
Abstract:A model is presented for computing theoretical results under different thinning management. Statistics for the dominant portion of normal, unmanaged stands on different site classes provide starting data at age 30. A tree-growth equation estimates diameter growth following thinning. Two diameter-based spacing rules to control stocking were studied: (1) Mitchell's S = (D + X)2 and (2) a new biological spacing rule S = (D + X)2F. In these, S is the average space provided per tree in square feet, D is the diameter of the dominant and codominant tree of average basal area, X is a value added to the diameter in inches, and F is a factor, specific for each site class, varying with age up to about 50 years, then becoming a constant. F values are read from curves. Suitable combinations of spacing (values for X) and thinning intervals are: Mitchell's rule, X = 6 for all sites using thinning intervals of 20 years for site 60, 12 years for site 80, 9 years for site 100, 7 years for site 120, and 5 years for site 140; for the biological rule, suitable combinations are, (D + 0.5)2F every 5 years, (D + 1.1)2F every 10 years, (D + 1.8)2F every 15 years, or (D +- 2.2)2F every 20 years. Other combinations may be read from curves. Examples of theoretical growth and yield were computed for site indexes 60, 80, 100, 120, and 140 for both rules. Little difference in average diameter at rotation end resulted from use of the two rules. A range of combinations is suitable where residual trees appear to be held in "free-growing" condition. Diameters at rotation end were greater for thinned than for the dominant portion of normal unthinned stands except for site 80 (essentially equal) and site 60 (much less). Total yields of cubic- and board-foot volumes at rotation end in thinned stands under the biological rule exceeded those under Mitchell's rule, but both were greater than from normal unthinned stands except in two instances.
Document Type: Journal Article
Affiliations: Professor Emeritus of Forestry, School of Forestry, Duke Univ., Durham, N. C.
Publication date: March 1, 1963
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- Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
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