THINNING WESTERN LARCH 



Arthur L. Roe and Wyman C. Schmidt 

 INTRODUCTION 



Overstocking threatens production on more than 1 million acres of western larch (Larix 

 occidentalis Nutt.) in the northern Rocky Mountains. Dense stands have developed on favorable 

 seedbeds found on many large burns and cutover areas in this region. The great number of 

 stems in many of these stands precludes optimum growth and development of individual trees 

 because growth is being distributed over too many stems per acre. These trees are likely to 

 remain overcrowded for long periods if stands are unmanaged. Trees in such stands will not 

 reach commercially desirable size within a reasonable time. The obvious solution to the over- 

 stocking problem is thinning. 



Few western larch stands have been thinned, and little information has been published on 

 thinnings in larch. Forest managers are now guided principally by information developed in 

 other forest types. This paper reports results of two western larch thinning studies located on 

 the Lolo National Forest in western Montana. Briefly, the results show that diameter, basal 

 area, height, and cubic-foot volume growth can be improved by thinning. Concentrating growth 

 on fewer trees per acre will produce larger trees earlier. 



DESCRIPTION OF STUDIES 



West Fork Plots 



Five plots were established in the West Fork of Petty Creek on the Lolo National Forest, 

 at an elevation of about 4,200 feet. Slopes on plot locations range from 25 to 55 percent, and 

 exposures are principally north to northeast. The average site index of the area, determined 

 by using Cummings' site classification curves,^ is 52 feet at 50 years, or site class III. 



The stand originated following a burn and consists principally of western larch trees, with 

 lesser numbers of lodgepole pine and Douglas-fir. Ponderosa pine, Engelmann spruce, grand 

 fir, and subalpine fir are minor constituents only. The stand was about 50 years old when the 

 study was established in 1949. Two crop-tree thinning treatments were applied on four randomly 

 selected ^-acre plots; the fifth plot was left unthinned as a check. Crop trees were chosen on 

 all the plots at the rate of about 150 per acre, spaced roughly 15 feet apart. Preference was 

 given to western larch, ponderosa pine, Douglas-fir, and lodgepole pine, and in that order. As 

 far as possible, only dominant and codominant trees of good form and fair to good vigor were 

 left. The treatments were: 



1. On plots 1 and 2, the "D-l-4" rule of thumb was applied to individual crop trees. All 

 trees were cut around each crop tree for a radial distance in feet equal to the diameter of the 

 tree in inches plus 4. 



Robert A. Smart, former District Ranger, Lolo National Forest, furnished valuable 

 cooperation in this study; and Kenneth Boe , formerly with the Intermountain Forest and Range 

 Experiment Station , prepared the study plan and installed the plots . 



^Cummings, L.J. Larch- -Douglas -fir board-foot yield tables. U.S. Forest Service, 

 Northern Rocky Mountain Forest and Range Expt. Sta. Applied Forestry Note 78, 3 pp., illus. 

 1937. 



