© 1957 by Institute of Chartered Foresters
THE ACHIEVEMENT OF SUSTAINED YIELD BY VARYING THINNING TREATMENT AND ROTATION
Forestry Commission
In a forest with a very abnormal age-class distribution it may be possible to achieve a more normal distribution by a number of methods singly or in combination. A worked example is presented showing the implications of different combinations of two methods, namely felling before or after the normal rotation age, and varying the thinning grade. The example taken is a hypothetical block of 1,200 acres which has been planted at the rate of 40 acres a yearover a 30-year period and which consists entirely of Norway spruce 2nd quality class. Nine combinations of felling and thinning treatments have been investigated, and for each the development during the conversion period of growing stock, increment, and yields computed. It was found that conversion to a sustained yield presents no particular difficulties, and need involve little sacrifice either in increment, or interest earned on the invested capital, especially if ample time is allowed for achieving normality. In all the nine conversion methods tested, yields rose sooner and fluctuated less than they would have done in the absence of conversion. Choice of methoddepends on the relative importance which the forest owner attaches to each of several facets of management.