SOME PROBLEMS AND APPROACHES IN CLASSIFICATION OF SITE IN JUVENILE STANDS OF DOUGLAS FIR

Abstract

Although several easily-determined, single-factor approaches to estimation of site quality are available for use in juvenile stands of Douglas fir (Pseudotsuga taxifolia), not one of them is wholly suitable. Conventional height-age relationships in use are based on scanty data for very young stands, are most representative of fully stocked stands, and depend considerably upon the yield table used as a reference.Recently the growth-intercept method (Wakeley, 1954) has been developed independently for Douglas fir by Wiley (1951) and tested fairly generally by Warrack and Fraser (1955). The growth-intercept method employs the lengths of the first few internodes above breast height as indicators of site quality. This method has the advantages of direct measurement and early classification but indicates current or juvenile site qualities rather than total site capabilities over a long period of time. The utility of another measure of site quality, number of years to reach breast height, is demonstrated by data secured in this study. Schmidt (1954) illustrated possible uses of stump diameters to indicate site quality; unfortunately only past site quality is estimated and direct examination of stumps is necessary. Topographic positions (ridge, upper slope, lower slope, and valley) are, in themselves, often indicative of site quality. Species and abundance of lesser vegetation will also provide indications of the site quality of Douglas fir, but these interrelationships are often complicated and require interpretation by experts. This report illustrates certain problems and possible uses of most of the above-mentioned methods. In addition problems of age-class distribution and succession are discussed. Data used were collected in Douglas fir types on the University Research Forest at Haney and on Vancouver Island.