[Fertility index and fertility equations for the douglas fir stands (Pseudotsuga menziesii (Mirb.) Franco) in Belgium]
1995
Thibaut, A. | Claessens, H. (Faculte Universitaire des Sciences Agronomiques, Gembloux (Belgium). Centre de Recherche et de Promotion Forestieres. Section Ecologie) | Rondeux, J.
Height growth, site index curves and equations for managed even-aged pure stands of douglas-fir under management in the Southern Belgium are presented. They were derived from 256 temporary sample plots, 87 of which were remeasured to give top height periodic increments. The range age and site classes being not equally covered, a special attention was paid to the increments of the total height of dominant trees (1 tree per are of sample plot). A large number of equations were tested to determine which was best suited to express the relationship of age and the top height. Regression was employed to fit 4 digitized freehand curves drawn on the average pattern of top height increments observed at various ages. A form of the Johnson-Schumacher model is used in this study, with coefficients estimated for the 4 curves. Each of the resulted equations was solved for height at age 50, thereby assigning a site index value to each equation. Site index was introduced into the height-age equation as an independent variable by expressing the coefficients as function of site index itself. Three site index curves corresponding to 36, 33 and 30 m attained at age 50 were then derived. The logical issue of this study is to develop a prediction equation based on ecological factors which could be most correlated with site index.
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