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A comparison of conventional and natural height=age curves for Douglas fir Heger, Ladislav

Abstract

Literature dealing with the development of height-age curves was reviewed. The advantages of “natural" height-age curves, which have variable rather than the "conventional" fixed form for all sites, were examined. Data collected from stem analyses of 53 dominant and 44 codominant Douglas-fir trees felled on five permanent sample plots in the University Research Forest, Haney, were analysed in order to develop natural height-age curves. A growth curve was constructed for each tree. Master curves were prepared for each plot and for each crown class. [The site index of each plot and for each crown class.] The site index of each plot was determined at the standard age of 100 years. Straight line regression equations of height over site index by age classes were developed. The feasibility of harmonization of the regression coefficients was examined. Sheaves of natural site-index curves were derived. The analysis was repeated three times with various modifications of the basic data. Analysis II was selected as the basis against which 11 sets of "site-index" curves derived by 10 different authors from data collected in various environments by various methods were compared. A comparison of three different height-age natural curves with the derived curves was made for very young trees. Also, the five-year growth in height on five permanent sample plots was compared with height-age curves derived from data collected on the same plots. The advantages of natural "site-index" curves as compared with standard height-age curves were discussed.

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