A Method for Estimating Crown Weight in Eucalyptus, and Some Implications of Relationships between Crown Weight and Stem Diameter
1966
Attiwill, P. M.
Equations relating crown weight to diameter at breast height outside bark (dbhob) are developed for approximately 50—year—old, even—aged stands of Eucalyptus obliqua from initial branch weight—branch girth relationships. These equations are used to predict crown weights of individual trees; the predictions of n'trees per unit area have standard errors of 15%/n' of the summed branchwood weights. Although stem weight is a function of dhob², considerations both of (crown weight)–dhob and (crown weight)—(stem diameter at base of crown) relationships show that crown weight is a function of (stem diameter at base of crown)²=consent (dhob)³, thus accounting for form factor. There is no logicval basis, therefore, for selecting a tree of mean dhob as a unit for estimating (weight of mean tree x number of tees) dry weight per unit area. The bias (in this sense meaning the deviation from the true value) of estimates so obtained are discussed; an index of the error is provided by the distribution of dhob³ with respect to dbhob. The error, one of underestimation, is likely to increase with stand age, and this must be an important deficiency in some of the productivity—age sequences which have been developed. Expressions defining the tree of mean crown weight are derived, but confidence limits for estimates of dry weight based on a limited number of mean trees, no matter how they are defined, cannot be set until population variation has been estimated.
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