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Methods for describing distribution of soundwood in mature western hemlock trees Munro, Donald Deane

Abstract

Estimation of soundwood volume and value is particularly important in British Columbia because nearly half of the forests are overmature or decadent. The objective of this thesis was to develop analytical techniques to define distribution of gross and net volumes within individual standing trees in order that appropriate reductions for decay could be made for estimates of volumes of logs of specified sizes and grades. Relationships of heartrot to stand and tree characteristics and to external abnormalities were analysed for 369 western hemlock (Tsuga heterophylla (Rafn.) Sarg.) trees from the Yale Public Sustained Yield Unit in British Columbia. Comprehensive sorting, correlation and regression analyses were carried out on an I. B. M. 7044 electronic computer. One multiple regression equation provided estimates of total decay volume within individual trees from DBH, total height and external indicators of decay. It had a standard error of estimated decay volume of 18.7 cubic feet (19.5 per cent). A second equation estimated decay volume within individual logs in standing trees from the above variables and from section height. It had standard errors of estimate ranging from 13.7 cubic feet (31.6 per cent) in butt logs to 0.1 cubic feet (2.9 per cent) in top logs. The best taper function which could be derived to estimate upper stem diameters inside bark had a standard error of estimate of 1.29 inches using measures of DBH and total height. Combination of the log and tree decay estimating functions and the taper function facilitated complete description of the soundwood volumes in the sample of 369 trees. A graphical analysis was developed whereby percentages of trees in a stand with more or less than specified decay volumes could be estimated. Preliminary chemical studies of western hemlock wood infected with Echinodontium tinetorium E. and E. indicated that cellulose yields were slightly less than those from soundwood. Such partly decayed wood might be used for the manufacture of pulp without serious reductions in yield on a volume or weight basis. Further research is needed to substantiate the possible cyclic nature of decay losses and to determine the influence of bark thickness and natural pruning on the distribution of decay within individual trees. Application of the analytical techniques developed for western hemlock to other species should result in more precise estimates of soundwood volumes and values, thereby contributing to improved management planning and utilization.

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