Predicting knot diameter of Pinus sylvestris in Sweden

Average diameter of the thickest knot of each whorl within a specific stem section of Scots pine (TK) was studied using functions based on growth ring widths, diameter of dry branches, site index, stand age, and latitude. Data from the Pine Stem Bank-a database of external and internal properties where knots were detected by computerized tomography (CT) scanning-were used. A high value of the corrected coefficient of determination, R-2(adj) = 0.63, was found between TK and two independent variables, average width of growth rings 11-20 at stump height and latitude. It is argued that TK is a good parameter for describing timber quality, and that it now is predictable on standing trees as well as on existing data from the National Forest Inventory (NFI). An attempt was made to quantify the change in the TK-value by site index, tree class, age class, and region by applying functions to NFI data from 1988-92. In a second analysis, also based on NFI data, the TK-value had increased by 17% from 1966 to 1988-92. The authors believe that this is mainly a result of the silvicultural systems used and that it is possible to reverse the negative trend by changing silvicultural methods.