A switching model of bole taper

Numerical switches are employed to change the values of two exponents in a variable-form model of bole taper. The taper of a bole is modeled, with res pect to height from the ground, by three connected geometric segments (i.e. , a basal, middle, and top segment). The numerical switches provide for eit her graded or abrupt transition from the basal to the middle segment and fr om the middle to the top segment. The height of the base of the crown was a ssumed to be the point of transition between the middle and top segments. C rown height can be either measured or estimated with a simple submodel that emerged from the taper model. Compared with estimated crown height, the us e of measured crown height improved the precision of the taper model when f itted for Liquidambar styraciflua L., but not Pinus elliottii Engelm., or P inus ponderosa Dougl. ex P. & C. Laws. The taper model also was fitted for Liriodendron tulipifera L., but crown height was not available. Correlation among residuals within individual boles was accounted for in the fitting p rocedure. The taper model proved to be reasonably precise for all four spec ies, and the parameters are easy to interpret.