A switching model of bole taper

Abstract

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 respect to height from the ground, by three connected geometric segments (i.e., a basal, middle, and top segment). The numerical switches provide for either graded or abrupt transition from the basal to the middle segment and from the middle to the top segment. The height of the base of the crown was assumed to be the point of transition between the middle and top segments. Crown height can be either measured or estimated with a simple submodel that emerged from the taper model. Compared with estimated crown height, the use of measured crown height improved the precision of the taper model when fitted for Liquidambar styraciflua L., but not Pinus elliottii Engelm., or Pinus ponderosa Dougl. ex P. and 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 procedure. The taper model proved to be reasonably precise for all four species, and the parameters are easy to interpret.