Probability of a Tree Being Unsound in Board Foot Volwne — Unforked and Forked Trees 



The probability of a tree being unsound in board foot volume, to be applied to both 

 International 1/4-inch and Scribner board foot predictions, is predicted by 



PrC„ = 1.0/(1.0 + e 



where 



PrCg = Predicted probability of a -tree being unsound in board foot volume 



Xg = A function of d.b.h., total tree height, number of tree tips, and the 

 presence or absence of significant damage. 



The equations for Xg were also fitted using weighted, nonlinear regression procedures, 

 and the results are given in table 14, along with the number of trees used. Again, the 

 equation for blackjack pine on the Lincoln National Forest proved to be significant at 

 the 95 percent level, whereas all the other equations were significant at the 99 percent 

 level . 



Two damaging agents, sweep (or crook) and porcupine, proved to be useful in predict- 

 ing whether a tree was sound or not. A damaging agent is recorded only if it is severe 

 enough to (1) prevent the tree from surviving; (2) preclude the production of a market- 

 able product; or (3) diminish the quality or quantity of that product. Damage is 

 entered into the equations through the usage of dummy variable (s). If the tree has the 

 particular damage, the dummy variable is set to 1.0, otherwise it is 0. Only one damag- 

 ing agent is recorded per tree, and, therefore, equations with two or more dummy variables 

 in them would have at most only one of them set to 1.0 and the rest to 0. Methodological 

 details can be found in appendix XIII. 



22 



