-39- 



Wasserman pp. 163-4 (1974). It is equivalent to fitting a regression for 



each of the three groups using pooled data from each species in the group. 



However the method used is far more efficient. We simply define T , t , and 



MSE for each summary group as a function of T, t, and MSE for every species 



in that group. For instance, suppose we want SE for hardwoods where the 



n 



hardwood group in this stratum consists of three species. Then, 



* 



T = T + T + T 

 1 2 ^3 



. MSE, (t,-2) +MSE_(t,-2) + MSE-(t_-2) 

 MSE = ^^ 2 2 3 3 



(t^-2) + (t2-2) + (t3-2) 



Using these new values, SE is calculated as before. 



H 



Percent Cruise 

 Percent cruise is simply the percent of the population actually sampled. 

 When sampling with fixed-radius plots, percent cruise is easily calculated 

 as follows: 



Let P = percent cruise 



PLT = plot size in acres 



n = number of plots sampled 

 AC = tract size in acres 

 Then. P = " '^J^'^ (100) 



When sampling with variable-radius plots (point sampling) the true value 

 of P is unknown. However, based on our sample estimate of MSD we can estimate 

 the value of P (Cunia, 1959). 



Let P = percent cruise 



n = number of sample points 

 AC = tract size in acres 

 BAF - basal area factor of angle used 



B = total basal area of all trees on tract 

 T = total number of trees on tract 



MSD = mean stand diameter (quadratic mean) 



100 • n • B _ 0.5454 • n • MSD^ 

 ' T • AC • BAF ~ AC • BAF 



