For example, PCT(I) = 100 implies that the ith tree is the tree of largest diameter in 

 the stand. PCT(I) = 75 would correspond to the tree whose position in the diameter 

 distribution was such that 25 percent of the stand basal area was in trees having a 

 larger d.b.h. than the ith tree, and 75 percent was in trees having a diameter less 

 than or equal to the ith tree. Percentile in the basal area distribution has a very 

 simple interpretation when sampling with a wedge prism or other angle gage. If 8 

 trees were found to qualify at a point sample, then a ranking by diameter would permit 

 one to calculate the percentile simply as 100 for the largest tree, 100*7/8 = 87.5 for 

 the second largest, 100*6/8 = 75 for the third largest, etc. If several points are 

 tallied in the same stand, the procedure would be the same. For the ith ranked tree, 

 in a sample of N trees, percentile could be calculated as: 



PCT(I)= *^ * 100 



When the calculations are based on a stand table, or a list of sample trees having 

 varying numbers of trees-per-acre associated with each tree record, then two computer 

 subroutines can facilitate the computation of percentile. The first routine, IDSORT, 

 is a general sorting program that indexes an array of tree records according to a 

 decreasing sequence of d.b.h. 's. The second routine, PCTILE, uses the indices from 

 IDSORT to calculate the percentile in the distribution. These two routines are listed 

 in figure 4. 



The use of these two routines is illustrated in the following segment of a FORTRAN 

 IV program: 



C N = NUMBER OF TREE RECDRDS 



C DBH = ARRAY OF DIAMETERS OF SAMPLE TREES 



C FNO = ARRAY OF NUMBER OF TREES PER ACRE CORRESPONDING TO THE DBH 



C ARRAY 



C IND = ARRAY OF INDICES INDICATING ORDER OF SIZE (DBH) 



C BA = ARRAY OF BASAL AREAS /ACRE 



C PCT = ARRAY OF PERCENTILES CORRESPONDING TO DBH ARRAY 



C TOT = TOTAL STAND BASAL AREA 



INTEGER*2 IND 



DIMENSION DBH(N), FNO(N) , PCT(N) , BA(N) , IND(N) 

 DO 1 J = 1,N 



1 BA(J) = DBH(J)*DBH(J)*FNOCJ)*. 0054541 



CALL IDSORT (N,BA,IND) 



CALL PCTILE (N, IND, B A, PCT, TOT) 



PCT and TOT are assigned values by PCTILE that can be utilized along with other 

 descriptors of the tree to produce data for building growth or mortality prediction 

 models by statistical estimation procedures. 



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