Table 21 . --^Vumber of subplots by size, plot number, and presence of highway 



Subplot Plot 61 Plot 62 Plot 71 Plot 72 



size No No No No 



in highway Highway highway Highway highway Highway highway Highway 



acres intrusion intrusion intrusion intrusion intrusion intrusion intrusion intrusion 



0.50 

 .70 

 .90 

 1.00 

 1.90 

 2.00 

 2.20 



30 

 35 

 40 

 45 



50 



2.60 

 2.80 

 2.90 

 3.00 

 3.05 

 3. 10 



20 



28 



23 



Number 

 of 



subplots 

 seriously 

 affected 

 by 



highway 



25 



31 



24 



31 



4. Variable plot sizes . --As mentioned earlier, sizes on the uneven-aged subplots range 

 from 0.5 to 5.1 acres (table 21), and the even-aged plots from 0.75 to 1.25 acres. Curtis and 

 Pope^ hypothesize that "small" plots can result in erratic estimates of stand attributes, such 

 as basal area, because of within-stand clumping. As a result, the deviation of plot estimates 

 of growth and basal areas from their respective stand means will be correlated and, therefore, 

 the regression of diameter class growth as a function of basal area will also reflect plot 

 size. They conclude that this problem would not produce biased results if the regression 

 equation were applied to inventory plots of the same size and design, and if the stands to 

 which they are applied had similar spatial patterns. Recognizing that these conditions are 

 seldom met, Curtis and Pope suggested that the problems would be minimized if large plots were 

 used in developing growth equations. 



Plot size is important to this study because the two data sets (even- and uneven-aged) 

 have different plot sizes, both within and between the data sets, based on the Curtis and 

 Pope argument, the coefficients for the "separate" models (even- and uneven-aged) may be con- 

 founded by the plot size differences, making a statistical combination more difficult. To 

 help minimize the problem with the uneven-aged subplots, all subplots below 2 acres were 

 eliminated. This action, coupled with the realization that the even-aged plots are fairly 

 homogeneous (because of stand treatment) and good sized, might reduce the problem of within- 

 stand clustering and the possibility of locating a subplot within one cluster of the stand. 



^Curtis, Robert 0., and Robert B. Pope. 1972. Some considerations in design of growth 

 studies and associated inventories of the western National Forests. Draft of the internal 

 report. USDA For. Serv., Pac . Northwest For. and Range Exp. Stn., Portland, Oreg. 



47 



