BJBAG 1 = .05 .05 .05_ 



Diameter Class Size in Inches 



Figure 3 . --Predicted 5-year mortality rate for even- and uneven-aged blackjack pine by diameter 

 size class, MBA2 class, and even- and uneven-aged blackjack pine basal area growth (BJBAGl) . 



During data collection, all trees were initially categorized by vigor class, and then 

 those trees not cut on a plot were reclassified every 20 years (that is, at the start of 

 every fifth growth period) . An examination of the data available for modeling conversion 

 indicated the following problems: 



1. While growth, mortality, and ingrowth could be predicted every growth period, conver- 

 sion from blackjack to yellow pine could only be predicted after every fourth growth period. 

 This might cause the number of trees in each vigor class to change abruptly after every fourth 

 growth period. 



2. Cutting of blackjack trees between the reclassification times negates the utility of 

 .the plot for predicting conversion because of the uncertainty of whether those trees cut would 

 have converted or not. The plot and classification period combination without cutting are the 

 first classification period of plot 62 and both periods of plot 61. 



3. The conversion from a blackjack pine to a yellow pine is a slow but continual process, 

 and therefore, the discrete classification of a tree as either blackjack or yellow pine is 

 extremely subjective. This subjectivity can become a problem on long-term studies because the 

 classification of vigor classes is done by different people with individualized critera for 

 classification. An examination of the conversion rates for the first 20 years on plots 61 and 

 62, compared to the conversion rate on plot 61 in the second 20 years, shows that the rates 

 differ considerably between the two classification periods. While it cannot be proved, it is 

 likely this difference is due in part to the different individuals performing the classifica- 

 tions . 



Based on these problems, 1 decided to use only the data from plot 61 (both classification 

 periods) to develop the conversion rate model. The data for the first classification period 

 on plot 62 were eliminated since including that data would unduly weight the resulting model 

 towards the low conversion rate of the first classification period. By using just the data 

 from plot 61, an approximately equal weight is given to both periods. 



20 



