RESEARCH SUMMARY 



A simulator for predicting even- and uneven-aged stand 

 development was constructed and validated for the ponderosa 

 pine/Arizona fescue habitat type of the Southwest. The structure 

 and dynamics of the simulator make it potentially useful for 

 answering both even- and uneven-aged management questions. 



The primary framework for the simulator is two diameter 

 distributions, one for blackjack pine and the other for yellow 

 pine (both are different vigor classes of ponderosa pine) . The 

 diameter distributions are expressed as number of trees in each 

 1-inch diameter class, and the lowest diameter class is 4 inches 

 for uneven-aged stands and 1 inch for even-aged stands. Within 

 this framework, there are four basic components: upgrowth, 

 mortality, conversion, and ingrowth. 



Upgrowth is the movement of trees from a given diameter 

 class into larger diameter classes. It was modeled as a function 

 of the distribution of trees within the diameter class and of 

 basal area growth of the diameter class. During modeling, diam- 

 eter class basal area growth rates of even- and uneven-aged 

 stands were shown to be logically interrelated if the structure 

 of within-stand competition is incorporated in the model. 



Diameter class mortality was modeled as the proportion of 

 trees dying to eliminate the problem of negative survival rates. 

 Even- and uneven-aged endemic mortality rates also proved to be 

 logically interrelated if catastrophic mortality was treated in a 

 fashion similar to cutting "mortality." 



Conversion is the process in which blackjack pines transform 

 into yellow pines. As with mortality, conversion was modeled as 

 a proportion of the diameter class transforming. 



The final component of the simulator is ingrowth, which is 

 the number of trees growing into the 4- or 5-inch diameter classes 

 of blackjack pine. Data restrictions precluded the development 

 of a regeneration model and limited the ingrowth model to uneven- 

 aged stands. For even-aged stands, it is assumed that no (or 

 insignificant) trees exist below the 1-inch diameter class. 

 Simulator applications are further restricted to stands with an 

 average stand diameter of 4 inches or greater. 



Two equations were needed to model the ingrowth process. 

 The first predicts the total number of trees ingrowing into the 



4- and 5-inch diameter classes. The second equation predicts 

 the proportion of total ingrowth that will through grow into the 



5- inch diameter class in the same growth period. 



During the validation process, an assumption made by past 

 uneven-aged modelers was tested: that small plots have the same 

 structure and dynamics as the total stand and can therefore be 

 used to develop whole stand simulators. From this analysis, I 

 concluded that developing a simulator, using 2.5-acre plots, and 

 then using it to predict stand averages generally reduces both 

 the precision and accuracy of the stand estimates. In this 

 study, however, the loss appears not too severe for most potential 

 uses of a whole stand simulator. 



