INTRODUCTION 



Because mortality is an important component of stand development, models that pre- 

 dict mortality over time must be included in systems that project stand growth. The 

 mortality models described in this paper were developed for a stand growth prognosis 

 model devised by Stage (1973). Other stand growth models, such as those developed by 

 Myers (1973), Lin-^, Stiell^, and Bartos^, also require some form of mortality model to 

 deal with the mortality component of stand development. 



The mortality model can be used to help schedule management activities. Stands 

 of trees for which the model predicts high mortality rates should be considered high 

 risk stands susceptible to insect and disease outbreaks and should be logged, salvaged, 

 or otherwise treated before stands composed of trees with low predicted mortality rates. 



Mortality models also reveal relationships that may provide a better understanding 

 of how and why mortality occurs in a stand. This information is valuable in management 

 planning and in developing strategies to control mortality. 



The models discussed in this paper were developed by means of a three-step analy- 

 sis. The first step is to screen the independent variables for those that show the 

 strongest relationships to the probability of mortality. The variables selected as 

 most significant by the screening algorithm are used as predictors of the probability 

 of mortality in a logistic model. The regression coefficients for this model are then 

 estimated by a nonlinear regression program, RISK (Hamilton 1974) . The final step, 

 model verification, employs a chi-square statistic to evaluate the accuracy with which 

 the proposed model predicts the mortality that occurred on an independent data set. 



^Lin, Jim Y. 1973. Stand growth simulation models for Douglas-fir and western 

 hemlock in the northwestern United States. Paper presented at Joint Meeting of Subject 

 Groups S4.01 and S6.02, Int. Union For. Res. Organ., Vancouver, B.C., Can., Aug. 

 20-24, 1973. 



^Stiell, W. M. 1973. An application of stand volume and tree mortality models 

 in yield table construction. Paper presented at Joint Meeting of Subject Groups 

 S4.01 and S6.02, Int. Union For. Res. Organ., Vancouver, B.C., Can., Aug. 20-24, 1973. 



^Bartos, Dale L. 1973. A dynamic model of aspen succession. Paper presented 

 at Joint Meeting of Subject Groups S4.01 and S6.02, Int. Union For. Res. Organ., 

 Vancouver, B.C., Can., Aug. 20-24, 1973. 



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