A Survival Model for Individual Shortleaf Pine Trees in Even-Aged Natural Stands

-A model was developed that predicts the probability of survival for individual shortleaf pine (Pinus echinatu Mill.) trees growing in even-aged natural stands. Data for model development were obtained from the first two measurements of permanently established plots located in natural ly occurring short leaf pine forests on the Ouachita and Ozark National Forests in western Arkansas and eastern Oklahoma. The logistic function was used to model survival probability. Parameters were est imated by using logist ic regression in which the dependent variable was “1” for trees al ive during both inventories and “0” for trees that died prior to the second inventory. Examination of several combinations of independent variables (representing tree size, relat ive posit ion of the tree in the stand, stand density, and stand age) yielded the following model: POS = (i + exp(-(b, + b,lDR + b,SBA + b,DH)))-’ where POS is annual probability of survival, DR is the ratio of quadratic mean diameter to individual t ree dbh, SBA is stand basal area in square feet per acre, DH i s average height of dominant and codominant trees in feet, b,, b,, b,, b, are parameter estimates. A chi-square evaluation was performed to test model performance. This tree survival model is being used to est imate probabil i ty of individual t ree survival in a distance-independent individual tree simulator for short leaf pine. A survival model is an integral part of the ShortLeaf Pine Stand Simulator (SLPSS) (Huebschmann et al. 1998) an individual tree model that has been developed for evenaged natural shortleaf pine forests. Other components of the model include an individual tree basal area growth model (Hitch 1994) and a compatible height prediction and projection system for shortleaf pine trees in even-aged natural stands (Lynch and Murphy 1995). Hamilton (1974) proposed that the fol lowing logist ic equat ion be used to model probability of individual tree mortality: P = 1 + exp(-Vo + jfl pjxi) [ 1 -1