Estimating region-wide damages caused by the southern pine beetle

Abstract

A methodology is presented for simulating the damage caused by individual southern pine beetle infestations as well as the damages caused on a region-wide basis. The number of infestations likely to appear in a region in a year is estimated by a southern pine beetle spot incidence model. This model predicts the probability that an infestation will occur in a stand of given characteristics. Each stand in a region is stochastically tested, based on this probability, to determine whether or not an infestation occurs. Thus, an estimate of the total number of spots occurring in a region can be obtained. The eventual size of each infestation is predicted by a southern pine beetle spot severity model. A sub-model for predicting the rate of spread, in terms of trees killed per day, was formulated and combined with a function giving the probability of a spot becoming inactive within 30 days of observation. When combined, these produce a method for simulating the growth of individual infestations. This combined model performed well when tested on independent data. The incidence model is joined with the severity model to produce a region-wide southern pine beetle impact projection system (DAMBUGS). In this system, the incidence model estimates the number of infestations occurring in a region in a year and the severity model estimates the size of each infestation. The damage from all simulated infestations is summed to arrive at an estimate of the damage caused by the southern pine beetle to the region. The methodology for developing and implementing such a system is illustrated using the North Central Forest Survey Unit of Georgia as an example region.