Conceptual Model of Infestation Probability Based on Bark Beetle Abundance and Host Tree Susceptibility

Abstract

The probability of a bark beetle infestation starting and growing in any given stand of trees is termed stand risk. This probability is defined by a conceptual model that describes the functional relationship between beetle population size and the physiological condition of the stand of trees. The relationship is dynamic, so that changes in either insect population levels or stand condition result in changes in risk. Stand risk approaches zero when stands are in good condition or beetle populations are very low. The risk increases in a logistic fashion as insect populations increase or stand conditions decline, and it is asymptotic for a probability approaching 1. The model incorporates a threshold concept for stand risk and can be integrated into population dynamics models to assess future risk.