A Spread and Intensification Model for Southwestern Dwarf Mistletoe in Ponderosa Pine

Spread and intensification of Arceuthobium vaginatum subsp. cryptopodum in even-aged and two-storied stands of ponderosa pine in Arizona, New Mexico, and Colorado were examined. Prediction equations for spread, intensification, and proportion of trees infected were developed. Computer programs were written for generating stem maps which showed the distance and circular pattern of spread, and the relationship between spread and stand density. An intensification equation for all infested stands throughout the area was derived, and separate spread equations were developed for even-aged and two-storied stands. The proportion of trees infected was found to increase linearly from 0.0 to 1.0 over a distance of 10.7 m (35 feet), as distance back to the infection source decreased. Using equations developed here and growth equations from existing yield models, a simulation model called SPREAD was written. SPREAD will aid forest managers in making decisions concerning dwarf mistletoe-infected stands, and in the evaluation of various management alternatives. Forest Sci. 25:43-52.