Predicting the distribution of a novel bark beetle and its pine hosts under future climate conditions

Understanding the distribution of key biotic elements of forest ecosystems is essential in contemporary forest management and in planning to meet future management needs. Habitat distribution (niche) models based on known occurrences provide geographical structure for such management as the environmental factors change. Bark beetles play critical roles in coniferous forest dynamics in western North America. Among these insects, Dendroctonus rhizophagus Thomas and Bright, which occurs in the Sierra Madre Occidental in Mexico, is unique in that it attacks only immature trees (Pinus spp.) and therefore represents a threat to forest regeneration. We developed current habitat distribution models for D. rhizophagus and its Pinus hosts and projected these to future climate scenarios. Predicted suitable habitat of D. rhizophagus currently covers approximately 119 000 km2 of which approximately 11% is occupied, and overlap with suitable habitat for all Pinus hosts exceeds 99.5%. Some suitable habitat occurs isolated from known D. rhizophagus occurrences in Mexico and the south-western U.S.A. Habitat distribution models were projected to four potential climate scenarios for the period 20402060 and this predicted the gains and losses of suitableD. rhizophagus habitat throughout the region. Areas of north-western Mexico maintain large areas of suitableD. rhizophagus and Pinus host habitat in all scenarios. Dispersal to isolated areas of D. rhizophagus habitat appears unlikely. The results of the present study can be used to target D. rhizophagus monitoring and management activities and may serve as a model for the management of other invasive species.