Changing climate and disturbance effects on southwestern US forests

Abstract

Changing climate and its interaction with disturbances is reshaping forests of the western United States and southwestern forests are experiencing these changes at an accelerated pace. Southwestern forests are fire prone and a legacy of fire exclusion from past land use and management have homogenized many frequent fire forests, increasing the chance that disturbances reinforce landscape homogeneity. Widespread disturbances, especially those that cause a vegetation type change from forest to non-forest, are and will continue to influence the provision of ecosystem services upon which society depends. Here we review our current understanding of changing climate and disturbance and how they will influence southwestern United States forests (defined as California, Nevada, Arizona and New Mexico). We synthesize the literature on climate-driven changes in disturbance and how disturbance combined with changing climate will alter forest structure, forest cover, and species composition. We then synthesize management options for improving forest resilience and present them in the context of the resist-accept-direct framework for managing in a changing climate. Managing for more resilient southwestern forests will require a more nimble approach to forest management than is currently practiced in the southwestern US. Our current process of years-long planning for a document that charts the course for several decades of management action is ill-suited to the rate of change that southwestern forests are undergoing. Effective management will require truly adaptive management, with frequent monitoring that informs decision-making and some level of experimentation with management approaches as a hedge against the uncertainty facing southwestern forests.