Pinyon-juniper woodlands and Wyoming big sagebrush ecosystems have undergone major changes in vegetation structure and composition since settlement by European Americans. These changes are resulting in dramatic shifts in fire frequency, size and severity. Effective management of these systems has been hindered by lack of information on: (1) presettlement fire regimes and the spatial and temporal changes that have occurred in Intermountain Region woodlands and sagebrush ecosystems since settlement; (2) changes in fuel loads and the consequences for the ecosystem types and conditions that currently exist on the landscape; and (3) the environmental and ecological factors that influence community susceptibility to invasion by nonnative species. This project utilized an integrated, collaborative project of the Joint Fire Sciences Program to address each of these information needs.