We evaluated ponderosa pine forest structure after 25 years of Wildland Fire Use (WFU) in the Gila Wilderness (Gila National Forest, New Mexico) and the Rincon Wilderness (Saguaro National Park, Arizona). We compared areas burned 0, 1, and 2 or more times. Our goal was to understand the consequences of repeated treatments as a result of this 25-year experiment in restoring natural fire regimes. Extensive areas have burned multiple times in WFU treatments, resulting in the conversion of previously dense forests to structurally diverse stands with both small and large trees, as well as snags and logs. High intensity fires have opened holes in previously continuous canopies and high tree density. We present preliminary results from ongoing research designed to answer these questions: Are there thresholds in pre-fire stand structure in ponderosa pine/Douglas-fir forests that lead to undesired levels of canopy mortality in WFU operations?, To what degree can repeated fires alone (without mechanical treatment) restore sustainable forest ecosystems?, and what are the trends in canopy openings and other landscape patterns through time relative to drought and climate change? Empirical research can provide the information needed to evaluate the options for, and consequences of different fire management strategies for ecological restoration of forest structure and natural fire regimes.