Excluding fire can have dramatic effects on ecosystems. Decades of fire suppression in national parks and other protected areas have altered natural fire regimes, vegetation, and wildlife habitat (Chang 1996; Keane et al. 2002). Suppressing lightning-ignited wildfires removes one of the most important natural processes from fire-dependent ecosystems, and runs counter to the untrammeled characteristics for which wilderness is to be managed. Many, if not most, lightning-ignited fires are suppressed in wilderness for myriad reasons and yet resource specialists have not had a good way to measure or monitor the effects of these management actions. What if we did not suppress these fires? Where would these fires have spread, and what would the effects have been? Can we quantify the impacts of suppressing these fires?

Recently, we asked these questions for two case study areas in the Sierra Nevada of California, both of which are almost entirely designated wilderness: the 74,057-acre (29,970 ha) South Fork of the Merced River watershed in Yosemite National Park and the 223,573-acre (90,480 ha) Upper Kaweah watershed in Sequoia–Kings Canyon National Parks. Yosemite and Sequoia–Kings Canyon National Parks have been leaders in the restoration of fire as a natural process. By 1970, both parks had instituted a policy whereby lightning-caused fires could be allowed to burn in certain areas. Despite these efforts, the parks continue to struggle with restoring natural fire regimes, and the majority of lightning-caused ignitions are suppressed for myriad biophysical and social reasons. For example, most of the South Fork of the Merced watershed has not burned since before the 1930s. This watershed contains the townsite of Wawona and the Mariposa grove of giant sequoia trees (Sequoiadendron giganteum), and fires are typically suppressed, which has led to unnaturally high fuel accumulations. In the Upper Kaweah watershed in Sequoia–Kings Canyon, about half of the lightning-caused ignitions are suppressed. The Upper Kaweah watershed contains most of the park’s infrastructure and giant sequoia groves, and has a diversity of boundary interface issues. Because of the watershed’s proximity to developed areas and topography that drains into the San Joaquin Valley, smoke and its impacts on air quality are a primary concern.