In the lower-elevation sequoia-mixed-conifer and ponderosa pine forests, however, a considerable fire hazard has built up because of the exclusion of natural fire during the past half century or more (Leopold et al., 1963; Biswell et al., 1968). What may have once been natural crown-fire immunity has now been lost. A wildfire in 1955 swept up from the chaparral country below the Grant Grove of giant sequoias in Kings Canyon National Park. In a short time, it had devastated more than 5,200 hectares (13,000 acres) of brush and mixed-conifer forest and had threatened a grove of giant sequoias.