One hundred years of fire suppression in a mixed-conifer forest which evolved with frequent natural fires has shifted successional patterns, increased density of small trees, and produced an unnatural accumulation of ground fuels. Analysis of species composition, vegetation structure and age distribution in each of four forest types within the mixed-conifer zone of Sequoia and Kings Canyon National Parks, California, has documented a substantial increase in young, shade tolerant white fir in each type. The original dominant species have decreased in relative abundance in most cases. The sequoia type has been most effected by the fire suppression policy. Giant sequoia show poor reproduction in the absence of fire. The sequoia type also exhibits the greatest accumulation of ground fuels. The ponderosa pine, white fir and mixed forest types also show successional changes as well as significant accumulations of flammable ground fuels following a century of fire exclusion. The management implications of these findings are discussed. ©1979 Elsevier Science.