Estimates of changes this century (1890-1990) in the total mortality from natural causes (wildfire, pests) and harvesting in the Rocky Mountain and Pacific Coastal regions of the United States (excluding Alaska) were based on yearly national forest statistics. Total accrual per year doubled this century as a result of fire suppression and accelerated tree growth. Total depletion per year did not change significantly from 1920 to 1985; after 1985, extensive pest and wildfire mortality sharply increased total losses. A model of accumulated fuel loads and shifts in forest density and species composition was used to account for this catastrophic jump in tree mortality concurrent with severe drought. The implications of a destabilized forest structure are discussed in terms of the needs to "defuel" many dominant forest types and to restore long-term sustainability.