Western white pine (Pinus monticola) has been seriously affected by the white pine blister rust (Cronartium ribicola), a fungus that was accidentally introduced from Europe in 1909. The United States Forest Service estimates that 90% of the Western white pines have been killed by the blister rust west of the Cascades. Large stands have been succeeded by other pines or non-pine species. The rust has also killed much of the whitebark pine outside of California. Blister rust is less severe in California, and Western white and whitebark pines have survived there in great numbers.