Ecology: The Siskiyou and Cascade mountains of southwestern Oregon are occupied by a complex mix of forest types. Forests near the coast are dominated by conifers in the upper portion of the overstory and hardwoods in the lower portion of the overstory, while forests nearer the Cascades are dominated by conifers, with fewer hardwoods. There are relatively few pure stands of any single species. Because conifers are the commercially important species, these forests are often lumped together as "mixed-conifer" forests.

Elevation, distance from the ocean, fire history, and past management practices all influence these forests. Near the coast, Douglas-fir and tanoak are the most important species. Golden chinkapin, Pacific madrone, and canyon live oak are secondary hardwoods, while sugar pine, ponderosa pine, and incense-cedar are secondary conifers. Port-Orford-cedar and bigleaf maple occur on moist sites, while Jeffrey pine is common on serpentine soils (high in magnesium). With increasing elevation, hardwoods become less common, and grand fir and white fir join the mix of conifers. Near the Cascades, forests are dominated by mixed stands of Douglas-fir, ponderosa pine, sugar pine, incense-cedar, and white fir. This is the northern-most extension of the mixed-conifer forests that dominate the Sierra Nevada Mountains of California. Throughout the mixed-conifer forests, understories are sparse and shrubby with lots of poisonoak.

Climate: Climates range from cool and moist near the coast to hot and dry in the interior. Complex topography creates a variety of microclimates that supports such diverse forests.