Since 1977 Oregon State University and the Forest Service have jointly administered the Andrews Experimental Forest to enhance the research and educational use. The landscape is deeply dissected and heavily forested. Old-growth forests with dominant trees in excess of 400 years of age cover about 55 percent of the Andrews Forest. The most common forest types at lower elevations are dominated by Douglas-fir, western hemlock, and western red cedar. As elevation increases western hemlock is gradually replaced by Pacific silver fir, and Douglas-fir and western red cedar decline in importance.
Upper elevation stands consist of mixtures of true firs and mountain hemlock.
Virgin forest when established in 1948, approximately one-third of the Andrews Forest has been logged or manipulated for research. The maritime climate is mild with wet winters and cool, dry summers. Little or no rain falls during July and August. Rapidly flowing mountain streams are the primary type of aquatic ecosystem on the Andrews Forest. Streamflow follows the precipitation pattern with winter maximum flows three orders of magnitude larger than summer minimum.