The Andrews Forest is situated in the western Cascade Range of Oregon in the 15,800-acre (6400-ha) drainage basin of Lookout Creek, a tributary of Blue River and the McKenzie River. Elevation ranges from 1350 feet (410 m) to 5340 feet (1630 m). Broadly representative of the rugged mountainous landscape of the Pacific Northwest, the Andrews Forest contains excellent examples of the region's conifer forests and associated wildlife and stream ecosystems.
The research program has been diverse throughout the history of the Forest, with the dominant themes changing over the years. Today, several dozen university and federal scientists use this LTER site as a common meeting ground, working together to gain basic understanding of ecosystems and to apply this new knowledge in management policy.
Located at 44.2 degrees north latitude and 122.2 degrees west longitude, the Andrews Forest is in the western Cascade Range of Oregon in the 15,800-acre (6400-ha) drainage basin of Lookout Creek, a tributary of Blue River and the McKenzie River. Elevation ranges from 1350 feet (410 m) to 5340 feet (1630 m). Broadly representative of the rugged mountainous landscape of the Pacific Northwest, the Andrews Forest contains excellent examples of the region's conifer forests and associated wildlife and stream ecosystems.
Lower elevations of the Forest are underlain mainly by Oligocene-lower Miocene volcanic rocks composed of mudflow, ash flow, and stream deposits. In higher areas bedrock is composed of andesite lava flows of Miocene age and of younger High Cascade rocks. Stream erosion, a variety of types of landslides, and glaciation have created a deeply dissected, locally steep landscape. Soils developed in these parent materials are mainly Inceptisols with local areas of Alfisols and Spodosols.
The maritime climate has wet, mild winters and dry, cool summers. At the primary meteorological station near headquarters at 1400 feet (430 m) elevation, mean monthly temperature ranges from near 34 degrees F (1 degree C) in January to 64degrees F (18 degrees C) in July. Average annual precipitation varies with elevation from about 91 inches (230 cm) at the base to over 140 inches (355 cm) at upper elevations, falling mainly in November through March. Rain predominates at low elevations; snow is more common at higher elevations. Highest streamflow occurs generally in November through February during warm-rain-on-snow events.
When it was established in 1948, the Andrews was covered with virgin forest. Before timber cutting began in 1950, about 65% of the Andrews Forest was in old-growth forest (400-500 years old) and the remainder was largely in stands developed after wildfires in the mid-1800's to early 1900's. Clearcutting and shelterwood cuttings over about 30% of the Andrews Forest have created young plantation forests varying in composition, stocking level, and age. Old-growth forest stands with dominant trees over 400 years old still cover about 40 percent of the total area. Mature stands (100 to 140 years old) originating from wildfire cover about 20 percent. Wildfire was the primary disturbance in the natural forest; windthrow, landslides, sites of concentrated root rot infection, and lateral stream channel erosion were secondary disturbances.
Lower elevation forest are dominated by Douglas-fir, western hemlock, and western redcedar. Upper elevation forests contain noble fir, Pacific silver fir, Douglas-fir, and western hemlock. Low- and mid-elevation forests in this area are among the tallest and most productive in the world. Average heights are in excess of 75 m and a typical stand stores in excess of 600 megagrams of carbon per ha. These forests are also noteworthy for the large amounts of fine and coarse woody debris they contain. As elevation increases, Douglas fir and western red cedar decline in importance and western hemlock is gradually replaced by Pacific silver fir. Non-forest habitats include wet and dry meadows, rock cliffs, and talus slopes.
Rapidly flowing mountain streams are the primary type of aquatic ecosystem in the Andrews Forest. Streamflow follows the precipitation pattern with winter maximum flows three orders of magnitude larger than summer minimum. First and second-order streams under natural conditions are dominated by coarse woody debris and receive-a large annual input of litter which provides the energy base for the aquatic organisms. Larger order streams have a higher proportion of the energy base provided by in-stream photosynthesis, but litter inputs and coarse debris remain important components of all stream ecosystems.
In terms of biological diversity, the Andrews Forest supports a rich flora and fauna for a north temperate ecosystem. More than 500 vascular plant species are known to occur on the Andrews Forest, and the nearby RNA's include more than 100 additional species. Typical 0.5-ha plots in the upland sites include 35 to 40 species of vascular plants and riparian sites twice that number. Over 3,400 arthropod species have been reported, which probably represent slightly more than half the estimated total. About 20 species of reptiles and amphibians, seven species of fish, and 50 species of mammals are found on the Andrews. Over 70 species of birds are known to nest here. Plant and animal species associated with old-growth forests of the Pacific Northwest, including Vaux's swift and the northern spotted owl, are especially well represented. Other vertebrate species include pileated woodpecker, black bear, mountain lion, black-tailed deer, and Roosevelt elk.