The investigations were conducted in a 300-km transect of western coniferous forest in Oregon. Measurements were collected at six sites across an elevational and climatic gradient that stretched from the Pacific coast 300 km to the east. The first of the intensively studied sites, Site 1 (44° 03' N, 123° 57' 30" W ) Cascade Head, began at the Pacific coast and contained an alder stand. Site 2 ( 44° 36' N, 123° 16' W) was Warings Woods. Site 3, Scio (44° 40' 30" N, 123° 36' 40" W), was a dense Douglas fir forest. Site 4, Santiam Pass (44° 025' 20" N, 121° 50' 20" W), was a mountain hemlock/subalpine fir community. Site 5, Metolius [44° 25' N, 121° 40' W (control) and 44° 40' 30" N, 123° 36' 40" W (fertilized)], was a Ponderosa pine community. Site 6, Juniper (44° 17' 30" N, 121° 20' W ) was the site farthest east.
OTTER combined laboratory studies with field work and remote-sensing techniques to help simulate and predict ecosystem processes. Data collection began in the summer of 1989, and intensive field campaigns were conducted during 1990 and 1991. The field campaigns were coordinated with a Multi-sensor Airborne Campaign (MAC). The four 1990 data collection periods were timed to coincide with (1) pre-budbreak at the sites (late March to early April); (2) maximum understory leaf area index (LAI), minimum starch, maximum nitrogen, and maximum LAI in the overstory (late May to early June); (3) maximum LAI and water stress (mid-August); and (4) senescence of understory vegetation and reduced LAI and water stress (October). Additional data were gathered in May 1991. Airborne sun photometer data were also collected from 1990 through 1991 to provide quantitative atmospheric correction to remotely sensed data of forest reflectance and radiance.
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