About the Forest
About the Forest
Andrews Watershed 6 - WS06
Andrews Experimental Forest (HJA)
Watershed above the Watershed 6 gaging station
Bounding Coordinates (decimal degrees):
Slope (%): 25.19
Aspect (degrees): 165
Watershed 6 was 100% clearcut in 1974. Logging began in May 1974 and was completed in August 1974. All timber was removed in a clearcut. Logs in 90% of the watershed were yarded uphill by a high-lead cable system; logs in the remaining 10% were yarded by tractor. Logging residue was broadcast burned in the spring of 1975, and the watershed was planted with Douglas-fir seedlings in the spring of 1976. A road (still present and maintained) was contructed through the watershed. WS#6 was replanted with Douglas-fir seedlings in 1976 and has reached canopy closure (2004). WS#6 is adjacent to WS#7 which is adjacent to WS#8 (the control). No significant difference was found among WS 6, 7, 8 basal area pre-treatment. The Hi-15 Meteorological Station (H15MET) is centrally located just below the WS#7 gaging station. GIS estimated percent harvest: 90.9%
Soils derived from deep andesitic landslide deposits occupy about 75% of the total area in Watersheds 6, 7, and 8. Texture is generally gravelly loam to sandy gravelly loam with gravel content ranging from 5 to 20% by volume (Dyrness and Hawk, unpublished). In most locations, effective rooting depth is virtually unlimited because of very deep, unconsolidated parent material. Silt loam soils derived from andesite and associated tuffs and breccias occupy approximately 10% of the watershed area, mostly at higher elevations in Watersheds 6 and 8 (Dyrness and Hawk, unpublished). Because the texture and structure of soils in Watersheds 6, 7, and 8 are nearly identical to those of the lower-elevation watersheds, Harr et al. (1982) suggest that the soil hydraulic properties should be nearly identical as well.
The H. J. Andrews Experimental Forest is underlain exclusively by bedrock of volcanic origin. Three geologic formations have been mapped for the HJA and correspond roughly with elevation (Swanson and James 1975). Little Butte Formation bedrock (< approximately 760 m elevation), dated as Oligocene to lower Miocene, consists of massive tuffs and breccias derived from mudflows and pyroclastic flows. Sardine Formation bedrock (760 m to 1200 m), dated as middle to late Micocene, consists of two units: a lower unit containing welded and non-welded ash flows (notably less altered than underlying Little Butte rocks of similar lithology), and an upper unit containing basalt and andesite lava flows. Andesitic and basaltic lava flows (>1200 m), termed "Pliocascade" Formation, were deposited during the Pliocene and overlie Sardine Formation material. Watersheds 6, 7, and 8 range in elevation from 860 m to 1200 m and are underlain by two units of the Sardine Formation (Swanson and James 1975). Basalt and andesite lava flows underlie ridges of all three watersheds and near the outlets of Watersheds 7 and 8. Welded and non-welded ash flow tuffs underlie middle elevations of all three watersheds and the lower elevations of Watershed 6. This rock is of similar lithology as in the middle elevations of the lower watersheds, but is noticeably less weathered. No flow rock is exposed in Watersheds 6, 7, or 8.
Gauged watershed area: 13.0 ha (original surveyed value used in rating equation calculations)
Prior to cutting, the overstory was dominated by Douglas-fir (Pseudotsuga menziesii)and western hemlock(Tsuga heterophylla) trees ranging in age from 100 to 250 years. Understory species communities included vine maple-Oregon grape (Acer circinatum-Berberis nervosa), vine maple-whipplea (Acer circinatum- Whipplea modesta), and rhododendron-Oregon grape (Rhododendron macrophyllum-Berberis nervosa). Pre-treatment: stocking density = 383 stems per ha; basal area=70 m2/ha (std dev 10.5 over 3 1-acre plots)
Typically, snow begins falling in November with peak snow water equivalent storage estimated to occur in Feb-April. Mean annual maximum is about 400-650 mm water equiv. at highest elevation.