In 1960, two random, parallel transects, each about 125 m long, were laid out up and down a 30 percent, SW-facing slope on the watershed. One of the transects was located well within one of the patches (9 ha) that was clearcut in 1962-63, while the other was in undisturbed forest for the entire study. Six equal segments (approx. 25 m each) are established in two strips parallel to the cutting boundary, one strip on either side. Soil moisture stacks were placed at random within each segment, and the stack becomes the center of a 0.16-ac circular plot (6 plots in old-growth, 6 in cutting area, but one plot (plot 7) was lost to road construction in the cutting area). Soil moisture, vegetation cover, and throughfall are measured on each plot. The plots were installed in HJA WS 3 in October 1959. The cutting area was clearcut in winter 1962-1963, completed in February 1963, and broadcast burned in September 1963.
NOTE: Plots 1-6 are in the forest; plots 8-12 are in the clearcut; plot 7 in clearcut was lost to road construction.
In 1960, soil pits were dug andnd a soil moisture stack was installed at a random location near each sample point. Each stack consisted of laboratory-calibrated fiberglas resistance blocks and thermisters at three depths of 6, 18, and 36 in. (30, 60, 120 cm) to monitor soil moisture (in resistance units) and soil temperature. Resistance measurements were taken about every three weeks from mid-spring to mid-autumn in 1960-63, along with bulk soil samples for gravimetric analysis and field calibration of the resistance units. [Three gravimetric samples were taken using the King tube at random locations in the plot. Samples were collected at 0-6, 6-18, and 18-36 in. depths and placed in cans. The gravimetric samples were used to calibrate the Coleman fiberglas soil moisture units.] Due to a constantly shifting calibration, however, the resistance units were abandoned in 1963 in favor of gravimetric samples (1964-65). Conjecture is that fine clays infiltrate the fiberglas units yielding higher soil moisture readings. The gravimetric samples were oven-dried to determine soil moisture content. Bulk density of soil at the measurement depths was determined on installation of fiberglas units. Soil bulk density and soil moisture are used to determine inches of soil water. A neutron probe (Troxler probe and scale) was acquired for more accurate and direct soil moisture measurement and neutron probe measurements (1966, 1967, 1969, 1971, 1974, 1977, 1980, 1983) were taken over a similar seasonal schedule (from April until November). Neutron measurements were taken with a calibrated probe at three randomly located access tubes around each sample point, with gravimetric samples also taken periodically to verify probe results. A new neutron probe was acquired for 1983 measurements. April measurements have been used to measure soil field capacity.
All soil moisture data were converted to percent by volume and cm of moisture values using local soil bulk densities and coarse-fragment contents. Field capacity moisture contents were measured using soil cores collected 3-10 days following rain in winter. Plant-available moisture content was calculated as the field capacity moisture content minus the moisture content at -15 atm, using the pressure membrane method (Richards 1965). Available moisture capacity has since been more carefully defined to consider plant uptake of moisture at potentials lower than -15 atm (Flint and Childs 1984). Moisture at these lower potentials may only represent 2-4 percent water by volume (Flint 1983), however, so the data are still considered representative of nearly all of the available moisture in these soils.
Vegetation type and cover was measured on four, 4.0 square meter plots (6.7 ft squares (milacre)) orthogonally located within the circular plot around each sample point on the transect in the treatment area. Herbs, bare ground, and litter are assessed on macro plots occupying one quadrant (1/4 milacre). This macro plot is divided into nine systematically located 0.1 sq. m micro plots and used to measure herb and low shrub (less than 60 cm tall) cover, whereas the entire 4.0 m(square) plot was used for measurements of trees and vegetation >60 cm tall. Vegetation surveys were conducted in late July or early August starting in 1964, and subsequently in the same years as the soil moisture measurements. Data for individual species were stratified into herb and low shrub or tree and tall shrub cover consistent with Dyrness (1973). Data from different transects used by Dyrness (1965) provide estimates of plant cover in 1963.
One interception gage is located in each plot. Each gage is rotated around plot circumference at the four cardinal direction points. Gages are rotated at each collection time. A precipitation gage (no vegetation obstructions) is located on Plot 11 and serves as the standard for all soil moisture plots.
Dyrness, C. T. 1965. Soil surface condition following tractor and high-lead logging in the Oregon Cascades. Journal of Forestry. 63(4): 272-275.
Dyrness, C. T. 1973. Early stages of plant succession following logging and burning in the western Cascades of Oregon. Ecology. 54(1): 57-69.
Flint, A. L. 1983. Soil physical properties and available water capacity of southwest Oregon forest soils. M.S. Thesis. Oregon State University. Corvallis, Oregon.
Flint, A. L. and S. W. Childs. 1984. Physical properties of rock fragments and their effect on available water in skeletal soils. In: Erosion and productivity of soils containing rock fragments. SSSA Spec. Pub. No. 13. p 91-103. Soil Sci. Am., Madison, Wisconsin.
Richards, L. A. 1965. Physical condition of water in soil. In C. A. Black, D. D. Evans, J. L. White, L. E. Ensminger, and F. E. Clark. eds. Methods of soil analysis: Part I. A.S.A. Monograph 9. p 371-375. Amer. Soc. Agron., Madison, Wisconsin.
6 .016 acre plots in the leave strip area of old-growth, and 5 (originally 6) .016 acre plots in the adjacent clearcut
The study area is located within a 101 ha watershed (WS3) in the H.J. Andrews Experimental Forest, 60 km east of Eugene, Oregon (Lat. 44 degrees 13 minutes N, Long. 122 degrees 15 minutes W). The watershed extends from 500 to 1070 m in elevation, with slopes averaging about 53 percent (Fredriksen 1970). Soils in the watershed have developed from the local andesitic breccia bedrock found at 1-4 meters, and are predominantly classified as loamy, skeletal Typic Dystrochrepts. Some baseline physical properties of the soil are given in Table 1. Weather data collected since 1952 on an adjacent watershed show a mild, humid, temperate climate with an average annual temperature of 9.4 degrees Centigrade, and an average annual precipitation level of about 225 cm. Precipitation normally occurs as rain, which is concentrated between October and May. Summers are typically cool (ave. July temp. = 20.6 degrees C) and dry (Rothacher 1965).
Old-growth (300-500 yr) Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) dominates the undisturbed forest on the watershed, accompanied by numerous western hemlock (Tsuga heterophylla (Raf.) Sarg.) of various ages. Local site productivity for Douglas-fir is moderate (43 m height at 100 yr), and when the study began (1960), the basal area of the Douglas-fir-Hemlock stand was about 90 m(square)/ha. Major prelogging understory communities on the watershed were rhododendron-salal (Rhododendron macrophyllum-Gaultheria shallon), vine maple-salal (Acer circinatum-Gaultheria shallon), vine maple-Oregon grape (Acer circinatum-Berberis nervosa), cutleaf goldthread (Coptis laciniata), and swordfern (Polystichum munitum) (Dyrness 1973).
In the winter of 1962-63, 25 percent of the watershed was clearcut logged with a high-lead cable system in three patches of 5, 9, and 11 ha. The logged patches were broadcast burned in September of 1963, followed soon by planting of Douglas-fir seedlings. Log yarding resulted in largely minor and shallow soil disturbance in the cutover areas (Dyrness 1965), and moist conditions during burning produced only light, discontinuous charring of the surface litter (Fredriksen 1970).
