Plot establishment. In 1962 (prior to logging), 194 permanent understory plots (2 x 2 m, slope corrected) were established across the two watersheds: 133 in WS1 and 61 in WS3. Plots are spaced at 30.5 m slope-corrected intervals along six transects in WS1, and along two to four transects in each of the three harvest units in WS3. Plots were not established if they fell in a stream channel, on a rock outcrop, or on a roadbed (present in WS3).
Plot classification and environmental characteristics. Prior to logging, plots were assigned to (1) one of six plant communities reflecting the dominant understory species, and (2) one of six soil types reflecting parent material, soil depth, and profile development (for details see Rothacher et al. 1967, Dyrness 1969). The plant communities represent a strong gradient in soil moisture availability. Ranging from “dry” to “moist” these are Corylus cornuta - Gaultheria shallon, Rhododendron macrophyllum - Gaultheria shallon, Acer circinatum - Gaultheria shallon, Acer circinatum - Berberis nervosa, Coptis laciniata, and Polystichum munitum.
In 2004, plot locations (UTMs) were determined using a differentially corrected Trimble GPS. Direct readings were made on 91 plots; the remaining locations were interpolated. The elevation, aspect, and slope of each plot were determined from GPS locations and a 10-m digital elevation model and later, a 1-m LIDAR coverage.
Disturbance history. Both watersheds were logged and broadcast burned. All 96 ha of WS1 was clearcut logged over a 4-year period (1962-1966). Logs were yarded with sky-line cables that required no road construction within the watershed. Slash was burned in fall 1966. In WS3, three harvest units (5, 9, and 11 ha, totaling 25% of the watershed) were logged over winter 1962-1963. A high-lead cable system was used to yard logs to three roads constructed within the watershed. Slash was broadcast burned in fall 1963, initiating succession 3 years earlier than in WS1.
Following burning, each plot was assigned to one of four soil disturbance classes representing a gradient in disturbance intensity (Dyrness 1973: (1) undisturbed: minimal mixing of mineral soil and litter but no evidence of fire; (2) disturbed/unburned: soil disturbance from logging evident but no evidence of fire; (3) lightly burned: surface litter charred by fire but not completely removed; (4) heavily burned: surface litter completely consumed by intense fire exposing highly colored mineral soil.
Reforestation. The history artificial seeding and planting differ between watersheds. In WS1, Pseudotsuga menziesii was aerially seeded in October 1967; 10 ha were reseeded in October 1968. Early establishment was generally poor and in April/May 1969, 2-year-old Pseudotsuga were planted at 3-m spacing. Because survival was poor, 40 ha of the south-facing slope were replanted at 2.4 m spacing in April 1971. In WS3, 3-year-old Pseudotsuga were planted between March and May 1964. Despite aerial seeding and planting in both watersheds, a large percentage of Pseudotsuga—and all stems of all other coniferous and hardwood species—regenerated naturally by seeding or resprouting.
Recent snow-down and wildfire events. Both watersheds have experienced recent windthrow related to snow-loading of tree canopies (2019 and 2020) and large portions of WS1 burned during the Holiday Farm Fire (September 2020). Four plots in WS1 were lost during the creation of fire lines.
Rothacher, Jack; Dyrness, C. T.; Fredriksen, Richard L. 1967. Hydrologic and related characteristics of three small watersheds in the Oregon Cascades. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 54 p.
Dyrness, C. T. 1969. Hydrologic properties of soils on three small watersheds in the western Cascades of Oregon. Res. Note PNW-111. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 17 p.
Dyrness, C. T. 1973. Early stages of plant succession following logging and burning in the western Cascades of Oregon. Ecology 54: 57-69.
Understory sampling. Initially (1962-1979), shrub and tree species’ cover were estimated in the full 2 x 2 m understory plot; cover of herbaceous species was estimated in each of nine, 0.33 x 0.33 m subplots, from which frequency and mean cover were estimated for each plot. Any additional herbaceous species present in the full plot were also recorded. Plots were sampled annually through 1972 or 1973 but less frequently thereafter (every 2-6 years).
After 1979, cover of all species (herbaceous and woody) was estimated in the full 2 x 2 m plot. Additional stem measurements (basal diameter or height) were also taken for shrub and fern species rooted in each plot to estimate above-ground biomass (for details, see “Sampling Protocols” listed under “Related Materials ”). In 1979, four additional 2 x 2 m understory plots were established to increase the sampling intensity at each location. These “satellite” plots were placed on perpendicular radii at approximately 5 m from the plot center (see “Plot layout” listed under “Related Materials”). Measurements of these satellite plots were terminated after 1987, but the original center plots have been sampled continuously. Four plots in WS1 were compromised by creation of fire lines during the Holiday Farm Fire of 2020; these plots are no longer sampled. For a complete history of understory sampling by plot see “TP073_sampling history” under “Related Materials”.
Overstory sampling. In 1979/1980, a permanent tree plot was established at the location of each understory plot. Tree plots are circular and 250 m2 in area (8.92 m radius, non-slope corrected). At each remeasurement all previously tagged trees (conifers or hardwoods) greater than or equal to 1.4 m tall are measured for diameter and recorded as live or dead. Any new recruits (ingrowth) are tagged and measured. For each dead stem, an assessment is made on probable cause of mortality (e.g., suppression, mechanical damage, pathogen, etc.) and the physical condition is described (e.g., stem intact, uprooted, or snapped). Since establishment, tree plots have been remeasured at 2- to 6-year intervals.
To ensure continuity of the measurement point on each tree, conifers with a dbh of at least 2 cm are nailed at breast height. For smaller trees that cannot hold a nail, tags are placed on zip-ties looped onto a sturdy branch, and diameter is measured at the base (dba). Once trees are large enough to be nailed, the tag is transferred from zip-tie to nail and both the dba and dbh are measured.
Hardwoods (typically stump sprouts forming “clumps”) were tracked initially in one of two ways: stems were tagged and measured at dbh if they were greater than or equal to 5 cm dbh. Smaller stems were tallied by diameter class (0.1-3.0 cm or 3.0-4.9 cm dbh). If tagged and tallied stems were physically associated they were assigned a shared “clump” number (number of the tagged tree). After 2001, all hardwood stems were tagged and measured for dbh or dba, similar to the procedure for conifers.
Important historical note: In summer 2019, a reduced tree-sampling protocol was employed to assess the extent of snow-related tree damage/mortality incurred during the previous winter. Sampling was limited to an assessment of survival/mortality of trees greater than or equal to 5 cm dbh at the previous measurement (2017). Measurements of diameter were not taken and smaller trees (<5 cm dbh) were not assessed.
In 2020, four plots in WS1 were compromised by creation of fire lines during the Holiday Farm Fire; these plots are no longer sampled. For a complete history of overstory sampling by plot see “TP073_sampling history” under “Related Materials”.
For additional details on understory sampling see Halpern (1988, 1989), Halpern and Franklin (1990), and Halpern and Lutz (2013). For additional details on overstory sampling, see Lutz and Halpern (2006). For detailed descriptions of field sampling procedures, see recent “Sampling protocol” documents listed under “Related Materials”.
For plant community and soil type definitions and descriptions see:
