Wickersham CALM Site

Wickersham CALM Site (U 17)

The Wickersham CALM site was established as part of a major fire-effects study conducted by the Institute of Northern Forestry following the 1971 Wickersham Fire.

As part of these studies a series of thaw probe lines were established to follow the changes in the active layer as a result of the fire and fireline construction. Details of the fire and related studies were presented by Viereck and Dyrness (1979). The data for the Wickersham CALM site comes from an undisturbed black spruce stand that was established as a “control” for the studies of active layer changes in the burned and fireline areas.

The Wickersham site is approximately 50 km northwest of Fairbanks and adjacent to the Elliot Highway. (65 o 10’N: 147 o 54’W) The probe line is at an elevation of 335 m near the foot of a long west-facing slope. The vegetation along the probe line is an open black spruce forest type (Open Picea mariana/Ledumgroenlandicum/Sphagnum spp-Cladoniaspp community) (Viereck et al 1993). The black spruce have a density of 1240 trees/ha and 45% canopy cover. Average diameter of the trees in 1971 was only 5.2 cm. A detailed description of the vegetation at the site can be found in Viereck, 1982. The soil at the site is a Saulicch silt loam (a Histic Cryaquept (USDA 1975). These are poorly drained soils formed of a silty loam more than 75 cm in depth with a shallow active layer. There is a moss-litter layer (01 and 02) of 25 to 30 cm underlain by approximately 10 cm of a dark grayish-brown silty loam A horizon over a frozen C horizon of olive-gray silty loam.

Methods
A probe line 20 meters long was established parallel to the slope: 10 probing sites at 2-meter intervals were permanently marked along the line. A trail was established below the line to avoid disturbance of the vegetation at each of the probe sites. For the first four years of the study the active layer was measured at two-week intervals. Starting in 1975 soil temperatures were also taken at two-week intervals at depths of 5, 10, 20, and 50 cm with a steel probe with a thermistors at the tip. In 1978 a set of thermistors was installed near one end of the probe line at depths of 5, 10, 20, 50, and 90 cm and were read weekly or biweekly. In addition, in October of 1978 a thermograph and weather station were installed at the site to record air temperatures. Snow depth was measured throughout the winter using two permanent snow poles. These weekly observations were continued through October of 1983. After that the active layer was measured at the ten points along the probe line once a year, usually in mid September.

Results:

By comparing the air temperatures for the period that the site was instrumented with the Fairbanks Airport records it appeared that at the Wickersham site the mean annual temperature was about 1.7 o C colder than the -3.5 o C of the Fairbanks Airport and was thus estimated to be –5.2 o C (Viereck 1982). Snowfall was about 25% more than that at the Fairbanks Airport. The annual thaw at the Wickersham site was approximately 10 cm shallower than at the Pearl Creek site (Figure XX). There appears to be no increase in thaw depths over the 29 years of the study. Shallow thaw years which result from low snow years the previous winter are similar to those found at the Pearl Creek site, i.e. 1976, 1997 and 1999. There is less agreement in the pattern of deeper thaw years: however the two sites do show similar annual fluctuations, especially during the period from 1990 to 2000. As with the Pearl Creek site there appears to be little to no correlation between annual depth of thaw and the Accumulated Thawing Degree Days (DDT).