Soils of the - Agriculture and Agri-Food Canada

STRACHAN SOILS (SN)
Location and Extent : Strachan soils are common on the lower mountain slopes, mainly in the Coast Range .
Although only 260 ha of pure map units are mapped, soil complexes dominated by Strachan soils occup y
23 720 ha . The complexes are mainly with Burwell and Cannell soils and less commonly, with Eunice, Paton ,
Sayres and Palisade soils .
Topography and Elevation : Strachan soils are very steeply to steeply sloping . Slope gradients vary from 2 0
to 70 percent but mostly are between 40 and 60 percent . Elevations range from about 150 to 700 m above se a
level .
Parent Material and Texture : Strachan soils have developed from moderately coarse textured glacial til l
modified in the upper part by colluvial action, or capped by colluvium . Surface and subsurface textures are
sandy loam or gravelly sandy loam containing numerous stones and some boulders . The subsoil is dense ,
compact, cemented, stony gravelly sandy loam or gravelly loamy sand . Bedrock occurs at depths deeper than
1 m .
Soil Moisture Characteristics : Strachan soils are mostly moderately well drained with some well draine d
inclusions . They are moderately to rapidly pervious in the surface and subsurface but this decreases to slowl y
pervious in the cemented subsoil . Variable amounts of telluric seepage flows along the surface of the cemente d
layer, mainly during and after heavy rain or during snowmelt . There is moderate surface runoff and the wate r
holding capacity is moderate .
General Soil Description : Strachan soils usually have 10 to 20 cm of organic forest litter on the soil surface ,
most of which is black to dark reddish brown, matted to amorphous and well to partially decomposed . Th e
organic surface layer is underlain by a gray to dark reddish gray, strongly leached, sandy layer from 2 to 5 c m
thick . The leached layer is abruptly underlain by about 40 cm of friable, weakly to moderately structured, dark
reddish brown to dark brown, sandy material containing 10 to 15 percent, variably distributed organic matte r
and usually, a few, hard, spherical concretions . Under this is about 50 cm of weakly structured, friable, reddishbrown
to yellowish-red, sandy material which contains concentrations of roots in the lower part as well a s
variable amounts of seepage . Abruptly underlying this is grayish-brown to olive-gray, very firm, massive ,
strongly cemented, sandy material containing common, brownish to yellowish or reddish mottles . Gradation t o
unweathered, brownish-gray or olive-gray glacial till occurs below about 150 cm . Soil reactions are extremel y
acid in the upper 50 cm then gradually grade to medium or very strongly acid in the lower subsoil . Soi l
classification is Duric Ferro-Humic Podzol.
Commonly Associated Soils : Burwell and Cannel) soils are usually closely associated with Strachan soils .
Burwell soils are generally similar to Strachan soils but usually occur on lower slope or depressional landscap e
positions and are imperfectly drained . Cannell soils differ from Strachan soils by being underlain by bedroc k
within 100 cm of the surface .
Vegetation : The natural vegetation on Strachan soils is dominantly coniferous and includes western hemlock ,
western red cedar and coast Douglas-fir with mountain hemlock and yellow cedar also sometimes present a t
the soils' upper elevational range . Various deciduous species, including red alder, tend to invade logged an d
other severely disturbed areas . Rooting is generally unimpeded to about 100 cm depth but is severely restricte d
below that by the dense, cemented subsoil .
General Land Use Comments : (1) Strachan soils are unsuited for agricultural or urban uses due t o
excessive slopes and stoniness . (2) Forest growth is good although moisture deficiencies during the latter part s
of the growing season develop during dry summers . Limited plot data indicates wood production by Douglas-fi r
and western hemlock to be about 9 to 12 m 3/ha/yr. During forest harvesting, special care is required to prevent
surface erosion and to control seepage into road cuts and ditches .
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