The Sub-Boreal-Pine-Spruce (SBPS) zone
occupies the high plateau regions of the west-central interior (mostly
in the Chilcotin west of Williams Lake). Elevations are typically
between 900m and 1250m in the eastern part of the zone and 1150-1500m
in the southern part of the zone (Steen and Coupe 1997). This zone
occurs above the Interior Douglas-fir zone and Subboreal Spruce zone
and below the Montane Spruce zone.
The climate of the SBPS is characterized
by cold, dry winters and cool summers. Mean annual precipitation ranges
between 335-580mm and mean annual temperature ranges from 0.3-2.7oC
(Meidinger and Pojar 1991). Approximately 30-50% of the annual precipitation
falls as snow (Steen and Coupe 1997). The dry climate is influenced
strongly by the rainshadow of the Coast Mountains.
Steen and Coupe (1997) recognize four subzones
in the SBPS. The driest subzone (SBPSxc) occurs adjacent to the Coast
Mountains and is influenced the greatest by rainshadow. One dry subzone
(SBPSdc) and two moist subzones (SBPSmc and SBPSmk) occur in the northern
and eastern end of the zone range.
Soils are generally quite young in this
region and are represented by the Brunisolic and Luvisolic orders.
While many soils are coarse textured sandy loams, clay enrichment
can occur resulting in slow drainage. This zone is typified by very
slow decomposition of organic matter and soil development processes.
Humus forms reflect this environment and are well-developed Mors.
Ecosystems
The dominant tree species in this zone
is lodgepole pine which has resulted largely from a frequent fire
return interval of large scale, stand-replacing fires. White spruce
occurs less frequently and is restricted to wet sites or rarely occurring
old forest stands that have been missed by several fire cycles. Meidinger
and Pojar (1991) reports that, although white spruce is the theoretical
climax tree species in this zone, forest stands tend to be dominated
by lodgepole pine and never actually pass through succession to a
white spruce dominated ecosystem.
In the drier subzone, white spruce is
virtually absent and is replaced by lodgepole pine and subalpine fir.
Much of the understory on zonal sites is dominated by Pinegrass (Calamagrostis
rubescens) and kinnikinnick (Arctostaphylos uva-ursi). Terrestrial
lichens such as Cladonia spp and Cladina spp are also dominant. In
the SBPSdc subzone, white spruce becomes more dominant along with
red-stemmed feathermoss (Pleurozium schreberi). In the two moist subzones,
white spruce is more dominant and the understory is represented by
greater cover of mosses (Steen and Coupe 1997).
Wetlands are common in this area due to
the poor drainage patterns resulting from the subdued topography and
fine-textured soils. Common wetlands include fens, shrub carrs, swamps
and wet meadows.
Resources
Timber harvesting in the SBPS is relatively
common and has been quite high in response to Mountain Pine Beetle
outbreaks in the region. However, low productivity has resulted in
dense stands of small diameter trees over wide areas. Many of the
trees have diameters ranging between 15-25cm and heights between 15-25m.
Agriculture is often limited due to the
short growing season. Fishing, hunting and horseback riding are all
common activities in this region. Many guide-outfitting and guest
ranch operations are active in this region.
References
Meidinger, D. and Pojar, J. 1991. Ecosystems
of British Columbia. British Columbia Ministry of Forests. 330 pp.
http://www.for.gov.bc.ca/hfd/pubs/Docs/Srs/SRseries.htm
Steen, O.A., and R.A. Coupé. 1997.
A field guide to forest site identification and interpretation for
the Cariboo Forest Region. B.C. Min. For., Res. Br., Victoria, B.C.,
Land Manage. Handb. No. 39. http://www.for.gov.bc.ca/hfd/pubs/docs/lmh/lmh39.htm
Images © Ministry of Forests and Derek
Marcoux
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