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Plateau (between 1000 and 1500 metres) contributes to the cold climate. As a result, the
growing season is short, and frost can occur at any time of the year at all elevations. The
Plateau is also strongly affected by the Coast Mountains rainshadow, which results in very
dry conditions, including summer moisture deficits – a significant factor effecting soil and
plant productivity. The season of moisture deficit can be from May to September, which
includes most of the growing season. The dry conditions also result in frequent wildfires
across the landscape of the Plateau.
• The Chilcotin Ranges part of the study area also has a dry, continental climate in the
rainshadow of the Coast Mountains, but receives more precipitation than the Chilcotin
Plateau landscape due to moist, coastal air pushing through the lower mountain passes.
Summer moisture deficits are lower and the season of deficit is shorter than in the
Chilcotin Plateau. However, the colder temperatures in this area significantly limit plant
growth, with similar overall effects as the moisture deficits on the Plateau.
The strong climatic gradient that occurs from the moist coastal mountains to the dry
Chilcotin Plateau results in a diversity of ecosystems, and plant and animal life. The study
area includes some of the coldest and driest forested landscapes in the province.
4.2. Biogeoclimatic (BEC) Zones
Steen and Coupe (1997) describe the cold, dry climate of the XGCA in their discussion of
biogeoclimatic subzones in the Cariboo Forest Region. The biogeoclimatic classification
system groups forests in British Columbia into areas of broadly uniform climate, geology,
and biology. The following comments are drawn from the work of Steen and Coupe, as
extracted
by Hammond and others (2004), and highlight the exceptionally harsh climate of
the
study area
(Figure 3):
• The Very Dry Very Cold Engelmann Spruce Subalpine Fir subzone (ESSFxv) has a
very cold, very dry climate. Although no climatic data is available, the vegetation
indicates that the ESSFxv is probably the driest area of the ESSF zone in British
Columbia. Due to relatively low humidity and clear skies,
overnight radiation cooling
is intense, and frosts occur very frequently during the growing season.
• The Very Dry Very Cold Montane Spruce subzone (MSxv) is the coldest and driest
Montane Spruce subzone in British Columbia, and is one of the least productive
biogeoclimatic units for tree growth. Winters are cold and summers are cool with
frequent growing‐season frost.
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