Soils of the - Agriculture and Agri-Food Canada

during the growing season (May to September), average monthly precipitation is frequently less than 50 mm ,
especially in areas at low elevations and near to the ocean .
Table 1 shows the average May to September potential evapotranspiration (PE), average seasona l
precipitation (P) and their difference (P-PE) for several stations in or near the Langley-Vancouver .map area . I t
indicates that potential evapotranspiration exceeds precipitation for almost all low elevation locations and that ,
particularly in the coarser-textured soils, drought conditions are likely to develop . In the mountains (Coquitla m
Lake), potential evapotranspiration tends to be lower and precipitation higher, making soil moisture deficiencie s
less likely.
TABLE 1
Average seasonal (May-Sept) potential evapotranspiration (PE) ,
average seasonal precipitation (P) and difference (P-PE )
for several stations in or near the Langley-Vancouver map are a
Station
Avg . Seasonal
PE (mm)
Avg . Seasonal
P (mm)
P-P E
(mm)
Elevatio n
(M)
Abbotsford (airport) 381 306 - 75 6 0
Agassiz (CDA) 340 369 29 1 5
Chilliwack 382 375 -7 7
Coquitlam Lake 327 639 312 16 1
Hope 368 303 -65 3 8
Vancouver (Int. Airport) 379 221 -158 5
White Rock 336 231 -105 61
Source-Air Studies Branch, B .C. Ministry of Environmen t
The longest frost-free periods in Canada occur on the Pacific Coast of which the Langley-Vancouver ma p
area is part . Appendix C contains frost data for several stations in the region and shows that the average f rostfree
period varies from about 170 to 210 days, depending on location . In the mountains, increasing elevation s
produce corresponding decreases in frost-free period . Growing degree days (>5° C) range from about 1700 t o
2100 days for most lower elevation locations .
Hours of bright sunshine occur mainly during the summer months . Out of about 1925 hours per year a t
Vancouver International Airport, 1420 hours occur during May to September, inclusive .
VEGETATIO N
The native vegetation in the Langley-Vancouver map area reflects the relatively warm temperatures an d
high rates of precipitation that occur. The lower elevations (below about 500 m) lie in the Coastal Douglas-fi r
Biogeoclimatic Zone (Krajina, 1965) or, by Rowe's classification, in the Strait of Georgia and Southern Pacifi c
Coast sections of the Coast Forest Region (Rowe, 1972) . The dominant natural tree species are coast Douglas -
f ir, western hemlock and western red cedar . In many areas this climax forest has either been removed or strongl y
altered by logging and land clearing . Red alder and bigleaf maple often vigorously invade logged areas, to th e
detriment of coniferous regeneration . Arbutus occurs along the coastal fringe and black cottonwood is usual i n
alluvial areas where Sitka spruce is also present .
Between about 500 and 1000 m elevation occurs Krajina's Coastal Western Hemlock Zone (this zone is stil l
part of Rowe's Coastal Forest Region). In this cooler and moister climate, western hemlock dominates althoug h
western red cedar also occurs as does coast Douglas-fir at the lower elevations . Pacific silver fir is common a t
the upper elevations and yellow cedar is usually also present .
From about 1000 m elevation to tree-line occurs the Mountain Hemlock Zone (Krajina) or the Coasta l
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