The Interior Douglas-fir Zone (IDF) occupies
mid to low elevations throughout the southern and central interior
of British Columbia. Elevations ranges between 300m-1450m. The IDF
occupies sites that range from wet coast/interior transition to the
interior wetbelt. Generally, this zone occurs above the Ponderosa
Pine zone and below the Montane Spruce zone. In the coast transition,
the IDF can occur below the Coastal Western Hemlock zone and in the
north it can occur below the Sub Boreal-Pine –Spruce zone and
Sub Boreal-Spruce zone.
The IDF typically dominates an area that
is in the rainshadow of the major mountain ranges of BC. In the west,
it is the rainshadow of the Coast Mountains and toward the eastern
end of the range, it is the rainshadow of the Columbia and Purcell
Mountains. Annual precipitation ranges from 295-750mm and mean annual
temperatures ranges between 1.6-9.5oC (Meidinger and Pojar 1991).
Meidinger and Pojar (1991) recognize seven
subzones in the IDF. They range from the very dry, hot (IDFxh) to
the wet, warm (IDFww). The location of the various subzones varies
due to subtle changes in local climate.
Soils range from Chernozems to gray luvisols
and eutric brunisols. Humus forms will likely range between mulls
and moders. Mors humus forms occur in wetter sites and on north facing
slopes. Morainal, colluvial, glaciofluvial, glaciolacustrine and fluvial
parent material occur most frequently.
Ecosystems
The IDF is comprised of open to closed
forests of Douglas-fir, Ponderosa pine Lodgepole pine (absent from
drier regions) and hybrid white spruce. Open grasslands are common
in the drier regions. In some situations, these are classified as
phases of biogeoclimatic variants (eg IDFdk1a) (Lloydd et. al. 1990).
Ponderosa pine occurs on dry sites in the southern part of the range
and western redcedar is sometimes found in moist draws in the drier
parts of the zone and on zonal sites in the transitional areas with
the interior wetbelt. Lodgepole pine and Trembling aspen (Populus
tremuloides) occur commonly as seral species in all regions except
where it is dry. Pinegrass (Calamagrostis rubescens) is a common understory
species throughout all of the subzones.
Very dry subzones have an understory consisting
of pinegrass (Calamagrostis rubescens), Birch-leaved spirea (Spiraea
betulifolia), bluebunch wheatgrass (Pseudoroegneria spicata), stonecrop
species (Sedum spp.) and red-stemmed feathermoss (Pleurozium schreberi)
and Peltigera lichens (Peltigera spp.).
Dry subzones are typified by the occurrence
of lodgepole pine and western larch in the overstory and twinflower
(Linnaea borealis), falsebox (Paxistima myrsinites) in the understory.
The moist and wet subzones typically have
understory species such as thimbleberry (Rubus parviflorus), Douglas-maple
(Acer glabrum), Hooker’s Fairybells (Prosartes hookeri), beaked
hazelnut (Corylus cornuta) and black huckleberry (Vaccinium membranaceum).
Grasslands within this zone are typified
by communities of bluebunch wheatgrass, Idaho fescue (Festuca idahoensis),
Spreading needle grass (Acnatherum richardsonii), Rough fescue (Festuca
campestris), Junegrass (Koeleria macrantha) and Pasture sage (Artemesia
frigida). Degraded sites (usually from overgrazing) are dominated
by Cheatgrass (Bromus tectorum), Knapweed (Centaurea spp.) and Oyster
plant (Tragopogon spp.)
Resources
Forestry is an important use of the resources
in the IDF. Silvicultural options are wide ranging on these sites
and are often well-suited to uneven aged management and various forms
of shelterwood cutting. This is largely due to the moderate shade
tolerance of Douglas-fir which makes it suitable for regeneration
under its own canopy. Interior Douglas-fir is a prized species for
sawlog production due to the slow growing rate which provides strong
wood with tight annual ring growths.
Cattle grazing is common and extensive
areas are under grazing leases. Pinegrass is the dominant species
for forage throughout the zone.
Recreation opportunities include many popular
sports such as hunting, fishing hiking, biking and cross-country skiing.
References
Lloyd, D., K. Angove, G. Hope, and C. Thompson.
1990. A guide to site identification and interpretation for the Kamloops
Forest Region. B.C. Min. For., Res. Br., Victoria, B.C., Land Manage.
Handb. No. 23. http://www.for.gov.bc.ca/hfd/pubs/docs/lmh/lmh23.htm
Braumandl, T.F. and M.P. Curran. 1992.
A field guide for site identification and interpretation for the Nelson
Forest Region. B.C. Min. For., Res. Br., Victoria, B.C., Land Manage.
Handb. No. 20. http://www.for.gov.bc.ca/hfd/pubs/docs/lmh/lmh20.htm
Images © Derek Marcoux and Evan MacKenzie
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