TABLE 4. Climatic characteristics for the biogeoclimatic zones of

Range and Mean annual Mean summer Mean precip. Mean precip. Lat. Long. Elevation precip. of driest of wettest Driest Wettest Zone reference precip. ( ° ′ )(° ′) (m) (May-Sept) month month month month station (mm) (mm) (mm) (mm)

AT Old Glory Mtn. 49 09 117 55 2347 755.5 287.0 40.0 84.1 Jul Dec

BG Max 588 335.7 174.5 17.3 55.4 Min 297 205.6 98.0 8.0 27.3 Kamloops 50 40 120 20 379 241.7 111.4 8.0 36.1 Mar Jan

BWBS Max 840 503.7 305.3 24.3 879.0 Min 382 327.1 144.7 8.3 41.1 Fort Nelson A 58 50 122 35 382 451.8 297.9 16.7 84.3 Apr Jul

CDF Max 223 1262.6 238.3 38.6 232.9 Min 8 647.2 107.3 13.4 119.2 Victoria Int'l A 48 39 123 26 19 872.9 141.9 18.1 157.3 Jul Dec

CWH Max 671 4386.8 1162.0 151.0 625.4 Min 0 990.2 159.3 16.8 145.7 Haney UBC 49 16 122 34 143 2140.1 467.8 65.5 331.7 Jul Dec RF Admin

ESSF Max 1862 1995.4 424.5 64.8 297.4 Min 863 514.1 204.6 26.6 57.4 Boss Mountain 52 06 120 53 1532 1177.1 401.6 63.5 140.6 May Dec

ICH Max 1085 1419.0 439.3 57.2 224.3 Min 314 497.7 199.9 21.4 57.8 Revelstoke 51 00 118 12 456 1063.7 325.0 51.4 177.0 Apr Jan

IDF Max 1128 1198.9 290.7 37.6 208.8 Min 122 295.1 107.5 13.5 34.8 150 Mile House 52 07 121 56 738 414.2 214.0 15.8 60.7 Apr Jun

MH Hollyburn Ridge 49 23 123 12 930 2954.3 694.4 106.9 434.8 Jul Dec

MS Max 1554 663.8 252.1 38.5 108.1 Min 1128 380.8 158.2 17.9 45.2 Peachland 49 52 120 00 1520 638.3 197.0 29.3 89.1 Apr Dec Brenda Mines

PP Max 939 604.5 270.3 30.7 77.6 Min 244 319.5 86.3 11.0 34.5 Kelowna 49 54 119 28 354 332.2 136.3 15.3 45.1 Apr Dec

SBPS Max 1219 517.8 299.8 21.1 86.5 Min 914 464.1 242.6 20.8 36.4 Alexis Creek 52 33 123 11 1219 464.1 242.6 20.8 57.6 Apr Jun Tautri Creek

SBS Max 1245 1588.2 352.6 36.8 278.7 Min 488 438.9 188.9 15.2 49.8 Prince George A 53 63 122 40 676 628.3 300.8 27.4 68.2 Apr Aug

SWB Cassiar 59 17 129 50 1078 699.5 275.1 25.7 84.2 Apr Oct

Zone key AT Alpine Tundra IDF Interior Douglas-®r BG Bunchgrass MH Mountain Hemlock BWBS Boreal White and Black Spruce MS Montane Spruce CDF Coastal Douglas-®r PP Ponderosa Pine CWH Coastal Western Hemlock SBPS Sub-Boreal Pine Ð Spruce ESSF Engelmann Spruce Ð Subalpine Fir SBS Sub-Boreal Spruce ICH Interior Cedar Ð Hemlock SWB Spruce Ð Willow Ð Birch

56 TABLE 5. Occurrencea of trees in the biogeoclimatic zones of British Columbia

Gymnosperms BG PP IDF ICH MS SBPS SBS BWBS SWB MH CDF CWH ESSF ATb

Abies amabilis (amabilis ®r) - - - + - - - - - +++ - +++ (+) - A. grandis (grand ®r) - - ++ ++ + - - - - - ++ + - - A. lasiocarpa (subalpine ®r) - - - ++ +++ (+) +++ ++ +++ ++ - + +++ - Chamaecyparis nootkatensis ------+++-++(+)- (yellow-cedar) Juniperus scopulorum (Rocky Mountain juniper) + + ++ - - - + (+) - - ++ (+) - - Larix laricina (tamarack) ------(+)++------L. lyallii (alpine larch) ------++- L. occidentalis (western larch) - + +++ ++ +++ ------+ - Picea engelmannii (Engelmann spruce) - - + ++ +++ - - - - + - - +++ - P. engelmannii x glauca - (+) ++ ++ +++ + +++ - - - - - ++ - (hybrid white spruce) P. glauca (white spruce) - (+) + - + +++ ++ +++ +++ - - - + - P. glauca x sitchensis - - - ++ - - - - - (+) - ++ - - (Roche spruce) P. mariana (black spruce) - - - + - - ++ +++ + - - - - - P. sitchensis (Sitka spruce) ------+++++-- Pinus albicaulis (whitebark pine) ------+--++- P. banksiana (jack pine) ------(+)------P. contorta (lodgepole pine) (+) - +++ ++ +++ +++ +++ +++ ++ + ++ ++ +++ - P. ¯exilis (limber pine) --(+)------(+)- P. monticola (western white pine) --++++-- --+++++- P. ponderosa (ponderosa pine) ++++++++------Pseudotsuga menziesii (Douglas-®r) + ++ +++ ++ +++ + ++ - - (+) +++ +++ + - Taxus brevifolia (western yew) --+++------++++-- Thuja plicata (western redcedar) - (+) ++ +++ + - + - - + ++ +++ + - Tsuga heterophylla (western hemlock) - - + +++ + - (+) - - ++ + +++ + - T. mertensiana (mountain hemlock) - - - + - - - - - +++ - + ++ -

59 TABLE 5. Continued

Angiosperms BG PP IDF ICH MS SBPS SBS BWBS SWB MH CDF CWH ESSF ATb

Acer macrophyllum (bigleaf maple) --+------++++-- Alnus rubra (red alder) ------++++++-- Arbutus menziesii (arbutus) ------+++-- Betula neoalaskana (Alaska paper birch) ------++------B. occidentalis (water birch) + + + (+) - - (+) + ------B. papyrifera (paper birch) + + ++ ++ + - ++ ++ - - + + - - Cornus nuttallii --+------++++-- (western ¯owering dogwood) Populus balsamifera ssp. balsamifera ------+ +++----- (balsam poplar) P. balsamifera ssp. trichocarpa + + + ++ + + ++ + - - ++ ++ + - (black cottonwood) P. tremuloides (trembling aspen) + ++ +++ ++ ++ + +++ +++ + - + + +

Prunus emarginata c c c (bitter cherry) --+++ --+ ---+++-- Quercus garryana ------++(+)-- (Garry oak)

Rhamnus purshiana d (cascara) ---++ ------+++-- a Occurrence classes: +++(abundant); ++(common); +(present but uncommon); (+)(very rare); -(absent). b Tree species occur only in krummholz form in the Alpine Tundra zone. c P. emarginata occurs in these zones, but only rarely as a (small) tree. d Rarely as a small tree.

60 Chapter 14: Sub-Boreal Spruce Zone

by D. Meidinger, J. Pojar, and W.L. Harper

LOCATION AND DISTRIBUTION ...... 210

ECOLOGICAL CONDITIONS ...... 210

NOTES ON CLASSIFICATION ...... 212

SUBZONES ...... 212

SOME REPRESENTATIVE SITE ASSOCIATIONS ...... 213

Hybrid spruce — Huckleberry — Highbush-cranberry ...... 213

Lodgepole pine — Huckleberry — Cladonia ...... 216

Hybrid spruce — Oak fern ...... 216

Hybrid spruce — Devil’s club ...... 217

WILDLIFE HABITATS ...... 217

RESOURCE VALUES ...... 220

LITERATURE CITED ...... 221

209 LOCATION AND DISTRIBUTION

The Sub-Boreal Spruce zone (SBS) is the montane zone dominating the landscape of the central interior of British Columbia (Figure 50). It occupies the gently rolling terrain of the Nechako and Fraser plateaus and the Fraser Basin and fingers into more mountainous areas along its western, northern, and eastern boundaries. The SBS is found over a wide latitudinal range, from 51° 30′ to 59°N latitude. The zone generally occurs from the valley bottoms to 1100-1300 m elevation. The SBS adjoins the Boreal White and Black Spruce zone in the north, the Interior Cedar — Hemlock zone in the wetter areas to the northwest and east, the Sub-Boreal Pine — Spruce zone in the dry southwest, and the Interior Douglas-fir zone in the south. The Engelmann Spruce — Subalpine Fir zone is the subalpine zone above the SBS.

ECOLOGICAL CONDITIONS

The climate of the SBS is continental, and is characterized by seasonal extremes of temperature; severe, snowy winters; relatively warm, moist, and short summers; and moderate annual precipitation (Figure 51 and Table 4). In contrast to the boreal, sub-boreal climate is slightly less continental, thus slightly warmer in January and cooler in July (Table 4). Sub-boreal winters are shorter and the vegetative season slightly longer with, in some cases, lower evapotranspiration. Mean annual temperature of the SBS ranges from 1.7 to 5°C. Average temperature is below 0°C for 4-5 months of the year, and above 10°C for 2-5 months. Mean annual precipitation data from long-term stations ranges from 440-900 mm, of which perhaps 25-50% is snow. Short-term data indicate that mean annual precipitation can range from 415 to 1650 mm in the SBS. The SBS is part of the Canadian Boreal Forest Region (Krajina 1965). Krajina’s original concept of the SBS was expanded southward following the work of Annas and Coup´e (1979). Recently, a new zone, the Sub-Boreal Pine — Spruce zone (SBPS), was recognized in the driest, coldest parts of the former SBS in the south and southwest. We now consider the forests of the SBS as broadly transitional between the true montane forests of Douglas-fir to the south; the drier, colder pine — spruce forests to the southwest; boreal forests to the north; and subalpine forests at higher elevations. Upland coniferous forests dominate the sub-boreal landscape. Hybrid white spruce (Picea engelmannii x glauca) and subalpine fir are the dominant climax tree species. Lodgepole pine, a seral species in the SBS, is common in mature forests in the drier parts of the zone and both lodgepole pine and trembling aspen pioneer the extensive seral stands. Paper birch is another pioneer tree, often on moist, rich sites. Douglas-fir is usually a long-lived seral species in the SBS, occurring abundantly on dry, warm, rich sites and as a consistent, although small, component of many mesic forests, especially in the southeastern part of the zone. Black spruce also occurs occasionally in climax upland forest.

210 FIGURE 50. Sub-Boreal Spruce zone.

FIGURE 51. Representative climatic diagram for the Sub-Boreal Spruce zone.

211 Upland soils are primarily from the Luvisolic, Podzolic, and Brunisolic soil orders. Podzols and Brunisolic and Orthic Gray Luvisols are the most common soils found on the abundant morainal deposits. Imperfectly to poorly drained sites in the SBS typically have Gleysols or gleyed subgroups of Luvisols, Podzols, or Brunisols. Alluvial forests of black cottonwood, often with a minor component of spruce, occur to a limited extent on active floodplains of the major streams and rivers. Wetlands are common and dot the landscape in poorly drained, postglacial depressions or river ox-bows. Wetland community types include Carex (sedge) marshes, shrub fens of Betula glandulosa (scrub birch), B. pumila (swamp birch), and Salix spp. (willows), treed fens and swamps with black and hybrid white spruce, and black spruce — Sphagnum bogs. Acidic, nutrient-poor bogs are less common than the richer wetland types (marshes, fens, and swamps). Tamarack is a rare species in the SBS and occurs in only a few fens and swamps of the Nechako, Chilako, and Blackwater drainages. Natural grassland and shrub-steppe are uncommon in the SBS, occurring on some warm, dry sites scattered in the major valleys.

NOTES ON CLASSIFICATION

Krajina (1965) classified much of the southern SBS as a northern subzone of his Cariboo Aspen — Lodgepole Pine zone (CALP), a zone the Ministry of Forests no longer recognizes. The dry, cold areas recognized as part of the SBS before 1988 (i.e., SBSa and SBSb) are now part of the Sub-Boreal Pine — Spruce zone.

SUBZONES

Ten subzones are recognized in the SBS (Table 29). Species characteristic of the warmer, drier subzones include Douglas-fir, Shepherdia canadensis (soopolallie), Calamagrostis rubescens (pinegrass), and Oryzopsis asperifolia (rough-leaved ricegrass) (Figure 52). The moister, cooler subzones typically have subalpine fir, Rubus pedatus (five-leaved bramble), Petasites frigidus var. palmatus (palmate coltsfoot), Streptopus amplexifolius (clasping-leaved twistedstalk), and Gymnocarpium dryopteris (oak fern). Two of the three dry subzones occur on the . The SBSdw is found in a long northwest to southeast band from about Stuart Lake to Canim Lake. The SBSdk is centred around Francois Lake and extends, at lower elevations, from Trembleur Lake in the north, to Ootsa Lake in the south. The third, the SBSdh, is found in the Rocky Mountain Trench and Fraser River valley near Valemount. The moist subzones are found throughout the SBS zone. The SBSmh is in the Fraser and Quesnel River valleys from Alexandria and Hydraulic to Prince George.

212 The SBSmw is mainly in the and the SBSmm is near Clearwater. The ‘‘typical’’ SBS subzone is the SBSmk, ranging from Prince George — Fort St. James to Nation Lakes — Williston Reservoir. The somewhat colder SBSmc occurs at middle elevations from the Blackwater — Ootsa Lake area to Babine Lake and River.

TABLE 29. Synopsis of subzones in the Sub-Boreal Spruce zone (SBS)

Subzone Code Old code

Dry Hot SBS SBSdh (SBSh) Dry Warm SBS SBSdw (SBSk) Dry Cool SBS SBSdk (SBSd) Moist Hot SBS SBSmh (SBSl) Moist Warm SBS SBSmw (SBSc) Moist Mild SBS SBSmm (SBSm1) Moist Cool SBS SBSmk (SBSe2/o) Moist Cold SBS SBSmc (SBSm2/e1/e/i) Wet Cool SBS SBSwk (SBSj/n) Very Wet Cool SBS SBSvk (SBSf)

The wetter subzones are found in the northern and eastern parts of the SBS. Part of the SBSwk occurs around Takla Lake, with the majority occurring in the east from the Peace Arm of Williston Reservoir south to the upper Quesnel River. The SBSvk occurs in mountainous terrain from the Bowron River to north of Mackenzie.

SOME REPRESENTATIVE SITE ASSOCIATIONS

The following four site associations are common on the SBS landscape. They form a typical sequence of ecosystems in the SBSmk (Figure 53).

Hybrid spruce — Huckleberry — Highbush-cranberry The Hybrid spruce — Huckleberry — Highbush-cranberry association is common in the SBS moist and wet subzones. This association is the zonal association in the SBSmk, and occurs on ‘‘drier’’ sites in the SBSwk. It is mostly found on moderately well-drained sites on morainal deposits, although it can also be found on glaciofluvial deposits. Soils are a mixture of Brunisolic Gray Luvisols, Orthic Humo-Ferric Podzols, Orthic and Eluviated Dystric Brunisols, and Orthic Gray Luvisols. Hemimors are the most common humus forms. Mature stands are usually well stocked with hybrid white spruce, lodgepole pine, and subalpine fir. Trembling aspen and paper birch are frequent components of seral stands. The shrub layer is moderately developed with species such as Vaccinium membranaceum (black huckleberry), Rubus parviflorus (thimbleberry), Viburnum edule (highbush-cranberry), and Alnus crispa ssp. sinuata (Sitka alder). Advance regeneration of subalpine fir and some spruce is a consistent feature.

213 214 215 Common herbs include Cornus canadensis (bunchberry), Clintonia uniflora (queen’s cup), Orthilia secunda (one-sided wintergreen), Linnaea borealis (twinflower), Smilacina racemosa (false Solomon’s-seal), Lycopodium annotinum (stiff clubmoss), and Rubus pedatus. The well-developed moss layer is primarily composed of the mosses Pleurozium schreberi (red-stemmed feathermoss), Ptilium crista-castrensis (knight’s plume), and Hylocomium splendens (step moss), and the lichen Peltigera aphthosa.

Lodgepole pine — Huckleberry — Cladonia The Lodgepole pine — Huckleberry — Cladonia association is found on dry, nutrient-poor to -medium sites that generally occur on rapidly drained glaciofluvial, colluvial, or eolian materials in the moist, cool, and cold SBS subzones. Soils are predominantly Orthic Humo-Ferric Podzols and Eluviated and Orthic Dystric Brunisols. Typical humus forms are thin, crusty Xeromors. These ecosystems are characterized by open stands of lodgepole pine with poorly developed shrub and herb layers, and a well-developed ‘‘moss’’ layer dominated by lichens. Tree regeneration is sparse and consists of lodgepole pine with some subalpine fir and hybrid white spruce. The dominant shrub is generally Vaccinium membranaceum (black huckleberry) of poor vigour; Vaccinium myrtilloides (velvet-leaved blueberry) can be abundant in the SBSmk. Arctostaphylos uva-ursi (kinnikinnick) is the dominant species in the herb layer. The ‘‘moss’’ layer is dominated by lichens of the genera Cladina, Cladonia, Peltigera, and Stereocaulon. The most common mosses are Polytrichum juniperinum (juniper haircap moss) and P. piliferum (awned haircap moss).

Hybrid spruce — Oak fern The Hybrid spruce — Oak fern site association is found on fresh, nutrient-poor to -rich sites throughout the moist to very wet subzones. This is the zonal association in the SBSwk. Soils are usually gleyed subgroups of Humo-Ferric Podzols, Brunisols, Gray Luvisols, or Brunisolic Gray Luvisols. Humus forms include Mormoders, Leptomoders, and Hemimors. Subalpine fir and hybrid white spruce are the climax tree species. Viburnum edule, Lonicera involucrata (black twinberry), Vaccinium membranaceum, Ribes lacustre (black gooseberry), and Rubus parviflorus are common in the moderately developed shrub layer. The well-developed herb layer is dominated by Gymnocarpium dryopteris (oak fern); Cornus canadensis, Rubus parviflorus, and Clintonia uniflora are also frequent. The moss layer is dominated by Pleurozium schreberi, Ptilium crista-castrensis, Hylocomium splendens, Bracythecium hylotapetum, and Mnium spp. (leafy mosses; mostly Plagiomnium and Rhizomnium spp.).

216 Hybrid spruce — Devil’s club The Hybrid spruce — Devil’s club site association occurs on moist, nutrient-poor to -very rich sites in the moist to very wet subzones. Such moist, rich habitats typically are found on or at the base of long, steep slopes, in ravines and gullies, and along streams. However, the Hybrid spruce — Devil’s club association occurs on zonal sites in the SBSvk. Soils are generally gleyed subgroups of Gray Luvisols, Brunisols, or Humo-Ferric Podzols; Gleysols also occur. Humus forms can be Hemimors, Humimors, or Mormoders. The tree layer comprises large but widely spaced hybrid white spruce and subalpine fir. The favourable habitat is reflected in excellent tree growth. The dominant shrubs are Oplopanax horridus (devil’s club), Rubus parviflorus, and Lonicera involucrata. The common herbs are Gymnocarpium dryopteris, Athyrium filix-femina (lady fern), Tiarella trifoliata (three-leaved foamflower), Cornus canadensis, and Streptopus amplexifolius. The Mniaceae mosses (mostly Plagiomnium, Rhizomnium, and Mnium) are the most common in the moss layer along with Brachythecium spp., Pleurozium schreberi, and Ptilium crista-castrensis.

WILDLIFE HABITATS

Important ecological factors for wildlife in this zone are the long snowy winters, the dominance of dense spruce — subalpine fir and pine forests on gently rolling terrain, and the abundant wetlands. Wildlife that inhabit this zone (Table 30) are adapted to either survive or avoid the severe winters. Moose are the most common large ungulate; in fact, the Sub-Boreal Spruce zone represents the centre of abundance of Moose in British Columbia. Moose are well adapted to survive the severe winters of much of the SBS. Their long legs reduce the energetic costs of locomotion in deep snow and their large body generates and maintains heat efficiently. Smaller mammals survive the winter by constructing burrows under the snow (e.g., Deer Mouse) or by travelling on top of the snow (e.g., Snowshoe Hare). Most birds migrate south in winter, but some such as the Pine Grosbeak and Red Crossbill remain year-round. Old-growth coniferous forests in this zone provide thermal and hiding cover for Moose, as well as early winter habitat for Caribou when it is adjacent to the higher elevation Engelmann Spruce — Subalpine Fir zone. These forests also provide abundant habitat and prey for several predators such as the Gray Wolf, Fisher, Marten, and Ermine. Marten are very abundant in this zone, feeding primarily on Southern Red-backed Voles. Other common rodents include Red Squirrel, Northern Flying Squirrel, Woodchuck, and Deer Mouse. Mature coniferous forest meets the habitat requirements of different birds for a variety of reasons. Pine Siskin, Magnolia Warbler, and Yellow-rumped Warbler all prefer coniferous trees for nesting, while the Golden-crowned Kinglet feeds on foliage

217 TABLE 30. Selected wildlife habitats and species in the Sub-Boreal Spruce zone (adapted from Wildlife Branch 1989)

Habitat Habitat Representative wildlife species Wildlife species at riska distribution

Old-growth Extensive, Moose, Mule Deer, Black Bear, ♦ Caribou spruce and dwindling Gray Wolf, Lynx, Red Fox, Fisher, subalpine ®r Marten, Ermine, Big Brown Bat, forests Little Brown Myotis, Snowshoe Hare, Woodchuck, Red Squirrel, Northern Flying Squirrel, Southern Red-backed Vole, Deer Mouse, Pygmy Shrew Great Gray Owl, Boreal Owl, Three-toed Woodpecker, Black-backed Woodpecker, Gray Jay, Magnolia Warbler, Yellow-rumped Warbler, Pine Siskin, Ruby-crowned Kinglet, Golden- crowned Kinglet, Pine Grosbeak, White-winged Crossbill, Red-breasted Nuthatch

Riparian Common Moose, Mule Deer, Black Bear, ♦ Caribou, Grizzly Bear, areas, Beaver, Meadow Jumping Mouse Western Grebe wetlands, meadows, and Bald Eagle, Ruffed Grouse, ¯oodplains Trumpeter Swan, Canada Goose, Herring Gull, Ring-billed Gull, Black Tern, Eared Grebe, Common Loon, Barrow's Goldeneye, Harlequin Duck, Rusty Blackbird Common Garter Snake, Western Toad, Spotted Frog, Wood Frog

Seral pine Extensive Moose, Mule Deer, Black Bear, forests Lynx, Snowshoe Hare, Porcupine, Yellow Pine Chipmunk, Deer Mouse, Southern Red-backed Vole, Deer Mouse Northern Goshawk, Great Horned Owl, Northern Hawk-owl, Ruffed Grouse, Spruce Grouse, Red Crossbill, Black-capped Chickadee

Mixed Extensive Moose, Mule Deer, Black Bear, ♦ Caribou, Northern Long-eared deciduous and Gray Wolf, Lynx, Marten, Ermine, Myotis, Black-throated Green coniferous Red Squirrel, Porcupine, Snowshow Hare, Warbler, Canada Warbler forests Deer Mouse Northern Goshawk, Northern Hawk-owl, Great Horned Owl, Common Raven, Northern Flicker, Downy Woodpecker, Yellow-bellied Sapsucker, Pine Siskin, Yellow Warbler, Dark-eyed Junco, Black-capped Chickadee, Chipping Sparrow

Agricultural Limited Moose, Mule Deer, Black Bear, areas areal extent Coyote, Deer Mouse American Kestrel, Sandhill Crane, Canada Goose, Mountain Bluebird

Grasslands Limited Rocky Mountain Elk, Mule Deer, ♦ Grizzly Bear and shrub- areal extent Gray Wolf, Coyote, Black Bear steppe American Kestrel, Ruffed Grouse

218 TABLE 30. Continued a Wildlife species and subspecies at risk are those on the preliminary Red and Blue Lists proposed in the Provincial Wildlife Strategy, B.C. Ministry of Environment (October 1989 draft). ∇ Red-listed wildlife species. These are being considered by the Wildlife Branch for designation as endangered or threatened in British Columbia. ♦ Blue-listed wildlife species. The Wildlife Branch considers these species ``sensitive'' and/or deserving of management attention. Population viability is a concern for these species because of (a) major declines in population numbers; or (b) major changes in habitat that will further reduce existing distribution. Species that are generally suspected of being vulnerable, but for which information is too limited to allow designation in another category, are included in this category. insects, including the spruce budworm. Seeds from cones provide food for birds such as the Pine Siskin and Pine Grosbeak, and predatory birds like the Great Gray Owl and Boreal Owl feed on the rodent populations. Young seral forests are created through removal of the forest canopy by logging or burning. These changes to the structure of wildlife habitat change the distribution and abundance of wildlife species. Logging prevails in this zone, so there are abundant young seral forest habitats in various stages of succession. Some wildlife species benefit from the early successional scrub that develops after disturbance. Moose and Mule Deer will browse available forage in these shrublands, given adjacent thermal and hiding cover. Voles and mice are common, and avian predators that prefer to hunt open areas (e.g., Northern Hawk-owl and Great Horned Owl) do well in this successional stage. Other animal species become more abundant as natural succession proceeds to lodgepole pine and aspen forests. Snowshoe Hare support an abundant Lynx population in the young seral forests. Species such as Porcupine, Red Crossbill, and Spruce Grouse occur in this type because their habitat requirements include pine. Next to coniferous and mixed forests, the second most abundant wildlife habitat type in the SBS includes riparian areas, wetlands, meadows, floodplains, lakes, and streams. Moose forage on aquatic vegetation in shallow lakes and swamps, and on the early successional shrubs of active floodplains. Dense deciduous vegetation in riparian areas provides thermal and hiding cover for Moose. The omnivorous Grizzly Bear forages on roots, shoots, and small mammals, in a variety of wetland and riparian habitats. The wetlands common in this zone provide excellent habitat for waterfowl. There are high breeding concentrations of Eared Grebe, Herring Gull, and Black Tern. These wetlands are the most important breeding centre in the world for Barrow’s Goldeneye. Amphibians and reptiles are poorly adapted to cold temperatures and deep snows; hence, only three amphibian and one reptile species occur in this zone. The Western Toad, Wood Frog, Spotted Frog, and Common Garter Snake are found in riparian and wetland habitats, as well as in the adjacent forests. Agricultural areas also provide habitat for some wildlife species in the SBS. Field crops often supply forage for Moose, Mule Deer, and Canada Goose. Coyotes feed on abundant vole and mouse populations, and both the Mountain Bluebird and American Kestrel hawk insects. These man-made habitats also provide staging areas for migrating Sandhill Crane.

219 Natural grasslands and shrub-steppe, although scattered and uncommon, support many wildlife species. Rocky Mountain Elk are of particular note, because they are not found in any abundance elsewhere in this zone.

RESOURCE VALUES

Forest harvesting is very active in the SBS. Slightly dry and fresh sites generally have moderate capability for producing spruce and lodgepole pine; moderately dry sites have low capability for lodgepole pine; moist sites have high capability for spruce and subalpine fir growth. The SBS landscape provides large tracts of moderately productive forests and offers excellent potential for increasing fibre yields through intensive silviculture. Most of the SBS has low capability for agriculture because of adverse climate, topography, bedrock, stoniness, or poor drainage. Lacustrine soils at the lower elevations have moderate capability, with limitations from poor soil structure and poor drainage. Alluvial deposits at lower elevations along the major rivers have the best capability for agriculture. Throughout most of the SBS, present agricultural activity is forage-based to support both cattle and dairy operations. On some of the more favourable sites, field crops and cereal grains are produced. Early seral and open mature forests, especially in the drier subzones, are used for seasonal grazing of livestock. Important range can be provided by seeding clearcuts and landings. Fur harvest from this zone is among the highest in the province. Recreational pursuits in the SBS include fishing, hunting, camping, studying natural history, cross-country skiing, and snowmobiling.

220 LITERATURE CITED

Annas, R.M. and R. Coup´e (editors). 1979. Biogeoclimatic zones and subzones of the Cariboo Forest Region. B.C. Min. For., Victoria, B.C. Krajina, V.J. 1965. Biogeoclimatic zones and biogeocoenoses of British Columbia. Ecol. West. N. Amer. 1:1-17. Wildlife Branch. 1989. Regional wildlife habitat maps. B.C. Min. Environ., Victoria, B.C. 15 maps, 1:500000.

221 BGC Units

TABLE 4.2. Environmental characteristics of all zones in the PRFR, south half

Biogeoclimatic zone CWH ICH SBS

Extent Area 2 454 911 ha 1 020 684 ha 2 399 697 ha % of PRFR, south half 22.1 % 9.2% 21.6% Elevation range 0 - 1000 m 100 - 1100 m 550 - 1300 m

Physiography Physiographic units Coast Mtns.; Hecate Nass Basin; Skeena ; Lowland Hazelton mtns. eastern valleys of Hazelton and Skeena mtns

Terrain Mostly steep moun- Mountainous with Mostly gently rolling tainous with narrow wide valleys; some with many lakes; valleys; undulating hummocky, rocky more mountainous in lowlands on outer terrain in Nass Basin west coast

Climate Maritime to Transitional; moder- Continental; moder- submaritime; rainy ately wet to dry, warm ately dry with warm and mild winters with summers and cool, wet to cool summers and heavy wet snow inland winters cold winters

Soils Dominant soils Humo-Ferric and Humo-Ferric Podzols; Gray Luvisols; Ferro-Humic Podzols; Gray Luvisols Brunisols; Humo Folisols Ferric Podzols

Humus forms Hemimors and Hemimors, 5 - 15 cm Thin Hemimors, Humimors; 5 - 30+ cm thick Mormoders, and thick Moders, 5 - 10 cm thick

Tree speciesa Major coniferous trees Hw, Ba, Cw, Ss Hw, Cw, Bl, Sx, Pl Sx, Pl, Bl Major deciduous trees Dr, Act Ep, At, Act At, Act

a Tree species codes are found in Appendix 3.

4 • 6 SBPS/SBS

SBPSmc

54 928 ha 0.5% 900 - 1300 m in the north 850 - 1400 m in the south

Nechako Plateau

Entiako drainage; south of Ootsa and Netalkuz lakes

Drier, colder, more severe than SBS; short growing season marked by frost; long cold winter with low snowpack

Brunisolic Gray Luvisols; Dystric Brunisols

Hemimors; ±8 cm thick

Pl, Sw, Sb

Dominant throughout; almost all Pl-dominated; At uncommon

Pl - Feathermoss - Cladina

4 • 51 BGC Units BGC 4 • 52 • 4

FIGURE 4.12. Vegetation table for SBPS and SBS subzones and variants in the PRFR, south half. SBS

4.2.7 SBS Sub-Boreal Spruce Zone Location and Distribution: (Figure 4.11; Table 4.2) The SBS covers most of the interior lowland forest in the south half of the PRFR. It occurs mainly on the Nechako Plateau, with some western and northwestern extensions into the Hazelton and . The SBS makes up 21.6% of the south half of the PRFR. It is the main forested zone within the Lakes, Morice, and Bulkley forest districts and extends also into northeastern portions of the Kispiox and Kalum forest districts. The SBS ranges in elevation from 500 to 1350 m. Lower elevation limits are set by the elevation of the valley bottoms. The upper elevation at which the SBS grades into the subalpine ESSF zone varies from 900 to 1350 m, depending on local topography and climatic conditions. Climate: (Table 4.3) The climate of the SBS is primarily continental; some lingering coastal influences still reach the lower Bulkley Valley and the middle Skeena and upper Nass drainages. The sub-boreal climate is characterized by seasonal extremes of temperature, with severe, snowy winters and relatively warm, moist, and short summers. It has a longer, moister, but slightly cooler growing season than the true boreal forest, and is therefore more productive for tree growth. Annual precipitation is roughly 440 - 650 mm; less than half of it falls as snow. Soils are deeply to lightly frozen during the winter months, but there is no permafrost. Vegetation: (Figure 4.12) Upland coniferous forests dominate the SBS landscape. Hybrid white spruce and subalpine fir are the major climatic climax tree species and often occur in mixture. Pure stands of either species are uncommon, but subalpine fir tends to dominate older stands in the higher-elevation and moister sections of the zone. Black spruce also occasionally occurs in climax forest, usually in wetlands or areas of cold air ponding. Because of the pervasive fire history of this subzone (fire-free intervals longer than 300 years are rare and most stands are probably burned every 100 years, on average), lodgepole pine and trembling aspen form frequent and extensive seral stands — with pine more abundant on coarser-textured, more acidic soils, and aspen dominating on finer-textured soils. Paper birch and black cottonwood are also common seral species. Interior Douglas-fir reaches its northwestern limit within the SBS of the PRFR, but it is uncommon. Small areas of grassland and shrub-steppe vegetation are found on some warm, dry sites scattered throughout the major valleys. Understory vegetation on zonal ecosystems typically includes a variety of shrubs (black huckleberry, thimbleberry, prickly rose, highbush-cranberry, soopolallie, saskatoon, black twinberry, green alder, and black gooseberry), a moderately to well-developed herb layer (bunchberry, twinflower, heartleaved arnica, queen’s cup, five-leaved bramble, purple peavine, and showy aster), and a well-developed feathermoss carpet (red-stemmed feathermoss, knight’s plume, and step moss).

4 • 55 BGC Units

Soils: (Table 4.2) Three soil orders, Luvisols, Brunisols, and Podzols, dominate the SBS. Brunisolic and Orthic Gray Luvisols are the most common soils in the fine-textured glacial till that dominates the Nechako Plateau. These soils have an accumulation of clay in the B-horizon that can impede soil drainage and restrict root growth. Under wetter conditions or in coarser-textured soils, Brunisols, Podzolic Gray Luvisols, and Humo-Ferric Podzols are formed. In general, with increasing elevation (and thus, higher effective precipitation) there is a gradation from Luvisolic to Podzolic soils in fine-textured material and from Brunisolic to Podzolic soils in coarse-textured material. Humus thickness also increases with increasing moisture availability. The typical humus form is an Orthihemimor, 5 - 10 cm thick. Moder humus forms are common on warm, moist ecosystems with a deciduous tree component. Gleyed subgroups and Gleysols are common in imperfectly drained depressions or moisture-receiving sites, Regosols exist on active floodplains, and Organic soils occur in the many small wetlands that dot the landscape. Differentiating Features: The SBS zone can be distinguished from adjacent ICH and CWH subzones by the absence of western hemlock (and amabilis fir, for the CWH) in the overstory, or by the general lack of any significant amount of hemlock regeneration within older stands on zonal ecosystems. It can be distinguished from the SBPS by the abundance of spruce (and subalpine fir) in the overstory of stands on zonal sites. Zonal ecosystems in the SBS do not have lodgepole pine regeneration, common juniper, or abundant Cladonia-type lichens on the forest floor. The transition from SBS to ESSF — at elevations ranging from 900 to 1350 m — is subtle and marked by a shift towards almost total dominance by subalpine fir, and the presence (even on zonal sites) of subalpine indicator plants such as false azalea, Sitka valerian, Indian hellebore, arrow-leaved groundsel, heron’s-bill mosses, leafy liverworts, and, in the western ESSF, mountain hemlock or whitebark pine. Subzones and Variants: (Figures 4.11 and 4.12; Table 4.7) There are three subzones of the SBS (two variants) in the south half of the PRFR: SBSdk - Dry Cool subzone SBSmc - Moist Cold subzone SBSmc2 - Babine variant8 SBSwk - Wet Cool subzone SBSwk3 - Takla variant8 The SBSdk is the most developed sub-boreal subzone of the PRFR. This is where almost all of the human settlement and agriculture are found. The climate is drier and warmer and the growing season is longer than in the SBSmc. Winters in the SBSdk are just as cold and possibly colder, than those in the SBSmc; there is considerably less snowfall and a shorter duration of snowpack. Major tree species include hybrid white spruce,

8 Other variants of the SBSmc and SBSwk occur in the Prince George and Cariboo forest regions.

4 • 56 SBS

lodgepole pine, trembling aspen, and black cottonwood. Black spruce, subalpine fir, paper birch, and Rocky Mountain juniper are minor species and Douglas-fir is rare. The vegetation on zonal ecosystems typically has well-developed, diverse shrub and herb layers, and a moss layer that is not nearly as well developed as in the SBSmc. The SBSmc is the main timber-producing sub-boreal subzone in the PRFR. It is found at higher elevations and in areas of wetter climate than the SBSdk, and it is generally poorly suited for agriculture. The climate is cooler and moister in summer; the winters are longer with deeper snowpacks. In the SBSmc, subalpine fir is abundant, Rocky Mountain juniper and Douglas-fir are absent, and seral stands dominated by trembling aspen are relatively uncommon. On zonal ecosystems, shrub and herb layers are rather sparse and the understory is dominated by a well- developed feathermoss carpet. In the PRFR, the SBSmc is represented by a single variant, the SBSmc2, or Babine variant. A third subzone, the SBSwk, extends into the PRFR from the Prince George Forest region to the east. The SBSwk3, or Takla variant, occurs east of Babine Lake in the vicinity of Natowite and Tochcha lakes. This variant is of limited extent (and transitional to the SBSmc2) in the PRFR and is not described in this guide. Readers should refer to MacKinnon et al. (1990) or use the description provided here for the SBSmc2.

4 • 57 4 • 58 BGC Units

TABLE 4.8. Environmental characteristics of all forested zones in the PRFR, north half

Biogeoclimatic zone BWBS SWB SBS

Extent Area 2 479 000 ha 4 854 206 ha 163 278 ha % of PRFR, north half 17.6% 34.6% 1.2% Elevation range 300 - 1150 m 900 - 1700 m 100 - 800 m

Physiography Physiographic units Stikine Plateau; Yukon Stikine Plateau; Yukon Eastern valleys of Plateau; Liard Plain; Plateau; Cassiar Mtns; Coast Mtns., Boundary Cassiar Mtns.; St. Elias Liard Plain; St. Elias Ranges; westernmost Mtns.; northernmost Mtns. portions of Yukon and Skeena Mtns. Stikine plateaus

Terrain Flat to rolling plains Gently rolling plateaus Lower slopes and and plateaus in the to steep, heavily floors of major river east; narrow mountain glaciated mountain valleys valleys in the west slopes

Climate Northern continental Northern interior Continental, but with with frequent arctic subalpine, with slight coastal influ- airmasses; long, very frequent arctic ence; moister, with cold winters and short, airmasses; very long, longer growing season dry, quite warm cold winters and very and milder winters summers short, cool summers than BWBS

Soils Dominant soils Brunisolic Gray Humo-Ferric Podzols; Probably Humo-Ferric Luvisols; Dystric Eutric and Dystric Podzols and Gray Brunisols Brunisols Luvisols

Humus forms Hemimors; Hemimors and Hemimors > 10 cm thick Mormoders

Tree speciesa Major coniferous trees Sw, Sb, Bl, Pl Sw, Bl, Pl Sxw, Bl, Pl, Sb Major deciduous trees At, Acb or Act, Ep Willows, At, Acb Act, Ep (At)

a Tree species codes are found in Appendix 3.

4 • 60 BGC Units BGC 4 • 64

a Bars indicate the relative abundance of plants across all site series within a biogeoclimatic unit. These bars are defined in Section 3.2.2, page 3•6.

FIGURE 4.13. Vegetation table for all forested zones in the PRFR, north half. 4 • 65 All Zones — North — Zones All

a Bars indicate the relative abundance of plants across all site series within a biogeoclimatic unit. These bars are defined in Section 3.2.2, page 3•6.

FIGURE 4.13. (Continued) BGC Units BGC 4 • 78 • 4

FIGURE 4.16. Distribution of CWH, ICH, and SBS zones in the PRFR, north half. SBS — North

4.3.7 SBS Sub-Boreal Spruce Zone Location and Distribution: (Figure 4.16; Table 4.8) There is only a small area of SBS in the north half of the PRFR (1.2%) and it is very poorly studied. This northern SBS lies in the coast/interior transition along the low-elevation valleys of the Stikine and Taku rivers and their tributaries. In the Stikine drainage, the SBS is bordered to the west by the ICH zone and to the east by the BWBS, and it extends from Glenora downstream to Dokdaon Creek. It includes most of the Chutine and Barrington river valleys. In the Taku, the SBS occupies a 30-km wide band between the CWH and the BWBS, including most of the Sloko, Nakonawe, King Salmon, and Sutlahine valleys and the lower half of the . In elevation, the SBS ranges from approximately 100 m to 800 - 900 m. In drainages with extensive glaciation and heavy snow (e.g., the Chutine), however, the SBS gives way to the ESSF at elevations as low as 250 - 300 m. Climate: A broad coast/interior transition exists in the Taku and valleys because coastal weather systems are able to penetrate up these low-elevation river valleys, losing their warmth and moisture gradually. No climatic data exist for this zone, but topographic and vegetative characteristics suggest that it has a longer growing season, a greater accumulation of growing degree days, warmer soils, and significantly more moisture than the neighbouring BWBS. The increased moisture appears to increase the extent of hygric (seepage) sites rather than increasing the extent of poorly drained sites with cold soils as in the BWBS. Vegetation: (Figure 4.13) Dominant tree species in the SBS of the Cassiar Forest District are hybrid spruce (apparently Roche spruce), subalpine fir, black cottonwood (not balsam poplar), paper birch, and, less commonly, lodgepole pine and trembling aspen. Understory dominants include black huckleberry, bunchberry, five-leaved bramble, step moss, knight’s plume, and red-stemmed feathermoss. A characteristic feature of the SBS is the abundance of devil’s club, a species that is uncommon in the BWBS. Differentiating Features: The SBS of the Cassiar Forest District has abrupt boundaries with the adjacent CWH or ICH to the west, in which western hemlock is present, and with the BWBS to the east, in which white spruce is dominant. The ESSF, which lies above the SBS, is a less productive zone with more snow and a shorter growing season. The transition to ESSF is not abrupt, and is marked by a gradual shift in dominance from hybrid spruce to subalpine fir, an increased dominance of shrubs in the heather family in the forest understory, and the appearance of subalpine herbs and dwarf shrubs in small forest openings.

4 • 89 BGC Units

Subzones: For the time being, it appears that these low-elevation transitional forests in the Stikine and Taku most closely resemble the SBSmc of the south half of the PRFR. For additional details, refer to Section 4.2.7, Table 4.7 and Figure 4.12. With further classification work, it may become necessary to designate a new subzone of the SBS in the Cassier Forest District.

4 • 90 SBS

SBS Sub-Boreal Spruce Zone

Overview Location and Distinguishing Features The Sub-Boreal Spruce (SBS) Zone is part of the Canadian Boreal Forest Region (Krajina 1965) but is broadly transitional between the true boreal forest (BWBS Zone) to the north and to both the warmer montane Douglas-fir forest (IDF Zone) to the south and the drier lodgepole pine – white spruce forest (SBPS Zone) to the southwest (Meidinger et al. 1991). The SBS Zone is distinguished from other zones of British Columbia by the following set of characteristics: 1) hybrid white spruce and subalpine fir are climax tree species on zonal sites; 2) lodgepole pine is a common seral species on zonal sites; spruce and subalpine fir are principal species of regeneration in pine stands; 3) Douglas-fir is occasionally a long-lived seral species on warmer sites and on zonal sites near the southeastern limits of the zone; 4) subalpine species characteristic of the MS Zone (grouseberry, black crowberry, Utah honeysuckle) or the ESSF Zone (white-flowered rhododendron, Sitka valerian, arrow-leaved groundsel, bracted lousewort, mountain sagewort) are rarely present.

The Sub-Boreal Spruce Zone dominates the landscapes of the central Interior of British Columbia (Meidinger et al. 1991) and is extensive on the plateau landscapes of the southern Prince George and Prince Rupert forest regions. The southern and warmest limit of its range is in the Cariboo Forest Region and the northeast Kamloops Forest Region. In the Cariboo Forest Region, it occurs primarily in the moist climatic transition east of the drier IDF and SBPS climates, and west of the wetter ICH and ESSFwk climates. In the Cariboo Forest Region, the SBS Zone occurs primarily on gently to strongly rolling topography of the eastern . It occurs over a relatively wide elevation range from approximately 750 to 1350 m in the south, 450–1250 m in the northeast, and 750–1500 m in the northwest.

5•11 - 1 BGC UNITS b -11.1 SBSwk1 a b 12.3 13.1 1990. SBSmc2 et al. 14.1 SBSmh SBSmw SBSmc1 -11.0 -10.8 -12.6 ) in the Cariboo Forest Region and is not included here. Refer to Lloyd 14.8 14.9 16.6 2 750–1200 750–1200 450–750 700–1000 1250–1350 1200–1500 900–1250 SBSdw1 SBSdw2 Br.G.L.HR (RM) Br.G.L. HR Br.G.L.RM HR, Br.G.L. HR (RM) Br.G.L. HR (RM) HR (RM) Br.G.L. HR (RM) Br.G.L. d c ) 3443 2567 789 1374 419 1205 1473 2 Mean annualMean summerMean winterMean annual snowfall (cm) 182Mean annual 585Mean - warmest month 286 198 298 487 252 197 235 559 3.7 257 297 3.4 328 4.6 298 229 237 575 334 2.9 240 354 719 1.5 429 2.4 Mean - coldest month -10.4 Precipitation (mm) Zonal soils Zonal humus form Temperature(°C) Frost-free days 152 170 179 151 117 Climatic data are from the Prince George and/or Rupert forest regions; few or no available Cariboo. HR = HemiMor; RM MorModer The SBSmm has a very small area (86 km Br.G.L. = Brunisolic Gray Luvisol Climate TABLE 14 Environmental characteristics of SBS subzones and variants in the Cariboo Forest Region TABLE Area (km Elevation range (m) a b c d Soils

5•11 - 2 SBS

Climate The SBS Zone in the Cariboo Forest Region has a cool continental climate characterized by warm, moist summers and cool to cold, snowy winters. Mean annual temperatures range from 1.5 to 4.6°C (Table 14) with a general mean of about 3.7°C, which is similar to the IDF Zone. Frost can occur at any time of the year, especially in low- lying areas, but is less frequent than in the SBPS or MS zones. The similarity in temperatures between the SBS and IDF zones in the Cariboo Forest Region is a reflection of the location of the Cariboo Forest Region at the northern limit of the IDF Zone and the southern limit of the SBS Zone. In this area, mean climatic parameters for these two zones differ more in terms of precipitation than temperature. Mean annual precipitation in the SBS Zone ranges from about 487 to 719 mm. Peak precipitation periods are early summer and early winter. About 50% of the precipitation falls as snow. Maximum annual snowpacks are approximately 60–200 cm, with the deeper snowpacks at higher elevations in wetter subzones.

Vegetation Climax tree species on zonal sites in the SBS Zone are hybrid white spruce and subalpine fir. However, due to frequent wildfires in the past, climax stands are uncommon at low to moderate elevations (<1200 m). Lodgepole pine is the principal seral species throughout the zone. Douglas-fir is also a common seral species at low elevations (<1000 m) but it is seldom abundant at higher elevations. In contrast to the IDF Zone, mature Douglas-fir stands in the SBS are mostly single-storied and even-aged. Little Douglas-fir regeneration is present in these stands. Trembling aspen is also a common seral species in the Cariboo SBS but is less common than in other portions of the zone further north.

The forest undergrowth on zonal sites is characterized by a moderately well-developed shrub layer and a large number of shrub species. The herbaceous layer is variable. On the low to moderate elevations of the zone, the undergrowth is characterized by abundant pinegrass and a large number of forb species ranging from a few centimetres to a metre tall. Although mosses are abundant, their presence is often obscured by the herbaceous species. At higher elevations, fewer shrubs are present and the herbaceous layer is moderately to poorly developed. Mosses and low-growing forbs such as five-leaved bramble typically dominate the undergrowth at these elevations.

5•11 - 3 BGC UNITS

Small wetlands are common in the SBS Zone but less numerous and extensive than in the SBPS or IDF zones where drainage patterns are typically less well developed. They are predominantly fens. Bogs are present but much less common than in portions of the SBS Zone further north. Grasslands are uncommon and occur only locally on steep south- facing slopes. Soils Soils of the SBS Zone in the Cariboo Forest Region are developed primarily on base-rich morainal deposits derived from weathering of local volcanic rock. Morainal deposits dominated by granitic rocks occur locally, especially in the Dragon Mountain and Mount Timothy areas. On zonal sites, the soils are predominantly Brunisolic Gray Luvisols with loamy texture and moderate (25–50%) content of gravels and cobbles. Brunisolic soils occur on well-drained sandy parent materials, while Gleysol and Organic soils occur on wet lower slopes and depres- sions.

Subzones and Variants of the SBS Zone in the Cariboo Forest Region Ten subzones of the SBS Zone are recognized in British Columbia (Meidinger et al. 1991). Six of these, two with two variants each, occur within the Cariboo Forest Region. SBSdw - Dry Warm SBS Subzone SBSdw1 - Horsefly Variant SBSdw2 - Blackwater Variant SBSmh - Moist Hot SBS Subzone SBSmw - Moist Warm SBS Subzone SBSmm - Moist Mild SBS Subzone SBSmc - Moist Cold SBS Subzone SBSmc1 - Moffat Variant SBSmc2 - Babine Variant SBSwk - Wet Cool SBS Subzone SBSwk1 - Willow Variant

SBSdw Subzone The SBSdw is a relatively large subzone (approxi- mately 6010 km2 in the Cariboo Forest Region), which occurs on the gently rolling topography of the Fraser Plateau and southern Nechako Plateau near the southernmost limits of the SBS Zone. It extends from the southeastern portion of the Cariboo Forest Region (Bowers Lake

5•11 - 4 SBS area) northwestward to about the latitude of Prince George. Biogeoclimatic units bordering the SBSdw in the Cariboo Forest Region include the IDFdk along the drier, western portion of the subzone, the SBPSmk in colder areas, and the ICHmk3, ICHdk, SBSmw, and SBSmc1 along the wetter eastern portion. In terms of vegetation and climate, the SBSdw is transitional between the IDFdk and the ICHmk or SBSmw.

The SBSdw climate is relatively warm and slightly drier than the average for subzones of the SBS Zone in British Columbia. About half of the annual precipitation falls during the winter, and peak snowpack is generally about 1 m. The wettest period is typically late spring and early summer when thunderstorms are common. Vegetation of the SBSdw has similarities to Douglas-fir and lodgepole pine forests of the IDF Zone to the west and south. It is distinguished from all other subzones of the SBS except the SBSmc by constant and often abundant pinegrass on zonal sites (Table 15). It is distinguished from the SBSmc by the absence of five-leaved bramble on zonal sites. Climax forests are very uncommon due to frequent stand-initiating wildfires but, where present, are dominated by hybrid white spruce, subalpine fir, and scattered Douglas-fir. Seral stands are dominated primarily by Douglas-fir and/or lodgepole pine, although trembling aspen is also common. Douglas-fir and lodgepole pine stands are mostly single- storied with sparse to moderately dense tree regeneration consisting of sparse Douglas-fir and spruce and often abundant subalpine fir. The shrub and herbaceous vegetation is floristically rich and productive. Several forbs, grasses, and low shrubs are abundant. Common shrubs include thimbleberry, black huckleberry, highbush-cranberry, birch-leaved spirea, soopolallie, and Sitka alder. Common herbaceous species include pinegrass, rough-leaved ricegrass, sarsaparilla, baneberry, twinflower, bunchberry, and queen’s cup. Two biogeoclimatic variants of the SBSdw occur in the Cariboo Forest Region. A third, the SBSdw3, occurs only in the Prince George Forest Region at the northern limits of the subzone. The SBSdw1 Variant occupies the wetter, eastern portion of the SBSdw. It borders the ICH Zone in the south and the wetter subzones of the SBS Zone (SBSmc and SBSmw) in the north. Compared to the SBSdw2, the SBSdw1 zonal site vegetation has more vigorous and diverse shrub and herbaceous layers, subalpine fir is common in the understory, falsebox is present, and kinnikinnick is absent or incidental. Pinegrass is less abundant than in the SBSdw2.

5•11 - 5