Ministry of Environment

Soils

3.3 The Coast Mountains and Islands

J.R. Jungen and T. Lewis

The Coast Mountains and Islands occupy an area along the extreme western part of British Columbia stretching from the 49th parallel to the borders of Alaska and the Yukon. The area is large, about 1200 km in length, and is relatively narrow but variable in width. It is dominated by two parallel mountain ranges - the Coast Mountains and the St. Elias-Insular Mountains. These ranges are separated by a largely submerged lowland. Numerous major rivers from the interior flow across the Coast Mountains on their way to the Pacific Ocean. Notable features include, large mountain snowfields and glaciers, and well developed fjords.

The features of climate, geology and vegetation have been described in Parts 1.2, 1.3 and 1.4. These soil forming factors in combination with topography and surficial material give rise to the distinctive soil landscapes found in the region.

The Factors of Soil Formation

The region has high precipitation and generally moderate to cool temperatures, including, particularly in the south, a short dry period in summer. In winter, the moisture-laden air of a succession of low pressure systems rises in contact with the coastal slopes, to produce very cloudy and wet conditions. The soils are generally very wet. The upper elevations receive vast quantities of snow which protects the ground from freezing. In the summer there are frequent spells of fine sunny weather as the North Pacific high-pressure cells extend over the coast. The resultant dry period influences the type of soils found over the wide range of landforms in the region, particularly in the south at low elevations.

The terrain is underlain mainly by intrusive igneous rock with minor but significant areas, mainly on Vancouver Island and the Queen Charlotte Islands, of folded and faulted volcanic and sedimentary rocks, flat lying lavas, folded metamorphic rocks, and flat or gently dipping sedimentary rocks. The intrusive rocks are relatively resistant to weathering. The residue from prolonged physical and chemical weathering provides a coarse textured, acid parent material.

In general the vegetation is a coniferous forest blanket. The forest regions (see Rowe in Further Reading of Part 1.4) which occur are "Coastal", and "Subalpine". The biogeoclimatic zones include Coastal Western Hemlock, Coastal Douglas-fir, Mountain Hemlock, Engelmann Spruce - Subalpine Fir, and Alpine Tundra (see Figure 3.3.1 and Figure 3.3.2).

Figure 3.3.1

Glaciation has contributed a wide range of surficial materials in which the majority of the soils have formed. The coastal areas were depressed by the weight of ice during, and immediately after glaciation. They later rose by isostatic rebound, leaving behind a complex marine-influenced zone along much of the coast of British Columbia. Glaciation resulted in the typically rounded ridges and summits of all but the highest mountains, and the widespread morainal deposits found in the lower parts of the valleys.

The rugged, very steep terrain results in unstable areas where soil development is hindered by the slow creep of surficial materials. Vegetation holds this process in check until a major disturbance such as logging or fire takes place. Steep topography, therefore, has considerable influence on soil development through colluviation, erosion, talus slopes, and general soil disturbance. Other soil disturbance is caused by windthrow of very large trees which mixes upper soil horizons (turbic).

The main features distinguishing the soils of the coastal area are the prevalence of deep reddish to yellowish brown B horizons rich in iron and aluminum oxides, the thick surface organic horizons derived from forest litter, and the development of extremely compact cemented horizons or pans in the B and C horizons.

The Soil Landscapes

The soil map of British Columbia (Part 3.2) indicates the general distribution of soil great groups in the coastal region. It must be clearly understood that this generalized map cannot indicate all the small but never the less important soil landscapes which may occur in a particular area.

The Ferro-Humic Podzol Soil Landscape

The lower part of this landscape occurs within the Coastal Western Hemlock biogeoclimatic zone, on the windward side of the mountains. It ranges in elevation from sea level to 900 m in the south, decreasing to 450 m in the north. A cross section of this landscape with its associated soils is shown in Figure 3.3.3. Plate 3.3.l is an aerial view of part of it near Tofino on Vancouver Island.

The area has a moist, cool climate with abundant rainfall, low snowfall except in the north, and mild winter temperatures. The summers are cool and relatively much drier than are the winters. High humidity tends to restrict evapotranspiration rates. The soils are moist to wet over most of the year and rarely freeze to any significant depth. The soil temperature regime is mainly cold to moderately cold cryoboreal and the moisture regimes are dominantly perhumid. Excess moisture and a high incidence of associated poorly drained soils typify this landscape.

Figures 3.3.2 and 3.3.3

Plate 3.3.1
Soil Landscapes on the West Coast of
Vancouver Island

  1. Ferro-Humic Podzol, Humic Gleysol and Fibrisol landscapes on the marine and fluvioglacial sediments of the coastal plain. The Ferro-Humic Podzols will occur only on the coarse textured materials or on the better drained sites. There are Humic Gleysols and organic Fibrisols on the level to depressional topography of the marine clays.
  2. Ferro-Humic Podzol soil landscape on the morainal deposits that blanket the lower mountain slopes in the Coastal Western Hemlock biogeoclimatic zone.
  3. Ferro-Humic Podzol soil landscape on the colluvial materials of the upper mountain slopes in the Coastal Western Hemlock biogeoclimatic zone. There are also exposures of organic Folisol landscapes over bedrock.
  4. Ferro-Humic Podzol soil landscape on thin colluvial materials in the Mountain Hemlock biogeoclimatic zone. Organic Folisols and Fibrisols also occur.
  5. Alpine soil landscapes with shallow rubbly Regosols, exposed bedrock, snow and ice.

The upper part of this landscape occurs at elevations ranging between 900 to 1400 m in the Mountain Hemlock biogeoclimatic zone. This area is cooler, and receives more total precipitation than the lower part, much of it as snow. The soils rarely freeze due to the insulating effect of the deep snow. The soil temperature class is predominantly cold cryoboreal and the soil moisture regime is perhumid.

The main soil processes are the accumulation of complexes of amorphous organic matter, iron and aluminum producing soils with exceptionally strong podzol B horizons. In fact, most pedologists would agree that podzols have reached their maximum development in British Columbia within this landscape zone. The soils may or may not have thin eluvial (Ae) horizons; are dominated by thick dark reddish B horizons of ±l m rich in iron, aluminum and organic matter; have strong indications of turbic activity; are medium to coarse textured, and generally lack horizons in which clay has accumulated (Bt). Leaching is intense in these soils.

Much of the Ferro-Humic Podzol soil landscape is subject to continuous seepage. This excess moisture is not apparent in the soil in the usual form of gleying and mottling but rather is shown by a higher organic matter content and generally duller profile colours. The distribution of organic matter is typically uneven, and often reaches a maximum near the lower part of the solum. The organic matter content may reach or even exceed 30 percent.

This landscape supports some of the most productive forest land in British Columbia. Mean annual increments exceeding 20 m3/ha/yr are common on the best sites. Coastal western hemlock and Pacific silver fir (amabilis fir) are the dominant species. Sitka spruce occurs on coastal sites.

Forest production in the Mountain Hemlock biogeoclimatic zone is much lower. Extremely heavy snowfall and a short growing season limit forest growth.

Because the terrain is rugged and steep, the most common parent material in this landscape is colluvium, deposits of which are often shallow veneers overlying bedrock. These soils are deep (often between 1 and 2 m), well to moderately well drained, loose to friable, and do not contain any sign of cemented horizons.

Morainal deposits also mantle significant areas. These deposits typically flank the lower valley walls as a blanket or veneer. Thick organic mats of 20-50 cm which overlie the mineral soils are common, with Bf (Fe plus Al accumulation), and Bhf (Fe plus Al plus organic matter accumulation) horizons immediately underneath. The Bhf horizon is frequently most pronounced just above an indurated pan that occurs in the uppermost till. The Bhf and Bf horizons are together usually less than 1 m thick; the boundary between them varies from smooth to very irregular with tongues indicating turbic activity. The main distinction between morainal and colluvial soils is the presence of a tough, indurated pan (Bc horizon) in most morainal soils. Cementation is strongest near the upper boundary of the pan. Penetration is nearly impossible with normal hand tools. The average thickness is 20-50 cm; structure is coarse platy or massive; and texture is medium to coarse. Air-dry clods do not slake when immersed in water, and the porosity is low.

Gravelly fluvial materials have soil profiles similar to those on morainal deposits with respect to colour and cementation. These soils are mostly imperfectly to poorly drained.

Chemically the soils of the Ferro-Humic Podzol soil landscape have very low base saturation; low pH values (less than 5.0 is common); high organic carbon; and high Fe and Al contents. The upper part of the landscape is chemically and morphologically similar to the lower areas, except that the horizons contain somewhat greater amounts of Fe, Al, and organic matter.

The Folisol Landscape

Folisols are organic soils that consist of shallow organic material overlying bedrock. Folisols require a relatively high precipitation and low evapotranspiration in order to develop over otherwise dry, sterile bedrock. They are, however, not continuously saturated. Folisol landscapes are forested and the organic mat is derived from leaves, twigs, roots, branches, and mosses that accumulate over the bedrock. Folisols rarely occur as large, continuous units except in the north, but rather, as minor associates within the Ferro-Humic Podzol soil landscape (see Figure 3.3.3). They are most widespread at high elevations and on the windward outer coast. Without the wet, cool, perhumid moisture regime, the organic matter would not accumulate rapidly enough and outcrops would remain as bare bedrock. Unlike wet, organic soils, Folisols occur on a variety of slopes - crests of ridges, steep well drained positions, gently rolling to undulating bedrock areas.

This landscape is treed, and includes species such as western hemlock, western red cedar, and yellow cedar. Forest productivity is relatively low. Folisols are much more restricted along the east coast of Vancouver Island where the climate is warmer and drier.

The Humo-Ferric Podzol Soil Landscape

The Humo-Ferric Podzol soil landscape occurs predominantly within the Coastal Western Hemlock and Coastal Douglas-fir biogeoclimatic zones, on the eastern side of Vancouver Island, and in all low valleys away from the outer coast. The vegetation usually consists of a moderately dense Douglas-fir and western hemlock forest with a moderately dense understory layer. Upper elevation limits range from above 900 m on the east coast of Vancouver Island to below 450 m in the lower Fraser Valley (see Figure 3.3.4). In the north this landscape can be found only in the lower parts of valleys such as the Skeena and the Nass. Rapid gradation to the Ferro-Humic Podzol soil landscape takes place with increasing effective moisture.

The principal climatic features are relatively mild winters, cool to warm summers, and moderate to high precipitation. Summers are somewhat warmer and drier than in the Ferro-Humic Podzol soil landscape and evapotranspiration is correspondingly higher. Abundant precipitation occurs during the winter. The soil temperature classes include mild mesic, cool boreal, and cold cryoboreal while the soil moisture regime is dominantly humid. The snowfall is low to moderate, depending on elevation and latitude.

The major lowlands, including the Fraser and Nanaimo lowlands, the Alberni Basin, the Nass River and numerous low valley systems have Humo-Ferric Podzols. These areas are predominantly gently sloping to moderately rolling, but include areas of steeply sloping, rugged terrain along the mountain sides. The whole landscape has been glaciated resulting in a wide variety of glacial deposits. Morainal, colluvial, fluvial, and marine materials comprise the main surficial deposits in this landscape. Morainal deposits are probably the most extensive parent material.

The above combination of climatic, topographic, and landform factors has resulted in well to moderately well drained podzolic soils with dark reddish colours, low pH values of 4.0 to 5.0, moderate to high Fe + Al content, with low base saturations. Textures are predominantly coarse to medium. Where long term seepage occurs, levels of organic matter are sufficiently high to classify the soil as a Ferro-Humic Podzol. The interplay among the various environmental factors produces a boundary zone of considerable interfingering of the Humo-Ferric and Ferro-Humic Podzol soil landscapes.

Figure 3.3.4

The soil profiles have a sequence of organic surface horizons (L-F-H), possibly an incipient eluvial horizon (Ae), and a thick Bf horizon. An indurated pan (Bc and BCc horizons) is found in gravelly fluvial and morainal material wherever suitable textures and stable conditions exist. The degree of cementation of these pans varies from weak to strong; usually it is strongest near the top of the horizon. These horizons are massive; they do not soften or slake in water, and can be chipped only with difficulty using a geology hammer. Sometimes it is difficult to distinguish the pan from the original parent material because the underlying unweathered morainal material is also compact. Bulk densities are high, greater than 1.8. The pan is streaked with reddish brown colours and often contains mottles and black manganese oxide coatings, in contrast to the more uniform olive greyish colour of the C horizon. Moderate to fine textured soils generally contain concretions in the illuvial Bf horizon.

Colluvial deposits within this landscape are deep to shallow veneers overlying bedrock. The B horizons are deeply weathered, usually extending down from 1 to 2 m to the bedrock contact. Colluvial soils are loose to friable, well to rapidly drained, and contain no indurated pans.

This landscape has been the basis of the forest industry of the southern coastal area over the past century. It contained in vast quantities some of the most magnificent mature stands of Douglas-fir in British Columbia. Today these stands are mostly logged. Forest productivity is lower than in the Ferro-Humic Podzol soil landscape, but is reasonably high in receiving seepage sites where mean annual increments exceed 12 m3/ha/yr.

The Dystric Brunisol and Sombric Brunisol Landscapes

These landscapes occupy a minor part of the region; since they occur only in southeastern Vancouver Island and the adjacent Gulf Islands, with a minor pocket on the Skagit River next to the international border.

The climate approaches the Mediterranean type having dry warm summers with high moisture deficits and relatively low rainfall. Precipitation ranges from about 650 mm to about 1250 mm. Water deficits during the growing season are considerable, ranging from 140 to 270 mm. The soil temperature class is mild mesic and the moisture regime is semiarid.

The landscapes occur within the Coastal Douglas-fir biogeoclimatic zone. Major tree species include Douglas-fir, Garry oak, Pacific madrone (arbutus), and grand fir, which prefers the sites with impeded drainage.

Major parent materials include medium to coarse textured compact glacial till or colluvium and fine textured marine. The soils are Dystric and Sombric Brunisols. Of the two, the Sombric Brunisol occurs in the driest sites and is associated with an open Garry oak - grass community. It is usually found below elevations of 50 m where effective moisture is lower than it is in the Dystric Brunisol landscape. The soils of both landscapes are moderately to slightly acidic in reaction, and have low to moderate base saturations.

Soil Landscapes of Floodplain and Marine Deposits

The soil landscapes in these areas include Eutric Brunisol, Melanic Brunisol, Gray Luvisol, Regosol, Gleysol, and Humic Gleysol. The complexity of soil landscapes occurring on floodplains is readily apparent when one considers the variability which occurs. Textures range from extremely coarse to fine, soil drainage ranges from rapid to very poor, and soil reaction from slightly acid to slightly alkaline. Important industries related to agriculture, forestry and recreation occur, and many towns and cities have been built, causing much conflict at present between urban and agricultural land use. Plate 3.3.2 illustrates some of these floodplain landscapes in the Fraser Valley.

The Eutric Brunisol, Melanic Brunisol and Gray Luvisol landscapes are restricted to large floodplains such as that of the Fraser River. These soils are often neutral to alkaline, and are imperfectly to moderately well drained.

The vegetation cover is largely deciduous, consisting of red alder, broad leaf maple and cottonwood, with grasses, shrubs, and sedges, whose decomposition products contribute to the dark Ah horizons. The parent materials are youthful and fine textured. Many soil characteristics depend on sedimentation, and flooding rather than soil processes. The slightly acid to neutral reaction and moderate to high base saturation of the soil reflects the underlying water table and little-weathered nature of the alluvium. Illuviation of clay is weak to moderate, illuviation of Fe and Al is weak, and organic matter content is variable. Significant areas of poorly drained Gleysolic and Organic soil landscapes also occur.

The Regosol landscape occurs on the most recent fluvial deposits. It is commonly found on all river floodplains including those of the Fraser, Skeena, and Nass, as well as along most smaller streams and rivers. The vegetation is normally deciduous including such species as black cottonwood, red alder, and willow or the landscape may be devoid of vegetation.

Regosols are dependent on the fluvial process of continual lateral stream migration. This process is clearly evident on all major streams and rivers in the coastal areas. New areas are continually being eroded and deposited, changing soils from possibly an older more strongly developed soil back to a young Regosol. This cycle repeats itself over and over again as the streams and rivers meander back and forth across their valley floors. Climate over the whole watershed controls the amount of stream flow and the frequency and severity of flooding, both factors which produce constructive fluvial landforms on which Regosols are found. Low gradient streams common to most large rivers in this area have natural levees which usually occur close to the stream and somewhat higher than the surrounding terrain. During flood periods considerable erosion takes place and when the floodwaters overtop riverbanks and spread across the floodplain quantities of sediments are dropped on the levees and on the surrounding plain producing a Regosolic or Gleysolic soil.

Plate 3.3.2

Plate 3.3.2
Soil Landscapes In and Adjacent to the Fraser River Lowland

  1. Floodplain soil landscapes including Humic Gleysols, Gray Luvisols and scattered Mesisols and Humisols on fine to medium textured vertically accreting sediments. The complex pattern of these individual soil landscapes depends on soil drainage on the flat to gently sloping topography. The main tree species are Douglas-fir, Sitka spruce, red alder and black cottonwood.
  2. Floodplain soil landscapes including Eutric Brunisols, Melanic Brunisols, and Regosols on medium to coarse textured laterally accreting sediments. The topography is undulating and the trees are mainly black cottonwood and red alder with some Douglas-fir and Sitka spruce.
  3. Humo-Ferric Podzol soil landscapes on shallow and deep colluvial and morainal deposits. The main trees are Douglas-fir and western hemlock.
  4. Upper mountain slopes and peaks with Ferro-Humic Podzol and Folisol landscapes and bedrock. Mountain hemlock and Pacific silver fir (amabilis fir) are the main trees.

Regosols, Gleysols and Organic soil landscapes occur side by side depending on the soil drainage with the Regosols on the better drained sites, the Gleysols in the poorly drained sites and Organic soils in very poorly drained sites.

The Gleysol and Humic Gleysol landscapes occur on very gently sloping to flat terrain which is often associated with marine and fluvial deposits (see Plate 3.3.2). The main locations of Gleysolic landscapes are the Estevan Coastal Plain, the Nahwitti Lowland, Suquash Basin, the Milbanke Strandflat and the Hecate Lowland.

Poor soil drainage is largely responsible for Gleysolic soil formation. The fine textured marine lowlands are particularly suited for the development of Gleysolic soils. Humic Gleysols have an Ah horizon and underlying horizons that are strongly gleyed and mottled. Weakly developed eluvial and illuvial horizons may be present. Typical vegetation includes red alder, black cottonwood, willows, skunk cabbage and sedges. The wet coastal climate with its predominantly perhumid soil moisture regime leads to Gleysolic soils on low lying receiving areas. The wet conditions of a high or fluctuating water table result in rapid chemical reduction and the production of typical bluish or grayish coloured horizons. Gleysolic soils are less dependent on climate than other soils. For example, much of the Nanaimo Lowland receives considerable water from the mountains to the west. This source of groundwater helps to sustain the water table throughout the lowland and, as a result, contributes to the formation of Gleysols in depressions surrounded by the much drier Brunisolic landscapes.

Soil Landscapes of the Alpine Tundra

These landscapes occur at high elevations (generally over 1500 m on windward slopes, and over 1800 m on leeward slopes) where environmental conditions are severe, with rock, ice, snow and minimal soil development on shallow colluvium. High ridges and mountain peaks where cirques, tarns, horns, arêtes, rock bars, and intervening basins with glaciers and snowfields abound represent a significant part of the coastal region. The landscape includes such notable areas as Mt. Waddington, Silverthrone Mountain and the Homathko Icefield. The terrain is extremely rough and the vegetation and micro-climate changes rapidly over short distances. The soil temperature classes range from cold cryoboreal to subarctic. The area is nearly treeless except for scattered dwarf clumps of Pacific silver fir (amabilis fir), subalpine fir, and yellow cedar. Plate 3.3.3 illustrates some typical alpine tundra soil landscapes in the coast mountains just west of Tatlayoko Lake.

The high elevations make the climate colder, increase the amount of snowfall, and drastically shorten the growing season. Soil development is often absent or weak, occurring only in stable pockets where stunted trees, shrubs and heather, in combination with the harsh climate, have managed to develop a soil.

The processes of solifluction, nivation, and cryoturbation are all active. These processes have a strong effect on any soil development by disrupting and dislocating horizons, displacing and incorporating materials from other horizons, and mechanically sorting soil particles. Such effects in combination with the cold climate, which slows weathering, greatly retard soil development.

Alpine meadows are relatively small and are usually found in gently sloping to flat moisture receiving sites. This type of terrain in combination with large winter snow accumulations support nivation hollows which may or may not be permanently frozen depending on aspect and altitude. Shallow to deep Humic Gleysols and Organic soils are common in the alpine zone due to cold soil temperatures with low microbial activity. Organic matter accumulates. In the northern section of this region and on exposed north aspects Turbic Cryosols and Organic Cryosols are expected to occur. Regosols and Humic Regosols occur in relative abundance. Large areas of stones and boulders exist where cryoturbation and colluviation are common processes. In other well drained areas where tree islands and heather vegetation are found Ferro-Humic Podzols develop.

Because of its scenic beauty this landscape has tremendous potential for recreational activities such as hiking, rock climbing, and skiing.

The Saturated Organic Soil Landscapes

Organic soils occur where the decay of organic residues is inhibited by a lack of oxygen caused by submersion or saturation. Fibrisols, Mesisols and Humisols all occur in the coastal region. Fibrisols are the most common, and occur in the wet outer coast region, on some floodplains, and at upper elevations where undecomposed sphagnum and forest peat are the dominant organic source. The main trees are yellow cedar and shore pine with Labrador tea as the common shrub. The soils are extremely acid (pH values less than 4.0). Mesisols have a vegetation cover composed of sedges, hardhack, mosses, willows, grasses, and reeds. Numerous bogs of this type occur on the drier east coastal plain of Vancouver Island. The water comes from seepage inflow from adjacent mineral soils rather than from precipitation only, as is the case with Fibrisols, and is thus richer in nutrients. Humisols occur only rarely and appear to be restricted to the southernmost part of the region.

Organic soils occur as small pockets in the southern coastal region, ranging up to fairly widespread areas on the flat to concave lands of the outer coast and Queen Charlotte Islands. Many in the south are found surrounding small lakes and were originated by the continuous encroachment of vegetation around the margins of what were once much larger lakes. Humisols and Mesisols are widely used for agriculture in the south.

Plate 3.3.3

Plate 3.3.3
Alpine Tundra Soil Landscapes in the Coast Mountains West of Tatlayoko Lake

  1. Ferro-Humic Podzol soil landscape on shallow colluvial deposits over bedrock on steep upper valley slopes.
  2. Upper mountain slopes and alpine meadows with a very complicated pattern of soil landscapes. They include rubbly Regosols, Humic Gleysols, Organic soils and possibly Organic Cryosols.
  3. High ridges and mountain peaks with snow patches and glaciers. Soils are rocky, weakly developed and subject to frost action giving Regosols and probably Turbic Cryosols. Bedrock exposures are common with classic features of mountain glaciation such as cirques, horns and aretes.