A Visual Library of the CWH BEC Zone in B.C.

The Coastal Western Hemlock Biogeoclimatic zone (or CWH zone) gets its name from the abundance of Western Hemlock present across the Pacific coast region. Western Hemlock is also known as Tsuga heterophylla. This zone is a coastal temperate rainforest with dense conifer forests, relatively few herbs but with abundant mosses. Wind is the most common natural disturbance agent in this zone, creating a patchy mosaic of tree ages. The CWH zone is the rainiest zone in BC, due to moisture coming off of the nearby Pacific Ocean. This abundance of moisture plays a role in the lack of disturbance by fire in this zone, so trees are capable of reaching old ages and large sizes.

The CWH zone covers about 10.8 million hectares or 11.4% of the province of British Columbia, but these forests also extend northwards into Alaska and southwards into Washington and Oregon. Within BC, the CWH forests cover much of the low to mid-elevations along the Pacific coast, including Vancouver Island, Haida Gwaii and the Coast Mountains. These forests also extend inwards along the major river valleys of the Fraser and Skeena Rivers. They occupy elevations from sea level to 900 m on windward slopes in the south and sea level up to 300 m in the northern extent of the zone. Above the CWH zone, the ecosystems generally transition into the subalpine forests of the Mountain Hemlock Zone.

The CWH is, on average, the rainiest ecological zone in Canada, with annual precipitation ranging from 1400 mm to 5000 mm. This zone has mild winters and cooler summers, but hot dry spells are also typical. The mean annual temperature is about 8°C across the zone, but the average monthly temperature is above 10°C for about a third of the year. During the coldest month, the mean temperature is 0.2°C, but ranges from -6.6 to +4.7°C across the subzones.

The climate in the CWH zone is heavily influenced by the Pacific ocean and the mountain ranges in the region. The nearness to the ocean and the level of precipitation resulting from the rainshadow effect creates different conditions which result in slightly different plant communities. These different conditions are distinguished in the 10 subzones of the CWH zone. The nearness to the ocean is described as “continentality”. The areas closest to the ocean, such as the outer west coast of Vancouver Island, are known as hypermaritime, as they are directly exposed to the Pacific. The maritime zone exists in between the hypermartime and submaritime zones, and includes the eastern side of Vancouver island and the Greater Vancouver area. The submaritime subzones occur on the leeward side of the Coast Mountains and are further away from the influence of the Pacific ocean.

Although the CWH is the rainiest zone in BC, the amount of precipitation varies widely across the subzones. This is due in part to the rain shadow effect. As air moves up in elevation it cools and condenses, which causes it to release its precipitation as it rises up and over a mountain. The lower elevations tend to get less rain, and therefore are relatively drier than the higher elevations on the windward side of a mountain. There is also less moisture released on the leeward side of a mountain, which is why its called the rain shadow effect. There are several mountain ranges across the CWH region including the Olympic Mountains, Vancouver Island Ranges, and Coast Mountains, so the rain shadow effect repeats several times. The result is a high variability of precipitation throughout the CWH zone as air masses move up and over these different mountains. This variability is shown in the subzones as ranging in precipitation levels from very dry, dry, moist, wet, to very wet.

Although Western Hemlock is dominant throughout the zone, the cover of the other major tree species varies with climate across the subzones. Douglas-Fir (Pseudotsuga menziesii) is common in the drier and warmer subzones; Amabilis Fir (Abies amabilis) in the wetter and cooler subzones with higher elevation or latitude; and Yellow Cedar (Callitropsis nootkatensis) in the wetter, hypermaritime and maritime subzones. Local conditions also can determine which species will be present such as shore pine on very dry or wet sites, Red Alder (Alnus rubra) on disturbed sites, and Black Cottonwood (Populus balsamifera ssp. trichocarpa) on floodplains. The climate conditions also are transitional between Biogeoclimatic zones. For example, the driest maritime subzone in the CWH, the CWHxm, has plants such as Douglas-Fir, Grand Fir (Abies grandis), Arbutus (Arbutus menziesii) and Garry Oak (Quercus garryana), so it strongly resembles the nearby Coastal Douglas-Fir (CDF) zone, but has more Western Hemlock than the CDF.

The  bedrock geology  in the CWH zone, although variable, is frequently made up of  granodiorite rocks . These rocks form the parent material that developed into soils over time through various physical and chemical processes, including the massive forces of glaciation which impacted this region significantly. Granodiorite is a rock that is acidic in nature, low in nutrients and tends to break down into sand sized particles, rather than clay minerals. These factors all result in a soil that tends to be rapidly draining, acidic and low in nutrients. The low nutrient levels also influence the humus forms and soil organisms that are present.  Mor humus  forms are the most common, where the main decomposers are fungi.

The relatively high level of precipitation in the CWH zone also leads to the action of leaching and deposition within the soil profile. These soil forming processes are known as eluviation and illuviation. Eluviation, which is also known as leaching, occurs when water washes suspended materials from one soil horizon to another. Illuviation occurs when these suspended materials are deposited into a lower horizon. Through these processes Podzolic forest soils develop over time, where iron is moved into a lower horizon and accumulates, becoming a redder, iron rich horizon which is known as a  Bf . The upper horizons become stripped of iron, leaving them a paler, greyish colour, known as an  Ae horizon . These two horizons are diagnostic horizons of  Podzolic  forest soils.

The relatively high level of precipitation in the CWH zone, combined with cooler temperatures, leads to accumulations of organic matter on the forest floor. Sometimes in the wettest parts of the CWH zone, these form thick organic layers that can be more than 40cm thick. These thick organic layers change the soil type to be a  Folisol , which is a special type of Organic soil. Most  Organic soils  form in wetlands, but Folisols are the exception to the rule. Soil conditions vary across the zone, but these are some of the typical traits that you will come across in the CWH zone.

The Coastal Western Hemlock zone is the most productive forest region in Canada, so forestry is one of the major industries in this zone. Due to unfavourable topography, most of the region is unsuitable for agriculture, although there are significant agricultural lands along the Fraser Valley basin in Chilliwack and Abbotsford. Due to the scenic views and large trees, the CWH zone is a very popular recreational and tourism destination. Some activities the CWH zone offers include camping, hiking, backpacking, hunting, fishing, and wildlife viewing. Marine-based sports such as sea-kayaking, boating, stand up paddle boarding and sailing are also popular. The mild climate has made this zone a popular location to live, resulting in land loss to urbanization.

The habitat conditions across the CWH zone are incredibly variable and include coastal islands, estuaries, rolling uplands and rugged mountain slopes. This diversity in habitats creates the conditions for an amazing diversity of wildlife. Black-tailed Deer, Black Bear, Grizzly Bear, and Gray Wolf are the most common large mammals. Mountain Goat are found on rugged mountain slopes with exposed bedrock. The greatest diversity of birds, amphibians, and reptiles in BC is found within the Fraser Lowland portion of this zone. 

The forests provide both food and nesting habitat for a large variety of birds such as Spotted Owl, Great Horned Owl, Saw-whet Owl, Northern Flicker, Pileated Woodpecker, Hairy Woodpecker, Hammond’s Flycatcher, Gray Jay, Steller’s Jay, Common Raven, Chestnutbacked Chickadee, Red-breasted Nuthatch, Winter Wren, and Varied Thrush. On the damp forest floor, you can find many different amphibians including Northwestern Salamander, Western Red-backed Salamander, Ensatina Salamander, Clouded Salamander, and Western Toad. 

The CWH has many rivers, both large and small, with accompanying riparian areas and estuaries. Most of the estuaries within BC are found within this zone. The nutrient-rich, protected waters of these estuaries provide shelter for overwintering waterbirds, such as diving and dabbling ducks, Trumpeter Swan, grebes, scoters, and gulls. Nearly all the rivers and streams are used for spawning by salmon, and most of their young spend some time in these streams. The annual Eulichan (candlefish) run also provides a spring feast for California and Steller’s Sea-lion, Harbor Seal, Northern Fur Seal, Northern Elephant Seal, and Bald Eagles. This is just a small representation of the abundance of wildlife that calls this zone home. 

There are over 200 First Nations in B.C. each with their own language, culture, and history. Another map for viewing the territories, languages, and treaties of First Nations throughout the world and B.C. can be viewed through this link:  https://native-land.ca/ 

Although BEC is one way to quantify and view the environment in B.C. it is not the only way. Generally, First Nations lived and to this day still live close to the land in a way that shares reciprocity. In future iterations of this project we hope to share some of the diverse cultural values of First Nations throughout B.C. in a respectful way. 

Within the Coastal Western Hemlock zone, reside the Coast Salish peoples. The Coast Salish are a large grouping of culturally and linguistically diverse nations. The Coast Salish peoples have been living along the coast and managing the land here since time immemorial.

Indigenous languages in BC were almost completely eradicated due to harsh colonial policies, laws and the traumatic impacts from Residential Schools. ‘ Every language is an old-growth forest of the mind ’ and the loss of these languages is a loss of a storehouse of human experiences, knowledge, worldviews, culture and complexity of thought. The loss of languages is occurring across the globe at an alarming rate. However, many languages are currently undergoing revitalization efforts. Simon Fraser University has an Indigenous Languages Program that offers courses in 18 languages from British Columbia and the Yukon:  https://www.sfu.ca/inlp/programs.html  Another site, FirstVoices is a collaborative platform where Indigenous communities manage, curate and share their languages:  https://www.firstvoices.com/languages 

There are resources being created to help us all learn these amazing and diverse languages. For example, the Museum of Vancouver has worked with Elders to create an Indigenous Plant Guide, where you can listen to the names of common plants found in the CWH zone being spoken in the  Skwxwú7mesh Snichim (Squamish)  language and the  Hən̓q̓əmin̓əm̓  language. Another book that features plants, their uses and their names in the Skwxwú7mesh Snichim (Squamish) language is Held by the Land by Leigh Joseph.

Within the Coastal Western Hemlock zone, there are 10 different subzones which capture the diversity of conditions across the region. Each subzone is named based on its proximity to the ocean and its relative level of precipitation. Within each subzone, there are also variations across sites. There are upper slope sites that tend to shed water and be a little bit drier, midslope sites that tend to have moderate moisture (also known as mesic) conditions and lower slope sites that tend to be wetter. We will look at the variation of these conditions across one particular subzone, the Coastal Western Hemlock dry maritime or CWHdm. The CWHdm tends to be more mild and slightly drier than many of the other CWH subzones. 

Let's begin by looking at some of the drier sites in the Coastal Western Hemlock dry maritime subzone. On water shedding sites with coarse, rapidly draining soils, you will often find the plant association of Douglas-fir — Western hemlock — Salal. This association of plants is found in the CWHdm, but also in the CWHxm and CWHmm subzones. These plants are well adapted to handle moderately dry and nutrient poor to medium conditions, but their growth can be constrained as a result. During the growing season, there is often a water deficit along with severe nitrogen deficiency, which means plant growth is slower here than at other, wetter sites. 

The mature forests of the Douglas-fir — Western hemlock — Salal association have Douglas fir, Western Hemlock and Western Red Cedar. Underneath the forest canopy is a well developed shrub layer made up out of Salal (Gaultheria shallon), Dull Oregon Grape (Mahonia nervosa), and Red Huckleberry (Vaccinium parvifolium). There are also lots of small Western Hemlock and Western Red Cedar regenerating under the shade of the overstory trees. The herb layer is poorly developed with Bracken Fern (Pteridium aquilinum) as the only common fern. There is a moderately well developed moss layer which includes Oregon Beaked Moss (Kindbergia oregana) and Step Moss (Hylocomium splendens). 

In the drier sites of the CWHdm, such as the Douglas-fir — Western hemlock — Salal association, the soils develop into moderately deep  Orthic Humo-Ferric Podzols , which have less organic matter influence in their soil profile. The organic layers on top of the soil are  Hemimor humus  forms, which have fungal activity, but little to no soil fauna. Hemimors are common on moisture deficient sites and range from 5-10 cm in thickness. 

On sites that are well to moderately well drained, middle slopes and gently sloping heights of land you will find the Western hemlock — Flat moss plant association. The soils on these sites tend to be moderate in terms of their soil moisture and nutrient levels, which is what is known as a zonal site. Compared to other sites, there are neither significant losses nor additions of moisture and nutrients, which means the climate of the zone is reflected best at these sites. The Western hemlock — Flat moss association and soils are considered the zonal ecosystem for the CWHdm subzone.

Mature stands of the Western hemlock — Flat moss have abundant Douglas-Fir, Western Hemlock, and Western Red Cedar. In densely planted forest stands, the shrub layer is usually poorly developed with few plants, but there is usually regeneration of western hemlock growing in the understory. In areas with more light reaching through the canopy, you will find Vine Maple (Acer circinatum), salal (Gaultheria shallon), Dull Oregon Grape (Mahonia nervosa), and Red Huckleberry (Vaccinium parvifolium). There are few herbs to be found, but occasionally you will see Twinflower (Linnaea borealis), Sword Fern (Polystichum munitum), Trailing Blackberry (Rubus ursinus), and Broad-leaved Starflower (Trientalis latifolia). The moss layer is well developed, featuring Oregon Beaked Moss (Kindbergia oregana) and Step Moss (Hylocomium splendens), Lanky Moss (Rhytidiadelphus loreus), and Flat Moss (Plagiothecium undulatum).

The soils of the Western hemlock — Flat moss association tend to be very similar to the slightly drier soils of the Douglas-fir — Western hemlock — Salal. They are both nutrient-very poor to -medium soils, but the Western hemlock — Flat moss sites are slightly dry to fresh instead of moderately dry soil moisture regimes. They are both  Orthic Humo-Ferric Podzols  with  Humimor  humus forms, but can be slightly deeper soils then the drier sites, which means they are slightly better growing conditions for plants overall.  

On water-receiving sites that occur on imperfectly drained lower slopes you will find the Redcedar — Lady fern plant association. This association includes moist to very moist and nutrient-rich to -very rich sites in the CWHxm and CWHdm subzones. The accumulation of water and nutrients at these lower slope positions creates good conditions for plant growth. Douglas-Fir and Western Red Cedar attain their best growth on these sites. There can be even wetter conditions below these sites in water-collecting areas, which are known as the Redcedar — Sitka spruce — Skunk cabbage association. 

The mature forests of the Redcedar — Lady fern feature Western Red Cedar, Western Hemlock and Douglas-fir. Below the forest canopy, there is a well developed shrub layer dominated by Vine Maple (Acer circinatum) and Salmonberry (Rubus spectabilis). There is a rich and diverse herb layer, with plenty of Lady Fern (Athyrium filix-femina), Sweet-Scented Bedstraw (Galium triflorum), Sword Fern (Polystichum munitum), and Three-Leaved Foamflower (Tiarella trifoliata). The moss layer is less well-developed and includes Palm Tree Moss (Leucolepis menziesii) and Coastal Leafy Moss (Plagiomnium insigne).

The soils of the Redcedar — Lady fern association are wetter and more nutrient rich than the drier or zonal sites. The seepage of water from upslope brings additional nutrients to the lower slope positions. The wetter conditions also impend the breakdown of organic matter, leading to thicker accumulations of organic horizons. The more nutrient rich conditions encourage soil fauna to appear, which leads to the formation of  Moder or Mull humus  forms. The soil texture of lower slope positions also tend to be loamier than upper slope areas, as the finer textured silts and clays tend to wash downhill and accumulate. These conditions lead to the formation of moderately deep to deep  Sombric Humo-Ferric Podzols , which differ from Orthic Humo-Ferric Podzols by having an Ah horizon at least 10 cm thick.