The coastal temperate rainforest that runs along BC's Pacific shore from the US border to the Alaska panhandle is one of the largest remaining intact temperate rainforest systems on Earth. It accounts for roughly a quarter of the world's remaining coastal temperate rainforest, most of which has been cleared in Chile, New Zealand, and the US Pacific Northwest over the past 150 years. Understanding its ecology — what lives there, how the systems interact, and what makes old-growth forest structurally distinct from younger stands — is the starting point for understanding BC's coastal environment.
Climate and the Rain Shadow
Temperate rainforest in BC exists because of a specific confluence of maritime climate and mountain topography. Warm, moisture-laden air masses from the North Pacific rise when they hit the Coast Mountains, cool as they ascend, and drop their moisture as rain or snow. Some valleys on the west coast of Vancouver Island and in the BC mainland receive over 4,000 millimetres of precipitation annually. The Carmanah Valley on Vancouver Island has recorded among the highest rainfall totals in Canada.
The ocean moderates temperature extremes. Average winter temperatures on the outer coast rarely drop below 2 to 4°C, and summer temperatures seldom exceed 20°C. This mild, wet regime favours tree species that grow slowly but to enormous sizes, and it sustains a year-round cycle of biological activity — decomposition, growth, and reproduction — that differs substantially from the seasonal rhythms of continental forests.
Dominant Tree Species
Three species dominate most of BC's coastal rainforest at low to mid elevations:
Western Red Cedar (Thuja plicata)
Western red cedar is arguably the most culturally significant tree on the BC coast. It reaches heights of 60 metres and diameters of 6 metres in old-growth stands. Individual trees can live for over 1,000 years, and some specimens in the Carmanah and Walbran valleys on Vancouver Island exceed 800 years in age. Cedar's naturally rot-resistant wood and its ability to be split cleanly along the grain made it the primary material for canoes, longhouses, bentwood boxes, and ceremonial regalia among Coast Salish, Haida, and other First Nations. The inner bark was used for weaving clothing, mats, and rope.
Sitka Spruce (Picea sitchensis)
Sitka spruce occupies the outer, windward edge of the coast — it tolerates salt spray better than most tree species and often forms the first tree line behind exposed beaches. The largest individuals can exceed 90 metres in height. The Carmanah Giant, a Sitka spruce in the Carmanah Valley on Vancouver Island, was for years considered the tallest tree in Canada at approximately 95 metres before revised measurements placed it slightly lower. Sitka spruce wood is strong and light relative to its weight; it was used extensively for aircraft frames during the Second World War.
Douglas Fir (Pseudotsuga menziesii)
Douglas fir is more drought-tolerant than cedar or spruce and tends to dominate drier, south-facing slopes and areas further from the immediate coast. Old-growth Douglas fir can reach heights of 80 metres and diameters of 2.5 metres. The species is fire-adapted — thick bark protects mature trees from low-intensity ground fires, and the species regenerates well in burned areas. Logging of old-growth Douglas fir in BC began in the mid-19th century and continues in some areas today, though at sharply reduced rates following a 2022 provincial deferral order covering the highest-priority old-growth stands.
The Structure of Old Growth
Old-growth forest is structurally distinct from younger managed stands in ways that matter ecologically. A typical old-growth stand on BC's coast contains multiple canopy layers, a diversity of tree ages and sizes, large living trees with broken tops and cavities, large standing dead trees (snags), and abundant fallen logs at various stages of decomposition on the forest floor. This structural complexity is the result of several centuries of growth, disturbance, and succession operating simultaneously in the same stand.
Fallen logs are particularly important. A single large western red cedar log can take 500 years to fully decompose, and during that period it serves as a nurse log for seedlings, a moisture reservoir during summer drought, and habitat for dozens of invertebrate and fungal species. Some old-growth sites in BC's coastal rainforest contain more biomass per hectare than any tropical forest on Earth — up to 1,500 tonnes per hectare in the most productive stands.
Salmon and the Forest
The relationship between Pacific salmon and coastal forest is one of the best-documented nutrient-transport relationships in ecology. Salmon are anadromous — they migrate from the ocean into freshwater rivers to spawn and die. Their carcasses, distributed across the forest floor by bears, wolves, ravens, and eagles, deliver marine-derived nitrogen and phosphorus into a terrestrial ecosystem that would otherwise be nutrient-poor. Studies in BC have found marine nitrogen — traceable by its isotopic signature — in the tissues of trees growing up to several hundred metres from salmon streams.
Healthy salmon populations require healthy forests. Intact riparian canopy keeps stream temperatures low enough for salmon eggs to develop successfully; coarse woody debris from fallen trees creates pool habitat for juvenile salmon; and the root systems of large trees stabilize banks and prevent the kind of sedimentation that can smother salmon spawning gravels. The ecological link runs in both directions: logged watersheds often show declines in salmon productivity within a generation of the harvest, while restored riparian areas can show measurable improvements in stream habitat quality within 20 to 40 years.
The Great Bear Rainforest
The Great Bear Rainforest, a name coined by environmental organizations in the 1990s for the central and north coast of BC, encompasses approximately 6.4 million hectares. It is one of the largest remaining intact temperate rainforest systems on the planet. The area includes the territories of numerous First Nations, including the Heiltsuk, Wuikinuxv, Kitasoo/Xai'xais, Gitga'at, and others, who have lived in and managed these territories for thousands of years.
In 2016, following two decades of negotiations among First Nations, the province of British Columbia, forestry companies, and environmental groups, a formal agreement was reached protecting approximately 85% of old-growth forest in the Great Bear Rainforest from industrial logging. The remaining 15% is subject to ecosystem-based management, which sets ecological benchmarks that must be maintained even in harvested areas. The BC Ministry of Forests and the Coastal First Nations coalition both maintain current information on land management in the region.
The coastal rainforest is not a passive backdrop. It is an active, interdependent system in which the death of a single large tree sets off decades of cascading change in the plants, fungi, insects, and vertebrates that depend on it.
Key Ecological Facts
- BC coastal rainforest: approximately 25% of the world's remaining coastal temperate rainforest
- Maximum old-growth biomass: up to 1,500 tonnes per hectare
- Carmanah Valley annual rainfall: over 4,000 mm in some years
- Western red cedar maximum lifespan: over 1,000 years
- Great Bear Rainforest total area: approximately 6.4 million hectares
- Great Bear Rainforest old-growth protected: approximately 85% (2016 agreement)
- Time for large cedar log to fully decompose: approximately 500 years
Detailed species distribution data for BC's coastal forests is available through the BC Ministry of Forests Tree Book. Salmon and forest nutrient cycling research is documented extensively through the DFO Pacific Region and the University of Victoria's School of Earth and Ocean Sciences.
