The story of Coastal Douglas-fir forests: Classifying place

The ecological communities of the CDF are both rare and unique in Canada, this rarity makes conserving the ecosystems that remain a priority.

British Columbia’s Biogeoclimatic Ecosystem Classification system divides the province into 16 disparate, but connected zones. Such systems provide insight into the structure and function of infinitely complex and interconnected ecosystems at a scale that is comprehensible and applicable on the ground, ultimately making ecosystem management possible. However, because classification systems tend to be unique to countries or provinces, political borders often dissect places that remain connected on the ground.

Further, microclimates, soil gradients, shifting nutrient regimes, and other ecological influences and processes can create ecological variations between geographically similar places. As such, though habitats remain connected on the ground and seem similar on paper, across borders they may end up looking quite different due to the influence of local economies, industries, political alignments, climate change and other factors. 

In this article, Del Meidinger who led the development of the BEC system in British Columbia and was responsible for technical quality and standardization of methods and concepts for the BEC program, provides a simple explanation of the BEC system, and highlights the value of conserving unique CDF forests, particularly in the face of climate uncertainty. 

What is British Columbia’s Biogeoclimatic Ecosystem Classification (BEC) system and why is it used?

BEC is an ecological framework where ecosystems are classified at various levels of generalization. The broadest units on the landscape are biogeoclimatic zones, of which the Coastal Douglas-fir zone (CDF) is one. Most zones are divided into subzones, which are areas within the zone that differ in their component plant communities. The ecological concepts behind BEC were developed in the 1960’s by Dr. Vladimir Krajina and his graduate students at the University of British Columbia. In the mid-70’s, the British Columbia Forest Service Research Program adopted the classification framework and hired staff to develop the system in British Columbia. The BEC system has now been implemented in most areas of BC.

Three people walking by a large douglas-fir tree.
Coastal Douglas-fir forests are characteristic to most of the islands in the Salish Sea. Photo by Alex Harris / Raincoast Conservation Foundation.

BEC is based on an analysis of floristic and soil data from many thousands of plots in plant communities throughout BC. The data is used to classify mature plant communities and develop the classification framework, including biogeoclimatic zones and subzones, and the ecosystems within each. The BEC framework integrates vegetation classification with climate and site classification hierarchies (see references).  Maps of the distribution of biogeoclimatic units and field guides for the identification of the ecosystems are available for most areas. These products are used by foresters, biologists, and other interested individuals, to identify ecosystems, understand ecosystem properties and relationships, and apply this knowledge to various land management initiatives. 

The Coastal Douglas-fir zone as described in BC’s BEC system has a limited extent in Canada. Can you describe the similar forests and associated habitats on the American side of the border? How do they differ from Canada’s CDF forests?

In this series, the Coastal Douglas-fir (CDF) biogeoclimatic zone is used interchangeably with “Coastal Douglas-fir forests.” The CDF encompasses areas with a temperate, maritime climate where Douglas-fir, on sites intermediate in soil moisture and soil nutrient conditions (i.e., zonal sites), is a canopy species, but also regenerates in the understorey (i.e. it is shade tolerant). As the climate gets a bit moister, (e.g., at higher elevations or to the west), western hemlock has greater presence, particularly in the understorey and these areas are in the Coastal Western Hemlock (CWH) zone.

The ecosystems of the CDF in southwestern BC are considered one biogeoclimatic subzone—the Moist Maritime CDF (CDFmm). Mature forests on zonal sites are dominated by Douglas-fir with salal and dull Oregon-grape, and Oregon beaked-moss dominating the forest floor. Many other species occur in this plant association, but it is the occurrence of this association on zonal sites that characterizes this subzone. If, for example, there was a portion of CDF with a different plant association on zonal sites, based on a different floristic combination of species, it could be another subzone. The overall floristics and maritime climate would place the two areas in the same zone.

Purple berries (also known as oregon grapes) on a green plant.
Low (or dull) Oregon grape (Mahonia nervosa). Photo by Alex Harris.

The ecosystems of the CDFmm subzone range from moss/lichen communities to Garry oak woodlands and meadows, to Douglas-fir forests, to redcedar swamps, along a generalized soil moisture sequence from dry to wet. Forests with similar climate, tree species, and vegetation communities occur in the San Juan Islands, a short distance away from Canada’s Gulf Islands. They have been included in the CDF by some Canadian researchers due to their similarities to key features of the CDF. 

CDF likely also occurs across the Strait of Juan de Fuca, (e.g., near Sequim, WA) in areas with a dry, coastal climate and with the potential to develop Douglas-fir forests, without western hemlock, on zonal sites. Similar forests also occur in the Willamette and Rogue river valleys of Oregon and both areas have Garry oak on dry sites (called Oregon white oak in the United States). These areas have similar enough characteristics to be included in the CDF zone, but they would be in different subzones due to a somewhat different plant association on zonal sites.

The United States (US) uses different classification systems, often either ecoregion or vegetation-focused classifications and does not generally identify or map units equivalent in concept to the biogeoclimatic classification system. However, biogeoclimatic concepts have recently been applied to areas of the US Pacific Northwest by BC ecologists. This work identifies and maps areas of CDF in Washington and Oregon.

Does the extension of similar habitat types into the United States decrease the value of the CDF associated ecological communities in Canada? Do ecosystems in the CDF need protection?

The ecological communities of the CDF are both rare and unique in Canada. In Canada and the US, the CDF occurs in areas where humans like to live, so in both countries, mature plant communities are limited in extent. As noted, much of the CDF in the US would be in different subzones, and ecological communities would differ somewhat. It is possible that very similar ecological communities to those in Canada occur in the San Juan Islands of the US, and that they are in the CDFmm, but that does not diminish their importance to Canada. In NatureServe conservation ranking, ecological communities are evaluated globally, nationally, and regionally (by province/state) so that various jurisdictions can make their own conservation decisions.

Purple camas flower.
Camas are an iconic CDF species with tremendous value to many First Nation communities. Photo by Shauna Doll.

As noted in other articles in this series, natural ecosystems of the CDF in Canada are very limited in extent relative to their historical distribution. As such, remaining natural areas are of high priority for conservation.

What is species provenance and why does it matter, particularly in the context of threatened and endangered species?

Species provenance refers to the origin of a species and it is generally assumed that the subpopulation of a species that evolved in a particular climate is better adapted to the environmental conditions of that area. However, with a rapidly changing climate, this may no longer be the case. Over time, the climate may become unsuitable for some local subpopulations. It is possible that other provenances of an impacted species could be used to re-establish a species in an area, if desired; however, information on species provenances and their ecological tolerances is not generally available and is generally restricted to some commercial species, such as trees. 

Large douglas fir tree.
The coastal variety, menziesii, of common Douglas-fir grows more quickly than the interior, glauca, variety. The coastal variety typically will not survive or grow poorly in cool temperate climates. Photo by Alex Harris / Raincoast Conservation Foundation.

Threatened and endangered species are at risk of extirpation or extinction due to a multitude of threats. In the CDF, past land use decisions have greatly limited the present area of natural vegetation. Some conversion to agriculture or housing does still occur, along with some forest harvesting, but the biggest threat appears to be alteration of habitat due to exotic invasive species, woody vegetation encroachment, changes to hydrology, etc.

Do you have any recommendations for how residents, land managers, and others living in the CDF zone can best care for local ecosystems, particularly in the face of climate change? 

There is considerable uncertainty in how climate change will impact the species of the CDF. Most of the species of the CDF in Canada do have ranges to the south, where climates are hotter, but our local provenances may not have the same adaptive capacity to withstand hotter temperatures. Also new extremes of heat and drought are likely to impact some species. We are already seeing the impact on western redcedar on some sites in the CDF. 

At this time, the “best” option is to try to maintain the natural vegetation that remains and to do what we can to maintain or improve the ‘health’ of these ecosystems. Examples include removing and controlling the spread of exotic invasive species, maintaining the natural hydrology, and, for Garry oak woodlands, maintaining the open woodland tree cover. It seems inevitable that there will be climate change impacts to the remaining natural communities of the CDF—our goal should be to do what we can to minimize potential impacts. 

Overhead photo of a forest next to the ocean.
Photo by Alex Harris / Raincoast Conservation Foundation.

References and further reading

Klassen, H., and P. J Burton. 2015. Climatic characterization of forest zones across administrative boundaries improves conservation planning. Applied Vegetation Science 18: 343-356.

Mackenzie, W.H., and D.V. Meidinger. 2018. The biogeoclimatic ecosystem classification framework: an ecological framework for vegetation classification. Phytocoenologia 48: 203-213. 

Mackenzie, W.H., and C.R. Mahony. 2021. An ecological approach to climate change-informed tree species selection for reforestation. Forest Ecology and Management 481, 118705.

Wikipedia. 2023. Biogeoclimatic ecosystem classification. Biogeoclimatic ecosystem classification – Wikipedia 

About Del Meidinger

Del Meidinger has considerable experience in ecosystem classification and mapping. In his 30-year career with the BC Forest Service Research Branch he led the development of the Biogeoclimatic Ecosystem Classification (BEC) system. In doing so, he also worked with the BEC team to apply the classification to conservation and forest management including tree species selection, ecologically-based timber supply analysis, at-risk ecosystem assessment, and climate change implications to forestry. Del was responsible for technical quality and standardization of methods and concepts for the BEC program. He has also been intimately involved in the development of the ecosystem mapping protocols for BC, including writing the Terrestrial Ecosystem Mapping (TEM), Predictive Ecosystem Mapping (PEM) and map accuracy assessment standards. His field experience is throughout BC: collecting field data, correlating biogeoclimatic mapping and field guides, and assessing ecosystem mapping. 

For the past 14 years, Del has been consulting (Meidinger Ecological Consultants Ltd.), continuing to provide ecological classification services to clients such as Environment Yukon, Metro Vancouver, B.C. Ministry of Forests, Natural Resources Canada, and Western Forest Products. Del also sits on the Canadian National Vegetation Classification Technical Committee, is a Regional Editor of the US National Vegetation Classification and serves as a vascular plant specialist on the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).

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Research scientist, Adam Warner conducting genetics research in our genetics lab.
Photo by Alex Harris / Raincoast Conservation Foundation.