The Douglas-fir / dull Oregon-grape ecosystem is the predominant forest ecosystem forming the forest matrix within its range. In British Columbia this ecosystem occurs only in the Coastal Douglas-fir (CDF) biogeoclimatic zone (Green and Klinka 1994) which occupies a total of 2,593 km2. The CDF Zone lies in the rain shadow of Vancouver Island and the Olympic Mountains, and includes eastern Vancouver Island from Saanich Peninsula in the south to Bowser in the north, portions of the Gulf Islands south of Cortes Island, and pockets along the south coast of mainland British Columbia on the Sunshine coast and the Fraser River delta. It is also reported from the San Juan Islands of adjacent Washington, USA. It is found up to 380 m elevation on gentle to moderately sloping sites with mesic or slightly drier soil moisture regimes and medium to poor soil nutrient regimes, where sandy loamy soils are common. The overstorey is typically dominated by Douglas-fir, with a well-developed shrub layer dominated by dull Oregon-grape and/or salal, a sparse herb layer, and a well-developed moss layer dominated by Oregon beaked moss. Western redcedar and grand fir may co-dominate the overstorey. Historically, this was a late succession climatic forest ecosystem originating from infrequent stand-replacing fires, which typically retained veteran trees. Occasionally, windthrow results in a loss of mature, old, and veteran trees.
The total area currently occupied by the ecosystem, calculated from Terrestrial Ecosystem Mapping (TEM) (Green 2007, Madrone Environmental Services Ltd. 2008), is 83,473 ha; this is 37% of the total mapped CDF area. Mature or old forest covers 14,427 ha or 17.2% of this occupied area.
The Conservation Data Centre mapped 88 element occurrences for the Douglas-fir / dull Oregon-grape ecosystem based on TEM (Green 2007, Madrone Environmental Services Ltd. 2008). Element occurrences are ranked for ecological integrity following element occurrence specification documentation (Cadrin et al. 2012). Only 28 element occurrences are ranked with excellent or good ecological integrity based on ecosystem condition, size of occurrence, and surrounding landscape context, for a total of 17.2 % of the mapped area. Fourteen areas with some form of protection contain more than 50 ha of mature or old forests of this ecosystem.
The long-term trend indicates 89% of the ecosystem has been converted to other uses or harvested, with 3% remaining as old forest. The short-term trend indicates that 16% of the ecosystem was converted in the last 40 to 50 years. This conversion is still occurring, and will likely continue to occur due to most of the CDF zone being privately owned. The condition of the Douglas-fir / dull Oregon-grape ecosystem has been degraded by widespread fragmentation, development and harvesting that has occurred in the CDF zone. The dominance of younger age forests means that attributes of older forests are missing from stands.
There is moderate potential for restoration of the Douglas-fir / dull Oregon-grape ecosystem. The attributes of old-growth structure, such as coarse woody debris; complex canopy structure, including large old trees; and standing dead trees, can recover through natural processes, but may require more than 100 years, depending on the biological and structural legacies remaining after disturbance.
The most serious and on-going threats are clearing related to residential development and forest harvesting. Associated with these threats are road development, alien invasive plants and recreational use....
de Groot, A., Carmen C.. 2018. Ecosystem Status Report for Pseudotsuga menziesii / Mahonia nervosa (Douglas-fir / dull Oregon-grape) Ecological Community in British Columbia. Province of BC, Ministry of Environment and Climate Change Strategy