What is the history of the Coastal Douglas-fir biogeoclimatic zone?
Eleven and half thousand years ago is a mighty long time for a major forest ecosystem. Yet, that is how long Coastal Douglas-fir forests have existed on Canada’s west coast, longer than most other forested biogeoclimatic zones in British Columbia!
Rapid and sudden warming in that distant time fostered the establishment and spread of Douglas-fir in southwest British Columbia. Our regional climate quickly warmed such that Douglas-firs became important forest species beyond the range as we know it today, reaching the north end of Vancouver Island. The climate was warmer and summers drier than they are now much as we anticipate will be the case due to climate change. On south and central Vancouver Island where the typical western hemlock- western redcedar coastal temperate rainforest of the Coastal Western Hemlock Biogeoclimatic (CWH) zone grow now, drought tolerant Douglas-fir pre-dominated. Only about 4,000 years ago did the modern pattern of forest types arise as the climate moistened and cooled.
Those Douglas-fir forests no doubt changed over the eleven and half millennia since their origin. New species such as Garry oaks and Oregon ash were added as they migrated or were introduced to Vancouver Island. Early versions of the forests were more open as associated Garry oak meadow ecosystems developed. There was little or no western redcedar. Bracken fern grew densely as fires burned regularly. Nevertheless, with time the complex relationships among the processes and species we recognize today arose. Indigenous people lived in and used the forests and in time CDF’s globally unique biodiversity emerged.
How have CDF forests changed over time?
Canada’s CDF forests have always been resilient–as one can imagine having persisted for so long. For example, widespread climatic adjustments about 4,000 years ago ushered in modern climates in the northern hemisphere. In this time of transition, Douglas-fir trees growing on the Saanich Peninsula persisted through sudden and short-term climatic fluctuations. This resilience is recorded in the rings of tree trunks recovered from Heal Lake on the outskirts of Victoria, showing a pattern of sudden growth decrease and repeated decline and recovery. The trees and CDF survived to become the ancient ancestors or perhaps even grandparents of some of our recently living old-growth trees.
The forest’s continued resilience is evident today. Much of the CDF ecosystem has been converted to other uses or highly modified by repeated logging passes as eloquently described in other postings in this series. I am lucky to have part of about a 5 hectare stand that was clear cut logged only once in the early 1900’s. Thirty-five years ago when I first saw it, this same stand had a dense canopy and an almost uniform shrub layer of salal, with oceanspray growing in the more open spots. Ghostly stumps and rotting boles of old-growth were widely evident. There were single trillium and vanilla leaf plants. Much has changed since that time. The lowest branches of the firs have died, and many of those branches have dropped to the ground. The canopy has opened and, of course, the trees are much taller now. However, it is the ecological change in the herbaceous layer that attracted my attention.
The vanilla leaf has spread to cover many square metres, as have the trilliums. Pathfinder appeared about twenty years ago. Previously unnoticed or absent, there are now little patches of big-leaved sandwort growing at the base of several firs. The most stunning and wonderful change has been the explosion of orchids. Thirty-five years ago, there were none visible. Today many Calypso orchids bloom, this spring beginning as early as the first week of April. Coralroots have popped up from patches of bare duff, these certainly were not present 35 years ago. Rattlesnake plantain also now grows in the stand. Did they somehow persist in the stand through all those preceding decades, or did they disperse from elsewhere? I favour the persistence idea because no old-growth survived within at least a kilometre of our stand.
These dynamics emphasize two important points of resilience. First, a once-logged stand is not lost forever. It retains features of its past biodiversity which recover after many decades. This is not surprising since the CDF is a fire-initiated long-persisting ecosystem. It is no doubt adapted to profound understory disturbance, followed by a long recovery interval. While this is true, the second point is that it takes many decades to recover key biodiversity characteristics in a CDF stand after a disturbance event. This recovery is doubtlessly linked to mycorrhizal soil dynamics, of which we have little understanding, but are linked to ancient organic matter. The consequence of this is that we cannot keep logging second growth stands and hoping for quick recovery. Each clear-cut pass leads to further loss of life-giving soil organic matter and progressive loss of old-growth species. Who knows how quickly a double or triple-logged stand might get back to supporting the wonderful diversity of orchids I now see in my own stand. Considering climate change, and potentially sudden ecological tipping points we may lose much of the natural species legacy of CDF forests permanently.
There is unfortunately a negative aspect to the dynamics of my stand during the past 35 years. It was in an almost pristine natural condition, without any invasive species except wall lettuce and three holly shrubs, the last easy enough to control. In the past ten years the spurge scourge has invaded dramatically. Spurge laurel seedlings have popped up throughout much of the stand. A couple of plants escaped my notice and now I have several concentrations of seedlings. I am rooting them out. Many places on south Vancouver Island have such dense stands of the spurge scourge that the herbaceous understory is strongly suppressed. Despite the potential for excellent and natural recovery of second growth CDF stands, we have to be vigilant and patrol for and eradicate known and likely new future invaders!
How will climate change impact the CDF?
Ecological changes induced by climate change are underway and more are coming. Thirty years ago, I noted the potential for, and minor signs of western redcedar loss. Now decline is widespread–many trees have died. There is much concern about the species’ future. Even Douglas-fir trees are dying on dry rocky sites, creating openings for Garry oak and meadow ecosystems. Despite these trends, the future of the CDF would seem promising because of its greater range during earlier warm and dry climates, and projections of species and ecosystem impact models. Just how changes may play out over the next decades is not well understood because of the complexity of species-specific impacts and interactions. To have the best possible outcomes, rooted in the resilience of past CDF ecosystems and their inherent biological diversity, we must preserve all remaining old growth, even down to the individual tree, and conserve all second growth as an adaptation to the unprecedented challenges of climate change and biodiversity loss.
In this context, I am fascinated by the small openings associated with shallow soils in the neighbouring CWH stands. These forests often support herbaceous species typical of CDF ecosystems. One of my favourites is seablush, which colours these openings pink in the spring. These dry sites are potential centres for development and spread of the CDF ecosystem. In the CDF seablush patches signal future Garry oak and meadow sites.
What are your recommendations for land managers and others working in the ecosystems found within this zone?
We must see ourselves as part of the CDF, as the Indigenous People have for millennia, not apart from it. First, as has been mentioned many times in other postings, any remaining old growth, including surviving single old-growth trees, must be preserved. The lands surrounding Royal Roads University campus are an example of this. Even scrubby old stands on poor rocky sites deserve preservation! However, this will not be enough and second growth stands, 40 or more years old, also need to be preserved too. They are the stands of the future, and they have potential to develop old-growth characteristics, sequester carbon and keep the old soil carbon in storage.
Beyond preservation, there is a need to conserve CDF landscapes on which preserved stands can be reconnected into a network. Planning and identifying such conservation connection corridors is vital. Even individual older Douglas-fir trees, and natural patches along such corridors, need to be conserved so that they can act as centres of and anchor points for CDF reconnection.
Restoration of CDF and CDF attributes is a third critical action. This involves removing invasive species in stands especially in suburban areas (parks for example) where ivy, holly and now daphne are wreaking havoc. Otherwise, the understory biodiversity has little chance of recovery. Restoration in-planting where replacement trees and native species are added into degraded stands is vital too. In-planting assists the recovery process and adds resilience to climate change impacts.
In general, we need to shift to thinking of ecosystems as being highly dynamic, not only in their composition and their processes but also where they occur. The lessons of the past force us to think outside of the conceptual box and outside of the defined map boundaries of the CDF.
About the Richard Hebda
Richard Hebda is Curator Emeritus at the Royal British Columbia Museum (RBCM) and adjunct faculty at the University of Victoria (UVIC). He curated the museum’s Climate Change permanent exhibit and travelling fossil displays. He helped develop and has taught in the Restoration of Natural Systems Program at UVIC for 26 years. Richard Hebda is (co)author of hundreds of scholarly and popular articles ranging from vegetation history to growing native plants and including climate change. Thirty years ago, he helped save the exceptional CDF ecosystems of Gowlland-Tod Provincial Park on the Saanich Peninsula. Richard and his wife Elaine live in a 120-year-old CDF stand.
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