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By David T. Price and Robin Collins
To summarize, climate change is ongoing and is set to persist for decades, at a minimum. This phenomenon threatens all of Canada’s forests, jeopardizing their role as a “carbon sink”. Public efforts to curb climate change often coincide with a heartfelt urge to preserve our remaining old-growth forests from logging, even though these ecosystems and the carbon they store are vulnerable to a warmer and drier climate. Consequently, we call for a nationwide initiative to map the susceptibility of all forests. The boundaries are yet undefined, but we are hopeful that any resulting data would be used wisely and transparently.
We coined the term “triage” to categorize Canada’s forests into three main classes based on the degree of climatic harm (the specifics are yet to be determined). The “Protectable Forests” will likely endure the impacts of climate change for a significant duration without human interference. Conversely, the “Disappearing Forests” are unlikely to make it beyond 2100 despite our best conservation efforts.
Nestled between these two classes are the “Manageable Forests”, where the combined impacts of drought, wildfire, and insect herbivores may lead to significant degradation in ecosystem health, endangering their survival and biodiversity. This is where human intervention could alleviate these impacts.
We should focus our efforts on shielding old-growth forests in the Protectable category from logging. On the other hand, Manageable Forests should primarily provide raw materials, as any investment in shielding them from a warmer, drier climate must be recouped somehow.
It would be reasonable to expect Canada’s forestry industry to replant disturbed areas and make their practices as sustainable as possible. The typical forest management cycle-harvesting, regeneration, tending, and re-harvesting over a span of 60 to 80 years-allows tree species and forestry practices to adapt more swiftly to environmental changes. Harvested wood could serve as a renewable resource while also acting as a carbon sink.
It is crucial that the forestry industry enhances the utilization of harvested wood and expands the production of construction materials wherever possible. These materials keep carbon out of the atmosphere for longer than it typically stays in natural forests. Here, we address the questions our article has sparked:
The conventional understanding of forest “carbon sinks” is somewhat skewed. A natural forest carbon sink is the equilibrium of CO2 absorption and release-which, over multiple tree lifetimes and vast regions, balances out to zero (or close to it). The role of old growth forests as “carbon stores” is tied to this. When logged, a portion of that carbon can be quickly released into the atmosphere, and it may take years, even decades, for a replacement stand to sequester that carbon.
In a 2018 study published by Law et al. in the Proceedings of the (US) National Academy of Sciences (PNAS), they focus on temperate evergreen forests in Oregon. These forests, like BC’s coastal forests, can live up to 800 years, largely due to the mild wet climate that encourages growth while generally inhibiting intense stand-killing wildfires.
However, photosynthesis in any plant canopy is limited by leaf area. The maximum leaf area in an old forest is not significantly different from when the young trees first formed a closed canopy a century or more earlier. As the trees age, their respiring biomass increases, leading to increased respiratory CO2 losses. Additionally, as the forest grows, it houses a growing biomass of herbivores and decomposers, which release CO2 just by existing. All these CO2 releases must be deducted from total photosynthesis. In the long run, the net ecosystem C uptake tends to zero- making old forests weak carbon sinks.
Some old forests, due to their age and size, store carbon that was removed from the atmosphere centuries ago! If these forests were to be logged, much of the wood could be wasted, leading to the release of much of the stored carbon within a few decades. It would take much longer for a young stand to reach a stage where its net carbon accumulation surpassed the amount lost when the old stand was logged.
If forests are deemed able to withstand expected climatic changes over the next 100 years, they would be categorized as Protectable. We believe these should be protected at all costs, considering their intrinsic values, especially as ecological refugia, and their capability to keep large amounts of carbon out of the atmosphere. However, if their survival prognosis is grim, harvesting may be a preferable option.
Let’s be unequivocally clear: The responsibility for the decision to log a specific old-growth forest area lies with the elected government of the respective province or territory, guided by the best available science.
While Law et al. do not think wood products store a significant amount of carbon for a long duration, we question the validity of some of their assumptions and whether they apply to the Canadian context. Some of their cited sources, which we have reviewed, do not fully substantiate their assumptions!
A 2017 article by Tollefson reports on recent advancements in wood technology and the consensus among wood scientists that engineered wood products could play a vital role in mitigating GHG emissions. Despite supporting evidence from numerous global scientists, Law et al. appear to disregard these claims.
They found that logging old-growth forests on the Pacific coast of North America often leads to significant wastage and carbon loss. However, BC’s coastal forests account for merely about 10% of Canada’s forested areas-and most have already been logged at least once since the late 19th century. Environmentalists are, understandably, committed to preventing the industry from logging the relatively small remaining areas.
Across the border to New Brunswick and Newfoundland, while these forests are incredibly diverse, they share several common traits. Predominantly slow-growing due to the cold continental climate and short growing seasons and receiving low annual precipitation-particularly in the west- they frequently experience drought and wildfires.
Due to the frequency of fires, boreal trees rarely live past 200 years, and some pine-dominated ecosystems may only survive around 60 years. Boreal forests seldom reach the age of unlogged coastal old-growth, and trees are generally smaller at comparable ages. Consequently, boreal forests rarely hold as much biomass (and stored carbon) per hectare as coastal old-growth.
As our climate warms, it is reasonable to expect that drought, tree mortality from insects, and wildfires will increase, reducing the average amount of CO2 being absorbed and escalating the losses. Many northern boreal forests store significant organic carbon in soils and surface litter; these are also vulnerable to climate change, facing accelerated decomposition and burning as they warm and dry.
Although we cannot predict where or how much of Canada’s boreal forests would be classified as “Manageable,” we anticipate a significant portion of the total area.
Does half the carbon in houses built today remain intact for 100 years?
Several recent studies in Canada and the USA have explored how harvested wood products serve as carbon stores.
Long-lived wood products (LLWP), such as sawn lumber and various engineered materials like plywood and oriented strand lumber, used in timber-framed buildings, are protected from fire and decay. We can estimate how much wood was used to build houses in the early 20th century and how many buildings remain in use decades later from public records and house demolition studies (where all wood components are weighed).
The loss of carbon stored in housing due to demolitions, renovations, or house-fires, can be estimated from these data and follows an exponential decay curve. On average, about half of the wood used in single-family houses persists for around 100 years (with smaller fractions for multi-unit residential and commercial buildings.)
Taking this ~50% loss into account, we estimate that the LLWP obtained from logged areas between 2011 and 2020 will keep approximately 100 Mt C out of the atmosphere for a century. Wood recovered from demolished buildings might be processed into biochar for use in agriculture and horticulture, instead of landfills, further extending the persistence of carbon in LLWP.
Wildfire is a natural occurrence in most Canadian forests. As fire-suppression became more effective in the mid-20th century, the average age of managed forests increased, along with fuel accumulations. But a hotter and drier climate, along with extra fuel, now makes fires more intense and increasingly difficult to suppress-leading to larger areas burned on average. (One unavoidable consequence will be increasing areas with young stands and fewer old forests.)
Identifying forests which require intervention to survive climate change would allow better integration of fire management practices (e.g., controlled burning to reduce fuel loads) into a carefully planned cycle of regeneration, tending and harvesting on smaller patches of land. This strategy will enhance biodiversity, which could be lost from climate-caused large-scale fire damage. (We can also learn from traditional Indigenous burning practices.) A more fragmented landscape, possibly containing more deciduous species in place of conifers, should also help contain future wildfires. Fires will spread less rapidly across open areas cleared of fuel, and a well-planned network of roads and clearings allows faster and safer access and exit for fire-fighting crews and equipment.
David T. Price is a retired forester with Natural Resources Canada.Robin Collins writes about ideas, peace, and disarmament from Ottawa.