Climate change induced drought and water stress is increasing tree mortality in Canada's boreal forests, particularly in western Canada, resulting in a reduction in biomass which reduces it's capacity as a carbon sink. As tree mortality increases, there is reduced capacity to absorb carbon dioxide, resulting in a feedback loop where conditions become warmer and drier increasing the stress on the boreal forest ecosystem and ability to absorb carbon dioxide that humans keep on pumping into the atmosphere at increasing rates.
There are big changes happening in the high latitudes where global warming is stronger, and the increased temperatures are more pronounced. Canadian boreal forests cover 77 per cent of forested land in Canada and amount to 30 per cent of Boreal forests globally. The forests play a critical role in the albedo of Earth’s surface and in its global carbon budget.
The Pew Environment Group described the importance of the Canadian boreal forests:
Scientists have identified the 1.2 billion acre Canadian boreal forest as the largest intact forest and wetland ecosystem remaining on earth. Rivaling the Amazon in size and ecological importance, Canada’s boreal supports the world's most extensive network of pure lakes, rivers and wetlands and captures and stores twice as much carbon as tropical forests. It teems with wildlife—including billions of migratory songbirds, tens of millions of ducks and geese, and millions of caribou. The Canadian boreal is an irreplaceable global treasure.
Peatlands in Canada's Boreal Forests - Carbon Storage in Canada's Boreal Forest
Climatic warming has affected forests ecosystems around the world with changes in net primary productivity, forest growth, carbon balances, plant phenology and species distribution moving polewards. Much research has been done on impacts of tropical forests and temperate forests. The boreal forests in the high latitudes have been found to be sensitive to drought and have been identified as an important climate tipping point by research work lead by Dr Changhui Peng from the Laboratory for Ecological Modelling and Carbon Science (ECO-MCS) Lab from the University of Quebec at Montreal (UQAM).
A paper published in Nature Climate Change on 20 November 2011 by Changhui Peng et al - A drought-induced pervasive increase in tree mortality across Canada’s boreal forests (abstract) highlights the importance of this change:
The possibility of increasing tree mortality in boreal forests is a particular concern because boreal forests have been identified as a critical `tipping element' of the Earth's climate system and are believed to be more sensitive to drought than other forests.
The study found that tree mortality rates increased by an overall average of 4.7% per year from 1963 to 2008, with higher mortality rate increases in western regions than in eastern regions - 4.9 per cent in Western Canada and 1.9% in Eastern Canada. Drought has particulary affected the western provinces creating water stress and tree mortality. Regional drought has been assessed as the dominant contributor to widespread increases in tree mortality rates across tree species, sizes, elevations, longitudes and latitudes.
Drought and warmer temperatures brought about by climate change has increased the extent of outbreaks of beetle and insect infestations which can contribute to tree mortality. Drier forests adds to increasing wildfire frequency, intensity and size which releases carbon and affects the forest's capacity to regenerate. Scientific research has already identified that Wildfires in Canada are approaching threshold point due to climate change.
The researchers indicate that the increased tree mortality may not be adequately included in carbon-cycle modelling resulting in an overestimation of the carbon sink capacity in previous studies of the ability for these forests to offset anthropogenic carbon dioxide under a warmer, drier environment.
Despite recent progress, the uncertainty around the responses of tree mortality to climate change limits our ability to forecast the likelihood and the impacts of this mortality. Studies are needed to further explore the physiological mechanisms responsible for tree mortality in a wide variety of functional types, to connect patterns of mortality with extreme climate events and to forecast the potential impacts of tree mortality on carbon, energy and water fluxes.
Tree mortality has the potential to transform boreal forests from a net carbon sink into a carbon source, thus accelerating global warming. The scientists conclude in their paper on tree mortality:
Under future global warming scenarios, severe regional droughts are likely to become more frequent, and this trend is expected to continue for the foreseeable future. Drought-induced tree mortality in Canada may also co-occur with peaks of forest ecosystem disturbances such as insect outbreaks and increased fire activity. Such interactions among climatic warming, ecosystem disturbances and forest responses represent potential positive feedbacks that could dramatically alter future carbon sink-source relationships in boreal forests. If this tree mortality continues to increase more rapidly than growth in response to climate change, this will reduce net forest growth, transform Canadian boreal forests from a net carbon sink into a large net carbon source, weaken the terrestrial carbon sink and increase future atmospheric carbon dioxide levels during the twenty-first century.
Reduction in the biomass carbon sink of Canada's boreal forests
A second related paper was published by Changhui Peng and colleagues on January 30, 2012 in PNAS as Regional drought-induced reduction in the biomass carbon sink of Canada's boreal forests (abstract) which builds upon the tree mortality research to analyse the biomass reduction taking place. The article abstract says in part:
We found that in recent decades, the rate of biomass change decreased significantly in western Canada (Alberta, Saskatchewan, and Manitoba), but there was no significant trend for eastern Canada (Ontario and Quebec). Our results revealed that recent climate change, and especially drought-induced water stress, is the dominant cause of the observed reduction in the biomass carbon sink, suggesting that western Canada’s boreal forests may become net carbon sources if the climate change–induced droughts continue to intensify.
According to the study the annual mean temperature in Western Canada has increased significantly since 1963, and annual precipitation has decreased just as precipitously resulting in significant water deficits. In the eastern region of Canada both annual mean temperature and the annual precipitation increased significantly resulting in reduced water deficits.
The research identified that drought and water stress are primary factors in changes in stand density indicating the number of surviving trees is decreasing for all regions examined across Canada. However in the western region biomass showed a significant decreasing trend resulting from cumulative effects of increased mortality and decreased growth of surviving trees. In the eastern region biomass showed no significant change with a simultaneous increase in mortality and growth of surviving trees representing offsetting factors so that no trend in biomass change was present.
According to the study, the observed rates of biomass accumulation in western regions changed from
positive to negative after 2003, with a continuous decrease in biomass from the start of the study period. This may indicate that climate warming may soon begin to decrease the carbon sink and
change these forests into a net carbon source if the current trends continue.
The reduction in carbon sink capacity from forest mortality was calculated to be equal to 7.28 ± 3.13 million tons of carbon per year (Mt C year). The resulting reduction in the biomass carbon of Canadian boreal forests would amount to about 37% of the carbon source in the year 2009 (20 Mt C year) projected to be lost due to beetle caused mortality, about 27% of the direct emissions caused by forest fires throughout Canada from 1959 to 1999, and equivalent to about 3.6% of Canada’s total annual carbon emissions.
The studies on the boreal forests were undertaken from 96 long-term permanent forest observation plots in natural (unmanaged) mature boreal forests. The sample areas included plots in five Canadian provinces in both western Canada (Alberta, Saskatchewan, and Manitoba) and eastern Canada (Ontario and Quebec). The plots spanned 53° of longitude and 9° of latitude, and their elevations ranged from 59 to 2,609 m above sea level (asl). The plots ranged from 0.04 to 0.82 ha, and contained 22,425
living trees; the plot data included a total of 74,556 observations. The initial census year ranged from 1963 to 1994 and the final census year ranged from 1990 to 2008. The aboveground
stand biomass at each census was estimated by using published allometric models developed for Canadian boreal forests. The researchers used both the annual climate moisture index (CMI) and the annual moisture index (AMI) to measure water deficits.
With the impact of drought affecting tree mortality, increasing temperatures encouraging outbreaks of bark beetle (Dendroctonus rufipennis), increasing conditions for more frequent, more intense and larger wildfires, large parts of the boreal forests may become a landscape trap transforming the boreal forest ecosystem permanently to grasslands. (See example: mountain ash forest landscape trap of Victoria, Australia)
Watch this short video on the importance of Canada's Boreal Forest made by the Pew Environment Group
While the dieback of boreal forests progresses, the Canadian Environment Minister announced on December 12 that Canada was withdrawing from the Kyoto Protocol. Canadian carbon emissions are up 35% since 1990, despite a target under the protocol of 6% lower than 1990 levels by 2012.
Boreal Forests under threat from logging, mining and oil and gas development
The Canadian tar sounds are also located in Canada's boreal forest which has required substantial forest logging and destruction for the open pit mining techniques currently being employed. Tar sands production in Alberta emits 27 megatonnes of green hous gas emissions per annum and is expected to rise to 108-126 megatonnes by 2015. The tar sands are poised to become Canada’s largest single emitter of greenhouse gas, compounding the country’s contribution to global warming. Tar sands also require enormous amounts of water for processing resulting in huge toxic tailings ponds.
After the easy surface tar sands are mined, operators will need to access the deep tar sands, which are 81% of established reserves. For in situ recovery of all of Alberta’s underground reserves, the area impacted will be vast – approximately 13.8 million hectares (ha), or 50 times the area of the mining zone. This equals 21% of Alberta. In Situ mining will result in 296,000 ha of forest to be cleared for infrastructure and over 30,000km of access roads built. This will have a substantial impact on ecosystems with stress from climate change and proximity to human development affecting many species populations.
The Pembina Institute's 2006 report - Death by a thousand cuts. Impacts of in situ oil sands development on Alberta's boreal forest (PDF) - looked at the environmental impact of the tar sands on the boreal forest ecosystem and said that "Although precise ecological tipping points have not been defined, evidence is steadily mounting that ecological thresholds for many species are already being exceeded at current levels of industrial development in northern Alberta." (pp14).
There are over 170 square kilometres of toxic tailings ponds from tar sands mining, which annually kills a scientifically estimated minimum of 458 to 5,029 birds, many of them migratory species. The iconic critically endangered whooping cranes (World’s last wild migrating whooping cranes threatened by Alberta’s oil sands developments - PDF), with only 270 birds as of 2008, are particularly at threat as they migrate to breeding sites in Wood Buffalo National Park, located in the Northwest Territories and northern Alberta.
“The whooping crane is an archetypal symbol of North American conservation,” says Peter Lee, author and executive director of Global Forest Watch Canada. “The magnificent bird is endangered in both Canada and the United States, and exists only in North America. Still, there is little evidence that the Governments of Alberta and Canada have adequately considered whooping cranes in the approval of industrial developments in Alberta’s oil sands region.”
“The rapid pace and large scale of Alberta’s oil sands industrial developments within the flight path of migrating whooping cranes raises the concern that damage may already be done. Considering the endangered status of whooping crane and its central place in North American conservation, it is imperative that adequate information about the conservation needs of whooping cranes are dealt with explicitly in land use plans, environmental impact assessments and approvals for industrial developments. This is not the case so far.”
The Wilderness committee opened a Boreal Research Station in northern Alberta in 1992. They describe:
Our boreal studies also led us to conclude that scientific understanding of how boreal ecosystems function is in its infancy and that research on boreal forests is inadequate to justify massive extractive resource activity such as oil and gas, tar sands, mining and logging. Recent studies have found that the carbon stored in our boreal forests is equivalent to more than 900 years of Canada’s total greenhouse gas emissions. Another study found that the boreal forest in Canada is worth 13.8 times more than the combined value of all resource extraction. We must use precaution when managing the boreal forest. Industrial activities must be ecologically justified, and protected areas be prioritized.
In late January 2012 British Columbia Premier Christy Clark told the Association of Mineral Exploration (B.C.) that he would cut the red tape allowing mining companies to expand increasing development and exploitation. To the north in Nunavut territory there is already a uranium exploration boom happening with more than $322 million spent on uranium exploration in 2011, up from $189 million in 2009, with the mining boom often dividing Innuit communities.
Background information:
- International Boreal Conservation Campaign including detail on the Boreal Forest and Global warming with maps highlighting carbon storage.
- Pew Environment Group - International Boreal Conservation campaign
- Global Forest Watch Canada
- Yale Environment360, September 23, 2011 - A Troubling Decline in the
Caribou Herds of the Arctic
Sources:
- Changhui Penga et al, Nature Climate Change on 20 November 2011 - A drought-induced pervasive increase in tree mortality across Canada’s boreal forests (abstract)
- Changhui Penga et al, PNAS, January 24, 2012 - Regional drought-induced reduction in the biomass carbon sink of Canada's boreal forests (abstract)
- Climate Citizen
- Richard Schneider and Simon Dyer, August 2006 - Death by a thousand cuts. Impacts of in situ oil sands development on Alberta's boreal forest (PDF)
- Climate Citizen, December 18, 2011 - Wildfires in Canada approaching threshold point due to climate change
- Wilderness Committee - Canada's Boreal Region
- Image from Flickr by Gord McKenna - Wetlands near Utikuma Lake, northern Alberta 2010 Creative Commons (CC BY-NC-ND 2.0)
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