- Author: Jason Alvarez. University Communications
Reposted from UC Merced News
Yosemite Valley in the western Sierra Nevada Mountains.
What if nature were to become a polluter, discharging millions of tons of planet-warming carbon into the atmosphere in much the same way as diesel-fueled trucks or coal-fired power plants?
This nature-as-polluter scenario might seem far-fetched, but it's well on its way to becoming reality, according to a recent study co-authored by UC Merced Professor LeRoy Westerling.
In a paper published recently in Scientific Reports Opens a New Window.— “Potential decline in carbon carrying capacity under projected climate-wildfire interactions in the Sierra Nevada” — Westerling and collaborators from the University of New Mexico and Penn State University used three climate models and data from the Intergovernmental Panel on Climate Change to examine how rising global temperatures and increasingly severe wildfires will affect Sierra Nevada forests.
Their conclusion: Changing conditions will turn today's Sierra Nevada forests into tomorrow's greenhouse gas emitters.
“Forests play an important part in regulating the levels of atmospheric carbon,” Westerling explained. “Forests are carbon sinks, essentially giant stockpiles of carbon. Forests are also active carbon consumers. They remove carbon dioxide from the air and convert it into biomass. This traps the carbon, which is no longer free to act as a greenhouse gas in Earth's atmosphere.”
Professor LeRoy Westerling
But projections from Westerling and colleagues suggest that this may change. According to their models, Sierra Nevada forests will experience both a dramatic loss of stored carbon and a substantial decline in their ability to remove CO2 from the atmosphere.
Rising temperatures are creating a warmer, drier Sierra Nevada climate. Westerling previously showed that these changes are leading to dramatic increases in the frequency, size and duration of wildfires. The new study suggests that these same changes will make it harder for forests to regenerate, leading to a loss of forest density, with plants better suited to the new climate eventually replacing trees.
“As trees are displaced, the Sierra Nevada will lose its ability to sequester carbon,” Westerling explained. “The plants that spring up in their place will be significantly smaller, making them less effective carbon sinks than the trees they replaced.”
But the carbon stored in forest trees has to go somewhere.
As trees are burned in more frequent wildfires, and as dead trees undergo decomposition, Westerling and his colleagues predict that as much as 73 percent of the carbon in Sierra Nevada forests will be released, resulting in a dramatic spike in atmospheric carbon. This will transform the Sierra Nevada from a carbon sink into a carbon emitter, making the nature-as-polluter scenario a reality.
Westerling and his collaborators note that their predictions are actually conservative. The effects might be more extreme than their models suggest.
“Our study does not account for a number of factors that might influence the dynamics of forest carbon,” Westerling said. “However, the factors we ignored are likely to accelerate the loss of forest. Our predictions likely underestimate the severity of actual effects.”
Though the predictions are alarming, the authors remain optimistic, hopeful that their findings can contribute to a larger conversation about environmental policy and promote avenues of research that lead to sustainable forest management.
- Posted By: Jaime Adler
- Written by: Bill Stewart, UCCE Forest Specialist
Making estimates of the life cycle benefits of harvested sawlogs are now required as part of every timber harvest plan in California. While forest managers are intimately familiar with what happens in the forest and at the landing, we are dependent on others to synthesize current and historical data to come up with accurate estimates of the ‘carbon footprint’ of sawlogs after they have left our control. Unfortunately, a number of the common calculators used in California to estimate the life cycle benefits from sawlogs depend on historic and poorly documented estimates that significantly undercount the climate benefits of harvested products. This post highlights some noticeable differences between accounting systems and concludes that data-based estimates will clarify the often underestimated benefits of wood products with respect to global carbon storage impacts.
As anyone who has seen new wood buildings going up, there are many technological innovations, such as the I-Joists (shown below), that suggests that ever more building performance is being squeezed out of logs. A key question for any accounting system that is predicting future trends is how technological innovation is addressed in the estimates.
Both the Climate Action Reserve (CAR) Forest Protocol 3.2 (http://www.climateactionreserve.org/how/protocols/adopted/forest/current/) and the Calfire GHG Estimator (http://www.fire.ca.gov/resource_mgt/resource_mgt_forestpractice_pubsmemos_memos.php) refer to a USDA Forest Service document, GTR-NE-343 (Smith 2006) or the DOE 1605b publications with the same data tables as the key source for their estimates. For simplicity, I will compare estimates based on current efficiencies with the California relevant data tables in Smith (2006). The following bar chart compares the estimated climate benefits from an initial delivery of 100 tons of sawlogs to a sawmill in California through all the end uses over a century.
The bioenergy benefits estimates for the 2006 and 2009 USDA Forest Service publications are fairly similar but are ignored by both Climate Action Reserve (CAR) and Calfire. For whatever reason, CAR and Calfire treat bioenergy from wood residues as if they create no useful energy. However, the use of wood residues for energy is considered to be a climate benefit by both the California Energy Commission and in the national accounting that the US EPA provides to the International Program on Climate Change (IPCC) since they replace fossil fuel based sources of energy.
The other differences are how much wood gets wasted in the sawmill (an estimated 15.6% in Smith 2006 versus a measured 1.5% in the 2010 RPA document), the useful life span of the wood products, the efficiency of the collection of wood waste after consumers toss it out, and whether the landfill storage gets counted as carbon storage or not. We do not need to go into great detail here, but more recent data such as Skog (2008), Smith (2009), and US EPA (2011) all provide estimates that wood carbon is stored much longer in both products and landfills than estimated by Smith (2006). The difference between more recent and better documented life cycle analyses and the CAR and Calfire protocols are even greater since CAR and Calfire ignore bioenergy.
After all the numbers are in, it appears that the best practices for utilizing sawlogs in California can retain over 90% of the initial carbon storage benefits. Unfortunately, project level accounting systems that choose to use poorly documented historic estimates and ignore bioenergy (even though bioenergy meets the Renewable Portfolio Standard –RPS - in California) come up with much lower numbers that are out of sync with more recent work in North America and Europe. For example, accounting systems that only include the carbon in wood products assumes a carbon storage efficiency of only 25%. As I mentioned earlier, any consideration of technological innovation will further improve the amount of initial wood carbon that stays in storage or is used as bioenergy.
As California moves towards our stated goals to become more energy-efficient, reduce fossil fuel related emissions, and shift away from energy-intensive building materials, we will need to ‘double check’ our math when it comes to thinking about sawlogs once they leave the landing.
Skog, Kenneth E. 2008 Sequestration of carbon in harvested wood products for the United States. Forest Products Journal 58 (6):56-72.
Smith, James E., Linda S. Heath, Kenneth E. Skog, and Richard A. Birdsey. 2006. Methods for calculating forest ecosystem and harvested carbon with standard estimates for forest types of the United States GTR-NE-343. USDA Forest Service, Northeastern Research Station: Newtown Square, PA.
Smith, W. Brad, tech. coord; Miles, Patrick D., data coord.; Perry Charles H., map coord,; Pugh, Scott A. Data CD coord. GTR-WO-78. 2009. Forest Resources of the United States, 2007. Washington, DC: USDA Forest Service, Washington Office.
U.S. Environmental Protection Agency. 2011. Inventory of U. S. Greenhouse Gas Emissions and Sinks: 1990 – 2008. http://epa.gov/climatechange/emissions/usinventoryreport.html