Can Boise’s Foothills help fight climate change? Boise State researchers look at how much

Excess amounts of atmospheric carbon are dangerous, filling the sky with molecules that trap solar heat and increase the temperature of the Earth.

But carbon in nature is found in many other forms, too. It can be stored in oceans, in plants and in rocks. It can also be stored in soil, which Boise State University professors think could have significant implications for Boise’s fight to shut off carbon emissions into the air.

This month, the Boise City Council approved a $109,000 study to analyze carbon found in the soils of the Boise Foothills, a project designed to map the reserves of open land and calculate how carbon is sequestered, or stored, by various plants.

The money for the study comes from the city’s open space levy funds, which derive from a 2015 ballot measure. The fund, which is administered by the Open Space and Clean Water Advisory Committee, has $7.4 million available, according to the memo.

The city aims to use the carbon mapping to learn how leaders could maximize carbon storage through targeted plantings in the city’s 5,000 acres of open space in the Foothills, according to a memorandum from the Parks and Recreation Department. The study’s findings could also guide Boise’s future open-land acquisitions.

In 2021, Boise committed to conserving 30% of its lands by 2030. In December, nearly every country in the world approved an agreement to protect the same percentage of lands and oceans by 2030, a major development as the Earth’s biodiversity plummets. The U.S. did not sign onto the treaty, as Republicans in Congress oppose membership in the Convention on Biological Diversity.

Boise’s leaders are also working to electrify city buildings. On Jan. 10, the council approved $2.8 million in spending of federal funds to convert some buildings from natural gas to electricity. Natural gas accounts for 9% of the city’s overall emissions.

As a method of keeping carbon out of the atmosphere, sequestration of carbon in the soil is a form of “negative emissions.”

What is carbon sequestration?

When plants photosynthesize to grow, they absorb carbon dioxide from the atmosphere. Each plant is at least 40% carbon, Marie-Anne de Graaff, a Boise State biology professor and the study’s leader, told the Idaho Statesman by phone.

When trees drop their leaves or when plants otherwise die, the carbon in their organic material works its way into the ground through rainfall, the activities of voles and earthworms, and through decomposition by microbes. Plant roots also secrete carbon into the soil in the form of sugars. De Graaff described roots as “leaky straws.”

As plants grow in soil, the relationship of carbon to the dirt works kind of like a bank account. When microbes decompose plants, some of the carbon is spent by being released into the atmosphere as carbon dioxide, but some is saved in the soil.

“You have carbon coming in ... and then you have carbon going out through microbial decomposition,” de Graaff said. “What we are interested in with our project, is seeing how much is retained in soil.”

Once carbon gets into the soil, it is relatively stable, de Graaff said, so it is unlikely to be released.

Plants and soils absorb an estimated 30% of the carbon dioxide emitted by human activities each year, according to Stanford University researchers. Scientists are studying how carbon absorption will change in the future, as well as how different plant combinations change the equation.

“It’s a really big thing in science right now to understand, because it’s so important for the carbon balance globally, and (for) trying to model how our climate is going to change in the future,” de Graaff said.

Drier ecosystems, like the Boise area’s sagebrush steppe, tend to store less carbon than wetter ecosystems do, but the huge amount of dry lands in the world make them a significant carbon sink, de Graaff said. More carbon in the soil also makes the ecosystem healthier, she said.

“For us to be able to understand how much carbon we have in our dry lands or in the Foothills, we need to understand how the amount of carbon that sits in the soil changes when you have sagebrush, for example. Or when you have another kind of grass,” de Graaff said.

Using soil samples collected from the Foothills open space reserves, the research team will then make “informed extrapolations” to construct a map of Foothills carbon, said Kelly Hopping, an assistant professor at Boise State’s Human Environment Systems department and a co-lead of the upcoming study.

A graduate student will be collecting soil samples from areas within all of the Foothills reserves, including Camel’s Back Reserve, Hillside to Hollow Reserve, the Military Reserve and Stack Rock Reserve, Hopping told the Statesman by phone.

The Foothills are home to a number of native shrubs and flowers, like sagebrush, bitterbrush, arrowleaf balsamroot and rabbitbrush. There are also native grasses and non-native species, including cereal grasses and short annual grasses like medusahead and cheatgrass, Hopping said.

She added that the city could use carbon sequestration as a “new form of reasoning” when it looks to acquire more open space in the future.

De Graaff expects results to be available in about two years.