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Tallgrass Prairie and
Carbon Sesquestration

Carbon Cycle
Diagram adapted from U.S. DOE, Biological and Environmental Research Information System PD-USGov-DOE

The Carbon Cycle (pictured above) is a biological, geological and chemical cycle in which carbon is exchanged between the biosphere (global sum of all ecosystems), the Soil, rivers, lakes and oceans and the Earth’s atmosphere. The carbon cycle along with the nitrogen and water cycles are key to enabling the Earth to sustain life. The carbon cycle describes the movement of carbon as it is recycled and reused throughout the biosphere.

Photosynthesis At09kg (CC BY-SA 3.0)

PhotosynthesisPlants absorb carbon dioxide from the air and use the sun’s energy to ‘fix” this carbon to make sugars and other carbohydrates which the plant can store and use later or be used by other organisms. During this process plants give off oxygen. Photosynthesis is the biochemical process by which plants remove carbon from the atmosphere.  In prairie grasslands a large amount of fixed carbon is stored in plant roots. When the plant dies some of the root remains in the soil for hundreds of years as organic carbon humus. Prairie soil acts as a “carbon sink”.

Highly diverse prairie grasslands such as tallgrass prairie remnantsmay contain more than 200 species of plants many of which are perennials. A perennial plant is one that lives more than 2 years.

In a prairie creation project a highly diverse seed mix typically includes 25% wild flowers (forbs), a dozen or more species and 75% warm season grasses (Big Blue Stem, Little Blue Stem, Indian  Grass, Virginia Wild Rye, Switch Grass, etc.). Highly diverse means “many species”. Prairie forbs and grasses live for decades or longer in undisturbed settings and over time are able to produce extensive root systems. Perennial plant root systems store large amounts of carbon and in the process create rich, highly fertile soil.

Prairie Roots - US Environmental Protection Agency
Prairie RootsIn the photo to the left native prairie plants typically have deep and extensive root systems which help them survive dry conditions and which effectively hold soil. By comparison cool season turf grasses, such as Kentucky bluegrass at the far left in the photo (under the arrow), have very shallow root systems which are much less effective in controlling erosion and withstanding severe drought. 

Soils under long-established prairie grasslands can contain more than 10 tons of roots per acre with most of this bulk in the top 24 inches. The roots of some prairie plants can extend to a depth of 10 feet or more. Various studies of the potential for tallgrass prairie carbon storage have shown that the storage rates vary between .30 and 1.7 metric tons per acre per year.  This storage ability is cumulative over time so prairie soil is able to sequester or store large volumes of carbon in a natural, safe, effective and reliable way compared to the risky and expensive practice of pumping CO2 underground.  An additional benefit of this “grassland carbon storage system” is that the sequestered carbon is supporting a lush prairie ecosystem above ground.  

The discovery of Glomalin in 1996 improved our understanding of soil affinity for carbon. Glomalin is the superglue that soil uses to attract and hold carbon. Because of glomalin, prairie soils are able to sequester large amounts of carbon which over time changes the soil into Mollisol, a soil type found only under prairie grasslands.  Mollisol soil is extremely rich in organic matter and can extend to a depth of three feet.

Ironically and sadly, because they produce the best, deepest and richest soils, grasslands have been their own worst enemy as they have been rapidly converted to agriculture.

Soil carbon plays a key role in the carbon cycle and is important in global climate models.  The capacity of Earth’s soil carbon storage exceeds the amount of carbon contained in our atmosphere (as CO2) and all the carbon in the biosphere (biomass) combined. Because of the tremendous ability for soil to store carbon, modern agriculture can play a leading role in mitigating the effects of climate change by embracing Conservation Agriculture.   

Climate change or global warming is caused by an imbalance between energy received from the sun and energy reflected by the Earth back to space. This imbalance is estimated to be about .58 watts per square meter annually averaged over the entire surface of the Earth and is caused by greenhouse gases released by modern Civilization. Greenhouse gases prevent a small portion of the incoming Sun energy from escaping back to space; instead reflecting it back toward the Earth. Over time this small amount of extra heat accumulates in the Earth System (atmosphere and oceans) and becomes noticeable to humans (warmer seasons). Greenhouse gases disrupts climate by creating erratic and extreme weather events. The greenhouse gases that are the worst offenders are carbon dioxide (CO2), methane, nitrous oxide and chlorofluorocarbons (CFC’s). Currently CO2 is the chief culprit in climate change because of its abundance in the atmosphere which is increasing at an accelerating rate.

Ontario Municipalities and Provincial Road Authorities can help our pollinators and our environment by planting species diverse pollinator strips along roadsides and on municipally owned property. In places where roadside pollinator strips have been planted it has provided highly productive habitat for ground nesting birds and pollinating insects. Roadside buffers reduce drifting from blowing snow.

If you are a landowner or a municipality and would like more information about pollinator strips please contact Tallgrass Ontario at info@tallgrassontario.org