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07 August 2020

Carbon Sequestration in Grassland Ecosystems - A Review of Scientific Literature

Dr. Kay L Kottas and Alicia Admiraal; Prairie Legacy Inc. (March 2020). Carbon sequestration in grassland ecosystems. With appended details by James E. Ducey and Dr. David M. Sutherland.

Introduction

The Sands Hills occur primarily within Nebraska though also in a south-central extent of South Dakota – and comprise more than 19,000 square miles of vast native grassland tracts. The region is internationally recognized for its expanses of mixed-grass prairie since there are both cool-season and warm-season species. More than 95 species of grasses are known to occur (Dr. David M. Sutherland, 1984; Vegetative key to grasses of the Sand Hills region of Nebraska) and most thrive. The grasses are essential range forage for livestock but are also a key vegetative feature stabilizing the sandy soils and a key aspect to other essential environment values. This includes carbon sequestration. [Introduction by James E. Ducey, 15 May 2020]

Review of Scientific Literature

The amount of carbon in the soil worldwide (1,600 billion metric tons) is double that in vegetation (560 billion metric tons) or in the atmosphere (750 billion metric tons) (Rice et al. 1998). Carbon cycling through plants occurs when plants bring in atmospheric carbon for use in photosynthesis. The carbon is stored in plant tissues both above and below ground. Eventually that carbon is released back into the atmosphere as plant tissue dies and is decomposed by microbial activity. The same result happens more quickly if the vegetation is burned. Much of the below ground carbon remains there, even as it decomposes. Grasslands store most of their carbon below ground. The extensive root systems of these plants sequester nearly as much carbon as forested lands, but far more efficiently (Kerlin 2018). When a tree decomposes or a forest burns, most of the stored carbon is released to the atmosphere. When the above ground biomass of a grassland decomposes or is burned, the below ground biomass and carbon remains sequestered. Approximately 60 to 80 percent of biomass in a tallgrass system occurs below ground (Wedin and Tilman 1990).

The ability of prairie systems to sequester carbon is affected by soil texture, weather patterns, temperature and the amount of ground cover (Jones and Donnelly 2004, Mengistu and Mekuriaw 2014), and by several other factors including precipitation, season, management such as grazing, and functional group of the dominant grasses. Nitrogen input can also affect plant growth and therefore how well carbon is sequestered. Interactions between these factors greatly affect response of grassland in a particular location. We know that cropped land can reduce methane (CH4) oxidation by 90% of what it is in native grassland (Mosier et al. 1997). Methane is broken down (oxidized) by bacteria into carbon dioxide (CO2). Because methane is 25 times more potent than carbon dioxide as a greenhouse gas, that breakdown in grasslands is important. In cultivated soils among the tallgrass prairie, carbon cycling has been reduced by 50%. Even if cropland is returned to native perennial vegetation recovery of CH4 oxidation takes many decades (Mosier et al. 1997). Rosenzweig et al. (2016) estimate that in restored cultivated fields, the amount of time for soil carbon sequestration to return to the level of undisturbed native prairie can be centuries (more than 350 years).

In the Nebraska sandhills mixed grass prairie is similarly affected. Mixed grass communities provide ground cover in the sandhills across the dunes within the swell and swale topography. The swales have more above ground production and deeper A horizon soils and tend to hold more soil carbon than the swells (Hartmann 2013). In a study done by Hartmann (2013) removal of above ground vegetation, reduced CO2 flux rates by as much as 60%, but mean soil CO2 flux did not return to control levels even after ten years. In managing grasslands for carbon sequestration, limiting soil disturbance is of primary importance. Soil disturbance disrupts soil structure, results in increased soil temperature and aeration, allowing more decomposition and potential release or reduced uptake of carbon (Janowiak et al. 2013; Conant 2010). Disturbances to sandhills vegetation can therefore have serious long-term effects to carbon cycling and sequestration. Disturbances to soil, particularly in sandy soils, takes many decades of careful management to return soil carbon exchange to its natural state. Increased above ground biomass also increases potential for carbon storage. By managing plant growth and the cover on prairies and on agricultural land, we can help increase above ground biomass, help maintain or increase the presence of below ground mycorrhiza and enhance carbon sequestration.

Spangler (2011) presents some of the varied responses of grassland to grazing, citing studies that show both positive and negative grazing effects. Soil chemistry and associated microbial communities can change in response to grazing. Effects from trampling that would result from heavy grazing can remove aboveground biomass and change the physical characteristics of the soil. This in turn can limit water infiltration and root growth. Wilson et al. (2009) found a highly significant correlation between the abundance of arbuscular mycorrhiza hyphae in the soil and the ability of the soil to store carbon and nitrogen, exposing serious consequences to the soil ecosystem when disturbances cause a loss of arbuscular mycorrhiza. Ultimately, positive influence on soil organic carbon and nitrogen content seems to be realized under light grazing pressure, in contrast with heavy grazing or ungrazed treatments (Spangler 2011).

Precipitation also interacts with soil texture in regard to the impact of certain management practices, such as grazing. Grasslands on sandy, coarse-textured soils have increased soil carbon if rainfall increases under a grazing regime; grasslands on clay soils exhibit weak to strong decreases in soil carbon under these conditions (McSherry and Ritchie 2013). Conversely, with lower rainfall, clay soils show the largest increase in soil carbon compared to sandy soils (McSherry and Ritchie 2013). Soil carbon stocks already held in the soil tend to be higher in grasslands that have higher rainfall, but stocks decrease as temperature increases because evapotranspiration also increases (Janowiak et al. 2017).

By season, the average period of CO2 uptake was mid-April through late August, with tallgrass prairies in the southern Great Plains capable of accumulating more carbon; at other times of the year, the grasslands in the northern Great Plains and in short grass and mixed grass prairies, especially in the western part of the region, release carbon (Zhang et al. 2011).

The functional group of dominant grasses (C4, warm-season, or C3, cool season) was found to influence soil carbon uptake in several studies. C4 grasses, or mixtures of C4 and C3 grasses, were more resilient in their ability to accumulate soil carbon under increasing grazing pressure (McSherry and Ritchie 2013). Another 12-year study monitored net soil carbon and nitrogen and found that accumulation was positively affected by total root biomass, which increased with the presence of C4 grasses and legumes (Fornara and Tilman 2008). The inclusion of legumes was thought to be important because the ability of legumes to accumulate nitrogen helps to build soil organic matter and store more carbon. Further, this study showed that greater plant species diversity corresponded to greater uptake of carbon when compared to a monoculture (Fornara and Tilman 2008).

Another long-term study examined the effect of nitrogen inputs to mineral soils (Fornara and Tilman 2012). The addition of nitrogen contributed to increased carbon sequestration compared to unfertilized grassland, likely by increasing root mass, particularly of C3 plants. Aboveground biomass for both C4 and C3 grasses also increased during the 27-year study, but plant species richness decreased and dominance shifted to C3 grasses (Fornara and Tilman 2012). In 2017, Hungate et al. demonstrated the economic value of increased species diversity in carbon sequestration, furthering the economic argument for conservation of grassland biodiversity. For instance, an increase of 4 species over U.S. Conservation Reserve Program lands would provide 2.3 billion dollars in carbon storage value. Conversely, the loss of these species in remnant prairies would produce a similar economic devaluation of prairie land for carbon sequestration.

Summary

The loss of either cover, diversity, or both on grassland ecosystems translates to a large loss in carbon cycling, a huge opportunity loss in the below ground sequestration of carbon, and in the ability of grasslands to breakdown. Recovery from those losses of carbon sequestration to pre-disturbance rates can be an extremely long process, on the order of centuries. The gain or loss of carbon sequestration is variably dependent on soil type, precipitation, species dominance, species diversity, climate and management. While we have no influence on soil type and weather, we can influence species diversity, dominance and management. Expressed in dollars, the economic impact of such losses can be understood. The prevention of those losses, so much as is under our control amount to replacing diverse plantings on disturbed soil, protecting diversity where we can, increasing diversity where necessary, preventing disturbances and practicing careful management with responsible grazing.

Literature Cited

Conant, R.T., ed. 2010. Challenges and opportunities for carbon sequestration in grassland systems: A technical report on grassland management and climate change mitigation. Integrated Crop Management Vol. 9. Food and Agriculture Organization of the United Nations (FAO), Plant Production and Protection Division.
Fornara, D.A., and D. Tilman. 2008. Plant functional composition influences rates of soil carbon and nitrogen accumulation. Journal of Ecology 96:2 pp 314-322. https://doi.org/10.1111/j.1365-2745.2007.01345.x Fornara, D.A., and D. Tilman. 2012. Soil carbon sequestration in prairie grasslands increased by chronic nitrogen addition. Ecology 93(9):2030-2036. https://doi.org/10.1890/12-0292.1
Hartmann, A. A., R. L. Barnard, S. Marhan, and P. A. Niklaus. 2013. Effects of drought and N-fertilization on N cycling in two grassland soils. Oecologia 171:705–17.
Hungate, Bruce A., Edward B. Barbier, Amy W. Ando, Samuel P. Marks, Peter B. Reich, Natasja van Gestel, David Tilman, Johannes M. H. Knops, David U. Hooper, Bradley J. Butterfield, Bradley J. Cardinale. 2017. The economic value of grassland species for carbon storage. Science Advances. Vol. 3, No. 4, 05 April 2017.
Janowiak, M., T. Ontl, and C. Swanston. 2017. Chapter 4: Carbon and land management. Pages 21-35 in Considering forest and grassland carbon in land management. USDA United States Forest Service. General Technical Report WO-95. June.
Jones and Donnelly. 2004. Carbon sequestration in temperate grassland ecosystems and the influence of management, climate and elevated CO2. New Phytologist. Volume164, Issue3. December 2004 Pages 423-439.
Kerlin, K. 2018, UCDavis. https://climatechange.ucdavis.edu/news/grasslands-more-reliable-carbon-sink-than-trees/ Mengistu and Mekuriaw. 2014. Challenges and opportunities for carbon sequestration in grassland system, a review. Ent J Engineering Environmental Resources 1 (1) 1-12.
Mosier, A. R., W. J. Parton, D. W. Valentine, D. S. Ojima, D. S. Schimel, and O. Heinemeyer. 1997. CH4 and N2O fluxes in the Colorado shortgrass steppe. 2. Long-term impact of land use change. Global Biogeochem Cycles 11:29–42.
McSherry, M.E., and M.E Ritchie. 2013. Effects of grazing on grassland soil carbon: a global review. Global Change Biology. 19(5): 1347–1357. Rice, C. W., T. C. Todd, J. L. Blair, T. Seastedt, R. A. Ramundo, and G. W. T. Wilson. 1998. Belowground biology and processes. Pp. 244–264. In A. K. Knapp, J. M. Briggs, D. C. Hartnett, and S. L. Collins (eds.). Konza Prairie Long-term Ecology Research. Oxford Press, New York, New York. Rice, C. W., A. B. Omay, C. J. Dell, M. A. Williams, and Y. Espinoza. 1999. Soil organic matter in grasslands: Response to climate and land management. Global change and terrestrial ecosystems. P. 44 In Focus 3 Conference on Food and Forestry: Global Change and Global Challenges. University of Reading, Reading, U.K., September 20–23, 1999.
Rosenzweig, Steven T., Michael A. Carson, Sara G. Baer, John M. Blair, 2016. Changes in soil properties, microbial biomass, and fluxes of C and N in soil following post-agricultural grassland restoration. Applied Soil Ecology. Volume 100, April 2016, Pages 186-194.
Spangler, L. 2011. Rangeland sequestration potential assessment. Final Report. U.S. Department of Energy National Energy Technology Laboratory. DOE Award Number: DE-FC26-05NT42587.
Wedin, D. A., and D. Tilman. 1990. Species Effects on Nitrogen Cycling: A Test with Perennial Grasses. Oecologia 84:433–441. Wilson, G. W., Rice, C. W., Rillig, M. C., Springer, A. & Hartnett, D. C. 2009 Soil aggregation and carbon sequestration are tightly correlated with the abundance of arbuscular mycorrhizal fungi: results from long-term field experiments. Ecol. Lett. 12, 452–461.
Zhang, L., B. K. Wylie, L. Ji, T. G. Gilmanov, L. L. Tieszen, and D. M. Howard (2011), Upscaling carbon fluxes over the Great Plains grasslands: Sinks and sources, J. Geophys. Res., 116, G00J03, doi:10.1029/2010JG001504.

Addendum

These details indicate some of the main grasses of the sandhills and is courtesy of Dr. Sutherland, emeritus professor of botany at the University of Nebraska at Omaha.

“The main overstory grasses are: Calamovilfa longifolia, sand reedgrass; Andropogon gerardii subsp. hallii, sand bluestem; Stipa comata (Hesperostipa comata), needle and thread (Sporobolus cryptandrus); sand dropseed; Eragrostis trichodes (sand lovegrass); and, Bouteloua curtipendula (sideoats grama)

“Main understory grasses: “Bouteloua gracilis (blue grama); Bouteloa hirsuta (hairy grama) in rougher spots. There is also at least one very common sedge in the understory: Carex heliophila (sunsedge).

“Important grasses for stabilizing blowouts would be: Muhlenbergia pungens (sand muhly); and, Redfeldia texuosa (blowout grass).”

Other prominent warm-season grasses, according to details in historic published articles, are:

Big Bluestem: “In the sandhills it is the most important of the native hay grasses, growing best on subirrigated meadows where the water table is 1.5 to 3 feet from the surface.” “...may be considered the king of our native hay and pasture grasses.”
Indian Grass: “...rather common in the sandhills area, both in the meadows and as rather isolated colonies in the uplands. … one of the most important of the native hay and pasture grasses.”
Switchgrass: “a high producer of good quality hay, abundant pasturage and an excellent erosion control grass, it is considered among the more valuable native grasses.”

A ‘B’-Word Brief About Beautiful Cherry County

James E. Ducey. June 18, 2020. A ‘B’-word brief about beautiful Cherry County. Grant County News 135(46): 4, 7.

B is a bestest letter to bestow upon Cherry County, a Nebraska space well beyond banal and a beacon that has beckoned many with beguiling features to behold and which cannot be belittled.

This biggest county in Nebraska has more than 3.8 million acres. Its beginnings and subsequent bibliography of prose represented by some of the best and most brilliant writers is beatific.

Back in history, brave warriors bareback on their best buckskins chased bunches of roaming buffalo at one time, using bows and arrows and bone tools to gather natural bounty for winter days when there would be blowing snow blizzards and brutally cold days. There were no buildings.

A land of many grasses beckoned. Brash men from Omaha and North Platte with bravado and a bunch of bucks began brazen efforts that brought Texas beeves to the broad plains of the sand hills, bursting forth a big beef industry. Boys on horses briskly brought big herds to begin a cattle business. Beneath many bluffs, the cowboys with big guns – some loaded with buckshot – rode broncs beside sheltered herds were bugs were boisterous and making every attempt to bite. Meals of bacon and beans came from skillets bright from burning boughs. There was no bunkhouse buffet.

Bullwhackers brought supplies that certainly included bacon and other grub basics for a bland diet.

Burly men with bold brio in local bars and brothels used bullets blasted from barrels of big guns to settle disputes, often after only moments of bickering. They cowboys were boisterous. It was no bother to have a burial beneath a hillside bounded with bunch grass.

Basics of grass and water brought hearty settlers and their belongings for a new beginning, often behind a buckboard or after riding behind the whistle blast of a locomotive driven by essential black nuggets. Often on a bowed and bridled horse burdened with packs of basic supplies, or while breaking a team to pull beyond a bunch of reins as the drover built up the movement to get to the place where they would maybe break some sod. There were families big or small. Perhaps, buried between the canvas and between the board slats what was decided to essential to their bundle of a new life, including some beautiful and notable bibelots.

Women in bonnets walked town boardwalks looking for provisions, perhaps including some warm bread or getting some fine beef from a butcher. Maybe a few shiny pennies were spent to buy a broadcloth to make a dress of special bright colors that could raise the family spirit on a dreary day when there was a basic realization that there would be better times.

Beneath blue sky bunches of country boys gathered at small burgs of board-built havens, wearing ballcaps and carrying bats and gloves. With big swings, bounds with much bravado could make it to each beckoning base.

Amidst the big or little hills and meadows, small boys chased after bugs in the farmyard. Cute little girls wore bonnets as they roamed the ranch yards. There was a whole bunch of land to discover. There was more than once occasion when a bouquet was plucked and taken home to mom in the kitchen.

Basically now in this most beautiful of counties there are many bright basics. Bovines abound and browse the bunches of grasses including the bluestems. Mother cows are within barbed wire spaces. Beefy bulls from the best of the cattle breeds are brought forth and then basically bought with some bucks at some local sale barn. Bouncy and growing are growing baby calves. Then there are the essentials of a branding by a dedicated bunch that includes cowboys and cow girls. Please notice that horses are so essential and their name may start with the letter B.

Bison still roam now even during blinding blizzards or days with blistering heat. Bucks wander and at times avoid a bullet shot. Cottontail bunnies with bravado jump around. Bobcats slink beneath bodacious skies.

During the bountiful season bales of hay get bound with twine by balers. There are bountiful crops of amber waves of grain beneath the basic covers of big rig trailers bouncing along Main street.

There is a bevy of birds including the bluebird and Bobolink, also notable the Brown Thrasher and Brown-headed Cowbird. Grackles can do their best to empty my bank account while eating incessantly at the bird seed buffet. Majestic Bald Eagle soar above and treasure their little ones nestled amidst brought to build their home place using twigs or sticks suited built one at a time atop big tree branches. Binoculars are beneficial to get a bead on a bittern or bland warbler among some bulrushes, as well as many other sorts of biota. When the Great Horned Owl hoots it is a voice of their necessity while the land is dark space where they hunt without being able to see. They listen to bits of sound before swooping down to snag a bit to eat to take back to their babies in a branchy nest nearby.

There are the endangered American Burying Beetle that belay an indication the and Blowout Penstemon are a beatific bit of flora in broad, wind-blown blowouts where particular bugs occur. Or perhaps a bellowing bull frog or Blandings Turtle blending within a wind-blown meadow. Butterflies fly. Even brownish bats echo. A couple of local two local buff bunnies appreciate a basic, local, bird seed buffet without any blandness near the bluebird shack.

It is basically a broad basis for another breeding season, associated with the basics of boundless beginnings well known by nature.

B-places could be the place to be? There is Berry Bridge at the broad Niobrara. Borman Bridge has its own birdly boughs. Ballards Marsh has its own basics of origins. Brownlee has unique chronicles for the black settlement when softballs games were bunches of boys and men running the bases and throwing friendly bards with bawdy back talk. Brush Creek is biologically important because of itty-bitty fish. Anybody can go to Anderson Bridge and see how the beaver have established a hefty mound of mud and branches. Boardman Creek is a reality of times back in time and still now. How about learning via some book or another about the Badger Lake post-office. Big Springs on the North Loup River has its own video broadcast. Bowring Ranch is a special ranch of basic Hereford history and has its own Sunday day when friendly times blossom. Besides there is the Boiling Spring – which also once had a post-office. Buckhorn Spring that bubbles forth beneath hardy pines that have their own bit of sway in the breezes. The buck deer that was the basis for the name is long gone but the reality of the time meant its loss meant its loss was believed and thus the bequeathal of the name. There is Big Creek. Boardman Creek is a basic reality of times and now. What does the name Dipping Vat Meadow belay? Don’t forget Old Baldy Hill where cerulean blue meets sandy brown even when winds are boisterous and seem to be a bit much. The story of Bartlett Richards and the Spade Ranch is a grand story that can be enjoyed by reading a book of many words.

A bailiwick might include bicycling along B Street, shopping a nearby business in the biggest city within the boundaries of the county.

Merritt Reservoir is a beachy blue place for a boat with the basics to build memories for a beautiful day. Besides, there is the basis to bring bait to get a beautiful blue-gill or big-mouth bass near the boat after a delish breakfast or brunch.

Biodiversity is basic in Cherry county. Bioreserves associated with the Niobrara Valley Preserve with its basic herds of big grazers. The broad McKelvie Division of the Nebraska National Forest could be a beginning to beckon a nightly backdrop of beautifully bright stars. Birch boughs along the Niobrara River in the valley bluffs are part of the botany. Breath deep amidst the balmy blowing breezes of many times. There have been billions of billowing clouds bourgeon during a building thunderstorm as they have for centuries.

Don’t forget, there is a bunch of bloviating being done associated with what may not be the best for Cherry County. Brisk is an appropriate word to broach. There are braggarts. Some are brusque, others bumptious, perhaps because of a bureaucracy of bumpkins. Enjoy without bliss and boffo this basic land that does not need to be further bolstered with no bosh. There is no need to burnish because the reality belays some of the bestest of earth!

The history of our beautilicious Cherry county is not blah-blah-blah. It is known and beloved and written about by a bunch of believers that have known brave ancestors and have a belief in sharing essentials of this broad and essentially beautiful place in the world. It is a big land of grass and blowouts and beef and beautiful grasses that nourish.

Phantasmagoric by golly.