Lead Author:
Elise Pendall, Western Sydney University
Contributing Authors:
Dominique Bachelet, Oregon State University
Richard T. Conant, Colorado State University
Bassil El Masri, Murray State University
Lawrence B. Flanagan, University of Lethbridge
Alan K. Knapp, Colorado State University
Jinxun Liu, U.S. Geological Survey
Shuguang Liu, Central South University of Forestry and Technology
Sean M. Schaeffer, University of Tennessee
Science Lead:
Sasha C. Reed, U.S. Geological Survey
Review Editor:
Rachel Melnick, USDA National Institute of Food and Agriculture
Federal Liaisons:
Nancy Cavallaro, USDA National Institute of Food and Agriculture
Anne Marsh, USDA Forest Service


Grasslands cover 30% of North America and provide a wealth of essential ecosystem services, such as wildlife habitat, hydrological buffering, soil stabilization, carbon storage, and forage production. Grassland ecosystems are characterized by herbaceous vegetation, including grasses and nongrass species, with a minor component of woody vegetation in most regions. Most grasslands in North America are dominated by perennial vegetation, or species that continue growing for many years, although in parts of California and the Intermountain West, nonnative annual grasses now dominate. Grasses allocate 40% to 80% of net primary production (NPP) to roots (Hui and Jackson 2006), so most carbon storage takes place below ground (Silver et al., 2010; Smith et al., 2008; Soussana et al., 2004). Grasslands across North America occupy over 7 million km2 (see Table 10.1) and contain 10 to 90 megagrams of carbon (Mg C) per hectare in the top 20 cm of soil (Burke et al., 1989; Potter and Derner 2006; Silver et al., 2010).

Table 10.1. Average Modeled Net Ecosystem Production (In Tg C per Year During 2000 to 2006)

Country Approximate Grassland Area (km2)a Analysisb, c Atmospheric Inversion Modelsc, d Land-Surface Modelsc, d
Canada 3,920,000 –3.06 –51.2 –29.3
United States 2,580,000 –13.2 –266.2 –104.8
Mexico 760,000 –9.06 –15.1 +3.6
North America 7,260,000 –25.2 –332.5 –130.5

This table, adapted from Hayes et al. (2012), presents three different approaches for estimating net ecosystem production (NEP): inventory analysis, atmospheric inversion models, and land-surface models.

a Approximate grassland area is derived from www.statista.com/statistics/201761/projection-for-total-us-grassland-area-from-2010.
b Inventory analysis estimates, in teragrams of carbon (Tg C) per year, are the sum of livestock methane (CH4) emissions, livestock carbon dioxide (CO2) emissions, and grassland net ecosystem exchange (NEE) for Canada and the United States. For Mexico, the NEP value for “Others” was used from Table S10 in Hayes et al. (2012).
c A negative flux represents net ecosystem carbon uptake, while a positive flux indicates carbon loss from the ecosystem.
d Atmospheric inversion models and land-surface models are from Table 2 in Hayes et al. (2012) and exclude CH4 emissions and human settlement emissions.

Carbon storage, defined as the net uptake of carbon by a given pool or reservoir (IPCC 2013), can be quantified as the change in stocks measured over time, or as annual net ecosystem production (NEP), which can be measured as NPP minus losses from soil organic matter (SOM) decomposition (Chapin et al., 2006). NEP is also estimated from the sum of high-frequency net carbon dioxide (CO2) exchange (NEE) measurements from eddy covariance “flux tower” methods. By contrast, net ecosystem carbon balance (NECB) accounts for all carbon uptake and loss processes, including harvest, natural disturbance, leaching, and trace gas species in addition to CO2 (Chapin et al., 2006).

This chapter is relevant to both the Northern and Southern Plains National Climate Assessment regions, as well as the Southwest and Midwest regions. The spatial scope of this chapter encompasses the major North American grassland regions, which can be defined by climatic limitations. Grasslands occur where potential evaporation exceeds precipitation, such as in central North America from Canada through Mexico and in mountain rain shadows in the western United States (Sims and Risser 2000). They also occur in more mesic (wet) regions where disturbance, management, or soil conditions prevent woody growth, such as in central Florida (Stephenson 2011). North American grasslands generally increase in productivity and carbon storage as precipitation increases, from west to east (Sims and Risser 2000). This pattern is observed in Canada and to a lesser extent in Mexico. Mixed-grass prairie is extensive in south-central Canada, while more arid desert grassland and shortgrass steppe extend through the southwestern United States into Mexico (Sims and Risser 2000). Grasslands at the more arid extreme are considered more vulnerable to diminished productivity in a future warmer climate (Hufkens et al., 2016), whereas grasslands in more mesic climates may be vulnerable to woody encroachment (Knapp et al., 2008a).

Land management strongly affects productivity and carbon cycling in grasslands (see Figure 10.1). In the conterminous United States, grasslands, shrublands, rangelands, and pastures make up at least 40% of land cover (Reeves and Mitchell 2012; see Figure 10.1). Most areas of highly productive grasslands have been converted to agriculture (see Ch. 5: Agriculture for more details; Bachelet et al., 2017).


Figure 10.1: Management Activities and Their Effects on Grassland Carbon Cycling

Figure 10.1: Reduced fire frequency in mesic native grassland has allowed woody vegetation such as Juniperus virginia to expand and has been associated with rapid increases in carbon stocks in vegetation and soils (McKinley and Blair 2008). Other observed management impacts include lower carbon density in agricultural lands compared with grasslands (Zhu et al., 2011) and the rapid accumulation of soil carbon in intensively managed pastures in the southeastern United States (Machmuller et al., 2015). In addition, the rate of carbon uptake by croplands in the Great Plains is 30% lower than that of grasslands (Wylie et al., 2016)