Enhancing forage resources for beef producers to increase carrying capacity
How can plant physiology help?
By Justin D. Derner
Forage resources are key for range cow beef producers. Grazing lands provide these forage resources. These grazing lands can be simple monocultures of often introduced forages selected with genetic potential for higher yields. Or highly complex plant native communities occurring on diverse landscapes with different soils and topography.
Increasing carrying capacity for livestock from these forage resources is key for producers given the substantial increases in land values, both for purchase and rent.
Ecological sitesEcological sites are defined as distinct types of land on the landscape with different soils, plant communities, climate/weather and topography. Ecological sites have different forage production potentials (Reynolds et al. 2019), with both precipitation amount and pattern influencing forage production within and across years (Hoover et al. 2021). Forage production of an ecological site decreases when management induces a change in the species composition resulting in less productive plants (Porensky et al. 2016, 2017). Restoration actions can be undertaken by producers to reverse this decline in forage production, but the success of these management actions can differ across different grazing lands.
Sites can become invaded with plant species that compromise the production potential for range beef cow producers. For example, invasive annual grasses like cheatgrass (Bromus tectorum) can change nitrogen and water dynamics resulting in lowered forage production for native plants (see cover picture, photo credit Justin Derner)
Similarly, eastern red cedar (Juniperus virginia) is a tree that has, and continues to, expand across the Great Plains with reductions in forage production of sites as well as livestock access to the remaining forage due to its physical presence. (see picture on page 2).
Mechanical treatments and prescribed fire can be used to reduce eastern red cedar trees to increase the forage production potential and access to the forage produced.
For sites that have been previously cultivated or highly degraded due to previous poor management, changing the site potential can be accomplished through seeding and establishment of species with higher forage production. These seedings of monoculture (single species) or simple mixtures (a few species) require energy inputs with resulting “improved plant communities” often managed with agronomic rather than ecological principles.
How can plant physiology help? Plant physiology basics provide the foundation for increasing carrying capacity through greater forage production. Photosynthesis is simply the process of transferring sunlight energy into chemical energy for growing plants. Water (H2O) plus atmospheric carbon dioxide (CO2) in the presence of sunlight and adequate temperatures will yield plant growth.
Due to increases in atmospheric carbon dioxide, a 30% increase compared to values first measured at Mauna Loa Observatory in Hawaii in 1958, plant growth has benefited. Plants with the C3 photosynthetic pathway (cool-season plants) benefit more in terms of forage production than those with the C4 photosynthetic pathway (warm-season plants) (Morgan et al. 2011). Enhanced forage production has been quantified with increased atmospheric carbon dioxide concentrations in experimental field research for grazing lands.
Observations from a semiarid shortgrass rangeland in northeastern Colorado showcase a 60% increase in forage production from the 1960s to current, and livestock carrying capacity has also increased with a similar magnitude (Raynor et al. 2021). Field experiments that have added atmospheric carbon dioxide to levels expected mid-century suggest a further increase of over 25% in both shortgrass steppe (Morgan et al. 2001) and northern mixed-grass prairie (Mueller et al. 2016).
Although forage production increases with increasing atmospheric carbon dioxide, the tradeoff for range cow beef producers is that forage quality declines (Augustine et al. 2018). This reduction in forage quality will likely increase the need for supplementation of protein on grazing lands for livestock production.
For example, plant phenology advances more quickly with higher atmospheric carbon dioxide which leads to plants maturing earlier (i.e., becoming reproductive more quickly) and can result in a “summer slump” of forage quality where producers will need to feed supplemental protein to support livestock gain (Augustine et al. 2018).
Range cow beef producers can increase water on their grazing lands through improving soil health. Producers can manage to increase organic matter levels in soils which results in better water infiltration and soil water holding capacity. This provides a pathway to more effectively capture precipitation that falls on the site and prevent runoff of water as well as reducing associated soil erosion. Moreover, if neighboring lands have lower soil health, there is capacity for your lands with higher soil health to capture run off from those lands and result in more soil water for your sites and thus greater forage production.
Enhancing carrying capacity examplesProducers can use targeted grazing in early spring when precipitation amounts and reliability are greater to graze high growth C3 (cool-season) grasses such as the annual grass cheatgrass, or introduced forge grasses like smooth brome, crested wheatgrass and/or Kentucky bluegrass. By grazing these plants in the early spring, producers can capitalize on this “extra” forage as these plants quickly lose nutritional value when they move to a reproductive stage and not grazing these plants can reduce the forage production potential of other species, such as the C4 (warm-season) grasses in plant communities, through their uptake of soil nitrogen and water. Intensive early stocking (IES) in the tallgrass prairie region increases livestock gains per unit land area by maximizing forage utilization during peak precipitation periods during the year when forage growth and nutritive quality is high. Following the intensive early stocking, a non-grazing period can provide regrowth to accumulate with this forage being used later in the growing season or during the dormant season In many extensive rangeland landscapes, there is often unused and under-utilized forage that could be accessed to enhance carrying capacity. Managers have attempted to improved grazing distribution through development of additional water, strategic placement of supplements to attract grazing animals, individual animal selection, herding, and fencing (Bailey 2004).
Topography can substantially influence grazing distribution with producers using elevational gradients in topography (where present) to better match timing of grazing with topography. Emergent technological tools like virtual fence provide promise to assist producers in optimizing livestock distribution across landscapes. Substantial potential exists for expanded use of this technology through grazing management applications of environmentally sensitive areas like riparian areas, critical wildlife habitat and migration corridors, targeted grazing, and more effectively matching spatial and temporal patterns of forage quantity and quality across ranches and landscapes.
ReferencesAugustine, D.J., D.M. Blumenthal, T.L. Springer, D.R. Lecain, S.A. Gunter, and J.D. Derner. 2018. Elevated CO2 induces substantial and persistent declines in forage quality irrespective of warming in mixedgrass prairie. Ecological Applications 28:721–735.
Bailey, D.W., 2004. Management strategies for optimal grazing distribution and use of arid rangelands. Journal of Animal Science 82:147-153.
Hoover, D.L., W.K. Lauenroth, D.G. Milchunas, L.M. Porensky, D.J. Augustine, and J.D. Derner. 2021. Sensitivity of productivity to precipitation amount and pattern varies by topographic position in a semiarid grassland. Ecosphere 12:e03376.
Morgan, J.A., D.R. LeCain, A.R. Mosier, and D.G. Milchunas. 2001. Elevated CO2 enhances water relations and productivity and affects gas exchange in C3 and C4 grasses of the Colorado shortgrass steppe. Global Change Biology 7:451-466.
Morgan, J.A., D.R. LeCain, E. Pendall, D.M. Blumenthal, B.A. Kimball, Y. Carrillo, D.G. Williams, J. Heisler-White, F.A. Dijkstra, and M. West. 2011. C4 grasses prosper as carbon dioxide eliminates desiccation in warmed semi-arid grassland. Nature 476:202-205.
Mueller, K.E., D.M. Blumenthal, E. Pendall, Y. Carrillo, Y., F.A. Dijkstra, D.G. Williams, R.F. Follett, and J.A. Morgan. 2016. Impacts of warming and elevated CO2 on a semi‐arid grassland are non‐additive, shift with precipitation, and reverse over time. Ecology Letters 19:956-966.
Porensky, L.M., K.E. Mueller, D.J. Augustine, and J.D. Derner. 2016. Thresholds and gradients in a semi-arid grassland: long-term grazing treatments induce slow, continuous and reversible vegetation change. Journal of Applied Ecology 53:1013–1022.
Porensky, L.M., J.D. Derner, D.J. Augustine, and D.G. Milchunas. 2017. Plant community composition after 75 yr of sustained grazing intensity treatments in shortgrass steppe. Rangeland Ecology & Management 70:456-464.
Raynor, E.J., J.D. Derner, T. Baldwin, J.P. Ritten, and D.J. Augustine. 2021. Multidecadal directional shift in shortgrass stocking rates. Rangeland Ecology and Management 74:72-80.
Reynolds, A.Q., J.D. Derner, D.J. Augustine, L.M. Porensky, H. Wilmer, T. Jorns, D.D. Briske, J.D. Scasta, M.E. Fernández-Giménez, and the CARM Stakeholder Group. 2019. Ecological sites: can they be managed to promote livestock production? Rangelands 41:239-243.
Derner is a research leader and USDA-ARS Rangeland Resources and Systems Research Unit director for the Central Plains Experimental Range Long-Term Agroecosystem Research site.
