Climate, soils, topography, grazing, and fire have shaped the composition and structure of vegetation on rangelands in the American West. Collectively, the many possible combinations of these different factors should lead to diverse plant communities and associated diverse wildlife species.
Differences in vegetation structure (i.e., how tall above the soil surface the plants are) and composition (kind and amounts of different plants) are both important for biodiversity.
Yet, many rangelands across the American West have been managed through similar grazing management practices so that extensive areas of vegetation have comparable kinds and amounts of plant species (e.g., same grasses, forbs and shrubs; vegetation composition). As a result, the lack of many different plant communities can result in few differences in height of vegetation (or vegetation structure), which are often needed by grassland birds. This lack of vegetation diversity can translate to a lack of habitat diversity and biological diversity on these lands.
Rangeland plant communities often appear uniform or unvaried due to the fact that ranchers have an economic incentive to graze their livestock using management practices that emphasize “management to the middle” and “avoidance of the extremes.” These management practices are sustainable for livestock production,[i], [ii], as they optimize both weight gain per animal and per acre. Producers have an economic incentive to effectively use available forage and convert it to pounds of weight gain as the well-established market-driven system emphasizes price per pound. However, the resulting “sameness” of vegetation composition and structure, due to the application of similar management across large land areas, has triggered the demise of many grassland birds as well as reduced biodiversity. As a result, many of the “species of concern” on rangelands of the American West live on landscapes that have little variation of vegetation composition and structure. For example, the mountain plover, adapted for breeding on bare ground, and the lark bunting and western meadowlark, adapted for high cover areas, have been declining on rangelands.
Incentivizing ranchers to increase differences in vegetation composition and structure on rangelands of the American West will require 1) understanding how livestock can be used as tools to engineer rangelands for both provision of ecosystem goods (e.g., livestock production) and services (e.g., wildlife habitat, water quality and quantity, soil health, carbon sequestration and storage), 2) determining ecosystem services’ economic values, and 3) creating proper economic incentives that will foster vegetation—and greater biological—diversity.
Managing for diversity
What is vegetation heterogeneity? Livestock can engineer rangelands to produce differences in vegetation structure and composition. For example, intensive grazing in one area may result in higher amounts of bare ground, which benefits species such as the mountain plover. Resting a nearby area will allow the forage to grow taller, providing nesting habitat for grassland species such as the pintail, or in sagebrush, the sage grouse. This alternative approach to management increases percentages of the landscape with short and tall vegetation structure. Possible tradeoffs with livestock production merit additional investigation to provide economic valuations for the “costs” of providing vegetation heterogeneity.[iii]
Livestock can engineer differences in vegetation structure and composition within the framework of most current management practices. For example, ranchers can alter timing and intensity of grazing, length of rest periods, and type of livestock to create different levels in height of vegetation and kind and amount of plants. Ranchers can control when livestock graze certain areas, for how long, and how much vegetation is left ungrazed (to a certain height or residue level) following a grazing period. Through management decisions, ranchers vary the length of rest periods from relatively short (weeks-months) to long (one year or greater). Longer rest periods stockpile forage resulting in greater vegetation heights. Varying the time of grazing across years or stocking rates can shift vegetation composition. Combining different types of livestock, such as cow-calf pairs, yearlings, sheep, goats, or combinations of these, can strategically engineer the vegetation on rangelands due to different diet selections.
Combining grazing with prescribed fire in the Great Plains portion of the American West modifies the amount of bare soil, forage quality and quantity, vegetation structure and, in some cases, reduces unwanted species, such as prickly pear cactus or broom snakeweed (dry areas) or smooth brome (tallgrass prairie).[iv], [v] Burning patches within pastures encourages livestock to graze recently burned areas where forage quality is higher. In addition, less grazing activity will occur in the non-burned parts of the pastures, which results in more vegetation structure. This creates a greater range of vegetation structure in pastures with patch burns, compared to those pastures managed similarly but without prescribed fire. Combining fire and grazing in the Great Plains, does not, however, consistently create vegetation heterogeneity.[vi] Sites where the combination works effectively are those where fire is the primary driver of livestock grazing behavior, such as the tallgrass prairie. In addition, some invasive plant species, such as cheatgrass in the Great Basin and Lehmann lovegrass in the Southwest deserts, thrive following burns, so inclusion of fire as a management tool without consideration of the inherent risks associated with increasing vegetation heterogeneity in these ecosystems is not recommended.[vii] For these rangeland ecosystems of the intermountain west and desert southwest, fire can result in 1) large-scale conversions of native plant communities to invasive plants, and 2) altered fire regimes with fires becoming more frequent.
Taller vegetation can be attained by grazing an area and then not coming back to graze again for an extended period. For example, rest periods greater than one year generally result in taller vegetation structure due to an absence of grazing. However, this requires some flexibility in the livestock enterprise to accommodate this strategy. Livestock and vegetation management require flexibility to incorporate prior use patterns, and current and near-future grazing plans, into the overall management plan. This flexibility can involve using livestock as ecosystem engineers by putting more animals on a unit of land area, but for a shorter time. This will decrease the selectivity of grazing animals but increase the uniformity of grazing, as well as dung and urine deposition within a pasture, but with an overall objective of creating differences among pastures and across years. Grazing animals for a shorter time period, in different times of the year and sequences across years will increase differences in vegetation composition and structure. Temporary electric fencing can subdivide existing pastures to provide more control of livestock grazing for these shorter time periods of grazing and longer periods of no grazing.
Ecosystem services and livestock production
Achieving both provision of ecosystem services and maximal livestock production at the same time on ranches is difficult. On one hand, there is high demand to increase production of livestock to feed an ever-expanding world population.[viii] On the other hand, there is growing societal desire for rangelands to provide a suite of ecosystem services.[ix] Fundamental to these challenges is the stark reality that a developed economic market system drives livestock production whereas markets have yet to emerge for ecosystem services. The benefits of providing these services have yet to be monetized. Moreover, ranchers fear economic costs if they use livestock as ecosystem engineers such as lower livestock weight gains. For example, patch burning in pastures can provide greater heterogeneity of vegetation structure with no effects on livestock weight gains compared to pastures not burned,[x] but there are costs and risks to ranchers to incorporate these prescribed burns. Without incentives that compensate for this lost income, or developed markets for ecosystem services on which decisions could be made to modify management to emphasize additional outcomes that have economic rewards, this issue will remain problematic for ranchers. Preliminary efforts are unfolding in the western U.S. that may serve as a template for additional development of ecosystem service markets.[xi], [xii]
We are not suggesting that all current grazing management switch from a livestock production-centric basis to one that emphasizes provision of vegetation heterogeneity. Rather, judicious approaches that take advantage of pre-existing templates of heterogeneity of soils or topography can start the process. Changes in grazing management should take into account: 1) potential of different ecological sites to produce differences in vegetation, 2) determination that vegetation/habitat diversity is a desired outcome for management, 3) flexibility in the enterprise to accommodate modifications in grazing management, and 4) realization that there may be some tradeoffs associated with livestock production for certain aspects of this approach.
Figure: Photos representing vegetation heterogeneity created by engineering rangelands using livestock through differences in season and intensity of grazing in shortgrass steppe. Areas with high bare ground and limited plant cover were created by very heavy grazing in early spring (upper left), heavy grazing in summer created areas of very short structure (lower left), light grazing in the winter resulted in saltbush-dominated vegetation with more diverse vegetation structure (upper right), and diverse forb and grass species are enhanced with light grazing during the summer (lower right)[xvi][xvii][xviii] [xix] [xix]
Ranchers can use livestock to engineer landscapes for provision of both ecosystem goods and services,[xiii], [xiv] and this approach can be implemented on many rangelands, provided there are developed markets that value ecosystem services to determine economic returns associated with their decision-making. Given the current reality in which formal markets exist only for livestock weight gains, it is not surprising that management practices and associated decision-making processes are driven to maximize livestock production.[xv] This has led to increasing the “sameness” of vegetation composition and structure on landscapes through “management to the middle,” rather than management which embraces a much larger range in both vegetation composition and structure.
“Engineering” for greater vegetation heterogeneity will occur when markets for ecosystem services provide economic justification for ranchers to change management. Providing economic markets for these ecosystem services, and associated economic values for these services, are the nexus for facilitating more widespread engineering by livestock of rangeland ecosystems in the American West. Ranchers, land managers, policy makers, economists and others need to come together in confluence to create proper economic incentives that will foster changes in management practices to increase vegetation heterogeneity and produce marketable commodities from these rangelands. Then, development of markets to place economic value on these commodities for the rancher, as well as for the general public, should provide the foundation on which to foster more engineering of rangeland vegetation by livestock.
Dr. Justin D. Derner is a Rangeland Scientist for the USDA-Agricultural Research Service Rangeland Resources Research Unit in Cheyenne, WY. He currently serves as co-Lead Scientist for the project entitled “Improved Management to Balance Production and Conservation in Great Plains Rangelands.”
Dr. Emily J. Kachergis is a Landscape Ecologist and AIM-Monitoring Implementation Lead with the National Operations Center of the Bureau of Land Management in Lakewood, CO
Dr. David J. Augustine is a Research Ecologist for the USDA-Agricultural Research Service Rangeland Resources Research Unit in Fort Collins, CO. David is also a co-Lead Scientist for the project entitled “Improved Management to Balance Production and Conservation in Great Plains Rangelands.”
[v] McGranahan, D.A., D.M. Engle, S.D. Fuhlendorf, S.J. Winter, J.R. Miller, and D.M. Debinski. 2012. Spatial heterogeneity across five rangelands managed with pyric-herbivory. Journal of Applied Ecology 49:903-910.
[vi] McGranahan, D.A., D.M. Engle, S.D. Fuhlendorf, S.J. Winter, J.R. Miller, and D.M. Debinski. 2012. Spatial heterogeneity across five rangelands managed with pyric-herbivory. Journal of Applied Ecology 49:903-910.
[ix] Havstad, K.M., D.P.C. Peters, R. Skaggs, J. Brown, B. Bestelmeyer, E. Frederickson, J. Herrick, and J. Wright. 2007. Ecological services to and from rangelands of the United States. Ecological Economics 64:261-268.
[xi] Cheatum, M., F. Casey, P. Alvarez, and B. Parhurst. 2011. Payments for Ecosystem Services: A California Rancher Perspective. Conservation Economics White Paper. Conservation Economics and Finance Program. Washington, DC: Defenders of Wildlife. 65pp.
[xii] Goldstein, J.H., C.K. Presnall, L. Lopez-Hoffman, G.P. Nabhan, R.L. Knight, G.B. Ruyle, and T.P. Toombs 2011. Beef and beyond: Paying for ecosystem services on Western US rangelands. Rangelands 33(5):4-12.
[xiii] Derner, J.D., W.K. Lauenroth, P. Stapp, and D.J. Augustine. 2009. Livestock as ecosystem engineers for grassland bird habitat in the western Great Plains of North America. Rangeland Ecology and Management 62:111-118.
[xv] Dunn, B.H., A.J. Smart, R.N. Gates, P.S. Johnson, M.K. Beutler, M.A. Diersen, and L.L. Janssen. 2010. Long-term production and profitability from grazing cattle in the Northern Mixed Grass Prairie. Rangeland Ecology and Management 63:233-242.
[xvi] Knopf, F. 1996. Prairie legacies – birds. Pages 135-148 in F. Samson and F. L. Knopf, editors. Prairie conservation: Preserving North America’s most endangered ecosystem. Island Press, Washington, DC.
[xvii] Derner, J.D., W.K. Lauenroth, P. Stapp, and D.J. Augustine. 2009. Livestock as ecosystem engineers for grassland bird habitat in the western Great Plains of North America. Rangeland Ecology and Management 62:111-118.
[xviii] Augustine, D.J., D.T. Booth, S.E. Cox, and J.D. Derner. 2012. Grazing intensity and spatial heterogeneity in bare soil in a grazing-resistant grassland. Rangeland Ecology and Management 65:39-46.