By Sonia A. Hall, Center for Sustaining Agriculture and Natural Resources, Washington State University, and Tip Hudson, Washington State University Extension
We recently released StockSmart, a free, online decision support tool that we developed in partnership with the University of Arizona and the US Forest Service Rocky Mountain Research Station, that accesses remotely sensed forage production data and allows the user to easily define what is accessible to their livestock based on their fences, watering locations, the type of terrain their livestock will traverse and other parameters. Notably, the remotely sensed production data are available for the last 40 years, providing information on how variable production has been between wet and dry years, giving us a sense of any trends in that variability, and through that a glimpse to how that variability might change as the climate changes.
Why do we need this tool?
Managers’ ability to maintain a healthy herd of cattle and healthy rangelands is affected by many factors, including their decisions on the timing, duration, frequency and intensity of grazing. Managing grazing of native rangelands across the western United States, as in other arid lands across the world, is also complicated by the fact that the production of forage can vary widely across the pasture and between years, a source of variation that is increasing as the climate changes. As if all this is not complicated enough, ranchers and other rangeland managers also need to figure out to what extent that forage is accessible to their cattle, to say nothing about how much of the forage is sustaining wildlife herds, like deer or elk. So even something as basic as determining how many head of livestock can be sustainably fed for a season by a particular rangeland area—the stocking rate—is hard to do and is generally based on inaccurate and inadequate forage production data, which itself becomes outdated as climate change leads to changes in forage production.
Historically, managers have relied on general estimates of forage production based on the soil types in their pastures, developed as part of the US Soil Survey, or on sparse, one-time samples taken at a few locations within each pasture. Though the former provides a range of production, and the latter is based on field samples, neither approach—individually or in combination—adequately reflect the spatial and interannual variations in forage production that managers must work with, undermining their ability to effectively manage forage allocation and grazing pattern decisions.
The value of a tool that helps managers use data that captures these variations in forage production across the landscape and between years was clearly articulated during three listening sessions with federal, state and Tribal rangeland managers and ranching association representatives that we hosted in 2020.
First, the forage production data
Advances in remotely-sensed data and enhanced access to these data by ranchers and public land managers offer opportunities for improved calculations of stocking rates across vast rangeland environments. The primary data that StockSmart uses emanate from the Rangeland Production Monitoring Service (RPMS; Reeves et al. 2021) and the Rangeland Analysis Platform (RAP; Allred et al. 2021). Based on the RPMS data, StockSmart computes the historical mean and standard deviation of total annual production from 1984 to 2022, giving one value for each 30x30m square (less than a quarter of an acre). It then uses the most recent Vegetation Cover data from the RAP to divvy up that total production into what is produced by shrubs, herbs (annual and perennial), and tree growth. This allows StockSmart to provide estimates of how much edible forage is available: annually, with average, dry, and wet years, as well as for each small square of your rangeland, showing both the spatial and interannual variations.
Second, the accessibility of the forage
To determine what forage is actually accessible to the animals grazing these rangelands, StockSmart corrects the forage production values based on tree canopy cover and terrain. Where remotely sensed estimates of understory forage are unreliable because of the interference of tree canopies, some basic linear models are used to estimate forage growing beneath the trees. All the edible forage is then corrected, accounting for how steep a slope your livestock will traverse, and how far from water they will disperse. After also adjusting the accessible forage using a harvest coefficient—the fraction of total forage produced that is assigned to grazing animals for consumption—and a shrub utilization fraction (some animals browse shrubs, some don’t), StockSmart provides the user with a final number. This can be either the number of days your herd of cattle could graze, or the number of head of cattle that could graze there for a predefined length of time.
And third, the decisions StockSmart can inform
With access to accurate, spatially explicit historical forage production data, ranchers and other rangeland managers can fine tune grazing management decisions and compare scenarios (and save them, if you create an account). You can visualize what areas are too far away from water to be accessed by your cattle, and explore what happens to your stocking rate if you added a source of water in that part of your pasture. Or you can explore whether dividing pastures as well as developing water would make a big enough difference in terms of available forage to be worth the investment in fencing. The historical variations in forage production—and therefore stocking rate—are particularly valuable as users look to increases in variability among years as the climate continues to warm.
StockSmart will not tell you when, how, and how much to graze. But it will provide robust estimates of how much forage is available with realistic parameters on where your animals will graze, and will provide clarity on how variable that forage is likely to be from year to year. When paired with careful grazing planning and monitoring of rangeland health, it provides a very useful additional tool in the rangeland manager’s toolbox, to help understand and deal with the complexities of maintaining healthy herds and healthy rangelands, now and under a changing climate.
References
Allred, B.W., B.T. Bestelmeyer, C.S. Boyd, C. Brown, K.W. Davies, M.C. Duniway, L.M. Ellsworth, T.A. Erickson, S.D. Fuhlendorf, T.V. Griffiths, V. Jansen, M.O. Jones, J. Karl, A. Knight, J.D. Maestas, J.J. Maynard, S.E. McCord, D.E. Naugle, H.D. Starns, D. Twidwell, and D.R. Uden. 2021. Improving Landsat predictions of rangeland fractional cover with multitask learning and uncertainty. Methods in Ecology and Evolution. Online Access
Hudson, T.D., Reeves, M.C., Hall, S.A., Yorgey, G.G. and Neibergs, J.S., 2021. Big landscapes meet big data: Informing grazing management in a variable and changing world. Rangelands. Rangelands, 43(1) 17-28. Online Access
Reeves, M.C., Hanberry, B.B., Wilmer, H., Kaplan, N.E. and Lauenroth, W.K., 2021. An assessment of production trends on the Great Plains from 1984 to 2017. Rangeland Ecology & Management, 78, pp.165-179. Online Access
This article is also posted on WSU’s Center for Sustaining Agriculture & Natural Resources Perspectives on Sustainability blog.
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