Livestock producers exert a great deal of control over grazing impact on plants and plant communities by determining the number of animals to graze, the size of the grazing area, and the duration of grazing time. Together these variables determine the stocking rate. When managing grazing lands for livestock production and ecosystem management, there is no “right” stocking rate; rather, there will be numerous appropriate stocking rates to achieve multiple and often quite different ecosystem landscape objectives (Fuhlendor et al. 2012; Campbell et al. 2006). In the context of grazing for habitat, these may include:
- Using a high to very high stocking rate to encourage even use of all available forage, including grasses, legumes, forbs and shrubs, creating open and low vegetation structure and potentially areas of bare ground
- Using a moderate stocking rate to apply sufficient grazing pressure to create separation in use, such as between grasses and legumes or between forbs and shrubs
- Using a light stocking rate to support growth and reproduction of upright grassland species, many of which can be grazed out due to elevated growing points
Example 1.
Figure 1 illustrates use of multiple different stocking rates to different paddocks to increase heterogeneity of vegetation structure. This system is adapted from Clark et al. (2024) and referred to as Modified Twice-Over Rest-Rotation Grazing. At the beginning of the grazing season, target utilization rates are identified for each paddock. For example, 70-80% utilization in paddock A, 40-50% utilization in paddock B, 20-30% utilization in paddock C, and 0% utilization in paddock D. Most practically, the targeted utilization rate is achieved by varying the amount of time that the same number livestock (or AUs) spend in each paddock. Time in each paddock needs to be determined by monitoring forage utilization rates through pre- and post-grazing biomass estimations using a pasture stick or other method. The “twice over” component refers to rotating cattle through this system arrangement twice per season, applying the same utilization rate each time. Additional paddocks can be added, using multiples of the same utilization rates, or different.
Example 2.
The key to understanding how to apply proper stocking densities is to have clear goals. Whereas high stocking rate and utilization rate can negatively affect regrowth and thus reduce overall forage productivity, this same effect can be applied purposefully to reduce the competitive exclusion by cool-season grasses of native forbs. In Figure 1, a high stocking rate was applied in February-March prior to peak bloom of native forbs to purposefully set back non-native perennial grasses and allow light and room for Spring gold (Lomatium utriculatum) and Common camas (Camassia quamash, picture above as clumps of thick, grass-like leaves). The process has sometimes been referred to as “managed over-grazing”, but that is perhaps a misnomer, as the high grazing pressure is set on purpose to match the habitat objective, and thus is not excessive. A deferment began in mid-March 2022 (photo taken March 28th) following heavy grazing. Under continued deferment through May or early June, this field will become a carpet of Camas and Spring gold blooms and produce substantial seed.
Example 3.
Stocking rate can be used to apply full, partial, or no forage removal. Over time high stocking densities applied under continuous grazing will affect plant species composition through replacement of grazing intolerant with grazing tolerant species (species replacement). While stocking rate is generally (and in most cases should be) set to leave forage residual (2-4 inches, roughly optimizing carrying capacity), higher densities can be set to achieve more complete or full removal for specific habitat purposes (exceeding typical carrying capacity). In the two photos in Figure 2, we see two sites grazed in the fall that illustrate the effect of stocking rate and grazing system on vegetation structure as well as fall regrowth. The stocking rate at site A was determined to retain 4-6 inch summer stubble height with periodic rest. Stocking rate at site B resulted in consistent <1-2 inch stubble height with limited to no rest. Photos of the two sites were taken on in mid-September and are both on Nisqually gravelly sandy loam and within 20 miles of each other.
Example 4.
“Close herding” is a term that has been used to describe active, close-proximity management of a grazing herd. Many traditional herders in central Europe (such as the shepherd pictured in Figure 3 in the Carpathian Basin) have used this approach, and it has been adopted from there to a ranch in Idaho as well. The intent is to manage grazing time and animal numbers on the various pastures available to the shepherd; in other words, stocking rate.
Goals can be to reserve areas where new growth is tender, exert greater pressure on over-mature or less-preferred forages, maintenance of rare or medicinal plants in the sward, use of shrubs to prevent encroachment, and to utilize particular forages before they become too mature, among others (Molnar et al. 2016). The herder pictured here describes the herding process as “the whole afternoon involves them starting off and me walking out to head them off”. With such close attention, forage use or protection can be managed much more carefully and precisely with close herding than even high-intensity rotational grazing; although the objectives may be similar in terms of managing grazing pressure in specific areas for specific purposes (Molnar et al. 2022).
| Goal/intended outcome | Practices |
| Different utilization rates is achieved in different paddocks and maintained over the entire grazing season | Set specific utilization rate targets for each paddock across available paddocks in rotational systems |
| Inadvertent preferencing of grazing-tolerant species is prevented by avoiding SRs that lead to high harvest efficiency (i.e. non-selective grazing) | Manage grazing intensity and timing to offset competitive exclusion by dominant grass species of less-competitive sward elements such as native forbs and bunchgrasses (Figure 21) |
| The competitive exclusion by tall-stature grasses of forbs and other low-growing target species is eliminated | Apply sufficient (typ. moderate) grazing pressure to create separation in use between grasses/legumes and forbs/shrubs, but not so much that forbs are used overmuch |
| Forage species with tall-stature (height) and upright growth-form prevail in the sward | Apply consistently low SR to grazed areas over long periods of time, preferencing tall, upright species. |
| Forage species with low-stature (height) and prostrate or sprawling growth-form prevail in the sward | Apply consistently high SR to grazed areas over long periods of period, preferencing short, prostrate species |
| Forb grazing is minimized | Low SRs tend to maintain low forb use as an overall percent of intake |
| Full (complete removal), minimal (nearly no removal), and selective use of forage is achieved strategically; different SRs support a combination of heterogenous and homogenous grazing pressures. | Calculate and apply low, medium, and high SR to achieve varying utilization rates. Apply low to medium SRs for high grazing selectivity, and the opposite for low grazing selectivity (See Sidebar 7, Figure 22) |
| Overall sward biodiversity increases | Moderate grazing to increase species richness |
| Grazing selectivity is achieved in large continuously grazed and rotationally grazed paddocks; even (non-selective) use is avoided where uneven forage use is desired (e.g. separation between grass/legume and forb/ shrub use) | Use low SR; avoid uniform, complete application of high stocking densities in all paddocks |
| Specific vegetation uses are achieved, such as pressure on shrubs, protection of medicinal are rare plants, use of over-mature forage, and so on | Close herding, management intensive grazing (MiG), or other careful management of site forage for specific goals (Figure 23) |
Sidebar: Grazing Pressure Index
Managing stocking rate and density for a heterogeneity regime will require multiple rates and use of the Grazing Pressure Index (GPI) may be useful (Smart et al. 2010). The GPI can be applied as an objective means of quantifying grazing pressure to achieve high and low grazing pressure needed to create heterogeneous vegetation structure. In landscapes managed for patch-mosaic patterns, for example, GPI can be utilized to calculate animal units to deploy in a pasture in relation to available forage. Based on work by Smart et al. (2010), a pasture or patch receiving heavy disturbance to generate low-stature forage would be stocked at 36 AU/ton (1.2 AUM/ton), and a pasture or patch receiving light pressure for relatively undisturbed structure would be stocked at 13 AU/ton (0.43 AUM/ton). Variation and modification of these figures in practical application is inevitable and necessary, but they can serve as a starting point. Available forage estimation is required to use this approach, whether with a pasture stick, rising plate meter, or cut and weight methods.