What is the utility of utilization monitoring?
by Tip Hudson, WSU Extension Rangeland & Livestock Specialist
As featured in the May 2017 Ketch Pen
Utilization monitoring is sometimes called annual use monitoring, compliance monitoring, or grazing monitoring. The intent of utilization monitoring by most public land agencies is to serve as an easily measured guideline for limiting potential negative effects of grazing. This is a good goal; unfortunately, simple indicators often fail to capture the complexity of natural systems with lots of interacting parts. D. Costello, writing in the Journal of Range Management back in 1957, said: “Oversimplification leads to poor interpretation and poor interpretations leads to poor management.”
Before discussing various methods employed to measure utilization, I want to challenge the assumptions baked into this approach to public land permit policing and grazing guidance. Utilization monitoring is specifically designed to measure how much of the available forage has been consumed in a given grazing event, permit period, grazing period, or calendar year. Note that these are all different reference points and timeframes. Growing season measurements are complicated by regrowth. End-of-season measurements do not account for timing of grazing, uniformity of grazing impacts, species preferences, etc. These factors all matter to the actual long-term effects of grazing use on a plant community, which is what we’re really after.
Let me state here that I’m not supporting unregulated grazing of public lands. The West has oceans of sagebrush and cheatgrass that are largely the product of decades of season-long growing-season grazing at moderate to heavy stocking rates. I’ll mention at the end of this article some keys to sustainable grazing. Grazing forests and rangelands well is serious business. We’re trying to do something radical—produce food and fiber on naturally occurring ecosystems while allowing those lands to produce other less tangible “goods and services” such as wildlife habitat, open space, clean water, clean air, recreation areas. No other segment of agriculture can claim this. Dr. Jerry Holechek, New Mexico State University, has made the case that doing wildland grazing successfully is a matter of national security. All other methods of food production require destroying the native plant communities and replacing them with agro-ecosystems. Cropping systems are necessary, but I am saying that rangeland-based meat production is unique and important. Because we have limited ability to pour money into these vast areas if we mess it up, it is radically important to avoid putting so much grazing pressure on soils and plants that the plant community crosses an ecological threshold into a less desirable and less productive stable state. Once that hump is crossed, we can’t just remove the grazing pressure and go back to the earlier stable state. Therefore, it is monumentally important to avoid crossing that threshold in the first place. This is what well-meaning agencies seek to do with utilization monitoring. But utilization measurements are not likely the best tool to prevent degradation.
Measuring utilization assumes 1) that utilization data is meaningful data as an indicator, 2) that it can be measured accurately (once we define what “it” is), 3) that it can be interpreted profitably by untrained professionals, and 4) that the data provide some basis for action. All these assumptions are problematic and have been seriously challenged in the scientific literature.
First, is it meaningful? Well-respected range scientists with many years of real-world experience have been saying for 20 years that utilization monitoring is not management, that it provides little direction for improving grazing and improving range condition. The use of utilization standards can be traced back to a 1937 report by Dr. Robert Campbell (who was with the Forest Service) who was tasked with formulating sound utilization standards and simple, practical methods of measuring degree of forage use. He stated in this report that “continued productivity or gradual death of a good forage grass may depend upon a difference in foliage removal of as little as 10%.” This premise, that rangeland healthy rides on the razor’s edge of minor differences in forage utilization, seems to be unfounded and unsupported by later research. Numerous studies have documented widely varying utilization levels without long-term decline in rangeland health in different kinds of plant communities. A utilization value is usually an inadequately sampled data average about a single species at a single point in time at a severely small spatial scale that may not tell much at all about grazing on an entire grazing area of many thousands of acres, or even hundreds of acres. It is not a particularly good indicator of range trend (improving or declining condition). Research has shown that the effects of a particular utilization rate vary within species and across species.
Second, can it be measured accurately? Utilization on a particular species, such as a most preferred species, can be measured accurately with enough sampling areas and observer calibration. It is easier to measure accurately than other plant community attributes which are more indicative of trend, which is why it is used. Measuring actual utilization of the whole plant community on a large and heterogenous landscape is more more difficult. Using indicator species is valid only when those indicator species are the most preferred species and/or are leading indicators of damage.
The bigger problem is my third objection—can it be interpreted accurately? Rangeland and forest forage production can vary widely from year to year in response to a number of variables, most dramatically timing and amount of available water, but also temperature, insect herbivory, wild ungulate use, competition from non-herbaceous plants, etc. A constant stocking rate which is sustainable by the book and which is accompanied by consistent, well-planned animal distribution efforts may result in utilization values that vary significantly from year to year. Different methods of measuring annual grazing use mean something different, but most grazing plans provide a single percentage or a handful of percentages for different range areas such as in riparian zones, in rhizomatous plant communities, etc. Avoiding over-utilization of the most preferred perennial grass species is mission critical—but overgrazing may not be related to a particular utilization value or threshold. Wayne Burkhardt and Ken Sanders argued in a 2012 article that after 75+ years of well-built research on native bunchgrasses in the Intermountain West, one of the only truly solid conclusions we can come to on how to maintain the vigor and density of these key grasses is to make sure they are allowed to produce and set seed periodically, at least about every other or every third year. 35% utilization that removes all the seed heads between May 1 and 31 every single year meets utilization guidelines but will still cause the stand to decline and shift in species composition toward less desirable or at least more grazing tolerant species, which are usually less productive! However, 75% utilization which occurs after seed set every year is likely to have a strong positive effect on stand vigor and density because the plants have completed their reproductive cycle, produced and shed their seeds, and grazing use after that point just serves to plant seed, deposit beneficial plant litter on the soil surface, and cycle nitrogen back into the soil in an ecosystem where nitrogen is a bigger limiting factor to plant growth than water.
Unfortunately, many rangelands are not managed this way. There is no attempt to change season or timing of use from year to year, no attempt to ensure seed production occasionally, insufficient effort made to distribute animals across the landscape in space and time, and too many acres in Washington State show evidence of overgrazing. Again, utilization monitoring may provide a weak indication of overgrazing but it doesn’t help direct sustainable grazing. Utilization monitoring today may also reveal poor plant production resulting from overgrazing that happened 25 years ago rather than illuminate problems today.
Here are some common methods used by federal agencies to measure various kinds of utilization and my comments on their relative value. Note that these are well-established, published methods that have wide acceptance; as previously discussed, the value or potential for abuse is in interpretation and implementation.
Extensive Browse Method
With the Extensive Browse Method, pace transects are run to collect vegetation data. This method provides data on utilization, species composition, age classes, availability, and hedging for the browse component of the plant community.
TDH: This is reliable for measuring browse (shrub and tree grazing). Browsing is rarely a problem except in heavily-stocked winter pastures with antelope bitterbrush, newly planted regeneration areas on a harvested forest stand, or in riparian zones where woody species dominate and exceed nutrient values on adjacent upland grasses.
Residual Stubble Height Method
The Residual Stubble-Height Method measures stubble height or height (in centimeters or inches) of herbage left ungrazed at any given time. This method, because of its simple application, is becoming a well-accepted method for expressing rangeland use. This method would be used after stubble height standards for specific plant communities had been developed. An example, a stubble height of 4 inches might be specified to provide streambank protection, to trap sediments, and to rebuild degraded stream channels in riparian areas. This method is often prescribed in biological assessments and biological opinions in the Pacific Northwest Region.
TDH: Stubble height is a legitimate way to gauge negative site impacts. However, it often ignores selective grazing and site potential. It is relatively rare to have completely uniform grazing use in any ecosystem except one that is very homogeneous, so the target species could be grazed to 3" and trigger a violation when that species is only 20% of the plant community. Also, if Kentucky bluegrass is the target species and it only grows to 5 inches in a given environment, a 4-inch stubble height really isn't reasonable because it's not achievable.
The University of Idaho Stubble Height Review Team reported in 2004 that stubble height is effective when measured at the "green line", the narrow zone where water meets bank and vegetation and where vegetation is driving bank stability rather than shrubs, trees, and rock or cobble. Further, the review team says that stubble height as an annual indicator of riparian grazing impacts is NOT applicable "at the tops of streambanks above the influence of water in the rooting zone . . . [or on] erosional banks whose tops are above the bank-full level [and] are not favorable to hydric vegetation."
Paired Plot Method
Under the Paired Plot Method, forage from protected and unprotected plots is clipped and weighed at the end of the use period. The difference between those two weights represents the amount of forage consumed or otherwise destroyed during that period.
TDH: This is a good approach which does consider site potential as long as the protected plot moves annually. Otherwise, it's a long-term trend exclusion experiment. Note that several researchers have stated that using forage biomass weights “obtained from caged areas to calculate utilization will usually indicate higher utilization values than values calculated from actual yield” (Sharp, et al 1994).
Ocular Estimate Method
With the Ocular Estimate Method, utilization is determined along a transect by ocular estimate. The percentage by weight of forage removed is determined for individual plants of the key species of from all plants of the key species within small quadrats.
TDH: Ocular estimates are good for internal use where the same observer is used every year. I would never recommend this method for any measurement that would be used in an official capacity, such as alleging non-compliance on a federal land lease. This depends heavily on observer calibration, and even good observers can be tricky to calibrate.
Key Species Method
In the key species method (formally the modified key forage plant method) utilization levels are based on an ocular estimate of the amount of forage removed by weight on individual key species and observations are recorded in one of seven utilization classes.
TDH: This is a modification of the grazed-class method described below. The grazed-class method is as good as ocular estimation gets, i.e., is somewhat objective. This is better than stubble height, although less objective, and not as good as height-weight, which requires concrete measurements which could be performed/collected by different observers and still get the same answer.
The Height-Weight Method involves the measurement of heights of ungrazed and grazed grasses or grasslike plants to determine the average utilization. Measurements of plant heights recorded along transects are converted to percent of weight utilized by means of a utilization gauge (Lommasson and Jensen 1943). The utilization gauge is developed from height-weight relationships curves. The method provides a mechanical tool which can be used for training, checking personal judgment, and promoting uniformity of results between examiners, as well as for determining percent utilization. A utilization gauge developed by the U.S Forest Service, Rocky Mountain Forest and Range Experiment Station can be obtained from Colorado State University.
TDH: I like this approach. It isn't excessively time-consuming, allows focus on the most preferred plants, is objective, and can be fine-tuned for local conditions (height-weight curves can be easily developed and compared against the utilization gauge described above).
The Grazed-Class Method uses photo guides of key species to make utilization estimates. These estimates reflect herbage removed but also show herbage remaining.
TDH: These are okay. They are objective, but I think not as reliable as actual field measurements. If a person is on a specific site long enough to take some photos, it doesn't require that much more time to collect stubble heights. I think doing both is a winning combination.
Very brief grazing guidelines (adapted from Floyd Reed, retired USFS range con and private consultant, and added to by the author):
- Defoliate the primary forage species moderately.
- Change the season of use from year to year. This will let grasses go to seed periodically.
- Provide an adequate regrowth period before re-grazing the same area. October to April is not adequate regrowth because plants are not growing.
- Find ways to distribute animals on the landscape both in space and time.
- Not grazing everything is not leaving money on the table—it’s leaving money in the bank.