Get reliable rangeland science

Written by Rachel Frost, Montana State University

The most important decision for successful range management is determining carrying capacity and setting a proper stocking rate. Matching the number of grazing animals with the forage resource is an important management decision regardless of grazing system. Too many animals in a management unit or pasture will reduce livestock weight gain, conception rates, and body condition and cause undesired changes in the soil and vegetation.

• Carrying Capacity
• Stocking Rate

Carrying Capacity

The number of grazing animals a piece of land can support long term while maintaining or improving the rangeland resources (vegetation, soils, and water) is called carrying capacity. The characteristics of the land, vegetation, and soil determine the carrying capacity, not the land manager. Proper carrying capacity attempts to balance between long-term forage supply and forage consumption by all grazing animals, both livestock and wildlife. Determining carrying capacity is an important goal of any rangeland inventory or monitoring program and forms the basis of stocking rate decisions. Furthermore, an assessment of carrying capacity can provide information on potential economic returns from ranch developments and forms one basis of ranch value on the real estate market. The actual carrying capacity for any management unit varies across years because annual forage production fluctuates due to variability in both the annual and growing season precipitation and temperature.

Determining carrying capacity The simplest and most reliable way to determine carrying capacity is to obtain past stocking rates and grazing management information for a piece of land and then assess the ecological status or condition of the rangeland. If the condition is good or improving, the current stocking rates are below carrying capacity. If the condition of the rangeland is declining, carrying capacity has been exceeded, and grazing management practices or stocking rate may have to be adjusted.

What if there are no historical stocking rate data available? One can estimate carrying capacity for a parcel of land in several other ways, even without historical stocking rate information. The first way is to measure annual forage production on the land and calculate an estimate of carrying capacity.

This method is useful but is based on a series of estimates for annual forage supply and animal demand. Continued monitoring of range condition and adjustments may be necessary to determine a final carrying capacity. Your local Cooperative Extension Service or Natural Resources Conservation Service office can assist you in this process.

Another way to estimate carrying capacity is to compare the land to similar rangeland with a successful history of setting stocking rates. Find out the carrying capacity estimates of the area and use those as a guideline to begin the process of determining an appropriate carrying capacity for your particular piece of land.

Trial and error is an inherent part of estimating carrying capacity. Additionally, carrying capacity is complicated by the fact that both forage production and animal intake are dynamic factors that vary with ecological site, topography, time of sampling, and plant species composition. The diets of grazing animals also vary according to animal nutritive requirements and the unique dietary preferences of species, breeds, and individuals. Therefore, carrying capacity estimates should be treated as an initial starting point for the management unit that will almost certainly be revised with continued monitoring and current environmental conditions.

Adapted from: Determining Carrying Capacity by Ken Sanders

Stocking Rate

As stated above, the most important decision for successful range management is setting a proper stocking rate. Stocking rate is defined as the number of animals grazing on a given amount of land for a specified time. Stocking rates are often expressed in AUs/unit area (links to Animal Unit).

4 Steps to Setting a Basic Stocking Rate:

1. How much forage do you have? The first step toward determining how many animals the grazeable portion of a management unit can support is to measure how much forage the area produces. The amount of forage produced can vary greatly from year to year depending on weather; therefore, estimated forage production for determination of stocking rate should not be based on one year of forage production data. Managers can estimate the forage production of their land by mapping the management area into units of land that produce similar kinds and amounts of forage. These units are termed ecological sites or habitat types and most often will differ in soil type and plant productivity. Each unit should be surveyed to determine biomass production by 1) mowing or clipping small areas, 2) referring to picture guides to visually estimate amount of forage available, or 3) referring to site guides to estimate average productivity of the site. Only a certain portion of the biomass can be safely removed, and this depends on the vegetation and other management objectives. A common starting point is that 50% of the annual production that is potential forage can be harvested each year. Once a biomass estimate for each site has been obtained, multiply the number of acres within each site by its estimated biomass production per acre and sum these values for a total amount of potential forage produced. Finally, multiply the total amount of biomass by the percent of allowable use to obtain the total amount of forage available for livestock use.

2. How much of that forage can be used by grazing animals? (Usable Forage) Land characteristics such as topography and distance from water influence the amount of forage available to grazing animals. Forage in areas with very rough or steep topography may be inaccessible to grazing animals or used much less than forage on level ground close to water. For example, grazeable plants located two miles or more from water are essentially unusable for livestock. They represent potential forage for livestock if the animals could be enticed to use the area. All management units should be stratified into areas of available and potential forage. Areas of potential forage identify management opportunities to improve livestock distribution across a greater portion of the landscape.

3. How much forage do your grazing animals need? (Forage Demand) To calculate how much forage your grazing animals will need, you must determine the average weight of the animals in a herd or flock and the number of days the herd will graze the management unit. The average daily forage consumption of an animal — a combination of eating, trampling, and spoilage from urine or feces — will vary with the nutritive quality of the forage; however, an annual average of 2.6% is usually acceptable. For example, a 1,200-pound range cow that consumes 2.6% of her body weight requires 31 pounds of forage per day (1,200 pounds * 2.6%). When you multiply the animal's daily need by the number of days the management unit will be grazed, you obtain forage demand for that period. In the example above, if the cattle grazed the unit year round, then each cow would require 11,315 pounds (31 pounds * 365 days) of forage for the year.

4. What is your appropriate stocking rate? Now that you have answered the above questions — how many animals can you graze and for how long — to determine the number of animals that can be grazed on a management unit, you must divide the pounds of usable forage by forage demand. For example, if a management unit that is grazed year long has 465,000 pounds of usable forage, and annual forage demand per animal is 11,315 pounds of forage, then 41 cows can graze the unit for 12 months. If the grazing period is less than 12 months, then more animals can graze the area for a shorter period. A three-month grazing period would have a stocking rate of about 164 cows [465,000 pounds of available forage /(31 pounds forage/head/day * 91 days) = 164.8 head].

Administration of Fire Regimes 

" ...Institutions, not merely policies, of fire protection have rapidly and probably irreversibly undergone a metamorphosis. The evidence lies all around. Privatization, partnerships, the devolution of political decision making to more local jurisdictions, indigenous land claims, a near civil war over the destiny of the public domain- all are changing the attributes of how government administers these lands and how they cope with fire."
(Tending Fire: Coping with America's Wildland Fires. by Stephen J. Pyne, 2004, pg. 164).

 A Brief History of United States Fire Policy

From the creation of the Forest Reserves at the turn of the last century through the 1970's the USDA Forest Service was the preeminent wildland fire agency commanding the bulk of the nations firefighting resources and directing its fire research. While critics became vocal as early as the 1930's, the agency's policy during these 60 years was one of suppression (Pyne 1997). With the surge of environmental legislation in the late 1960's and the establishment of wilderness reserves, policies supported letting backcountry fires burn and reintroducing flame via prescribed fire. With this shift also came greater inter-agency coordination on fire management. By the 1990's on the heals of some devastating escaped prescribed fires and a general population increase adjacent to wildlands, the nation's resources turned to the control of fire in the wildland-urban interface. New forms of collaboration between federal, state, and local fire insitutions became essential. As one devastating fire season follows another, we now know that some fires, given current fuel loads and climatic conditions, may be beyond our control.

• Fire Policies and Legislation
• Fire Management at the Federal Level
• State and Local Fire Management
• Private institutions and Collaborative Groups

Where? How Big? How Much Money?

The earth's fire problem is one of maldistribution. There is too much of the wrong kind of fire in the wrong places or at the wrong times, and not enough of the right kind of fire at the right places and times. (World Fire: The Culture of Fire on Earth by Stephen J. Pyne, 1997, pg. 5-6)

In 2006, the largest US wildfire occured in Texas, burning over 900,000 acres of grassland. Acres burned by prescription were greatest in Alabama and Florida. In 2006 the USDA Forest Service reported spending over 1.5 billion dollars on wildfire suppression (NIFC). Wildfire is not unique to the US. Russia, Australia, and Canada also experience large and frequent wildfires (Pyne 2004). Want the latest on fires around the country and around the world? These sites provide up to the day information.

• Current U.S. Wildland Fire Information: The National Interagency Fire Center. Find out where fires are burning right now. Learn how many acres have burned each year since 1960. Learn what the annual costs have been for fighting fires. find out how much prescribed burning is occuring in your state. This site is the place to go for information.
   
• Current Global Fire Status: The Global Fire Monitoring Center. Where are fires occuring in the world? How do other countries cope with fire? The Global Fire Monitoring Center Offers Statistics, News, Maps, and other resources.

The wildland-urban interface (WUI) is the zone where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels (NIFC). Currently in the United States it includes 9.4 % of the land area and 38.5 % of all housing units and growing, with the largest number of homes in California (Radeloff et al. 2005). These areas pose the greatest threats to lives and property, pitting the fierceness of wildland fires against often indefensible homes, lacking the proper protections that could reduce fire risk. These fires often occur in locations that slip between the jurisdictions of urban and wildland fire agencies and outside effective county or rural fire districts, requiring action by outside agencies at the nation's expense (Pyne 2006, pg. 275). Such situations raise questions about who should pay for the protection of these homes from wildfire? What responsibilities should landowners have for the protection of their homes? Is building in a fire zone equivalent to building in a floodplain or at the base of a volcano? The wildland-urban interface has forced new forms of collaboration between the various fire agencies. Community wildfire protection plans now pose the greatest hope for defining roles and responsibilities before the flames come lapping.

The complexity of jurisdictions and sheer number of individuals involved in the management of wildland fire requires the establishment of a common lexicon of terms. For those unfamiliar with fire terminology we offer links to a widely accepted glossary of terms and provide connections to training materials highlighting fire fundamentals.

Fire, if properly controlled and managed, can be a valuable tool to manipulate vegetation composition, structure, and fuel loads on rangelands (and other wildland ecosystems). Managed fire can create and maintain a mosaic of plant communities, at appropriate locations on the landscape, to provide valuable ecological services that benefit many rangeland resources. Among these are:

1. “cleaning” or removing unwanted vegetation from landscapes to reduce fuel loads and the risk of large catastrophic fires
2. changing the relative balance between herbaceous (grasses and forbs) and woody plants to improve forage availability for livestock or wildlife
3. changing the structure or size class of plants across appropriate distances to benefit wildlife
4. creating variability both within and among plant communities for wildlife and other rangeland resources
5. promoting seed germination and the regeneration of desired plants; and
6. maintaining the hydrologic cycle to promote the infiltration of water and to prevent rapid runoff and accelerated erosion.

The use of fire as a management tool requires that it be applied at the correct frequency (return interval), intensity (heat release), and spatial scale so that burned and unburned patches remain on the landscape. A mosaic of burned and unburned patches typically results in a mix of early- to late-seral communities, which benefits more rangeland resources than a homogeneous landscape of either early- or late-seral plant communities.

The Importance of Fire Intervals

Prior to European settlement of North America, most American rangelands burned periodically. The return interval between fires varied widely among different rangeland ecosystems (e.g., tall-grass prairie, sagebrush steppe, ponderosa pine forest) but was relatively constant within an ecosystem. Some pre-settlement fires were caused by lightning, but others were intentionally set by Native Americans to achieve vegetation management objectives. Because fire, regardless of the source, was a recurring ecological event with a relatively constant interval, most rangeland vegetation has adapted to periodic burning. After a fire, the vegetation usually forms early-seral plant communities. If there are few unburned "islands," wildlife species that need mid- to late-seral plant communities to complete their annual life cycle cannot inhabit the area or they have very small populations. The same ecological effect occurs when fire return intervals become so short that mid- and late-seral plant communities never become established. Excessively long or short fire return intervals create uniform plant communities across large landscapes and tend to exclude (or dramatically reduce) the wildlife species that need a diverse habitat structure created by a mosaic of early- to late-seral plant communities.

Modern fire return intervals on most rangelands are either longer or shorter than the pattern that evolved prior to settlement. This has resulted in undesired vegetation changes that often adversely affect rangeland resources. Fire return intervals that are substantially longer than the evolved interval lead to a substantial increase in shrubs and/or trees (woody fuel) and a decline in many desired grasses and forbs. The long life span of most shrubs and trees, combined with the slow decomposition (compared to herbaceous vegetation) of their dead branches, stems, and leaves creates large fuel loads and a fuel ladder that can carry a fire into the upper canopy of the vegetation. Horizontal and vertical continuity of the vegetation (fuel), combined with excessive fuel loads, can result in large, intense wildfires across tens of thousands of acres or more. In the western United States, it is becoming increasingly common for individual fires to burn 100,000 to 200,000 acres or more.

Public land management agencies and some private owners of range and forestland are increasing their effort to thin the woody vegetation on land they administer or manage. Their goal is to reduce wildfire risks and create plant communities that are more resilient to insects, disease, and the inevitable wildfire that will occur. Treatments that thin shrub- and tree-dominated communities not only reduce fuel loads but can also provide large volumes of woody biomass for an alternative fuel for society. According to a recent national study, about 8.4 billion tons of dry biomass resides on range and forest lands, but only 60 million dry tons can be removed annually with current fuel reduction methodologies (USDOE and USDA, 2005). At the current removal rate, it will take at least 140 years to reduce woody fuel loads; thus, additional large-scale catastrophic fires are inevitable in many areas.

"On these landscapes four options exist for fire management... Simply put: You can do nothing, and leave the fires to God and nature. You can try to exclude fires and suppress those that do break out. You can do the burning yourself. Or you can change the combustibility of the landscape such that fires, whether from accident, arson, lightning, or prescription behave in ways you favor...Proper fire management requires bits of each, mixed to proportions suitable to the taste of particular sites."
(Tending Fire: Coping with America's Wildland Fires by Stephen J. Pyne, 2004, pg. 69).

Science can help us understand historic fire regimes, describe the benefits and impacts to ecosystems from different fire scenarios, and model fire behavior. Only humans can decide their role in fire management. Resource and property damage compel suppression, but at what cost? Some fires probably should be started or allowed to burn. How do we decide which ones? Thinning overgrown brush and forests can help prevent catastrophic crown fire. Can this be done in an ecologically sensitive manner that we all agree upon? How widely should it be applied? What role does wildfire play in global climate change and how do we decide when open fire is threatening public health? Decisions about how to respond to fire will be political ones based on society's values.

As appreciation of the important ecological role played by fire has increased, so has the debate over how to respond to wildfire and when to use prescribed fire as a management tool. Some fear that fire has become a panacea, and risks being applied indiscriminately. Others point to the successful achievement of management goals when prescriptions are right. For certain, more people are living on and adjacent to highly flammable range and forest lands creating formidable challenges for fire management. Some fires given current fuel loads are beyond our control. How will we respond to fire? Here are links to basic fire concepts, information about fire management, and highlights of some of the burning issues related to fire on Western Rangelands.

Rangelands across the globe are tightly coupled with local and regional climates, benefitting from periods of enhanced precipitation and suffering during prolonged drought periods. Climate variability and change pose unique challenges to livestock producers, pastoralists and land managers the world over. An increased understanding of large-scale modes of climate variability like the El Niño-Southern Oscillation have improved seasonal forecasts and can aid in rangeland drought planning and preparedness efforts, helping to sustain production operations and guide land stewardship. A changing climate shifting towards warmer conditions and increasing hydroclimatic variability is further raising the stakes on becoming ‘climate-smart’ in using climate monitoring and forecast information in managing rangelands.