Rangeland Health & Planned Grazing Field Guide
Gadzia is a grazing consultant; Sayre is a geography professor at UC-Berkeley.
The following is excerpted from the original guide, as edited by Leading Edge, a publication of No-Till on the Plains, Inc (see www.notill.org or call 888-330-5142 for subscription information). The original publication is available at www.quiviracoalition.org . While the subject is a slight departure from Leading Edge’s ‘standard’ content, the concepts are of critical importance, not widely understood or implemented, and more relevant to grain cropping than we realize.
This field guide is an introduction to grazing management designed to help landowners, stock handlers, and agency personnel make better decisions involving rangeland. Improved management decisions will increase vegetative cover, control erosion, protect water quality, and improve animal production.
Arid and semiarid rangelands (receiving less than 10 or 20 inches of rain per year, on average, respectively) defy some of the central assumptions of conventional range management. They are highly variable over time and space, making fixed measurements of carrying capacity or “the right” stocking rate questionable. Which plants grow, and how much they grow, depends not only on how much rain falls, but when and how quickly it falls, and on the weather that follows it.
Plants must be able to withstand drought and take advantage of rain when it finally arrives. Different plants will grow depending on whether the rain arrives in summer or winter, in large quantities or small. Over thousands of years of evolution, the vegetation of these areas has adapted to reflect these circumstances. In recent decades, scientists have begun to develop models to explain and explore these complex dynamics. This field guide presents some updated tools and concepts of range management that reflect the improved scientific understanding of range dynamics.
Central to an understanding of range dynamics is the concept of ‘disturbance.’ Droughts and wildfires are natural disturbances in arid and semiarid rangeland ecosystems. Grazing is also a type of natural disturbance to which many range plants are adapted. The effects of grazing depend—like those of other disturbances—on timing (when they happen), intensity (how severe they are), and frequency (how often they recur), and grazing can be managed in these terms. Vegetation is highly sensitive to variations in available water and nutrients, both of which cycle through the ecosystem in ways that can be indirectly influenced by management. Management tailored to these processes, and attuned to variability, can conserve rangeland resources and help restore areas that have been degraded in the past—while simultaneously producing greater returns for the ranch.
Ranching as Sustainable Agriculture
To be sustainable, ranching must convert natural forage into livestock in such a way that the perennial forage plants retain vitality year after year. This is possible because grasses (and many other rangeland plants) are resilient to grazing—they can recover from it, provided that the disturbance is not too great. However, grazing is not limited to the plants that are eaten. There are other factors to consider: water, soils, nutrients, other plants, wildlife, and a host of organisms that interrelate with all of them. Livestock are only one piece of a much larger puzzle that must fit together if ranching is to be sustainable.
At its simplest, ‘biodiversity’ is the richness or number of species (kinds of organisms) in a community. When the community is rich, the ecosystem is more resilient to disturbance. Therefore, it is necessary to maintain resources other than just grass, soil, and cattle. As one rancher put it: “My goal is to manage for diversity and complexity of life on the ranch: biodiversity. Each plant species has different growing seasons, different root zones, and different leaf capacity. Each provides a different pathway for conversion of solar energy to life. By maximizing the pathways of solar energy conversion, I maximize production. I have learned that biodiversity extends beyond a mixture of grass. Each animal, fish, and insect species expresses something . . .” about the health of the land.
Grazing is a natural process which has been occurring for millions of years. From the fossil record it has been determined that grasses and grazers evolved together some 45 million years ago. Having co-evolved, grazers and grasses are adapted to each other.
Imagine a perennial plant over the course of a year. Many plants go dormant during the part of the year when water is insufficient or temperatures not suitable for that species. Grazing during the dormant season is unlikely to cause damage, because the leaves are not active or living tissue at this time (i.e., they are not photosynthesizing and not exchanging materials with the plant’s roots). When moisture and temperature conditions reach certain levels, the plant enters a period of growth. Belowground, the plant’s roots begin to grow, drawing water and nutrients from the soil. Aboveground, the leaves begin to ‘green up,’ beginning at the base of the plant. New leaves form and some portion of the old leaves may regenerate, turning from brown to green.
Throughout the growing season, the plant responds to changing conditions of moisture and sunlight. If conditions permit, the plant continues photosynthesis through the growing season until temperatures become unfavorable again. It produces enough food to support growth in the roots and the leaves, as well as to develop tillers, vegetative branches, and/or seed stalks. It stores up energy for the upcoming dormant season. It flowers and sets seed. Eventually the plant returns to dormancy, its leaves again turning brown. The health or vigor of the plant depends on its ability to produce enough food during the growing season to survive through the dormant season and resume growth when conditions are again favorable.
In commencing to grow after dormancy, the plant utilizes stored energy to produce new aboveground growth. It thus takes a risk, so to speak, that the new leaves will be able to produce enough additional energy to replenish its supplies. At this early stage of growth, then, the plant is more vulnerable to leaf loss than it is later in the growing season.
Grazing disturbs the plant by removing leaf tissue. This can be good, bad, or indifferent for the plant as a whole. If very little leaf is removed, the effects of grazing may be negligible. A more severe, single grazing may slow growth in the roots (Table 1), and/or accelerate the growth of leaves, but recovery is likely if grazing does not recur for one to two growing seasons. Repeated defoliations in the same growing season, however, can set the plant back for many years to come (see Figure 1).
Percent leaf Percent root
volume removed growth stoppage
Grasses have several traits that enable them to tolerate grazing, and in many circumstances to benefit from it. Most importantly, they produce more leaf area than is necessary for optimal photosynthesis, meaning that some leaf area can be removed without damage. Younger leaves photosynthesize more efficiently than older ones, and defoliation of older leaves can expose younger leaves to greater sunlight. Overgrazing occurs when a plant bitten severely in the growing season gets bitten severely again while using energy it has taken from its crown, stem bases, or roots to re-establish the leaf area—something perennial grasses routinely do. Overgrazing can happen:
•when the plant is exposed to the animals for too many days and they are around to re-graze it as it tries to regrow;
•when animals move away but return too soon; or
•when grazing is allowed too soon after dormancy when the plant is growing new leaf from stored energy.
How plants respond to grazing also depends on larger conditions in the area: the other plants present, topography and soils, and whether it’s a dry year or a wet one. Two ecological processes strongly determine the vigor and composition of vegetation, especially in arid and semiarid rangelands: the flow or cycling of water, and of nutrients. Put simply, the plants on a range—what they are and how well they are growing—are a reflection of these underlying ecological processes. The goal is to develop means of managing grazing for improved water and nutrient availability.
Plants require water and nutrients for growth. These are not static quantities: they increase and decrease, sometimes rapidly, and they move around. The issue is not simply how much moisture or nutrients there are, but whether they are available to plants when they need them. In arid and semiarid regions, small changes in the availability of water and nutrients can have dramatic effects on vegetation. Therefore, we have to manage rangelands in a way that effectively uses available water and diligently recycles the nutrients in the soil and plant matter.
Effective Use of Water. Moisture is scarce in arid and semiarid areas, and precipitation is highly variable. The key issue is how much of the total precipitation is retained in the system and for how long, because this determines how effectively the plants use the moisture. A second, related issue is erosion: where erosion is high, water retention tends to be low.
Vegetation strongly affects the distribution of water in space and time. In the absence of vegetation, raindrops hit the ground surface at a high rate of speed. The impact dislodges fine soil particles, which then clog the pores of the soil. This greatly reduces infiltration and accelerates erosion, where soil particles are transported downhill in runoff. This reduces the quality of the soil that remains. In extreme cases, a thin crusty surface (‘capping’) develops which encourages runoff and prevents plant establishment, resulting in more bare ground.
If a raindrop hits plants or litter (mulch), on the other
hand, the impact on the soil is greatly diminished. Even a thin cover of litter will protect soil
from capping and reduce erosion. (Editors:
See the water infiltration article by
The more water that is retained in the soil, the more resilient the system will be to extremes of rainfall. The goal can be expressed simply: capture as much of the rain that falls as possible, retain that water in the soil so that it can be safely released to plants and downstream areas over time. Given that drought is almost ‘normal’ in the Southwest, this is an important goal.
Cycling Nutrients. The nutrient cycle consists of the movement of nitrogen, phosphorus, and other minerals from the soil, through plants, and eventually back into the soil. The more effectively the nutrient cycle functions, the more nutrients are available to support plant growth.
Decomposers—especially insects—are a key link in both the water and nutrient cycles. Termites can dramatically increase water infiltration rates by opening pores in the soil. Without plants to feed on, termites disappear and the soil becomes more compact and impermeable. Termites actually consume the majority of aboveground dead plant matter in Southwestern deserts. Without their activity, many of the nutrients in dead plants would remain trapped in standing matter, unavailable to other plants.
Disturbances like grazing and fire also play a role in the nutrient cycle by reducing the standing crop of old plant material and bringing it into contact with the ground, either as manure, ash, or by trampling. (Editors: Lest this be misinterpreted, fire was relatively infrequent in the native ecosystems of the North American prairies and the desert Southwest. Gadzia urges great caution when using fire as a management tool in ‘brittle’ environments.)
The nutrient cycle is strongly affected by the water cycle, for better and for worse. Plants cause the two cycles to reinforce each other. An area with good plant cover will retain more water and cycle more nutrients, allowing the plants to survive droughts better and to produce still more vegetation in good years. If the soil is hard and bare, on the other hand, less moisture penetrates into the ground, which dries out more quickly and makes plant growth more difficult, which in turn diminishes the amount of nutrients being cycled in the area. Plants and litter also have a strong effect on ground surface temperatures and evaporation rates. Bare ground is hotter, drier, more subject to temperature extremes, and less likely to permit germination of new plants. It is also poor habitat for microorganisms and insects that enhance nutrient cycling.
The processes that determine water and nutrient availability come together at the surface of the ground. If the soil is well-covered with plants and stable under the surface because of roots and biological activity, the ecosystem is functioning properly and the potential for long-term sustainable production of forage is good. The range will be able to recover from disturbances like drought and grazing. However, if there is poor vegetation cover, limited root mass, and minimal biological activity in the soil, and if the watershed drains precipitation too quickly via rills and gullies, then soil loss by wind and water will be higher and will weaken the resilience of the system, making it more vulnerable to disturbances. Productivity will gradually diminish, usually for a long time.
The water and nutrient cycles, and their effects on plants, are difficult to observe or measure directly. Most of a perennial grass plant is below the ground, in the root system. Nutrients like nitrogen and phosphorus are invisible to the eye. Monitoring is a way of measuring ecological processes indirectly. The processes themselves cannot be observed, but indicators of the processes can be observed and measured. Litter cover, for example, is an indicator of the cycling of nutrients, because litter is organic material (with captured nutrients) that remains on the soil for decomposition (release of nutrients).
Monitoring must be: 1) consistent; 2) practicable—that is, not too time-consuming or difficult; and 3) related to management goals and activities. The point of monitoring is simple: it provides feedback that is timely and objective. Monitoring data can reveal the effects of management decisions well before they are apparent to casual observation, greatly increasing one’s ability to avoid lasting damage and to encourage range improvement. Every manager learns from experience, but good monitoring allows that learning to happen more quickly and systematically. Lessons learned from monitoring also help range managers to adapt and update their management plans.
Managing Livestock Grazing
Two primary tools for the management of grazing are available: disturbance and rest. Some disturbances can be manipulated, like grazing and (to some degree) fire. Others, like drought and flood, are largely beyond the manager’s control. The central principle of improved grazing management is to use the tools skillfully and to plan for the disturbances that cannot be controlled.
For purposes of brevity, this field guide will only discuss the skillful use of the tools of grazing and rest. The main tool, controlled grazing (or planned grazing), is a disturbance that can be managed through three different parameters: intensity, timing, and density.
Intensity. Intensity refers to how much biomass is removed from a plant by livestock. It measures the percentage of net primary production that is channeled into herbivores rather than consumed by fire, (slow) oxidation, or decomposers. Intensity is a function of three variables: the number of animal units in a pasture, the length of time they are there, and the size of the pasture. To manage intensity, therefore, requires a tool with three components: one for animals, one for time, and one for area.
Animal-days per acre, or ADAs, contains all three components necessary to measure and manage intensity. Adjustment must be made for the class of livestock being grazed (cattle, sheep, goats, llamas, etc.). Once this adjustment is made, animal-days per acre is exactly what it says: animal units, multiplied by days in the pasture, divided by the size of the pasture in acres. (Editors: See the original publication for more on ADAs, and for specific rangeland health indicators.)
Timing. During the growing season, the challenge is to control the impact of grazing in such a way that the grasses have time to recover. It’s impossible to know when it will rain, how much, or how long the growing season will last. So there’s no telling exactly how long it will take for grasses to recover from grazing. But the principles of growing-season grazing management are fairly simple: 1) the more leaf area that’s grazed off, the longer recovery will take, and 2) a plant that is grazed again before recovering will store less energy in its tissues and will weaken over time. Finally, grazing should not happen at the same time of year, every year, in any given pasture. If it does, the palatable species that are young and green at that time will bear a disproportionate share of the impact and will eventually decline relative to other species.
Control over grazing boils down to control over the distribution of livestock across the range and over time. The most common way to do this is with fencing, but there are other ways to control the distribution of livestock as well. Mineral blocks have been used this way for decades. Where water can be turned on and off, it can also be used to control the location of grazing pressure. Herding is an ancient technique that is currently being reborn in a few areas. Riders and dogs move and control the herd. (Editors: Technological methods are becoming a reality, also, such as mobile fencing controlled remotely, etc.)
Density. Perhaps the most controversial issue in livestock distribution concerns density. Should livestock graze together in a herd, or should they be spread out across the range? For decades, ranchers and range conservationists have worked to spread cattle out in order to utilize forage more evenly across large pastures. Improved understanding of forage growth habits has prompted some ranchers to amalgamate their herds and work them as a single unit or, in certain circumstances, as two herds. The benefits they attribute to this are several. A single herd is more easily monitored. This decreases labor and other costs associated with routine care. Cattle in a herd are also better able to fend off predators than if they were spread out, just as wild ungulates are. Further, the herd will trample undesirable (unpalatable) species and restrain their growth or prevent their establishment and survival.
Developing a Grazing Plan
Planning is critical to sustainable grazing and to avoid overgrazing. Not only does good planning improve management, it also provides a greater sense of control over one’s livelihood, which can be an important boost to morale in a business characterized by uncertainty and risk. Grazing plans should be adaptable to annually changing circumstances and always be ready for the worst.
The central task of planning is to allocate grazing pressure and rest. This includes when the grazing will occur, at what intensity, and for how long. But planning is not complete until provision is made to monitor the effects of management actions and thereby learn from them. Without monitoring, mistakes may go unnoticed until it is too late to minimize the consequences, while successes may be misinterpreted. The grazing plan will need to take into account the ecology of each area and be flexible enough to cope with weather variability and respond to monitored indicators.
more information, refer to Harland E. Dietz, 1989, Grass: The Stockman’s Crop—How to
Harvest More of It, Sunshine Unlimited, Inc. (P.O. Box 471,
Lindsborg, KS); or
[Table 2] This is an example only. This simplified example assumes: A) Slow growth
requires 90 days of recovery; fast growth requires 30
days. B) Pastures are equal in
size and quality of forage (seldom true in the real world). Note the ‘Yeses’ in the
diagram. They indicate overgrazing: •Yes #1. During slow growth,
the recovery period is too short. A
90-day recovery period is needed, but only 30 days are given. •Yes #2. During fast growth, the grazing
period is too long. Animals stay in
the pasture too long and re-graze plants that have already been bitten and
have regrown from energy derived from the roots. •YES! #3. During slow growth,
the recovery period is too short. A 90-day recovery period is needed, but
only 30 days are given. This is
the worse scenario: Animals will
overgraze a higher percentage of plants because 31 land divisions would
have a smaller pasture size than with 8 land divisions. With low pasture numbers,
the only way to avoid overgrazing when vegetation growth rate is fast is to
move the animals quickly. The only
way to avoid overgrazing when vegetation growth rate is slow is to move the
animals slowly. With high pasture numbers (>30), the animals can be
moved slowly, without overgrazing, but there can be negative effects on
This is an example only. This simplified example assumes:
A) Slow growth requires 90 days of recovery; fast growth requires 30 days.
B) Pastures are equal in size and quality of forage (seldom true in the real world).
Note the ‘Yeses’ in the diagram. They indicate overgrazing:
•Yes #1. During slow growth, the recovery period is too short. A 90-day recovery period is needed, but only 30 days are given.
•Yes #2. During fast growth, the grazing period is too long. Animals stay in the pasture too long and re-graze plants that have already been bitten and have regrown from energy derived from the roots.
•YES! #3. During slow growth, the recovery period is too short. A 90-day recovery period is needed, but only 30 days are given. This is the worse scenario: Animals will overgraze a higher percentage of plants because 31 land divisions would have a smaller pasture size than with 8 land divisions.
With low pasture numbers, the only way to avoid overgrazing when vegetation growth rate is fast is to move the animals quickly. The only way to avoid overgrazing when vegetation growth rate is slow is to move the animals slowly. With high pasture numbers (>30), the animals can be moved slowly, without overgrazing, but there can be negative effects on animal nutrition.