I want to identify two of these common misconceptions and explain the nature of carrying capacity as used in range management.
Those misconceptions are:
- The carrying capacity of a ranch or grazing unit is a fixed number.
- The carrying capacity of a ranch or grazing unit is the same for any owner or manager.
How carrying capacity is expressed
A ranch is normally comprised of a number of pastures and several forage sources. These forage sources may include (but are not limited to) dryland pasture, irrigated pasture, dryland and/or irrigated hay, and crop aftermath.
Grain and other supplements may be available. Livestock are supported on the basis of their daily or monthly forage intake, which varies depending upon animal size, reproductive state, forage availability and supplementation.
Thus the amount of forage required per animal per month is variable, but has been standardized at about 750 pounds for a mature beef animal.
This is termed an AUM or animal unit month of forage. A cow/calf pair is usually considered as 1 AUM. As the calf develops it consumes considerable amounts of forage so the AUM for a “pair” may exceed 1.0.
Let’s consider a couple of basic “carrying capacity” examples.
Carrying capacity of a ranch
A ranch supported 400 head of cattle for an entire year (without harming livestock or pasture condition).
It thus had a carrying capacity of at least 400 animal units (AUs) or 4800 AUMs (400 x 12 months) for that year.
This is true so long as all of the forage required by the livestock during the entire year was produced on the ranch.
Carrying capacity of a pasture
A pasture that supported 100 head of mature cattle for two months (without harming livestock or pasture condition) has provided 200 AUMs of forage. This means that carrying capacity of the pasture was at least 200 AUMs for that year.
New owner Jake buys this ranch and has a hard time carrying 275 pairs on the ranch over the next three years. And the 200 AUM pasture only seems to support 200 head for a couple of weeks (100 AUMs).
He’s ready to sue somebody. What happened? This is where the misconceptions about carrying capacity enter the picture.
- Misconception 1 – Carrying capacity is a fixed number, e.g., the carrying capacity of this ranch is 400 AUs and the carrying capacity of the pasture is 200 AUMs.
- Misconception 2 – Carrying capacity of a ranch is the same for any owner or manager.
In our example, the carrying capacity of the ranch was shown to be at least 400 AUs and that of the pasture was shown to be at least 200 AUMs for a particular year.
Let’s suppose the ranch that carried 400 AUs in year one had to destock by 100 head in year two. Wasn’t the minimal carrying capacity of the ranch shown to be 400 AUs? What went wrong?
And let’s assume the pasture that successfully carried 100 head for two months in year one ran out of feed within a month in year two.
What went wrong? Wasn’t the minimal carrying capacity of the pasture 200 AUMs? Here are a couple of likely possibilities (and there are others), each of which is not at all uncommon:
- Year one was a “normal” or above-average year with good growing conditions. Year two was a drought year. Forage production declined by 100 to 150 percent (not unusual).
- The ranch changed ownership between years one and two. The new owner or manager was unable to harvest as much forage in the pasture or on the ranch as the previous owner or manager.
What does all of this tell us about carrying capacity? Simply that carrying capacity itself must be viewed as a strong variable, rather than as a constant, as reflected in changes from year to year and season to season and manager to manager.
The most important variables affecting carrying capacity are seasonal weather and growing conditions, range condition, forage sources and type/level of management.
Drought or above-average moisture conditions can cause carrying capacity to decrease or increase by 100 percent or more from year to year.
On a large ranch, the yearly variability may amount to several thousand AUMs. And a pasture rated at 200 AUMs from which 150 AUMs were taken in June may supply another 100 AUMs in October without overutilization. Grass grows!
Management styles and philosophies can play a critical role in carrying capacity. Under some types of intensive management, the carrying capacity of a ranch may be double that of conventional or conservative management – without overstocking.
The kind of grazing management program, the forage sources developed on the ranch, the kind of livestock distribution as affected by fencing, water sources, herding and the skill of the manager combine to produce greater or lesser carrying capacity for a given ranch.
How should carrying capacity be estimated?
Notice that my heading said “estimated” rather than “determined.” “Determined” would imply a level of precision or accuracy that is inappropriate.
Carrying capacity must be recognized as the strong variable it is and estimates should be identified as simply that, estimates.
If there is a saving grace in the use of carrying capacity as a concept, it is that experienced ranchers and range specialists can provide very good “guesses” about carrying capacity of pastures, rangeland and ranches.
The keys to good estimates of carrying capacity are having local and regional historical records of livestock carrying capacity, which can be extrapolated to the land in question, having long-time experience with the region and its climate and vegetation, having actual ranch production records and having knowledge and expertise in state-of-the-art grazing management.
This includes understanding the role of range condition and trend in interpreting historical and current carrying capacity, as well as predicting potential carrying capacity. It helps as well, to consider the experience, knowledge and expertise of the owner or manager involved.
Finally, any prediction of carrying capacity should state the caveats and assumptions under which it is made. Examples of carrying capacity estimates:
- Under average growing conditions and conventional grazing management using multiple pastures, the carrying capacity of the X Ranch is about 270 AUs with cow/calf pairs.
- Under average growing conditions and using intensive grazing management to maximize forage production and harvest, the carrying capacity of the X Ranch is about 350 AUs with cow/calf pairs.
Carrying capacity must be understood as a concept in order to use it wisely and appropriately. Because of widespread misconceptions about its meaning and its use, ranch brokers normally include disclaimers concerning carrying capacity of ranches they present. They are wise in doing so.
Carrying capacity is an important parameter in characterizing a ranch (or a pasture) and is a valuable and critical management tool. Properly estimated and used, it holds a key to ranch planning and reaching management goals.
TOP: Estimates for carrying capacity should also consider the experience, knowledge and expertise of the owner or manager involved.
BOTTOM: Under some types of intensive management, the carrying capacity of a ranch may be double that of conventional or conservative management – without overstocking. The carrying capacity of a pasture must be estimated using historical records and long-time experience with a region’s climate and vegetation. Photos courtesy of Brian Sindelar.