Grazing, The Most Abused Tool

Everyone “knows” that too many grazing animals destroy grasslands through overgrazing and over-trampling, don’t they? The evidence is everywhere, growing deserts, bare, capped ground around watering or feeding points. However, as Mark Twain said, “It ain’t what you know that gets you in trouble, it’s what you know for sure that just ain’t so.”

When Europeans arrived in the US and Africa, they described, simultaneously, grass belly-high to a horse and millions of moving wildlife – bison, pronghorn, deer, elk, wildebeest, springbok, zebra, elephant, along with their predators – wolves, lions, coyotes, hyenas. They named places for the abundance of water in the area, where today no trace of water remains above ground. How can we reconcile the historical record with the insistent call for reducing animal numbers to preserve the grasslands since then? How did it happen that land that once supported millions of head can’t support dozens now?

The answer lies not in the numbers of animals but in the time animals are exposed to plants. If animals stay too long or return too soon (before the plant has recovered), overgrazing occurs. The time is determined by the plant growth itself. When plants are growing quickly, the animals moved quickly and returning sooner. When plants grow slower, animals can stay longer, but return later. When one adds in the animal impact of trampling, urinating and dunging, which reduce the amount of fresh grass available and so cause the animals to move as well, the movement of animals, even in the absence of predators, is assured.

In addition, without the herding effect of bunched animals, especially in brittle environments, to disturb the soil and push old plant material to ground-level, many perennial grasses are weakened and die. Therefore, low animal numbers plus extensive grazing (partial rest) in brittle environments almost guarantees desertification.

Primary Considerations
Grazing is technically the eating of grasses, not other plants. Browsing is the eating of brush, trees, and/or forbs. However, the tool of Grazing includes both.

There is also the differences between annual and perennial plants, grass and non-grass plants, and the types of grazing animals.

Annual plants vary widely in numbers year to year due to moisture and other factors, in some years they fail to establish at all. They are difficult to overgraze as they are so short-lived, producing seed and dying. Perennial grasses, brush, trees, and forbs do not vary as much, thereby holding the soil in place and covering it year round. These plants perform a greater service the lower the rainfall and more brittle the environment. Their presence and health determine the advance or retreat of desertification. Yet, because they are perennials, they are easily overgrazed.

Perennials grow in two distinct ways, upright or prone, with runners. In more brittle environments, the upright growers tend be in bunches, in less brittle ones, they usually form a mat with individual plants difficult to distinguish. These differences can even be found within the same species where in brittle environments they grow upright but prone in non-brittle environments. The growth pattern of runner grasses change very little along the brittleness scale. They tend to become dominant in overgrazed, high animal impact areas. The growing buds of perennials can either be very near the ground or above near the end of the plant stems. It is believed that those with ground-level growth points evolved with severe grazing pressure while those above ground-level were not subjected to the same pressures.

Types of Grazers
There are three broad categories of grazers, one of which, the nibblers, have no domestic relatives. These nibblers, as the name suggests, nip a leaf here and there making if very difficult for overgrazing to occur. Most are solitary, nonherding small animals such as the steenbuck and duiker in Africa. They are self-regulating in number and never occur in high numbers.

Second are the broad-mouthed group, grabbing whole mouthfuls of forage. This group includes bison, horses, cattle, hippo, buffalo, and zebra. They are herding animals that are non-self-regulating and can be found in large numbers and graze plants severely.

Third are those capable of nipping a leaf here and there, but habitually take several at a sitting and concentrate on a single plant, thereby needing management as severe grazers. This group includes sheep, goats, antelope, pronghorn, and perhaps, some kangaroo. They are herding animals and non-self-regulating capable of attaining large numbers.

While not completely understood the self-regulating animals appear to adjust their numbers to social and environmental stress. Non-self-regulating animals depend on predation, accidents, parasitism, disease, or starvation should predation not be severe enough. All predator dependent animals appear to herd for protection.

Overgrazing
We have mentioned overgrazing, but what is it, exactly? Overgrazing is any grazing that takes place on leaves growing from stored energy, at the expense of the roots, rather than directly from sunlight. That is to say, it is grazing the roots. (Savory and Butterfield, 219.) That means that overgrazing can only occur in the growing season. In fact, it may be a benefit to severely graze in the dormant season in order to clear away old leaves and stems to make sure that the growing points are unimpeded when dormancy is broken.

Overgrazing can occur at three different times during the growing season:
1. when the plant is exposed to the animals for too many days and they are there to regraze as it attempts to regrow.
2. When animals move away but return too quickly to graze the plant before it has had time to regrow.
3. Immediately following dormancy when the plant is growing new leaf from stored energy (Ibid.).

Another point to keep in mind is that the root mass of most grasses is equal to or greater than the growing point, leaves, and stems above ground-level, and that the root mass is reduced equally to the mass removed by grazing. This is why overgrazed plants are killed, they lose so much root mass they cannot regrow. This is also why runner type grasses are less likely to be overgrazed because more of their leaves and growth points are below the height of most animals’ bites, therefore leaving a higher percentage of root mass in place.

Grazing and Extreme Environments
Let us now look at the effects of grazing on the four ecosystem processes at the extremes of the brittleness scale to gather an indication of management options.

Non-brittle Environments
1. Community Dynamics: Because plant spacing is close and soil cover hard to damage, grazing tends to maintain root vigor, soil life, and structure. It also impedes the progress of grasslands to woodlands in such environments.

Overgrazing reduces root mass but does not uncover soil, due to the close spacing. This most often leads to a thicker mat, even in upright species. Some species may disappear, which can lead to potentially more unstable communities should the remaining species be affected by disease. It may also push a shift toward woodlands as a reduction in grass root mass allows tap-rooted species to gain a foothold.

2. Water and Mineral cycles: Grazing does not expose soils, rather leading to a thicker cover and enhancing these processes. While never attaining the level of effectiveness found in forests in such environments, they work well.

Overgrazing can lead to grass root production and compaction negatively affecting the water and mineral cycles. Should continual overgrazing occur and woodlands incursion increases, these processes improve.

3. Energy Flow: Grazing increases energy flow above and below ground. It holds the community at the grassland level, at a lower amount than woodlands, but sufficient for this purpose.

Overgrazing reduces energy flow until the grasslands are replaced by woodlands at which time it again increases.

Very Brittle Environments
1. Community Dynamics: Grazing tends to increase cover and diversity, maintain grasslands and slows shifts to woodlands. It also increases organic matter, structure, aeration, and biological activity in the soil. In forest areas, it reduces buildup of dead material that acts as fuel for fire, maintains soil cover, and promotes organic material increases.

Overgrazing reduces soil cover and litter, damages roots, fosters shifts from grasslands and woodlands toward forbs (weeds), soil compaction, and shifts toward monoculture as grass species die off.

2. Water and Mineral cycles: Grazing improves both through maintenance of healthier and more stable root masses, increasing microorganism activity and aeration, production of plants with more shoots and leaves, therefore providing more litter.

Overgrazing inhibits both through exposing soil and limiting litter production. It reduces root mass, adversely effecting soil structure, reducing porosity, organic matter, and soil life leading to compaction.

3. Energy Flow: Grazing increases this process by removing old oxidizing material and promoting vigorous root and leaf growth. More massive and healthier root mass supports millions of microorganisms and other soil life.
Overgrazing reduces energy flow by reducing plant roots and uncovering the soil surface. When combined with partial rest, it leads to the replacement of perennial grasses by annuals, which have a much lower energy level than the perennials.

While these give us some idea of management guidelines, we must proceed with other forces in mind. When working with environments, with the myriad forces that must be considered, we must always assume we are wrong, we just can’t account for all the variables, and be watchful and ready to make adjustments in our management as soon as possible. By understanding how severe grazers and plants adapt to each other makes that process much less stressful and more rewarding.

Relationships and Adaptations of Severe Grazers and Plants
Severe grazers and perennial grass species evolved jointly over the eons toward mutually advantageous relationships. The plants provided protein and energy while the animals removed old oxidizing materials in the brittle environments and reduced woody species in less brittle ones. Only with human intervention and the distrust and mistaken ideas about livestock and their management have the great grasslands of the world been devastated by the combination of overgrazing and over-rest. By limiting stocking rate instead of time, the common continuous grazing management practices have surprisingly (to those practicing them) not led to restoration of overgrazed pastures but expanding ones with large bare areas between plants and old overgrown and oxidizing plants scattered throughout those same areas.

Only individual plants can be overgrazed, that is, bitten again before they have had a chance to regrow and restore their roots. A range-land can not be overgrazed, only the plants in that environment. While overstocking has been blamed for overgrazing, that does not explain how or why there are so many old large plants left. Again, it can only be from the lowered stocking rate and increased time animals spend on the same range, eating the same plant (young and tasty after being bitten) instead of one next to it (fibrous and tough from not being bitten) over and over again. The great herds of the past were forced to bunch up and keep moving by predators, thereby removing old growth through trampling or grazing and leaving the area and not returning for, at times, years. Once predators are removed, so does bunching and movement, leading to overgrowth and overgrazing.

Some plants have adapted to overgrazing by a variety of defenses. Some erect species begin to put out runners and become matted, while sacrificing the center of the plant. Many only grow under prickly plants of cracks in rocks, others form prickly hedged balls to protect themselves. Woody plants and forbs have adapted to overgrazing pressures by many of the same methods: hedging, shorter, tightly matted leaves, chemical defenses (tannins and other chemicals produced by the plant), browse lines, that is branches and leaves within the reach of animals are sacrificed so that those above remain growing. However these defenses generally do not work for seedlings and even though older plants can live for centuries, with no new plants growing, the species can be lost in that area.

The effects from overgrazing and over-resting can be minimized and reversed by planning the grazing and rest periods and increasing animal numbers, either through absolute numbers or by increasing the density of animal numbers on a particular area at a particular time period.

In conclusion, grazing can be a powerful tool for the improvement of grasslands, forests, and croplands if planned and used wisely in concert with other tools. Animal, plant, and soil health can be improved dramatically in a fairly short period if used right. However, overgrazing through poor planning and management can be just as destructive and lead to increasing desertification. The choice is ours and depends on our knowledge, our goals, and our management.

Savory, Allan and Jody Butterfield. 1999. Holistic Management, A New Framework for Decision Making (Washington, D.C: Island Press), 216-235.