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Overgrazing – I can’t believe I ate the whole thing!

Brian Sindelar Published on 24 September 2012
Overgrazed forage & Overutilized range

I constantly encounter ranchers, conservationists and even professional range managers who are more than a bit confused by some grazing semantics.

Particularly by the concepts of overgrazing, overutilization and over-resting.

Allan Savory sharply rapped some of us over the head many years ago with the little swagger stick he used in his early workshops to get our attention on the subject.

I eventually caught on to the not-so-subtle differences he identified in these terms and hopefully I can clarify them in this review.

A few years back, I examined a copy of an official National Park Service report on condition of Yellowstone Park’s winter range.

One of the first sections of the report dealt with overgrazing. Unfortunately, the first sentences revealed that the author or authors had no idea what overgrazing is (or isn’t).

What was being referred to as overgrazing was actually overutilization, a completely different thing. Nowhere in the report was overgrazing ever addressed.

This is one example of many where people in the business didn’t really think the grazing processes through.

Overgrazing

Overgrazing is something that can happen to individual forage plants during the active growing season.

It occurs when a plant is repeatedly grazed before it has recovered from a previous grazing event. Because regrown tissues of a forage plant are typically more palatable and nutritious, grazing animals are attracted to them.

The most desirable plants can thus be grazed repeatedly (overgrazed) and they eventually respond to this favoritism by dying.

They may be replaced by less desirable forage plants (or weeds) and range condition gradually declines.

Much has been learned about the response of grasses to defoliation. We know that a severely grazed plant (during the growing season) temporarily suspends root growth for several weeks.

There is a mistaken idea that the roots are killed by overgrazing. It “ain’t necessarily so.”

Normally about half of a grass plant’s root die every year and are replaced. That’s how we get the great quantities of humus in prairie soils.

Severe overgrazing does interfere with root replacement as the damaged plant loses vigor. Grass plants are amazingly resilient, though – they’ll tolerate abuse for years!

When a forage grass is defoliated during the growing season and root growth is suspended, the plant’s stored food and newly processed food is shunted to the shoot system to build new solar collectors.

Roots are not directly “sacrificed” or killed in this process. Nor are carbohydrates transferred from the roots to the shoots to build new leaves.

This time-worn myth was debunked more than 50 years ago when researchers were able to “tag” or label sugars with radioactive isotopes.

They could then track them through the plant and learn their pathways. The stored foods used to build new leaves come from crowns, stem bases and tillers that weren’t grazed.

What overgrazing does do is effectively starve a plant by denying it sufficient leaf surface for photosynthetic processing that will meet its needs.

If a grass plant is dormant or growing very slowly at the time of defoliation, there will be no regrowth to overgraze.

Thus a plant can’t be overgrazed in winter or during drought. Overgrazing is an individual plant phenomenon and it logically follows that a pasture cannot be “overgrazed” – only a plant can be overgrazed.

This may seem like a picky point in semantics, but I think it will be helpful in my discussion of overutilization.

Overutilization

While a pasture cannot by definition be overgrazed, it can definitely be overutilized. If more of the forage is removed than has been planned for or if the amount removed, especially during the growing season, is excessive, the pasture or range (plants and soils) can be damaged.

This is overutilization. Overutilization during the growing season is likely to result in overgrazing of plants and can have serious negative impacts on the soil and microenvironment.

If too much of the standing crop of forage is used, soil may not be covered in winter, with resultant winterkill of plants.

Erosion may also result. Litter needed by soil organisms as food substrates may be inadequate. Unused forage helps to trap and hold winter snow cover, an important water source on drier rangelands. Pastures and ranges can be overutilized in any season, including winter.

Well you’ve probably gotten the picture by now:

  • Overgrazed = I ate too often
  • Overutilized = I ate too much

This is an oversimplification, but it helps me keep the two concepts in perspective.

 overrested bluebunch wheatgrass plant

Over-resting

Until about 35 years ago, I was completely unaware of how detrimental over-resting of pastures (and other kinds of land) can be.

As a beginning range manager I often wondered why the vegetation in grazing exclosures wasn’t dramatically taller than the adjacent vegetation.

My university instructors didn’t explain the answer to me, but Allan Savory did.

I had never seen the concept discussed in the classic range management texts, and I used most of them when I taught range management at Montana State University.

What Savory explained was eminently simple; most grasslands (and their forage plants) evolved with grazing and therefore require grazing to be healthy.

For mineral cycling to work properly, biomass must be oxidized into basic components so that they can be re-used.

The breakdown can be slow, as in mechanical and photo-oxidation; it can be somewhat slow, as in decomposition by soil microbes; it can be moderately rapid, as in the oxidation in a rumen; and it can be very rapid, as in the oxidation of a range fire.

A system becomes out-of-balance if the rate of oxidation is so slow that litter accumulates to excess and stifles other soil and plant functions.

Both grazing and fire are historic and critical processes in maintaining healthy range ecosystems. Somewhere along the way, we (range managers) forgot that or, more likely, never learned it.

That made it very difficult – or impossible – to properly manage the millions of acres of rangeland/watershed that make up our ranches and public lands (including Yellowstone National Park). So remember:

  • Over-resting = I neglected to eat

Well, how about your pastures? Are they overutilized or over-rested? Are your forage plants overgrazed? You know what I mean?  end mark

Brian Sindelar is the owner of Rangehands Inc. in Belgrade, Montana.

PHOTOS

TOP: The range on the right has been seriously overutilized, and its forage plants overgrazed. Only a forage plant can be overgrazed, while a pasture or range is overutilzed.

BOTTOM: This bluebunch wheatgrass plant has been seriously overrested for 20 years in a grazing exclosure. It is infected with powder mildew and a variety of fungi. Most of the tillers are dead. Photos courtesy of Brian Sindelar.

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