Far too commonly overgrazing is ill-referred as being a matter of "too many animals" on a grassland, no matter if it's tame pasture or native grassland. Overgrazing also is referred to as land that is "grazed too heavily" so that vegetation becomes damaged and land becomes "liable to erosion." (These are actually two common definitions that are held by today's online and hard-copy dictionaries. Both must be corrected!!)
Often this term is over-used and abused as to justify the means to attempt to demonize livestock for the world's increasing environmental problems, such as soil erosion, desertification, and "climate change."
All in all, the term is actually highly misunderstood and misinterpreted. Even the dictionaries have it wrong.
So, what IS overgrazing??
Overgrazing is actually a function of time, not number of animals.
It does not matter how many animals you have or how many acres there are. Overgrazing can occur with few animals on a lot of land, just as with a lot of animals on a small amount of land.
Overgrazing is a result of timing, largely because of mismanagement. The real definition for overgrazing is not what the standard dictionary says, but rather this: "To defoliate a plant when its energy stores have been depleted in attempt to regrow after the first defoliation event." Or rather, overgrazing is when a forage plant is bitten more than once, when it is trying to regrow and replenish its emptied energy stores, pushing it further back to the point where its recovery period will be significantly longer, or it will die.
This is all a matter of timing.
Plants require time to grow and time to regrow after being defoliated. This is either by grazing, mowing, or even burning.
Just think of a lawn. A lawn is covered in living green plant matter called "grass" that regrows after mowing.
Here's the mind-blowing part: It takes time for that cut lawn to grow back before needing to be mowed again!
Let's go back to the pasture, because I find mowing lawns a rather unfair comparison. The pasture is largely composed of grasses, often with at least four different species. There may be some legumes in the stand. But let's focus on grasses for now.
I already mentioned that it takes time for grass to grow. Grass has a growth curve that is in the form of a face-down S curve (forage yield is the exact opposite), and this growth curve is broken up into three phases:
- Phase 1 ("baby" phase): Grasses begin growth (some have began growth the previous fall, then stalled because of freezing temperatures) from tillers, or seeds. After grasses are cut for hay or silage, this growth will also occur. The new plants coming up are actually from "tillers" at the base of the parent plant, or from spreading rhizomes. Grasses are most sensitive to defoliation/grazing because their energy reserves are being used for growth. Once they have put even one leaf up, they are starting to generate photosynthesis to supply more energy to the plant. But not all energy; right up to the start of Phase 2 plants are still relying on energy stores to continue growth, and will drain those stores right up until there is enough leaf area to convert sunlight energy into energy storage in the base of the plant and main roots.
- Phase 2 ("teenager" phase): Grasses experience the fastest rate of growth at this stage. Photosynthesis is being maximized because most of its leaves are out and collecting sunlight, and the plant is filling up its depleted energy stores from Phase 1 in preparation for Phase 3. Grazing early at this stage can be dangerous if animals are not controlled so that they move quickly after lightly grazing plants at this stage. There is a little more lee-way when grasses are later into phase 2, because their energy stores should be filled up enough to start pushing up a seed-head.
- Phase 3 ("oldie" phase): Grasses produce a seed head and begin flower production, which eventually moves into seed production, which leads to senescence or death of the parent plant. With the right growing conditions, the tillers at the base of this plant will begin to grow.
When grazing animals, we should not strive to have animals eat plants when they have the greatest quality in energy (sugars) and protein, but rather that optimal point when quality is decreasing as quickly as yield and fibre content.
Overgrazing occurs at three primary timing points (some call it the Three Cardinal Sins of Grazing, as from the grazing schools of Jim Gerrish):
- Staying too long
- Returning too soon
- Taking too much
Again, all three of these can and will occur no matter the size of the pasture or the size of the herd.
Animals that are allowed to stay too long in the pasture will take too much: They will take the "second bite" of grass that they grazed a day or two ago.
Often the reason for returning for that second bite is because they are allowed to select what plants they want to eat. Selectivity by all livestock is primarily based on taste and smell, and somewhat past teachings and experience by Momma Cow or the School of Hard Knocks. If a plant tastes good the first time, chances are that animal will return to that plant once it has been able to taste most of the rest of the plants in that pasture.
I've turned out our steers onto a 50 acre piece of pasture--only 60 animals--and what they do when they smell a tasty plant is to take a bite, then move on. They move on because of their strong herd instinct, and because they feel they need to peruse the pasture to taste and smell what's out there. Until they've gone over most of the pasture, will they come back to eat those plants they found quite tasty again.
This is what I've found in raising cattle the conventional way of selective, set-stock, continuous grazing.
In coming back again for that second bite, those animals are returning too soon. The bite they take can remove about half or more the leaf area of a plant (sometimes an entire plant)--if you don't believe me, find a decent stand of grass (again, not lawn) and pull up, with your hand, 10 grabs of grass. See how much is left in that spot you've picked from. One hand grab of grass is typically the same amount of grass and similar force required by the cow to graze.
So when cattle or any grazing animal is allowed to come back too soon for whatever reason, that means that plant isn't allowed enough rest to recover. Leaf area is needed for a plant to generate photosynthesis to replenish energy stores and generate energy to regrow. Not enough leaf area could mean that plant needs to rely on its energy stores for regrowth.
And when the plant is grazed when those energy stores are already depleted, means that the plant is either going to be growing much, much slower through the season, or it will die.
Do you see how the concept of time in regards to the subject of overgrazing is applied? Here it is in regards to phases discussed above:
One bite to a grass plant that is in late Phase 2 pushes it back to either early Phase 2 or late to mid Phase 1. Two bites pushes that same plant back to early Phase 1.
This is a result of staying too long, coming back too soon, and taking too much.
How do you mitigate overgrazing then?
Control animals using electric fence. Divide a big pasture into many smaller paddocks, and move the animals quickly enough that they are not going to selectively graze and take that second bite.
Doing so ensures plants get adequate rest, and there is plenty of residue left behind until the next grazing period.
The amount of rest a pasture needs depends on the stage of growth and time of year. Plants growing quickly will require you to graze quickly. Slow growing plants means you graze slower. Tighten up your paddocks when grasses are growing quickly, and make them bigger when plants are growing slower.
Rest can be anywhere from 3 weeks to 18 months. Native grassland requires longer rest periods than tame forage stands. Fast growing tame grass stands can be returned fairly frequently, unlike most native grass stands.
And do not be afraid to "waste grass." Wasting grass is a good thing because it covers the soil surface and slows the rain drops from impacting the soil surface. It also gives the soil flora something to eat and convert into organic material, topsoil, and sequesters carbon.
Good grazing practices that involve more management and less selective grazing also means mitigating soil erosion and desertification.
It all sounds counter-intuitive, but when you put the puzzle pieces together, it should all make sense.