Overgrazing. It is a very misunderstood term. Let me clear this up right at the start. It does not matter how many head of livestock. It does not matter how many acres.
Everyone wants to know, “How big do I make my paddocks? How many animals should I have on my pasture?”
Two ranchers can have the same sized paddocks, with the same number of fields, with the same number of cattle and one can be overgrazing and the other might not. Neither question is relevant until you understand the true definition of overgrazing.
Even the dictionary has it wrong:
— to graze (grassland) so heavily that the vegetation is damaged and the ground becomes liable to erosion.
Or from another source:
— a situation in which there are too many cows or other animals eating grass in an area, which damages the environment.
I disagree with both definitions. Overgrazing is a result of time, nothing else.
When we are managing perennial forages, what we are really managing is the energy stores of the plants. Think of it as the plant’s fuel tank. The energy needed to start growth in the spring comes from these stores.
If the plant is an annual or a new perennial, this energy will come from a seed, but with an existing perennial plant we need this fuel tank. Some plants store their energy in the roots and some store it in the crown. Every species is different. As ranchers, we just need to remember that we need to manage this fuel tank.
Spring has sprung and our dormant perennials want to start growing. With no green leaves yet, these plants need to take energy from the tank. The first growth in the spring starts from the energy reserves. (In some grasses, this actually starts the previous fall, another reason to leave residue in the fall). Once the first leaf is up it starts collecting sunlight and the magic that is photosynthesis can start supplying energy to the growing plant, only now the fuel tank is empty. If a plant is severely grazed when the fuel tank is empty, you are overgrazing.
Here is my definition. Overgrazing occurs when a plant is defoliated at a time when the energy stores in the plant are depleted. Simply put, it is a matter of timing. We need to manage both the graze period and the rest period together so that we don’t graze a plant when it doesn’t have enough stored energy to regrow.
Overgrazing can occur anytime during the year, not just in the spring.
Let’s look at that spring pasture again that just put up its first few leaves. The plants have used up their fuel in what is called stage one of growth, and are now collecting sunlight. We do not want to graze these plants hard at this point. (A light grazing can actually cause some species to tiller in this stage, but it has to be very light.) If we let them continue to grow, they start getting more and more leaves that are collecting more sunlight. This is stage two growth.
At the beginning of stage two, the energy reserves are low and overgrazing can easily occur. As we start coming to the end of stage two, the plant has collected enough sunlight and stored enough energy for its continued development. It can now replenish its own energy stores.
By the end of stage two when the plant has a full fuel tank and is preparing for seed production, it is safe to graze. Stage three is seed production.
Overgrazing can occur when the graze period is too long. If livestock are out on a paddock for too many days, they will start to take a second bite from the plants. This occurs when we turn livestock into a fresh pasture of late-stage-two forage and they graze all of the best plants. Once a plant is grazed, it will try to regrow; the speed of regrowth depends on the environment and the time of year. It will vary dependent on moisture, temperature, and growing conditions.
If the plant is severely grazed the first time and all of the green leaves are removed, the plant will need to call again on its energy reserves for growth in order to recover. As the plant puts up new leaves, it empties the fuel tank. At this point, if the livestock are still in the same paddock, they will take a “second bite” of new leaves from the same plant. Now, with no green leaves and an empty fuel tank, how is this plant supposed to survive? We just overgrazed the plant by not removing the animals from the paddock soon enough.
Every environment is different but regrowth in the spring can occur within two to three days in our part of Alberta. In drier environments, later in the summer or during a drought, the graze period may be longer. You will need to determine your desired graze period for your environment and adjust it for the time of year and the growing conditions. It changes.
We can also overgraze a plant when the rest period between grazings is too short, so the plant doesn’t have enough time to replenish the tank.
If you do not have enough paddocks and still maintain a short graze period, then your rest period ends up being too short. If you did not give enough rest to get your plants into late stage two where the fuel tank is full, you have hurt your plants.
Again, the rest period depends on your environment. It could be anywhere from 25 days in a very wet environment to 365 days in a very dry environment.
Overgrazing occurs when a plant is defoliated while the energy stores are depleted. Your graze period can be too long, or your rest period can be too short. Both cause overgrazing because the livestock are allowed to take a second bite.
A killing frost can also cause overgrazing. If we consider the killing frost in the fall as a grazing (or hay cut) and it hits when the plants have an empty fuel tank, they are overgrazed. They are going into winter with low energy reserves.
How will these plants grow up in the spring? As an example, if your killing frost comes at some point in September, paddocks that were grazed mid-August might be in early stage two growth and have very low energy stores going into winter. At this point the killing frost can harm the plants. Some people call it winterkill. I call it overgrazing.
We have four ways to cause overgrazing: 1) spring grazing, 2) fall grazing, 3) a graze period that’s too long, or 4) a rest period that’s too short.
Despite the complexity of our business we are lucky in that nature is very forgiving. We can get away with making a mistake in managing our pastures once in a while. Our grasslands will recover. The issues come when we make the same mistakes over and over again. That is unforgivable.
At Greener Pastures Ranching we graze some paddocks early in the spring. Sometimes, a killing frost affects some paddocks. Sometimes we have to overgraze. We all have an abused paddock, but being aware of how overgrazing occurs can help us avoid repeating this mistake.
I make sure that I change the time of year a paddock is grazed in each growing season. I might rotate in the opposite direction one year, or start on a different paddock another year. By changing up the timing we can reduce the overgrazing on individual paddocks. Nature is forgiving.
By my definition, overgrazing is a matter of timing. Nothing else.
Wikipedia has it closer:
— Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods.
This definition includes both the graze period and rest period! Way to go Wikipedia!