I just gave a pasture walk and talk to a group of ranchers from Manitoba. Several people in this group had extensive experience working with cattle yet most did not plan their livestock grazing. The lack of planned livestock grazing can lead to livestock over-grazing grass plants. This leads to the eventual extinction of these grass plant species. If livestock are left to their own devices, over-grazing will happen. This is how over-grazing happens and what it looks like when it does.
When a grass plant germinates from it’s seed it grows a single leaf using the stored energy in the seed. This leaf then photosynthesizes which basically means it is turning sunlight energy into stored energy. The stored energy is then sent to the roots for safekeeping underground. As the grass plant continues to grow, it increases it’s leaf area. Leaves are in effect solar panels designed to capture sunlight. This captured energy is continuously balanced between leaves and roots. A grass plant generally has as much biomass below ground as it does above ground.
When a grass plant is grazed, the solar energy gathering leaves are removed as well as any old dead leaves. What is left immediately begins to regrow. As an aside, there are enzymes in the livestock saliva that stimulate grass re-growth. The grass plant uses some of that safely stored root energy to re-grow the leaves. When the leaves have re-grown they can then send energy back to the roots to replenish the what was used to re-grow the leaves. This is all well and good as long as the plant is given enough time to re-grow and re-charge the roots in between livestock grazing the plant. However, should the grass plant be unlucky enough to be re-grazed prior to it having the opportunity to re-grow and re-charge it’s roots, then this is the beginning of the process of over-grazing.
Now let us say that this re-grazing happens many times during a growing season. Each time the grass plant uses a bit more root energy to re-grow the leaves only to have them consumed before they can re-pay the favour and send energy back to the roots. During this time the roots will get shorter and weaker. Eventually the roots become so weakened and short that the next time the grass plant is grazed, it is pulled completely out of the ground.
When you see dead grassplants lying on top of the soil surface with a small stub of a root attached, you can be sure that over-grazing is occuring. While on the pasture walk in Manitoba we looked at one ranchers two thousand acre pasture with only 200 mother cows on it. Although this rancher was planning his livestock grazing, we found numerous dead, broad-leafed, highly palatable grass plants. Even though there was abundant forage for these cows to choose from, they evidently had favorite species of grass that they wanted to graze and these grass plants were overgrazed to the point of being completely pulled out of the ground. I always like to say that a cow doesn’t have a degree in pasture management. Even when we do plan our livestock grazing, most ranchers continue to allow their livestock to dictate what and when they graze.
This particular rancher was planning his livestock grazing but unfortunately was at the recieving end of some bad advice. He is using a grazing system called Twice-Over Grazing. The name ‘Twice-Over Grazing’ says it all – if over grazing once is bad, why would you want to do it twice? Jokes aside, ranchers who use this system can only expect their palatable species to die out and few new plants to be established.
Holistic Planned Livestock Grazing is the best way to avoid over-grazing and ensure new grass plant germination. For thriving grasslands we need thriving grass plants and giving those grass plants a chance to re-grow before being re-grazed is the best thing we can do increase the amount and quality of the forage in our pastures.