Have you ever noticed when you overgraze range plants – I mean really hammer them – some get poor or disappear faster than others?
There's a reason, particularly where grasses are concerned. In fact, the best grasses which keep their quality longest and produce the most forage are sometimes called "long-shooted" grasses. The way I've always understood this is they push their growing points up away from the plant crown faster and when it's bitten off they must completely start over with new shoots from the crown. That takes extra energy. If the new growing points are bitten off again and again, like in continuous grazing situations, pretty soon they begin to run out of stored energy and they retreat to near death or sometimes they truly die.
Excellent examples of these plants are the best and most tasty grasses such as Eastern gamagrass, big bluestem and switchgrass. A couple of introduced species which are considered long-shooted are the smooth bromes and Johnsongrass.
Defoliate them quickly, sometimes even severely, and give them enough recovery time to really put on some leaf and recharge the carbohydrate storage system and they'll thrive.
Put too much grazing pressure of the wrong kind on them and they'll go into decline.
So, you might ask, what will replace them?
The answer is two-fold: First will be plants your grazing animals don't like. Second will be plants which hold their growing points closer to the crown for longer and can therefore withstand more frequent defoliation. They normally won't produce as much forage and their window of the best grazing quality will be shorter; sometimes much shorter.
In the interim timeframe of this decline some of the mid-successional grasses will do alright. Depending on where you live, these might be little bluestem or silverbeard bluestem or sideoats grama.
The Old World bluestems were selected from among these mid-successional type of plants on another continent.
But keep the pressure up, give the plants no rest, and you'll move your rangeland further down the scale until it becomes dominated by the unpalatable weeds and annual grasses.
The weeds thrive because the livestock just don't like their taste for at least the majority of the year and so leave them to their business of using up moisture and nutrients and sunlight. The annual grasses and lowest-quality perennial grasses generally have a very short grazing window. They might have tremendously high quality for a few hours or few days, but it's far too short to be useful. Think about sandbur and the cheatgrasses, for example. Great stuff for a couple days or a week each year, but whatcha gonna do for forage the rest of the year?
Buffalograss is an interesting example of all this. It's really not the normal state for it to be in monoculture, except perhaps on some thin-soiled outcrops. But in many places in the West it has been the species most capable of surviving continuous grazing at light stocking rates. It's a unique forage because it always has about the same quality, whether growing or dried down, but that quality is mediocre.
I've been on ranches where the managers were changing buffalograss flats to multi-species mixtures just by pulsing the grazing-recovery cycle. It takes time, but silverbeard and little blue start coming in, and then sometimes big bluestem in places.
Keep in mind, too, the tallgrasses have much deeper root systems and can reach moisture and nutrients the shorter grasses can't. I have a great picture of a young Eastern gamagrass plant green and alive in the middle of a brown, denuded bermudagrass pasture back in the drought of 1998 to prove the point.
These better forage plants could survive for eons because the giant herds of ruminant grazing animas all over the world moved far and wide seeking adequate forage of the right quality and avoiding predators. Their "circuits" of grazing seem to have been so wide and so erratic they usually gave plants more than enough time to recover before coming back.
So here's the thought for today: Would you rather have short, durable grass that doesn't produce much tonnage or quality but can take a beating? Or would you prefer tall, lush grass that will hold its quality and wait on you and the cattle to come back and take off the excess?
The choice is up to you. It's all determined by your management.