A trophic cascade is an ecological situation where the introduction or removal of a predator near the top of the food chain causes population changes all through the food chain. The case of interest to me is predators that chase large grazing animals.
Every continent except Antarctica has large, grazing animals, and many of the ecosystems within those continents. Most tend to group together in large herds, which find a happy place to graze, until a predator attacks them, at which point they run and find a new happy grazing place. The grasses they eat have developed in symbiosis with these grazing animals--it gets trampled and eaten, but the soil gets kicked around and a fresh supply of rich fertilizer gets left behind, as well as any fresh seeds that may have stuck to the grazers fur or survived the passage through its gut. As long as the grazers don't spend too long, it's good for the grass.
We humans have interfered with this process. Some grazers have been domesticated, and they stay in one place, often penned in, until the grass is gone, and then we provide them with hay or grain from some other place while they continue to destroy the land they are captive on. In other places, we've removed the predator, which removes the incentive for the animals to move now and then. An example is the mountain meadows of the rockies. When there were wolves, the elk could only stay in the bottomlands for a short time, and the grass grew slowed the creek. Beaver and other creatures came and made further changes, slowing the creek further and turning parts of it to wetlands, bringing even more diversity. A classic trophic cascade. Removing the wolves allowed the elk to eat all the grass in easiest place to get it, the bottomland, and the creek became a roaring stream and washed all of this away. Restoring even a few wolves after they'd been gone for a century brought it all back.
I've been reading about Joel Salatin and Allan Savory. They both come at this from a slightly different angle but they're saying the same thing. Salatin has developed a method of raising cattle and chickens where fences in a small herd--100 or so--and moves them almost every day. He sizes the pasture so that they consume most, but not quite all, of the best grass before he moves them. A few days later, he hauls a henhouse to the same pasture, where the chickens pick over the manure. He doesn't bring the cattle back until the grass is completely recovered, which happens pretty fast, because he didn't let cows graze too long. He points out that any bovine parasites that the birds eat don't go any farther, and the same is true of chicken parasites that the cattle may eat, so the animals are much healthier than their relatives on farms nearby. The grass is way healthier, and he says he gets more than 4 times the beef productivity for the same amount of land grazed the traditional way, and the eggs are essentially free.
Allan Savory has been trying to reverse desertification in Africa.. He tried reducing the trampling, including culling 40,000 elephants at one point, but that only exacerbated the desertification. What has worked, very much to his surprise, was encouraging cattle herders to graze their animals temporarily. Places where all the grass was gone but still had brush for the cattle to eat began to sprout grass a few days after the cattle left, and with each visit it became healthier. The animals become healthier too. The key is to not let the animals eat it all. The herders are playing the role of the predator. Perhaps, but maybe not, coincidentally, the herders have been finding that their animals are about 4 times as productive when they feed them this way, just as Joel Salatin has.
Grass and trees are the best way we have to reduce CO2 in the atmosphere. The carbon that makes up these plants cells is entirely extracted from atmospheric CO2. Monoculture agriculture is ruining our land, and making our crops, our animals and ourselves unhealthy.
