The wealth of any ecosystem is its perennials. The primal herbivore-predator-disturbance-rest dance is literally the breath and pulse of the earth. Grasses recycle oxygen far more efficiently than trees. The turnover is faster. Grass reaches out and turns solar energy into carbon. Tillage hyper-aerates the soil, burning out carbon. But because a plant creates bilateral symmetry at the soil horizon, it sloughs off root mass when the top gets chopped off.