The animals fanned out in the new paddock and lowered their great heads, and the evening air filled with the muffled sounds of smacking lips, tearing grass, and the low snuffling of contented cows… So far the relationship between Budger and this square foot of pasture might seem a little one sided, since viewed at least form where I stood, Budger’s bite appears to have diminished the pasture. But if I could view the same event from underground and over time, I would see that that bite is not a zero-sum transaction between cow and grass Plant. The moment Budger shears the clump of grass, she sets into motion a sequence of events that will confer a measurable benefit on this square foot of pasture. The shorn grass plant, endeavoring to restore the rough balance between its roots and leaves, will proceed to shed as much root mass as it’s just lost in leaf mass. When the discarded roots die, the soil’s resident population of bacteria, fungi, and earthworms will get to work breaking them down into rich brown humus. What had been the grass plant’s root runs will move through the earth, stimulating the process by which new topsoil is formed.

It is in this manner that the grazing of ruminants, when managed properly, actually builds new soil from the bottom up. Organic matter in a pasture also builds from the top down, as leaf litter and animal wastes break down on the surface, much as it does on the forest floor. But in a grassland decaying roots are the biggest source of new organic matter, and in the absence of grazers the soil-building process would be nowhere near as swift or productive.

Back up to the surface now. Over the next few days, Budger’s shearing of this grass plant will stimulate new growth, as the crown redirects reserves of carbohydrate energy from the roots upward to form the new shoots. This is the critical moment when a second bite would derail the grass’s recovery, since the plant has to live on these reserves until it has grown new leaves and resumed photosynthesis. As the plant adds leaves it adds new roots too, reaching deeper into the soil, making good use of the humus the first bite helped sponsor, and bringing nutrients up to the surface. Over the course of the season this one grass plant will convert more sunlight into biomass, both above and below the surface of the pasture, than it ever would have had it never encountered a cow.

Yet it’s misleading to speak about any grass plant in isolation, since many different plant species, performing many different functions, occupy even this one square foot of pasture, and Budger’s bite subtly alters the composition of this community. The shearing of the tallest grasses exposes the pasture’s shorter plants to sunlight, stimulating their growth. This is why a well-grazed pasture will see its population of ground hugging clovers increase, a boon to grasses and grazers alike. These legumes fix nitrogen in the soil, fertilizing the neighboring grasses from below while supplying nitrogen to the grazers above; the bacteria living in the animal’s rumen will use the nitrogen in these clover leaves to construct new molecules of protein.