How intensity shapes a sward
The amount eaten, by what animal and how often — grazing pressure — determines which plants survive and which disappear. It is not simply more or less of the same thing. Move from light to heavy pressure and the structure of the vegetation shifts: the sward drops, the gaps between plants open, and a whole stratum of life either finds its opportunity or loses it.
Heavy grazing selects for low rosette plants and prostrate growth forms that keep their growing points out of reach. Plantains, hawkbits, and mat-forming grasses persist because they offer the teeth nothing useful to grab. Tall competitive grasses — Yorkshire fog, false oat-grass — collapse out. On chalk downland this is the mechanism that once maintained the close-cropped turf in which small, slow-growing herbs could hold their ground against vigorous competitors; the herbivore was the arrested succession mechanism.
Too little grazing tips the balance the other way. Rank grass accumulates, litter builds, light at ground level falls, and the short-sward specialists vanish beneath the thatch before any woody plant arrives. The window between undergrazing and overgrazing can be narrow and shifts seasonally: the same stock level that maintains spring sward structure may strip a site bare by autumn if animals are not moved.
Animal identity matters as much as number. Cattle tear rather than clip, leaving an uneven surface with tussocks and poached mud — structural variety that supports different invertebrate communities than a sheep-grazed sward. Rabbits graze selectively and very close to the ground, mimicking the effect of heavy sheep pressure in patches. Deer browse woody stems at heights cattle ignore.
Frequency adds another layer. A field grazed continuously at low density differs from one grazed hard in rotation and then rested. Rest allows flowering and seeding; continuous grazing prevents it. The seed input to the seed bank depends on what was allowed to set seed before the animals returned.
Reading grazing pressure in a field means looking at sward height, litter depth, the proportion of rosette to tall-grass species, and the bare-ground fraction — not at the fence and the stocking notice.