To answer these questions requires understanding a principle of pasture management; that weeds and pests only invade an area when the conditions allow them to establish and thrive. Problem species only leave an area when the conditions prevent their reproduction. Does the movement of animals across a paddock influence pasture species?
In his book Grass Productivity, André Voisin describes a number of experiments that document changes in pasture species by altering grazing methods. In the diagram here, one German experiment shows how grazing could regenerate land from scrub and weeds. All the pastures started with the same proportion of species as the control; heather 51%, various brooms 11%, mat and hair grasses 11%, sheep’s fescue 11%, with the rest consisting of various grasses.
Within three years, the different grazing strategies and fertiliser applications
produced staggering results. In that time a pasture under an intensive
rotation experienced the complete loss of heather, brooms, matt grass,
sheep’s fescue, and sweet vernal; developed suitable levels of cocksfoot,
dogstail, and yorkshire fog; and saw the vigorous development of red fescue,
perennial ryegrass, meadow grasses, and white clover. The experiments themselves are not described in detail but the extensive grazing seems similar to set stocking, and from passages elsewhere in the book, the difference between the intensive rotational grazing regimes is the paddock size (big paddocks 7ha, small paddocks 1 ha) and the length of time animals are grazing in them (from one to several days).
The experiment illustrates how increasing animal density and planning the timing of grazing encourages desirable species to establish and thrive. Merely rotating animals around paddocks leads to the invasion of gorse, thistles, and buttercup because of the timing of grazing.
A curious phenomenon unfolded during the German experiment. All of the high fertility species appeared of their own accord. They were not sown. Just by changing the environment with animal grazing and an appropriate fertiliser regime valued pasture species began to dominate the sward. This phenomenon illustrates the whole point of Voisin’s book, that ploughing paddocks is no substitute for poor grazing management.
If the landscape is a result of how it is grazed, what are the possible land management roles that animals could perform? Creating firebreaks, maintaining grassland riparian, road, or rail verges, regenerating eroded land, and controlling weeds are tasks that graziers could be paid to do. Contract grazing rates could reward graziers for the loss of animal performance while landowners gain financial and other benefits.
Grazing animals could reduce insurance and labour costs for the forestry industry by crushing scrub and prunings to reduce the fire risk. Scientists with Environment Waikato have observed properly grazed riparian areas are less prone to debris build-up while flooding which leads to lower clean up costs. As well as bringing additional income for the farming family, such contracts could promote better land stewardship and public awareness of the importance of the grazing industry.