Most perennial species require rest following grazing to allow plants to replenish below ground reserves and to complete seed set, retain protective sheaths under moisture stress and regenerate from dormant buds.
The key to the long-term persistence of perennial pastures is to manage the carbohydrate reserves. Perennial plants store carbohydrate in their crown, tap-root, stolons and/or rhizomes and use this energy for the initial regrowth following grazing (or defoliation), to persist through periods of stress (e.g. drought, cold) and for regrowth in autumn for summer-dormant species.
If the carbohydrate reserves are continually exhausted and not fully replenished, then the stand density will gradually decline.
The response of perennial pastures to different grazing methods can be considered in terms of their requirements for strategic rest from grazing, the timing of the rest period and grazing pressure.
For example, the response of perennial grasses falls into four broad categories:
- Some species like cocksfoot require rest during a period of stress (e.g. drought) when growth rates are low. Rest is most likely required during these periods to retain active root systems and buds with low dormancy.
A rest in summer also enables sterile tillers to complete their lifecycle.
- Some species require a strategic rest during periods of active growth, particularly when regenerating from buds in autumn and during the reproductive phase (e.g. phalaris). These species have limited resources for regrowth if grazed during these periods probably because they have a low density of tiller buds.
- Species that respond to additional grazing pressure (e.g. kikuyu). These species exhibit rapid growth following defoliation and have many tiller buds close to the ground. Many possess rhizomes and/or stolons.
- Some species show minimal impact from different grazing methods (e.g. wallaby grass). There is some uncertainty regarding these plants as their lack of response may be the result of light grazing pressure.
Research has shown that perennial grasses, when set-stocked, persist better under cattle than sheep, most likely because sheep are more selective and graze more closely than cattle. In summer, selective close grazing by sheep results in a greater loss of perennial plants than cattle at a similar stocking rate (DSE/ha).
The appropriate grazing method(s) for each perennial species are discussed in their respective descriptions.
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