“Environments may be classified on a continuum from non-brittle to very brittle according to how well humidity is distributed throughout the year and how quickly dead vegetation breaks down. At either end of the scale, environments respond differently to the same influences. Resting land restores it in non-brittle environments, for instance, but damages it in very brittle environments.“- Allan Savory.
The prairies of North America with seasonal and at time minimal moisture could be considered brittle. There is not enough moisture for dead vegetation to decompose on its own. They rely on grazing by large livestock, like cattle, or fire or trampling to decompose that vegetation (in their rumens – this is part of their stomach) and return nutrients to the soil (through their manure) which are accessible to the plants. This is part of the mineral cycle. In high moisture environments, this decomposition occurs without a larger grazer. However, we must find the right balance of animal impact and grazing to avoid ‘overgrazing‘.
Exclosures allow us to monitor the success of our long term grazing program. The larger half acre exclosures (see above) are large enough to see the implications of excluding cattle from grazing, but obviously allow deer to enter and graze. This gives a control to compare the rest of the field against. Exclosures used by researchers for 20 years or more, have shown that in some environments exclosures have:
- A lower amount of decreaser plants than deferred grazing. This implies those plants need some grazing in order to flourish. Indeed, no grazing can result in lower biodiversity as certain species take over the stand.
- Complete (deer-livestock) exclosures had only a little more litter than the heavy grazed pasture. This could be from a lack of stimulation in the land, where the grass goes dormant because litter from previous years growth has not decomposed. There was nearly twice as much litter in the rotation pasture compared to the total exclosure and the heavily grazed pasture; other grazing practices did not show differences.
The goal is a grazing management program, that allows for the development of a highly productive vegetation complex; which supports the maintenance and improvement of the livestock and wildlife habitat.
Exclosures or ungrazed area needs to be monitored overtime. Vegetation may actually deteriorate and decrease after an extended period of total rest. A smaller exclosure of one square yard can be moved every year. This has allowed Lands Branch and a Forage Specialist at Saskatchewan Agriculture and Food to monitor annual production on the shortgrass prairie over the years.