The four types of plants and their role
Four types of edible plants are available for conducting a grazing enterprise. They are annuals, perennial grasses, perennial edible shrubs and fodder trees. Each type is very different in so many ways, with each type having a specific role. Those who have managed in both good and bad years, quickly come to realise that there was no such thing as the best plant. In good years the most productive plants are most appreciated and in the bad years the hardy ones. Each type has different management requirements and each type has a particular mechanism that ensures survival.
The four plant types animals rely on for energy and protein annuals, perennial grasses, perennial edible shrubs and fodder trees
How well these different groups are understood and how well they are managed, will make or break the grazing business and the landscape. When the four plant types are discussed, it is important to remember that there are the two seasons, summer and winter. There is also extreme variation in rainfall from year to year.
Just as animals need a variety of plants in the landscape for production and survival, likewise, soils function better if there is a variety of plants to allow carbon flows to be maximised over time. Nutrient cycling is more successful with a variety of plants. Some decompose quickly to release their nutrients, while others have deeper roots and are able to source nutrients that have escaped deep into the soil and return them to the surface.
If there is going to be climate change, due to global warming, then the location of specific species may move further south, as that is where their ideal environment will be.
Annuals are the opportunists of the pasture system and can be either grasses or broadleaf plants. They grow rapidly from seed when moisture and nutrients allow, and escape the adverse periods. With climate change, they might become less available due to increased variability in rainfall.
Perennial grasses are less palatable than the annuals, but supply the bulk of feed over time, if they are present. Perennial grasses are our most valuable resource, as they stabilise the landscape, trap nutrients and moisture, and provide animals with a readily available long term feed reservoir.
There are two basic groups of perennial grasses, the C3 group and the C4 group. The two groups absorb carbon dioxide differently through the process of photosynthesis. The two groups have different optional growing temperatures, with the C4 group functioning better at higher temperatures. The C3 plants need higher moisture and have higher nutrient requirements. In the areas suited to both groups, which is a large area of Australia, it is management which determines the availability of the more palatable C3 grasses.
Perennial edible shrubs include a variety of species, but the focus here will be on the main type, the saltbushes (chenopods). They are drought resistant, frost resistant and kangaroos do not eat them, so they are a long term source of "green leaf". It is their deep roots of up to 4 metres, and slower growth that makes them drought resistant. They can obtain moisture at depth during dry times, like trees do. Their leaf structure reduces transpiration, which increases water use efficiency.
Saltbushes are often criticised for being less palatable than the herbages and grasses, but this is their attribute as it guarantees they are still available for animal production and survival, when all other plants have failed. They are often incorrectly promoted as a fodder supply for dry times. Their true role under these conditions is to supply protein to allow ruminant animals to digest unproductive grasses and leaves.
For many, saltbush is just part of the nostalgia of the early settlers and the outback of Australia, as we like to romanticise it. The reality is that saltbush is a management tool supplying ecosystem services to the environment. An example of an ecosystem service supplied by Old Man Saltbush is its ability to change the soil structure in degraded landscapes, and so allow more water and air in. This results in the landscape becoming a more friendly environment for grasses to then enter. With the arrival of perennial grasses between the Old Man Saltbush, there is further ongoing introduction of carbon into the landscape.
Fodder trees include the edible component of the trees in the landscape. Examples are mulga, leucaena and tree lucerne. They are able to utilise past rainfall further into the future and they are part of the reliable component of the fodder supply.
Leucaena and mulga have the added advantage of directly introducing nitrogen into the landscape. If they are not a monoculture, then they can enhance the ability of grasses to introduce more carbon into the landscape.
In a country where we have the most unreliable rainfall in the world, the emphasis must be shifted to increasing the percentage of perennial plants in the pasture, be they grasses or shrubs. It is the perennials that can respond to isolated single falls of rain, while annuals can't.
It is the perennial grasses that are best at introducing carbon into the landscape. It is the perennials that we are thinking of with the statement "carbon makes carbon". Just as having money and managing it properly leads to more money, so having perennial grasses and managing them correctly, leads to more perennial grasses, (and hence further additions of carbon).
A correct balance of plants leads to ongoing photosynthesis (carbon storage) under all seasonal and climatic conditions, with the possible exception of extreme drought.
Maximising landscape carbon and soil carbon is all about trapping sunlight at a multiple of levels. Recycling of nutrients is all about having different depths of roots to bring the nutrients to the surface. Nutrients and carbon go hand in hand. Planting fodder trees, Old Man Saltbush, or any tree, into areas of straight grass, is returning the vegetation layers, just as thinning dense regrowth and allowing grass to grow is returning a vegetation layer.
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