The native grasses exhibit rapid growth and its chemical composition decreases rapidly with the advancement of their stage of growth. How are species well adapted to soils of low fertility, generally, the nutrient content is low. Moreover, have escape mechanisms to grazing by ruminants, notably high levels of fiber and anti-nutritional qualities that limit herbivory. Another important factor would be their morphology, since they have fewer leaves which reduces the capacity to seize the animals (size and volume bit).
Lucian,
I can't speak to the physiology of B ischaemum, but I come at this from the restoration and ranching perspectives. A few points:
B ischaemum is a grass and not many animals except for livestock or other native grazers consume grass tissue as a major portion of their diet.
Domestic livestock do consume B ischaemum, just not preferentially. Its thatch, which is of low nutritional value compared to green tissue, tends to persist much longer than that of our native species (I'm in Texas, USA). B ischaemum grows in and amongst its own thatch, so is afforded some protection by the thatch. The buildup of thatch also helps its competitive advantage.
Secondly, under grazing pressure it tends to grow more prostrate. Grazing animals usually first pick off the taller green leaves which are often the native species once B ischaemum lays down.
The ecological effect of these two strategies is that if given free choice, grazers tend to consume the native species first and utilize B ischaemum only when the natives are gone. Livestock can be paddocked or rotated and essentially forced to graze B ischaemum and native species equally which reduces the competitive advantage of B ischeamum. Keeping grazers grouped in tighter herds via paddocking also increases the physical animal impact (see: Alan Savory, Holistic Resource Management) which stimulates thatch breakdown and seedling germination of herbaceous sp.
Interestingly, not all grazers avoid B ischaemum to the same degree. Cattle are more selective in their feeding than the native bison, so they tend to prefer native species whereas bison graze natives and non-natives more equally.
Burning, particularly during the growing season, dramatically reduces B ischaemum because (we think) it has minimal belowground carbohydrate reserves during the growing season. Burning also removes the thatch and stimulates green regrowth which is highly preferred by grazers.
Bothriochloa genus has essential (aromatic) oil in its leaves and inflorescence and hence cattle avoid this genus.
Bothriochloa genus has essential (aromatic) oil in its leaves and inflorescence and hence cattle avoid this genus.
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