Biodiversity and Grazing in the Tropical Savannas
Important Concepts There are three important concepts to understand in order to value biodiversity .
1 . Ecosystem Services - the benefits that natural elements of the landscape ( soils , water , vegetation , wildlife ) provide to humans ( e . g . sustainable grazing enterprises ).
2 . Resilience - the ability of country to absorb disturbance ( e . g . droughts , floods , fires ) and recover quickly ( bounce back ) without dramatically changing .
3 . Threshold - the point where there is no recovery ( bounce back ) and the country changes .
A simple example illustrates these concepts .
A perennial grass tussock is by nature resilient . If it is burnt or grazed or suffers a period of water stress , it will generally re-sprout from its base or a nearby fallen seed . The grass tussock can absorb a degree of disturbance and bounce back . It is resilient .
We want this grass tussock to remain in the landscape because it provides ecosystem services . It provides feed for cattle , shelter and food sources for native animals and plays an important role in water infiltration , evaporation and soil health .
If the perennial grass tussock is overgrazed or suffers a prolonged period of water stress , it fails to re-sprout or set seed and simply dies . The threshold has been breached . It is then replaced by fast-growing annuals and less desirable grasses . Less desirable vegetation types become dominant . This changes the way that water and nutrients infiltrate or evaporate from the soil . The loss of the perennial grass tussock means reduced feed for cattle , reduced food and shelter for native wildlife . The ecosystem services provided by the tussock have been lost and replaced by a less effective service . The system is changed and has lost its resilience .
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