Tropical Grasslands (2000) Volume 34, 264270
Weeds in pasture ecosystems — symptom or disease?
A.C. GRICE1 and S.D. CAMPBELL2
1CSIRO Tropical Agriculture, Townsville
Plant species that become weeds in pasture ecosystems require the same resources as useful forage plants — light, water, carbon dioxide, oxygen and mineral nutrients. Their weediness stems from the fact that they package those resources in a form that makes them unavailable as livestock forage. Weed species are either strongly competitive for resources, or they exploit an absence of competitors in disturbed situations. Ecologically-based weed management must discover means of reducing the capacity of weeds to capture resources and of recapturing those that are already tied up in weed populations. Heavy grazing of palatable pasture species reduces the competition faced by invading weeds. Effective biological control agents reduce the capacity of weeds to capture resources and make them potentially available to more favourable plant species. Pastures that experience high levels of disturbance provide more opportunities for weeds to establish. Weeds can be interpreted as diseases of pasture but they may also be symptoms that indicate an unhealthy pasture.