Weeds in pasture ecosystems - symptom or disease?

Plant species that become weeds in pasture ecosystems require the same reso urces as useful forage plants - light, water, carbon dioxide. oxygen and mi neral nutrients. Their weediness stems from the fact that they package thos e 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 man agement must discover means of reducing the capacity of weeds to capture re sources and of recapturing those that are already tied up in weed populatio ns. Heavy grazing of palatable pasture species reduces the competition face d by invading weeds. Effective biological control agents: reduce the capaci ty of weeds to capture resources and make them potentially available to mor e favourable plant species. Pastures that experience high levels: of distur bance provide more opportunities for weeds to establish. Weeds can be inter preted as diseases of pasture but they may also be symptoms that indicate a n unhealthy pasture.