General Impact
Mauer et al. (1987) report that millions of acres of pasture and rangeland in western North America are infested with C. biebersteinii. The competitive superiority of this species suggests pre-adaptation to disturbance. Once a plant or colony is established, it may invade areas that are relatively undisturbed or in good condition with gradual, broad, frontal expansion. This invasion is associated with a decline in the frequency of some species and a decline in species richness overall. Widespread invasion often results from overgrazing. It has a low palatability, as it contains the bitter compound, cnicin. As the native grasses and forbs are continually eaten, the food reserves of their roots are depleted, and they are less able to compete. It is highly adept at capturing available moisture and nutrients, and it quickly spreads, choking out other vegetation. As the network root system of native species are lost and replaced by taproots of C. biebersteinii, the water storage capacity of the soil decreases and soil erosion increases. Zouhar (2001) states that secondary compounds in C. biebersteinii, such as cnicin, can negatively affect activity and growth of anaerobic rumen microorganisms in domestic sheep, reducing its digestibility. Large-scale infestations can impede access to more desirable forage for livestock and wildlife, especially when the presence of old, dried knapweed stems creates a dense and spiny overstory.
No Impact information recorded for Centaurea biebersteinii
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