Extending a Helping Hand

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Science  28 Nov 2003:
Vol. 302, Issue 5650, pp. 1481
DOI: 10.1126/science.302.5650.1481b

Invasive species introduced deliberately or accidentally by humans have become a major nuisance and threat to ecosystems worldwide. It is commonly thought that invasive alien plants are often able to overwhelm native plants because of superior competitive ability. In a study of the interaction between invasive and native species in California grasslands, Seabloom et al. show that this is not necessarily the case.

More than 9 million hectares of these grasslands have become dominated by southern European annual grasses and forbs, with important consequences for ecosystem processes such as nutrient leaching, carbon storage, and fire dynamics. Experimental alteration of parameters such as seed quantity, availability of nitrate and water, and disturbance produced conditions under which the native plants reinvaded the grasslands, edging out the usurpers. These results suggest that the exotics are not always superior competitors, and that native grassland can be restored by increasing the amount and dispersal of native seeds. As well as providing optimism that the invaded grasslands of California can be restored at least partially, this study suggests a potential approach for studying and alleviating the effects of invasions in other systems. — AMS

Proc. Natl. Acad. Sci. U.S.A. 100, 13384 (2003).

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