Why have European herbs so successfully invaded the Chilean matorral? Effects of herbivory,soil nutrients, and fire

We show field and experimental evidence that introduced herbivores and soil degradation strongly influence the distribution of introduced herbs in the Chilean matorral. In the field, the relative abundance of introduced speci es was higher on sites grazed by livestock and on very poor soils. Two fact orial experiments assessed the effects of rabbit grazing, nutrient addition , and fire. Native grasses were more sensitive than introduced grasses to g razing. With nutrient addition, native grasses increased while introduced g rasses tended to decline. Fire had no significant effects on our experiment al plots. We discuss several factors that might explain why alien herbs are more successful in the Chilean matorral than in the Californian chaparral. (C) 2000 Academic Press.