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Keywords:

  • Competition;
  • Exotic annual species;
  • Native perennial bunchgrass;
  • Nitrogen reduction;
  • Weeding

Question: What is the most appropriate combination of treatments to reintroduce Nassella pulchra, a perennial bunchgrass, into degraded mediterranean coastal grasslands?

Location: Central coast of California, USA.

Methods: N. pulchra was sown from seeds and transplanted into a degraded grassland in a multi-factorial experiment testing the effects of (1) two grazing intensities (lightly grazed by native mammal species or ungrazed); (2) topsoil removal and (3) reduction of plant neighbours. The experiment was carried out on two types of surrounding vegetation (exotic annual grasses and exotic forbs).

Results: Topsoil removal greatly enhanced establishment from seeds and transplant survival, mainly because it reduced the exotic vegetation and thus reduced competition. While removing neighbours was essential when topsoil was left intact, it had a negative effect on N. pulchra when surrounding species included exotic forbs (Brassica spec, and Asteraceae) at low density (after topsoil removal). Moderate grazing by native mammals (deer, rabbits and gophers) did not affect N. pulchra.

Conclusion: Our results suggest that seeding after topsoil has been removed is a promising method to reintroduce N. pulchra to highly degraded sites where there is little to no native seed bank.