Restoring the rare forb Erodium macrophyllum to exotic grassland in southern California

[摘要] ABSTRACT: Erodium macrophyllum is a rare annual forb that was once widespread in California, but has become largely restricted to clay soil outcrops. An effort was made to restore it to a soil where it was once likely abundant. This soil is now dominated by exotic annual grasses and forbs from the Mediterranean that grow in patches with native forbs. To determine whether there is a competitive hierarchy of E. macrophyllum with the dominant matrix species, we examined establishment and seed production of E. macrophyllum in patches of forbs and grasses in a southern California exotic grassland over 3 yr. We sowed seeds of E. macrophyllum into patches where the dominant species was either Amsinckia menziesii (native forb), Erodium brachycarpum (exotic forb) or Bromus spp. (exotic grasses) and into adjacent manually weeded control plots. All 3 competitors negatively impacted E. macrophyllum seed production, but seldom affected seedling establishment. Although we expected that a native forb would be most compatible with E. macrophyllum, A. menziesii in fact had the most negative effect or was equivalent to E. brachycarpum, and Bromus spp. had the least negative effect. Bromus plants had the lowest density of the 3 matrix species, the lowest rate of recolonization following removal, and grew in soil with the highest levels of extractable N and P. In this case, the competitive hierarchy was confounded by soil nutrients, so that establishment of E. macrophyllum was greatest in patches of Bromus. However, both native and exotic competitors reduced E. macrophyllum establishment, so weeding all known species of competitors will be needed to increase chances of seed production and promote restoration of this rare annual forb.

[学科分类] 动物科学

[关键词] Erodium macrophyllum;Competitive hierarchy;Fecundity;Invasive grasses;Invasive forbs;Rare forb