Nitrogen utilization efficiencies in mediterranean-climate shrubs of California and Chile.

Comparative studies of nitrogen utilization efficiencies (g assimilation mg-1 leaf nitrogen expended) for dominant chaparral shrubs of California and matorral shrubs of central Chile indicate varying relationships of these efficiencies to total shrub productivity and community dominance. In California where nitrogen is limiting for shrub growth, increasing nitrogen utilization efficiency is correlated with increased productivity, and species with the highest values are dominant on polar (north-facing) slopes. In Chile where soil nutrients are not strongly limiting, increased nitrogen utilization efficiency beyond a low threshold has little or no effect on productivity. This may be an important aspect of the relative ecological success of deciduous shrubs in Chile. High nitrogen utilization efficiency in Chile is associated with broad ecological amplitude rather than increased competitive ability through higher productivity.