Differences between grassland sites and years in rain-use efficiency (RUE, g m−2 mm−1) based on aboveground-(ANPP) and net primary productivity (NPP) in 2004, 2005 and 2006.

Significant differences in RUEANPP and RUENPP among years within a site are indicated by letters a-c and significant differences among sites within a year by letters x–z, respectively. Error: ± SE. Symbols for different sites as in Table 1.