Figure 1. Ecosystem functioning in grassland and forest experimental ecosystems.

In grasslands, trajectories of aboveground biomass (g m^-2) among plant species richness levels diverge over time (a). In forests, significant plant species richness effects on periodic annual increment of basal area (m² ha^-1) are consistent over time (b). The consistent positive effect of high-diversity communities on periodic annual increment of basal area may explain the temporal divergence in total basal area among plant species richness levels (c). For panels a and c, lines are mixed-effects model fits for each plant species richness level within each study (thin lines) or across all studies (thick lines). For panel b, lines are mixed-effects model fits for each study (gray lines) or across studies (blue line). For grasslands, aboveground biomass was significant affected by species richness (F_1,5754.7 = 14.21, p-value <0.001) and the species richness × time interaction (F_1,5754.7 = 8.53, p-value <0.01). For forests, periodic annual increment of basal area was significantly affected by species richness (F_1,1433.1 = 10.07, p-value <0.01), and total basal area was significantly affected by time (F_1,291.9 = 24.32, p-value <0.001) and the species richness × time interaction (F_1,291.9 = 18.39, p-value <0.001). See extended information in Supplementary Tables 2 and 4. Data from 14 grassland (1,045 plots n = 7,886 measurements (plot by age combination)) and from 12 forest experimental ecosystems were entered in the analyses (370 plots, n = 1,887 measurements (plot by age combination)).