Fig. 3
Total tree biomass, aboveground woody biomass per tree, root mass fraction, and tree nitrogen content over time for poplar (circles) and black locust (diamonds) in monocultures (white) and in mixtures (black) (means ± standard errors, n = 8). The effects of date (D), species (S), and treatment (T) and their interactions are indicated for *P ≤ 0.05, **P ≤ 0.01, and ***P ≤ 0.001; ns for non-significant. Different letters indicate significant differences among dates