Fig. 4

Biomass production per hectare, aboveground net primary production, leaf area index, and tree nitrogen per hectare over time for poplar (white) and black locust (black) in monocultures and in mixtures (means ± standard errors, n = 2). The effects of date (D), plot type (P: poplar monoculture, black locust monoculture, and two-species mixture), and their interaction are indicated for *P ≤ 0.05 and ***P ≤ 0.001; ns for non-significant. Different capital letters indicate significant differences among dates. Different small letters indicate significant differences among the three plot types