Fig. 2

Tree stem heights over time in monocultures (white) and mixtures (black) for poplar (circles) and black locust (diamonds) (means ± standard errors, n = 40) and soil volumetric water content at 10-cm depth (means, n = 8) between 2011 and 2015. At the end of each growing season, different letters indicate significant differences between species and treatments for P ≤ 0.05. Plantation and harvest dates are indicated by arrows