Height (a), diameter (b) and stem volume (c) increments (Δ<i>H</i>, Δ<i>D</i> and Δ<i>V</i> respectively) of hybrid aspens in control (C) and humidified (H) plots during the study period.

<p>The significance of treatment effect (<i>t</i>-test) in individual years is indicated with asterisks and <i>q</i>-values (model) show the summary effect over the years when humidification was applied (age 2–4 years). Whiskers denote ± standard error.