Effets du drainage sur la croissance et le statut nutritif d’un peuplement d’épinette noire de structure inéquienne : résultats de 10 ans

We present the 10-year results of a forest drainage experiment conducted in a pre-mature uneven-aged black spruce (Picea mariana (Mill.) BSP) stand, in Bas-Saint-Laurent, Québec, Canada. The set up included 20, 30, 40, 50 and 60 m ditch spacings, and the data were pooled in three diameter classes, ≤ 4 cm (small stems), 6-10 cm (medium-size stems) and ≥ 12 cm (large stems), in order to take into account stand structure in the analysis. The diameter growth of large stems (dominant cover, height ~ 8-12 m) was not improved by drainage. Medium-size stems (intermediate story, ~ 4-8 m) showed a better growth at a 5-10 m distance from the ditches, while small stems (understory ~ 1-4 m) reacted well to drainage, proportionally to ditch closeness. Generally, growth and gain attributable to drainage increased with the live crown ratio, from one third of the total tree height. We did not detect any effect of drainage or distance from the nearest ditch on the nutrient content of the current year foliage of the large stems. For small stems, even the individuals located at 25-30 m from the ditches showed a growth increase compared to the control, although the understory did not benefit from full light conditions. Results suggest that drainage aiming at correcting watering-up following harvesting could permit a rapid growth increase of advance growth.