Photo: X. Cavard

Black spruce forests have a low productivity of 1 m³ per ha per year. Trembling aspen stands growing on comparable sites are twice as productive. In black spruce-feathermoss stands, the low productivity of black spruce is attributable largely to paludification, a phenomenon caused by the accumulation of organic matter. However, black spruce itself is believed to contribute to the poor quality of the litter and the soil. 

Researchers at the Canadian Forest Service and the Université du Québec en Abitibi-Témiscamingue recently conducted a study in the Abitibi region, within the western black spruce-feathermoss bioclimatic domain, which focussed on the productivity of black spruce stands containing a proportion of trembling aspen. Mixed stands of black spruce and trembling aspen were found to be more productive than pure stands.

The researchers nonetheless observed competition between the two species for the ecosystem's limited resources. The results point up the greater overall productivity of the ecosystem of mixed stands. However, in some cases the presence of trembling aspen reduces black spruce productivity in mixed stands, whereas in other cases, the aspen trees help to maintain this productivity. It all depends on the relative proportion of trembling aspen, the position of the trees in the forest cover and soil productivity. Mixed stands in the boreal forest also hold more promise in terms of promoting biodiversity.