Pinus banksiana growth responses to a soil water recharge controlled by the Lichen organic layer.

English Abstract:

The forest industry must continually improve the environmental performance of its activities while preserving the environment and the sustainability of its ecosystem so that the forest remains an asset for future generations. In the boreal forest, soils have widely developed on coarse textured deposits. Following natural or anthropogenic disturbance, this type of substrate provides a capacity of resilience of the ecosystem which strongly varies in time and space. At the level of the station, we often observe a bimodal distribution in productivity between patches of dense populations and unproductive land forests covered with Lichens. Such a parcelling out of these stands conveys a strong possible occurence of their change into an unproductive alternative stable state. As far as the Boreal shield is concerned, some recent studies have confirmed the expanding of this opening phenomenon of the canopy. Once set up, the opened Lichens woodlands are considered as being relatively stable. The origin of positive feedbacks supposed to enhance the irreversibility of this unproductive state was the subject of many studies but has not succeed in reaching meaningful conclusions permitting to guide future strategies. The forest industry has therefore become very vulnerable in front of the evolution of these ecosystems. The present work is part of a project which aims at bringing elements of understanding necessary to develop tools for predicting and maintaining the productivity of Pinus Banksiana stands. We postulate that the organic layer originating from Lichens contributes to maintaining unproductive stands by limiting plant available water recharge. Hydrodynamic properties of organic and underlying layered mineral soil horizons would induce capillary barrier effects. These effects could significantly decrease available water holding capacity and consequently forest productivity. Preliminary results show that low-productivity stands are characterized by high hydraulic conductivity of the organic layer with respect to the underlying mineral horizons. When the infiltration is not restricted by the organic layer, gradation and layering of different soil textures can significantly enhance the tree growth.