On rapidly drained sites in the boreal forest, forest productivity can vary strongly in time and space. The mosaic of closed pine-moss stands and open pine-lichen woodlands suggests the existence of two stable alternative states. Open lichen woodlands in sites with a high potential productivity result from a tree regeneration and/or growth deficit that may be linked to the composition of the ground cover. We hypothesize that feather mosses constitute better seed beds and growth substrates for young jack pines than lichens. In several experiments, we tested the effects of three different ground layer treatments – absence of ground cover, feather moss cover (including Pleurozium schreberi (Brid.) Mitt.) and lichen cover (including Cladina spp.) – on different stages of the early development of young jack pines (Pinus banksiana Lamb.) including seed germination, and growth of seedlings and saplings. Seedlings and saplings were also subjected to different levels of soil nutrient availability.
Results/Conclusions
Pine germination success was reduced in absence of ground cover and tended to be higher in feather mosses than in lichens. Seedling growth during the six months following germination was much better in feather mosses than in lichens or in absence of ground cover. Similarly, biomass of the young pines after one and two growing seasons tended to be higher in feather mosses than in the other two treatments. Fertilization positively affected young pine growth and this effect did not differ among the three ground layer treatments. These results suggest that lichens are a less favorable substrate for young jack pine growth and, to a lesser extent, germination. Consequently, they may prevent forest regeneration and favor stand opening in sites with high potential productivity. Lichen expansion at the expense of feather mosses may contribute to reduce closed forest area in the boreal forest. This research gives new insights into boreal forest functional process and resilience and may have important implication in sustainable forest management.