Nutritional acclimation of sugar maple (Acer saccharum) under an increasing presence of conifers at various latitudes
The discipline of ecology suffers from a lack of knowledge to predict forest response to climate change. For instance, migrating species will increasingly interact with new species and cope with completely new soil conditions. Hence, the next generation of simulation models of forest response to climate change must build from local observations of species interactions and growth along climatic gradients. We examined whether sugar maple (Acer saccharum) has a competitive disadvantage for soil nutrients and water uptake over conifers as this could decrease its capacity to adapt to climate change. An experimental design was established on three sites forming the largest possible latitudinal/climatic gradient for sugar maple in Québec (Canada). The design was set up in a way to study seedlings of sugar maple on a gradient of increasing amount of conifers (three treatments replicated four times), thus simulating maple’s possible northern migration into the boreal forest under climate change. We tested if (1) soil types and climatic conditions influence foliar nutrient balances of maple seedlings; and (2) conifers adversely impact foliar nutrient levels of maple seedlings. To do so, soil samples and leaves were analyzed for nutrient composition.
Soil nutrients and water availability were influenced by the species cover: forests dominated by conifers had lower soil moisture, base cations and pH compared to hardwoods or mixedwoods. Foliar nitrogen and phosphorus of maple seedlings are also marginally decreased with the increasing presence of conifers. We found that climate and soil strongly affect nutrient availability for sugar maple seedlings: variations in foliar nutrient levels were significantly explained by a climate-pH model (50% of variation explained). Controlling for the climatic effects, we found a significant negative effect of conifers on maple seedlings foliar nutrient levels. Specifically, levels of foliar calcium and magnesium were lower with increasing amounts of conifers. These results are of concern as low foliar calcium and magnesium were shown to negatively impact sugar maple growth and survivorship. Our results also demonstrate the potentially negative effect of conifers on the nutritional acclimation (and thus competitivity) of sugar maple, regardless of latitude. This information needs to be taken in consideration when modeling the migration of sugar maple in the boreal forest under climate change.