Productivity of the Balsam Fir Boreal Forest in 2100: Experimental Interactions of Climate Change and Nitrogen Deposition

Loïc D'Orangeville1*, Benoit Côté* and Daniel Houle2

Most recent simulations of the future climate from the Canadian Regional Climate Model for the eastern boreal forest of Canada suggest an average annual temperature increase of 3 °C by 2050 whereas precipitations should increase by 5 to 20%. Such changes will certainly have a major impact on the growth of the boreal forest. But climate is not the only important factor: nitrogen is also a major growth-limiting factor in such biome. In fact, more and more studies show that the response of plants to climate change is strongly influenced by the availability of inorganic nitrogen, although this aspect is largely ignored in today’s predictive growth models.

The principal objective of this project is to identify the parameters that influence tree growth in boreal biomes by integrating, within the same study, an experimental manipulation of the climate (precipitations, soil temperature and growth season length) and nitrogen additions directly on the tree canopies.

The study site is located in a typical balsam fir forest near the calibrated watershed of the Lake Laflamme, Québec (Canada). The addition of artificial precipitations, enriched with nitrate-15 and ammonia-15, are carried out by means of independent water nozzles set up above each tree. Heating cables and thermocouples are buried under each tree, laid out in concentric circles on a radius of two meters.

To account for the effects of the experimental treatments, the measurement protocol consists in a continuous monitoring of stem diameter variations, analysis of wood cells formation using microcarots extracted weekly, measures of seasonal nutrient availability in the soil using adsorbing membranes, measures of soil and wood water content as well as analysis of leaf chemistry.

Preliminary results will be presented, with the intention of better quantifying the fine climate-growth relationships for balsam fir. This research will lead to the development of a quantitative model of the impact of climatic changes brought to the nitrogen cycle of the boreal forests following modifications in concentration of dissolved inorganic nitrogen in precipitations and to changes in the rate of mineralisation of the organic nitrogen in the soil. Moreover, a sound understanding of the cambial response of balsam fir species to the future climate will also be extremely useful for improving predictive power of forest dynamic models which for now do not take into account soil warming and more globally the effects of the climate change on the nitrogen cycle.

1 Department of Natural Resource Sciences, Macdonald Campus of McGill University, 21 111 Lakeshore Road, Ste-Anne-de-Bellevue, Québec, Canada H9X 3V9
2 Direction de la recherche forestière, Forêt Québec, ministère des Ressources naturelles et de la Faune du Québec, 2700 Einstein street, Sainte-Foy, Québec, Canada G1P 3W8
*Author for correspondence : Loïc D'Orangeville; tel: +1 514 9398884; email: