Print PageMost 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 are likely to have a major impact on tree growth. Climate, however, is not the only important factor: a growing number of studies showed that the response of plants to climate in such biomes is strongly influenced by the availability of inorganic nitrogen.
The main objective of this project is to determine the effect of increased soil temperature as predicted by the CRC Model and increased N deposition on tree growth in a boreal balsam fir forest in Québec (Canada). In situ experimental manipulations of climate (precipitations, soil temperature) and nitrogen availability were conducted out in a mature stand. The addition of artificial precipitation is carried out by means of water nozzles set up above each tree canopy. Heating cables and thermocouples are buried under each tree. The variables measured include stem diameter variations (continuous, with dendrometers), wood cells formation using micro-cores (radius=0.95 mm) extracted weekly, soil nutrients using buried adsorbing membranes, leaf chemistry, and soil moisture.
Results/Conclusions
After two years of treatment, soil warming has had a generally stronger effect on the ecosystem than canopy N fertilization. The disturbance associated with the installation of the membranes caused an initial peak in soil nutrient availability in the first year, while large intra-annual variations were possibly caused by seasonal fluctuations of temperature and precipitations. Soil heating increased the availability of several nutrients (NH4, K, Ca, Mg and P) and other elements sensitive to soil pH (Al, Fe and Mn). Canopy fertilization did not increase soil N availability, perhaps due in part to N interception by the foliage.
Although earlier snow melt did not affect the onset of radial growth, standardized basal area increments of heated trees were 30-50% higher than for control trees in the first year (p<0.01). In the second year, both the onset of diameter growth and the total basal area growth were not affected by the soil heating but trees growing in warmer soils showed an earlier peak of growth (p<0.01). A summer drought during the second year could explain this growth pattern. While these results suggest a short-term positive effect of increased soil temperature on balsam fir productivity, long-term effects could differ significantly.
