| Summary: | Greenhouse gases (GHG), especially carbon dioxide (C0₂), are believed to be the major cause of global warming today. The increased concentration of atmospheric CO₂ after the Industrial Revolution (late 18th and early 19th century) is attributed mostly to fossil-fuel combustion and deforestation. Consumption of fossil fuels and unsustainable use of forests are not likely to cease soon, hence alternative strategies for removal of atmospheric CO₂ are sought. This study provides information on the potential of forest fertilization with nitrogen (N) to sequester additional carbon (C) in tree biomass and soil. Two tree species (lodgepole pine and western hemlock), which are economically important in the province of British Columbia (BC), were examined. The amounts of C sequestered in tree biomass, understory vegetation, and soil after fertilization with N-alone (or N+B), and complete (N + other nutrients) were measured and compared with the amounts of C sequestered in non-fertilized plots. The effect of N on cellulolytic and ligninolytic enzyme activity was also examined. Fertilization increased the individual and stand-level tree biomass; although the stand-level tree biomass did not significantly differ between treatments. Understory vegetation biomass was not significantly affected by N fertilization; although there were some differences in species composition between treatments. Fertilization increased the soil C concentration (%) in the lodgepole pine stand and the soil C content (t/ha) in the western hemlock stand. Although there was greater average total ecosystem C stored in biomass and soil (to 40 cm depth) in fertilized plots, the differences between treatments were not statistically significant. Enzyme activity was not significantly affected by fertilization, except for one of the ligninlytic enzymes (peroxidase) for which activity increased after the N+B treatment. The results suggest that forest fertilization with N will accelerate C storage in these forests. However the decision as to whether this practice is the most beneficial way to sequester C should be made only after a detailed cost-benefit analysis and consideration of multiple desired outcomes for the forest in question. === Forestry, Faculty of === Graduate
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