Effects of climate change and nitrogen deposition on the carbon sequestration of a forest ecosystem in the boreal zone

Global warming and nitrogen deposition are expected to modify the carbon sequestration of boreal forests, causing feedback to atmospheric CO2 and climate. The objective of this study was to assess the effects of climate change and various N deposition rates on C sequestration of a forest ecosystem. The study uses a gap-type forest model for a managed Scots pine (Pinus sylvestris L.) stand in conditions representing southern Finland. Model computations indicated that, for both current and changed (+4°C and +10% in precipitation) climatic conditions, increased levels of N deposition from 6 to 12 kg·ha-1 per year increased C uptake by 4-6.5%. Total C stock (vegetation, litter, and soil organic matter) was 11% higher for current level of N deposition than without deposition. Changed climate resulted in a 10% higher C stock of the vegetation but 30% lower C stock in the forest soil. Consequently, the total C stock in forests was decreased because of the greater decline in soil C stock. The combined effects of climate change and N deposition decreased the average C stock of forest (over a 100-year rotation period) with annual deposition rates under 12 kg N·ha-1 but slightly increased C stock with deposition of 24 kg N·ha-1.