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 se questration of boreal forests, causing feedback to atmospheric CO2 and clim ate. The objective of this study was to assess the effects of climate chang e 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 sylv estris L.) stand in conditions representing southern Finland. Model computa tions indicated that, for both current and changed (+4 degrees C and +10% i n 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 (ve getation, 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 gr eater 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 rotati on period) with annual deposition rates under 12 kg N.ha(-1) but slightly i ncreased C stock with deposition of 24 kg N.ha(-1).