Can a bog drained for forestry be a stronger carbon sink than a natural bog forest?

摘要

pstrongAbstract./strong This study compares the COsub2/sub exchange of a natural bog forest, and of a bog drained for forestry in the pre-Alpine region of southern Germany. The sites are separated by only 10 km, they share the same soil formation history and are exposed to the same climate and weather conditions. In contrast, they differ in land use history at the Schechenfilz site a natural bog-pine forest (iPinus mugo/i ssp. rotundata) grows on an undisturbed, about 5 m thick peat layer; at Mooseurach a planted spruce forest (iPicea abies/i) grows on drained and degraded peat (3.4 m). The net ecosystem exchange of COsub2/sub (NEE) at both sites has been investigated for 2 years (July 2010a??June 2012), using the eddy covariance technique. Our results indicate that the drained, forested bog at Mooseurach is a much stronger carbon dioxide sink (a??130 ?± 31 and a??300 ?± 66 g C msupa??2/sup asupa??1/sup in the first and second year, respectively) than the natural bog forest at Schechenfilz (a??53 ?± 28 and a??73 ?± 38 g C msupa??2/sup asupa??1/sup). The strong net COsub2/sub uptake can be explained by the high gross primary productivity of the 44-year old spruces that over-compensates the two-times stronger ecosystem respiration at the drained site. The larger productivity of the spruces can be clearly attributed to the larger plant area index (PAI) of the spruce site. However, even though current flux measurements indicate strong COsub2/sub uptake of the drained spruce forest, the site is a strong net COsub2/sub source when the whole life-cycle since forest planting is considered. It is important to access this result in terms of the long-term biome balance. To do so, we used historical data to estimate the difference between carbon fixation by the spruces and the carbon loss from the peat due to drainage since forest planting. This rough estimate indicates a strong carbon release of +134 t C hasupa??1/sup within the last 44 years. Thus, the spruces would need to grow for another 100 years at about the current rate, to compensate the potential peat loss of the former years. In contrast, the natural bog-pine ecosystem has likely been a small but stable carbon sink for decades, which our results suggest is very robust regarding short-term changes of environmental factors./p.