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

摘要

This study compares the CO₂ exchange of a natural bog forest, and of abog drained for forestry in the pre-Alpine region of southern Germany. Thesites are separated by only 10 km, they share the same soilformation history and are exposed to the same climate and weather conditions.In contrast, they differ in land use history: at the Schechenfilz site anatural bog-pine forest (Pinus mugo ssp. rotundata) grows on anundisturbed, about 5 m thick peat layer; at Mooseurach a planted spruceforest (Picea abies) grows on drained and degraded peat (3.4 m).The net ecosystem exchange of CO₂ (NEE) at both sites has beeninvestigated for 2 years (July 2010–June 2012), using the eddycovariance technique. Our results indicate that the drained, forested bog atMooseurach is a much stronger carbon dioxide sink (?130 ± 31 and?300 ± 66 g C m?2 a?1 in the first and second year,respectively) than the natural bog forest at Schechenfilz (?53 ± 28and ?73 ± 38 g C m?2 a?1). The strong net CO₂uptake can be explained by the high gross primary productivity of the 44-yearold spruces that over-compensates the two-times stronger ecosystemrespiration at the drained site. The larger productivity of the spruces canbe clearly attributed to the larger plant area index (PAI) of the sprucesite. However, even though current flux measurements indicate strong CO₂uptake of the drained spruce forest, the site is a strong net CO₂ sourcewhen the whole life-cycle since forest planting is considered. It isimportant to access this result in terms of the long-term biome balance. Todo so, we used historical data to estimate the difference between carbonfixation by the spruces and the carbon loss from the peat due to drainagesince forest planting. This rough estimate indicates a strong carbon releaseof +134 t C ha?1 within the last 44 years. Thus, the spruces wouldneed to grow for another 100 years at about the current rate, to compensatethe potential peat loss of the former years. In contrast, the naturalbog-pine ecosystem has likely been a small but stable carbon sink fordecades, which our results suggest is very robust regarding short-termchanges of environmental factors.