Seasonal Net Ecosystem Carbon Exchange of a Regenerating Cutaway Bog: How Long Does it Take to Restore the C-Sequestration Function?

We measured the net ecosystem exchange (NEE) and respiration rates and modeled the photosynthesis and respiration dynamics in a cutover bog in the Swiss Jura Mountains during one growing season at three stages of regeneration (29, 42, and 51 years after peat cutting; coded sites A, B, and C) to determine if reestablishment of <i>Sphagnum</i> suffices to restore the C-sequestration function. From the younger to the older stage <i>Sphagnum</i> cover increased, while net primary <i>Sphagnum</i> production over the growing season decreased (139, 82, and, 67 g m⁻² y⁻¹ for A, B, and C respectively), and fen plant species were replaced by bog species. According to our NEE estimations, over the vegetation period site A was a net CO₂-C source emitting 40 g CO₂-C/m² while sites B and C were accumulating CO₂-C, on average 222 and 209 g CO₂-C/m², respectively. These differences are due to the higher respiration in site A during the summer, suggesting that early regeneration stages may be more sensitive to a warmer climate. Methane fluxes increased from site A to C in parallel with <i>Eriophorum vaginatum</i> cover and vascular plant leaf area. Our results show that reestablishing a <i>Sphagnum</i> cover is not sufficient to restore a CO₂-sequestrating function but that after circa 50 years the ecosystem may naturally regain this function over the growing season.