Time Since Rewetting Defines Vegetation Composition and Carbon Dioxide Fluxes on Former Milled Peatlands - Comparison With Undisturbed Bogs

Abstract

Rewetting is the most common restoration approach for milled peatlands in Europe, with the aim of creating suitable conditions for the development of peatland specific plant cover and carbon accumulation. Therefore, it is important to determine if time since rewetting is pivotal for milled peatlands to become functionally and structurally similar to their undisturbed counterparts. We investigate the temporal succession in rewetted peatlands in Estonia by a chronosequence of 4, 15, and 35 years before the measurements. Plant functional type (PFT) cover and biomass, bryophyte production and CO2 fluxes were measured on two milled peatlands, as well as undisturbed bogs adjacent to milled peatlands. Differences in vegetation composition and CO2 fluxes between the sites were greater for rewetted than undisturbed sites. The most recently rewetted site was mainly covered in bare peat and Eriophorum vaginatum and was a CO2 source. On the rewetted site of 15 years, Sphagnum was present in addition to ombrotrophic sedges, and in the rewetted site of 35 years, lawn-hollow microtopography is starting to develop with various PFTs. Both of these sites were CO2 sinks. Lawn Sphagnum was abundant on the two older rewetted sites, and was connected with CO2 sink functioning in the rewetted sites. Still, hummock Sphagnum species, which were present in undisturbed bogs, were absent from all of the rewetted sites. With time, CO2 fluxes, microtopography and vegetation develop after rewetting in the direction of undisturbed bogs, while vegetation composition still differs from the reference sites even 35 years after rewetting.