Introducing the VESBO Project - Impact assessment of vascular plant encroachment on water and carbon cycling in a Sphagnum dominated bog

Boreal and temperate peatlands cover less than 3% of the earth's surface but store nearly 30% of the terrestrial carbon. Natural raised bogs are characterized by a Sphagnum-moss dominated vegetation cover. The majority of bogs has been used for peat extraction or agriculture for centuries, but in the last decades the focus on restoration to protect climate and biodiversity was increasing. This includes the re-establishment of quasi-natural hydrological conditions as well as of ecosystem-typical vegetation.

Recently, a change in species composition of restored bogs from Sphagnum-dominated bryophyte communities to multi-layered tree and graminoid vegetation was observed. Current investigations report contradictory effects for the impact on throughfall, evapotranspiration (ET), gross primary productivity, respiration, net CO₂ balance (NEE) as well as soil carbon sink strength. A final conclusion with respect to altered ecosystem functioning through changing conditions for vegetation development in the light of climate change is missing.

The VESBO project aims at the mechanistic analysis of ET, NEE and soil carbon sink strength of a restored, atlantic-temperate raised bog during vascular plant encroachment. The two study areas are former peat extraction sites, with one being Sphagnum-dominated while the other one has been populated by Betula pubescens during the last years. Focus will be placed on the partitioning of total ecosystem ET and NEE fluxes by Eddy Covariance and chamber measurements in situ into bryophyte, graminoid and tree contributions. Results are used to parameterize a modern soil-vegetation-atmosphere-transport model able to simulate bryophyte and vascular plant layers on peat soil. The model, jointly with the empirical data, is used to quantify seasonal changes in plant functional group flux contributions depending on altered environmental conditions. The holistic process understanding is of high relevance for the NEE estimation of restored bog ecosystems under changing climatic conditions and vegetation compositions. The knowledge about different interactions of plant functional groups with mass and energy fluxes of the bog ecosystem will be valorised by the assessment of restoration and emission mitigation measures throughout Europe.