The amount of deadwood in rewetted boreal peatland forests

Restoration of forestry drained peatlands into functional mires by rewetting is becoming more common. However, the effects of rewetting on the tree stand, when aiming for a forested mire, are poorly known. A permanently higher water table level resulting from rewetting is expected to increase tree stress and subsequently tree mortality. We estimated the amount of deadwood on rewetted forested peatlands, assessed possible variables affecting it and estimated the carbon released from the decaying tree stems. We measured the living tree stand, standing deadwood, and downed deadwood at 76 measurement plots on 18 rewetted forestry drained peatlands in Southern Finland. The peatlands varied in their time since rewetting from 3 to 29 years and nutrient level from meso-eutrophic to oligo-ombrotrophic site types. We analysed the proportion of deadwood in the tree stand with generalized linear mixed-effects models using environmental variables and Saga soil Wetness Index as explanatory variables. Wetness and site type were the best predictors of deadwood proportion on rewetted peatlands, with deadwood volume (12–153 m 3 ha −1 ) and proportion (8–37%) increasing from nutrient-poor and drier sites to nutrient-rich and wetter sites. The rewetted peatlands in our study had mature tree stands and the volumes of living trees (150–375 m 3 ha −1 ) and deadwood were significantly higher than in typical drained peatland forests in Finland. Estimated carbon release from the decaying tree stems (175–789 kg C ha −1 year −1 ) was moderate in most cases but is a significant component of the carbon balance of rewetted peatlands.