Terrae incognitae - water and forest management of transformed drained peatlands

Drainage in peatland forests has onset a succession, where a mor humus has formed on the top of the peat. Our latest study revealed that trees on transformed drained peatlands grow better when the water table (WT) is rather close to the soil surface. This is due to the hydrological and biogeochemical function of the mor layer. Mor layer is a substantial nutrient storage and source, it contains most of the roots and includes macropores that enable oxygen supply for roots even when WT is elevated. This suggests that in future peatland forestry the improved growth under higher WT would be synergetic to several other ecosystem services (ES): Growing forests with higher WT improves climate change mitigation via reduced peat carbon (C) emissions and enhanced stand and ecosystem C sequestration, improved resiliency due to reduced drought risks and smaller nutrient export to water courses. The importance of mor layer has been unrecognized, and its characteristics, function and consequences for ES provision remain virtually unexplored. We outline how mor layer affects the function of transformed drained peatlands, and apply the understanding to define sustainable water and forest management strategies taking into account ES across site fertility range under current and changing climate. This is achieved through application of process-based Peatland simulator SUSI. Understanding the mor layer function supports renewal of forest regeneration, planning of water and forest management and adaptation to climate change. Wood production with higher WT is an intermediate form between rewetting and current water management. The new peatland management has potential to cause immediate climate cooling effects through enhanced forest growth and decreased soil C emissions whilst decreasing nutrient loading to water courses.