After-use of peat extraction sites - A systematic review of biodiversity, climate, hydrological and social impacts.

After drainage for forestry and agriculture, peat extraction is one of the most important causes of peatland degradation. When peat extraction is ceased, multiple after-use options exist, including abandonment, restoration, and replacement (e.g., forestry and agricultural use). However, there is a lack of a global synthesis of after-use research. Through a systematic review of 356 peer-reviewed scientific articles, we address this research gap and examine (1) what after-use options have been studied, (2) what the studied and recognized impacts of the after-use options are, and (3) what one can learn in terms of best practices and research gaps. The research has concentrated on the impacts of restoration (N = 162), abandonment (N = 72), and replacement (N = 94), the latter of which consists of afforestation (N = 46), cultivation (N = 34) and creation of water bodies (N = 14). The studies on abandonment, restoration, and creation of water bodies have focused mostly on analyzing vegetation and greenhouse gas (GHG) fluxes, while the studies assessing afforestation and cultivation sites mostly evaluate the provisioning ecosystem services. The studies show that active restoration measures speed-up vegetation recolonization on bare peat areas, reduce GHG emissions and decrease negative impacts on water systems. The most notable research gap is the lack of studies comparing the environmental and social impacts of the after-use options. Additionally, there is a lack of studies focusing on social impacts and downstream hydrology, as well as long-term monitoring of GHG fluxes. Based on the reviewed studies, a comparison of the impacts of the after-use options is not straightforward. We emphasize a need for comparative empirical research in the extracted sites with a broad socio-ecological and geographical context.