Fens are mire ecosystems that, in addition to precipitation, receive ground or surface water (minerotrophic peatlands), whereas bogs are exclusively fed by precipitation water (ombrotrophic peatlands; Gore 1983; Bridgham et al. 1996). For a more extensive discussion of different peatland types we refer to Moore and Bellamy (1974), Wheeler and Proctor (2000), Joosten and Clarke (2002) and Chapter 2.
The framework of fen restoration includes a variety of different concepts and techniques, which have been developed with different objectives and for diverse target states. Assessment of success can vary considerably, depending on the identified criteria, be it bird diversity, rare plants, peat formation or nutrient status. Some authors distinguish restoration of fens (i.e. returning damaged fens near to the pre-disturbance state) from mire rehabilitation (i.e. re-establishment of their selected functions, which may result in systems that have not existed at the restoration site in the past) (Wheeler et al. 1995; Grootjans et al. 2012), whereas others focus on restoring key ecosystem functions of fens, such as peat formation and role in carbon cycling, formulating long-term targets (Joosten and Clarke 2002). In this chapter we attempt to structure the discussion around fen restoration by identifying challenges and trade-offs in this field and to clarify how close these different concepts come to the objective of reinstalling or improving the provision of key ecosystem services. We focus on lowland fens in West and Central Europe (UK, The Netherlands, Germany, Poland). We will first discuss the concept of fen ecosystems, their ‘naturalness’, resilience and stability, and the ecosystem services they provide. Next, we introduce the main ecological gradients in fens, the drivers of fen degradation and the consequences for ecosystem services, followed by an overview of constraints, synergies and conflicting targets in fen restoration. We conclude with an overview of gains and trade-offs of various restoration strategies.
The concept of fen
The diversity of fen restoration concepts can partly be explained by different understandings of the compass of fen ecosystems. Some fen concepts only include peat-forming ecosystems, whereas others also cover derivative ecosystems, such as wet meadows and pastures on drained fens. In this chapter, we will use the term fen only for peat-forming systems.