Marley Fen is a peat-based calcareous or alkaline hillside spring-fed fen which has probably been there for over 10,000 years. Fens are rare species-rich habitats and only about 25,000 ha of lowland fen remains in England. Alkaline fens will only develop where specific geological and hydrological conditions are right and are sensitive to changes in climate, water supply, nutrient input and land use. Fens take many thousands of years to develop through the deposition and preservation of consecutive layers of plant matter as peat.
Marley Fen has been drying out since the 1950s when the water catchment was planted with conifers as well as loss of light and increased water demand caused by the encroachment of sycamore trees surrounding the fen.
The restoration of Marley Fen started in 2010 with the aim of finding the best way to manage the fen, increase its biodiversity, habitat structure and water supply thus helping to preserve its unique ecosystem for the future.
Since restoration started the water supply has been increased by thinning the catchment area by selective removal of conifers, the blocking of a Victorian spring water collection system and the selective removal of encroaching sycamore and scrub. Plant diversity has been encouraged by annual cuts of 60% of the reed dominated area. Nutrient enrichment has been reduced by the increase in water flow through the fen.
There are plans to restore fens in adjacent valleys within Marley Wood, which at present are almost completely covered with encroaching wet woodland and scrub causing increased peat loss.