Wicken Fen

By 1850, the alkaline peat soils of the Fenland had been drained and converted to agriculture, and from the 1950’s, the land was farmed intensively for arable agriculture. The long-term drainage of these peat soils over many decades led to shrinkage and oxidation of the peat, and lowering of land levels.

The goal for the Wider Wicken Vision, which began in 1999 is to turn ex- arable land over a 100-year period into a nature conservation site. This will add connectivity to the landscape for wildlife and contributes to reduced carbon emissions through peat conservation.

Restoration is primarily carried out through natural regeneration from soil seed banks, water table manipulation and low density, year-round grazing. It is open-ended because the starting point for habitat creation (degraded but highly fertilised peat soils) is novel, and because habitats are expected to keep evolving due to former land-uses, climate change, and re-wetting and grazing.

The experiment began in 2007 to find out how the grazing model used in the Wider Wicken Vision affects vegetation development across former arable areas which have different land-use histories.

Three areas make up the 119 hectares of the experimental area, and each of them differ in size, land-use history, soil profiles, water table depth and when they were last used as arable land. Seven grazing exclosures were established across the experimental area and vegetation plots were established for repeat vegetation surveys both inside and outside the exclosures.

Adventurer’s Fen (23.3 ha)

Year when it was converted from arable use: 1953

This site has the greatest depth of peat below which there are silty loam and gravel deposits on Gault clay, and it has the shallowest summer water tables.

Bakers Fen (50.4 ha)

Year when it was converted from arable use: 1993.

Guinea Hall (45.4 ha)

Year when it was converted from arable use: 2000.

This site is the driest of the three.

Since their conversion from arable land, they have each been undergoing restoration (natural regeneration, re-wetting and managed year-round grazing by low densities of free-roaming highland cattle and Konik ponies).

Animal grazing and previous land-use significantly affect the vegetation structure.

In the three experimental areas, Stroh et al. (2021) compared plant species diversity and composition between ungrazed plots and grazed plots from 2007 to 2017.

The vegetation differences between the grazed and ungrazed areas became more distinct over 11 years. Species inside the ungrazed exclosures tended to be associated with shady conditions and higher soil nutrient levels than plants in grazed areas. In the grazed plots, plant species richness was higher than in ungrazed plots.

The vegetation composition varied across the three experimental areas. Bakers Fen and Guinea Hall (which were used as arable land for longer and had a shorter restoration time) both had grassland species more typical of drier conditions while Adventurer’s Fen had more typical fen species.

Overall, this highlights that as well as grazing, soil hydrology and land use history are big factors in influencing vegetation development.

Restoration is increasing the wetland’s conservation value albeit slowly as indicated by using ground beetles as a proxy

Ground beetles (wetland ground beetles and Nationally Scarce ground beetles) serve as a good proxy for environmental change and restoration.

Martay et al. (2011) showed that restoration was successfully increasing the number of common wetland ground beetle species over time but not the Nationally Scarce beetles.

Beetle abundance, vegetation and soil measurements were recorded at Adventurers Fen and Bakers Fen, at two other restoration sites within the Wider Wicken Fen vision that had been out of arable production for one year and seven years respectively, and at an undrained site within Wicken Fen NNR.

High soil moisture and low vegetation density increased the abundance of Nationally Scarce and common wetland ground beetles. High vegetation density was more detrimental to Nationally Scarce ground beetles than to common wetland beetles. This suggests that any management method that decreases vegetation density (like grazing) and increases soil moisture (re-wetting) could increase the conservation value of a restoration site.

Hydrological and grazing management are the best methods to enable the soil seed bank to restore the wetland despite differences in land-use history.

When Stroh et al. (2012) compared the soil seed bank (SSB) across Adventurers Fen and Bakers Fen with a newer restoration site that had been under restoration management for 6 years and an undrained site within the Wicken Fen NNR, they found that the duration of restoration was a significant factor in giving each site its own unique SSB.

Vertical mixing of the SSB due to recent arable use occurred at the sites with the shortest restoration history and longest previous history of arable farming.

Despite the heterogeneity of the SSB diversity across all sites, there were seedbank species common to all three. However, relatively few plants from the wetter NNR sites were found on restoration sites though the wettest and longest established restoration site (Adventurers Fen) had the highest number of species in common with Wicken Fen NNR.

The notable lack of some wetland species from this long-established restoration site suggests that it takes a very long time before restoration by natural regeneration takes place even after a short history of drainage and ploughing of the delicate peat soils in the Fens. The results suggest that hydrological management and disturbance through grazing are most likely to promote the gradual restoration of wetland vegetation on degraded fen peat soils.

Dr Francine Hughes

Email: francinehughes13@gmail.com