Floating fire trays are not an obvious tool for conservation work perhaps. But Norfolk Wildlife Trust’s Cranberry Rough nature reserve, says Reserves Officer Robert Morgan, has something very surprising hidden beneath its rare habitat.

Norfolk Wildlife Trust’s Cranberry Rough nature reserve in the Brecks has a hidden secret, for lying beneath rough grassland, fen, alder carr and forestry plantation is a lost lake, or ‘mere’ to be exact. The Brecklands contains 12 meres in total, and these naturally occurring spring fed bodies of water have remained intact since the end of the last ice age. The largest, at seven hectares, is Fowl Mere.

Floating fire trays used in habitat restoration work

The ‘lost’ Hockham Mere is estimated to have been a whopping 81 hectares, with core samples suggesting it may have been up to 30 feet deep. The lakes sediment has provided scientists with a pollen record that gives an insight into the development of vegetation from the last ice age to present day.

 Evidence has been found of people settling around the original shoreline as far back as Mesolithic times, and accounts suggest it was still an open lake in the Tudor period. The mere had already started to silt up by the time it was first drained in the 18th century, but drainage requires a lot of upkeep.  The area was ‘swampy’ in the 1920s, and known to local naturalists for its botanical interest. The Forestry Commission commenced drainage again in the 1930s but had, fortunately, abandoned this work by the 1960s.

Now, as an NWT nature reserve, the site has returned to swampy mire. This has allowed water levels to stabilise and enabled an increase in the reserve’s exceptional range of plants and invertebrates, many unusual for East Anglia, with some being rare for the UK. This biological oasis has continued to thrive as the water, spring fed, is ‘filtered’ through sand and chalk, creating a pollutant free environment.

Much of the lake basin contains layers of peat that has formed into an acidic bog. Cranberry – only found at three sites in Norfolk – and royal fern – rare outside the Broads – grow here, as does bog-bean, marsh cinquefoil and cowbane. The narrow small reed grass, a possible relic from the Ice Age, has only one other record in Norfolk at NWT Thompson Common. More than 60 species of spider have been recorded, along with many rare beetles. Numerous bird species have bred, including the threatened and declining willow tit.

However, this open fen habitat is at risk of being lost to encroaching alder carr woodland. Norfolk Wildlife Trust staff undertakes a programme of scrub clearance in order to maintain and restore this important and unusual Norfolk habitat.

NWT Warden, James Symonds, fallen through the hover!

Due to the site’s challenging terrain this work has proved difficult and, without care, potentially dangerous. In parts the vegetation has grown across open water much like a skin on custard. Referred to as hover, walking across it gives a sensation of the ground moving in bouncing waves, and if you tread where the hover is thin you can fall through, one’s feet rarely touches a solid bottom.

To achieve this habitat restoration work, NWT staff employed floating fire trays to burn the cut material, aluminium liggers to spread their weight across the hover and a military style amphibious tracked vehicle. This work can only be carried out in autumn, of course this often means the site is even wetter, however this avoids disturbance to breeding bird and damage to its flora community. Despite these conditions, this important and tough work has ensured that this unique place remains in pristine condition.
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