Lake muds tell a 10,000 year-old story of environmental change.
Zoom in to the Google Map to find the points of interest.
Cranberry Rough is mostly a wilderness area of swamp and carr woodland; the remainder is damp meadows. In Tudor times, it was a large lake called Hockham Mere, fed by springs at its western end and deepest at its eastern end. It was drained over the next two centuries, and eventually turned into the swampy land we see today. It is a designated Site of Special Scientific Interest (SSSI) for its wildlife, and has recently seen much scrub clearance work in its southern area.
Cranberry Rough is one of the wildest parts of Norfolk. Its alder carr swamp has a primaeval feeling.
Hockham Mere was the largest of the ‘Breckland meres’ which include Fowlmere and Langmere; they formed over 10,000 years ago, probably by dissolution and collapse of the underlying chalk bedrock. Boreholes have shown that the lowest layer of sediment is sand and silt, washed or blown in off bare land surfaces at the end of the last Ice Age (the Devensian period). Since then the basin has been filled with over 9 m (29 ft) of mud, with a layer of recent peat on top. Fossil plant pollen has provided evidence of changing vegetation at Hockham Mere. Patchy birch and Scots pine forest surrounded the lake at the end of the Devensian, then thick forests of hazel, oak, alder and elm grew as the climate warmed up. The lake muds were rich in water plants such as bog-bean and holly-leaved naiad.
Patchy birch woodland colonised the late glacial landscape. Oak and hazel had arrived by 9,000 years ago.
Diagram showing percentage of pollen types, covering the period from 10,000 to 2,000 years ago. [Image courtesy Prof Keith Bennett, adapted from QRA Field Guide 1991, fig.34]
Silver birch pollen. Each grain is about 20 microns in diameter. [Image courtesy Dr Steve Boreham, University of Cambridge]
Local finds of flint tools (blades, scrapers, microliths and axes) show that the Mere attracted human settlement in Mesolithic times. Layers of charcoal particles have been found in the sediment, and are evidence for camp fires or local episodes of forest burning; they have been dated using the radiocarbon technique. A rise in grass pollen shows that clearings in the forest had certainly been made by Neolithic farmers about 5,000 years ago. The local economy seems to have been a pastoral one until cereals began to be cultivated more extensively in the late Iron Age and Roman periods, about 2,000 years ago. Some of the Breckland heaths are thought to have formed as early as this.
[Image courtesy Beverly Curl]
Mesolithic flint tools (microlith and arrowheads) found at Hockham Mere. [Image courtesy the Prehistoric Society]
Old maps show that Hockham Mere had dried up by the mid 18th century, thanks to a network of drainage ditches. Parts of the western end had become an acidic peat bog, with sphagnum moss, hare’s-tail cotton-grass, royal fern and cranberry. Sedge peat followed by fen-carr peat had developed in other areas – this is what is being deposited here today.
Sphagnum and cranberry are evidence for peat bog in recent centuries. This is one of only three sites in Norfolk where cranberry still survives. [Image courtesy Beverly Curl]
Recently restored wetlands and grazing meadows.
Two interpretive panels explain the site’s heritage. They are located beside the old railway line.
The southern half of Cranberry Rough is public access land - see Ordnance Survey Explorer map no.229 ‘Thetford Forest in The Brecks’ (c. TL 933 937). However please do not enter the site in the bird breeding season. You can visit by walking along the old railway line (see map). Do not stray off the footpath: much of the site is dangerous swamp. There are two interpretation panels beside the path (see map). Another footpath approaches the south-eastern end of the site, starting from Puddledock at Hockham (see map).