Ecological History

pebbles

The Pebblebed heaths are named after the Budleigh Salterton (Bunter) Pebblebeds which underlie them. These are over 30m deep in places and extend some 40 miles inland to the Somerset border. The rock that formed the sandstone pebbles originated 440 million years ago, with the pebbles themselves forged and deposited by riverine erosion in a mountainous, arid landscape at a time when all the world’s contingents were joined as the ‘supercontinent ‘Pangaea’. Parts of these beds were subsequently overlain by sandstones and mudstones, with the former comprising wind-blown and river deposits, and the latter finer-grained material laid down in temporary lakes. The Pebblebeds themselves have subsequently been exposed by latter erosion of the overlying rocks. The Pebblebeds give rise to freely draining, very acid, sandy and loamy soils of low fertility.

In 1990 geologists from Bristol and Plymouth University discovered the remains of a large reptile-like creature near Ladram Bay dating back to about the same time as the Pebblebeds were being deposited. This was later identified as a rhynchosaur, an ancestor of the dinosaurs that were to come later. The fossils of this creature are in the Royal Albert Memorial Museum, but Clinton Devon Estates commissioned a life-size model to be made to celebrate one famous lifeform known to have occurred in the area at the time the Pebblebeds were being deposited. Local school children subsequently christened the creature ‘Woody’, after Woodbury Common.

reptile

Devon was never covered by ice during the last glaciation. The vegetation present after the last glacial era ca. 11,000 years was likely tundra-esque, and covered in snow during the winter. At this time the sea level was much lower and Devon’s earliest settlers could have walked across to colonise a landscape that was quickly becoming clothed in trees, at first birch and pine and then hazel and oak.

Most heathlands are derived from the clearance of woodland on light soils by Neolithic or later Bronze or Iron Age farmers. Use of the land for arable and pastoral farming, often accompanied by burning to provide fresh grazing kept the land open, but over time, this wasted the original brown earth soils and left light, acid, freely draining ground, ideal for the growth of heather Calluna vulgaris and other heathland plants. Down the centuries, continued grazing and burning, removal of turves, bracken and scrub for fuel and animal bedding, cutting of timber and exploitation of other heathland products, prevented woodland from re-establishing. These activities also resulted in the continual removal of nutrients from the system, maintaining the poor soils and their heathland vegetation.

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