Dunscombe

Executive Summary

Dunscombe, a "secret wooded combe" located near Sidmouth on the East Devon coast, represents a critical intersection of active geology and rare ecology. Part of the Jurassic Coast World Heritage Site and managed by the National Trust, the area is defined by its inherent instability. The slow-motion crumbling of Cretaceous-era cliffs—driven by "large-scale pervasive dissolution"—continually reshapes the landscape, creating a "mosaic of crucial habitats" including undercliffs, coastal seepages, and flower-rich grasslands.

This geological disturbance is the primary engine of the area’s high biodiversity, preventing any single ecosystem from dominating and providing niches for some of the UK's rarest invertebrates. Notable residents include the Morris's Wainscot moth, found nowhere else in Britain, and the Spanish Snout Cranefly. The site further preserves human history through abandoned "Salcombe Stone" quarries and historic agricultural "plats." Dunscombe serves as a profound example of how "creative decay" and constant environmental change can foster a thriving and unique natural world.

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Geological Foundations and Landscape Dynamics

The physical identity of Dunscombe is dictated by its underlying rock structures and the constant forces of erosion and dissolution.

• Stratigraphy: The landscape is dominated by the Upper Greensand Formation, deposited approximately 100 million years ago during the Cretaceous period. Specific geological layers include:

  • Foxmould Member

  • Whitecliff Chert Member

  • Bindon Sandstone Member

  • Younger caps of white Chalk in certain areas.

• The Process of Dissolution: The cliffs are shaped by "large-scale pervasive dissolution." Slightly acidic rainwater dissolves the carbonate cements within the sandstone, honeycombing the rock and making it structurally weak.

• Active Undercliffs: This weakness leads to constant slumping and the creation of "undercliffs"—wild, jumbled slopes of land that have slipped toward the sea. This instability ensures a perpetual supply of bare ground and prevents ecological stagnation.

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Habitat Mosaic

The valley and its adjacent coastline comprise a finely grained patchwork of ecosystems, each supporting specialized species.

Habitat Type Characteristics and Ecological Function

Crumbling Undercliffs Unstable slopes providing bare ground and nesting sites for solitary bees.

Coastal Seepages Calcareous springs and streams where water emerges from the rock; vital for rare flies.

Flower-Rich Grasslands Found on cliff tops and landslips; provide food sources for butterflies and bees.

Wooded Combe Sheltered valley environments (primarily ash trees) offering a refuge from coastal exposure.

Shingle Beaches Located at the cliff base; host specialised species dependent on driftwood.

Historic "Plats" Terraced fields on south-facing slopes; former agricultural sites that now harbour chalk-loving plants.

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Critical Biodiversity and Rare Species

Dunscombe is recognised as a national "invertebrate hotspot," home to species that depend on the area's specific geological and micro-climatic conditions.

Moths and Butterflies

• Morris's Wainscot Moth: A flagship species for the area; it is found only on this specific stretch of coast. Its caterpillars feed on Tall Fescue grass growing on the most unstable ground.

• White Spot Moth: A specialist whose caterpillars feed exclusively on the seeds of the Nottingham Catchfly.

• Wood White Butterfly: One of Britain's smallest butterflies, maintaining Devon populations in the sheltered undercliffs where caterpillars feed on vetches.

Flies, Bees, and Beetles

• Spanish Snout Cranefly: A southern-European species whose only known British habitat is the spring-fed streams of these coastal cliffs. It is considered highly precarious due to threats from drainage and pollution.

• Broad-faced Furrow Bee: Utilises the fine cracks in sun-baked clay cliffs as nesting sites.

• Cliff Tiger Beetle: Known as the "cheetah of the insect world," this predator hunts across the bare, warm ground of the south-facing cliffs.

Aquatic and Coastal Life

• Scaly Cricket: A rare nocturnal insect found on shingle beaches; it lays eggs in driftwood, making it vulnerable to the removal of beach debris.

• Fairy Shrimp: A rare and protected crustacean found in man-made dew ponds on the grasslands above the cliffs.

Larger Fauna and Flora

• Avian Predators: Peregrine Falcons use the high cliff vantage points for hunting.

• Reptiles: The sunny paths and slopes support populations of Adders.

• Botanical Diversity: The area features chalk-loving wildflowers, including common rockrose, sweet violet, and salad burnet.

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Human and Cultural History

The natural resources of Dunscombe have been integrated into human industry and agriculture for centuries.

• Salcombe Stone: Historically extracted from valley quarries, this coarse sandstone was a durable building material used in prestigious structures, most notably Exeter Cathedral.

• Early Agriculture: The "plats" (terraced fields) utilised a frost-free micro-climate to grow early potatoes. Farmers traditionally fertilized these fields with seaweed harvested from the local beaches.

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Conclusion: The Value of Disturbance

The central insight of the Dunscombe landscape is that stability is not a prerequisite for ecological health. Instead, the "constant, creative decay" of the coastline acts as the architect of its biodiversity. By maintaining a state of flux, the geology of Dunscombe creates a unique refuge for specialised life forms that would be unable to survive in more stable, uniform environments. This "secret combe" remains a vital laboratory for understanding the relationship between a shifting physical earth and the rare life it supports.