Rocks and soils

Devon’s geology and soils vary hugely, from wet and acid peat bogs on the Dartmoor granite to shallow calcareous soils on the Devonian limestone in Torbay.

Up to 1.5 kg of living organisms can live beneath one square metre of soil.

Rocks, caves and mines provide habitat for rare spiders, lichens and bats.

What we need to do and where

A pair of hands hold brown soil. — Soil, Becky Halterman Robinson

A worm is seen half coming out of the ground. — Worm, Alexa Hunt

A metal spade can be seen in a square hole dug into brown soil, with worms and other bugs visible. — Soil, Richard Smith

1. About

Rocks

Devon’s landscape, soils and wildlife habitats are largely a reflection of our underlying and very varied geology. Devon’s rocks have been formed over millions of years through periods of sitting under warm shallow seas (shells and corals formed the Devonian limestone of Torbay and much later the Cretaceous chalk around Beer), mountain building and volcanoes (formed Dartmoor acidic granite) and hot dry deserts (formed the red sandstone of east Devon).

Rocks largely control the natural processes we find in any landscape, from the shape of the hills and valleys to the patterns of drainage and coastal erosion. Crucially, different rocks influence the development of different types of soils which in turn support different types of vegetation and wildlife habitat. You can see a simple map of Devon’s geology below.

This strategy does not include details relating to the conservation of geological sites. However, County Geological Sites are shown on the viewer (under Other Useful Layers) and you can see links to more information in Find out more below.

Slider: Devon’s geology, Soilscapes and soil habitat

Rocks and the features that they form (caves, cliffs, boulders and tors) are also valuable wildlife habitats that support many Devon Special SpeciesDevon Species of Conservation Concern which have been 'shortlisted' as needing particular action or attention. identified in this strategy. A few examples include:

Limestone and chalk caves created in the Devonian limestone at Berry Head, Chudleigh and Buckfastleigh provide roosts for bats including Greater and Lesser Horseshoes. Caves in the Cretaceous chalk at Beer have both species of Horseshoe bats as well as the very rare Bechstein’s bat. The British Cave Shrimp lives in underground aquifers in caves and mines.
Mines. The area around the edge of the Dartmoor granite is especially mineral rich (it’s known as the ‘metamorphic aureole’) and has a strong mining heritage. Many of these mines provide wildlife habitat, including for bats (there are large Greater Horseshoe roosts in the old Tavistock copper mines) and for rare lichens and mosses.
Bare rock in natural cliff faces, man-made cuttings (railways, roads, towns) and quarries can provide unique wildlife habitats for plants, invertebrates and bird nesting sites. The large china clay quarries at Lee Moor and ball clay quarries in the Bovey Basin provide unique opportunities for wildlife with mosaics of ponds and seepages supporting Great Crested Newts and rare dragonflies such as the Scarce Blue-tailed Damselfly. Sand cliffs provide nesting sites for Sand Martins and areas of bare sand and clay provide habitat for bees, wasps and beetles.
Granite tors and boulders (clitter fields) on Dartmoor support rare lichens as well as providing habitat for mosses and ferns and shelter for birds and invertebrates.
Rare spiders live on screeA mass of small or loose stones lying on a slope or at the base of a hill or cliff. slopes on the upper Teign Valley gorge as well as on the cliffs around Start Point on the south coast.

Soils

Soils are composed of clay, silt and sand from weathered rocks, pores full of air or water, dead and decaying vegetation and billions of tiny organisms. Different physical conditions create different soils over thousands of years (most of our soils are around 10,000 years old). Key things are the type of underlying rock, climate (wet or dry), landform (flat, steep, wet or dry) and vegetation. Soils are critically important to our lives and are an integral part of wildlife habitats. Soil functions help deliver our food production systems, store carbon, control flooding and water quality and recycle organic matter and nutrients. They also contain a vast and under-explored reservoir of biodiversity.

Over a quarter of all known species live in the soil, where they often go unnoticed. A few examples are earthworms, insect larvae, mites, springtails, nematodes, billions of bacteria, archaeaSingle-celled microorganisms that love harsh environments such as high temperature, very saline or very acid. Play an important role in nutrient cycles. and fungi. These organisms play a vital role in helping to form the soil structure. Soil particles have a film of water around them, which is where lots of microorganismsAn organism that can be seen only through a microscope. (bacteria and fungi) live and are preyed on by larger organisms. Earthworms, ants and other animals that move the soil such as moles, are known as earth engineers because their burrowing activity changes the structure of the soil. Earthworms ingest soil and produce casts which help to create new soil habitats. Diverse soil communities help to control outbreaks of pests and diseases by feeding on problem organisms.

Soils, Soilscapes and wildlife habitats

As Devon has such varied geology and landscapes we have lots of different types of soil. These soils all have different characteristics (wet and dry; acidic and calcareous) and so support different plant species, which in turn create different habitats. For example, thin, free-draining, calcareous soils have developed over the limestone rocks on the Torbay coast. These soils support lime-loving (rather than acid-loving) plants, which together form species-rich calcareous grasslands. In contrast, wet and acidic soils have developed over the clay shale rocks and mudstones of north Devon. Completely different plants thrive in these conditions, creating the wet Culm grasslands of north Devon.

Most of our free-draining, less acidic brown earth soils are now used for intensive agriculture, along with hedges, remnant woodlands and scattered species-rich grasslands. However, bats and birds feed on the earthworms, beetles and ants that live in the soils of arable and improved grassland fields for all, or part of, their lives.

Soils can be classified into a number of broad groups:

Soil Group	Key characteristics
Brown earth soils	Freely-draining soils or with slight impeded drainage. Soils are slightly acidic, neutral or calcareous depending on parent material. They support woodlands and other woody habitats (orchards, wood pasture, parkland, scrub), species-rich lowland meadows and east Devon coast chalk grasslands.
Gley soils	Soils with long periods of seasonal waterlogging near the surface. Soils support mosaics of wet woodland, wet heath, mires and wet acid grasslands (Purple moor-grass and rush pastures). Soils can have peaty layers.
Podzolic soils	Very acid soils either freely-draining or with impeded drainage. Soils support mosaics of dry and wet heath and acid grasslands. Soil acidity and wetness form peaty layers.
Deep peat soils	Deep peat supports the bogs on Dartmoor and Exmoor.
Shallow soils	Thin soils over bedrock with varying acidity and drainage. Includes Torbay coastal limestones and sand dunes. Can be rich in mosses and lichens and provide important invertebrateAn animal that doesn't have a backbone, such as insects, spiders, worms, crabs and slugs. habitat, for example, bare areas for nesting bees.
Man-made soils	Soils found in urban areas, verges, gardens, old quarries and mine spoil heaps. They have huge potential for wildlife restoration and the creation of interesting plant communities.

These broad groups consist of lots of different types of soil known as Soil Series. Soilscapes is a simplified national soils map that was produced to help show how different soils underpin different wildlife habitats (see the slider above). The Soilscapes have been used to help map the LNRS High Opportunity Areas for habitats (see the Mapping Methodology paper on the Mapping page). For more details on Soilscapes see the Soilscapes map on the LNRS Viewer (Other Useful Layers) and links in Find out more below.

For more details see a summary of the Devon Soil Groups and the LNRS overview of soils, geology and wildlife habitats, which sets out the relationship between geology, soils and habitats.

Key pressures and opportunities

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Geological habitats

Disturbance to caves and old mines is one of the main pressures, especially due to their attraction to ecologists, geologists, archaeologists, climbers and cavers. Blocking cave entrances to prevent illegal entry can prevent bats entering and leaving.

The removal of mineral-rich tip material for hardcore or as part of restoration schemes can be a significant issue for rare species, especially lichens, bryophytes and invertebrates, which are easily overlooked.

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Land management and soils

Impacts of land management on soils: Devon’s habitats are an expression of the soil properties beneath them and the management they’ve received. Habitats supported by a given soil type are a continuum: depending on if they’ve been managed through grazing or burning, a thick acid soil might support acid grassland, heathland, scrub, bracken or upland acid oak or birch woodland. The habitat feeds back to the soil, altering its functions and biological communities. Major changes in land use and land management take soils away from these natural states, changing their biological communities, chemical, nutrient and hydrological status. For example, poorly-drained soils in mid Devon are naturally wet and slightly acidic, supporting wet Culm grassland habitats. These soils may have been under-drained, limed and fertilised to the extent that restoring Culm grasslands would require extreme measures (such as turf stripping and drain blocking) or the recovery of natural processes over a long time.

Loss of habitats on brown earth soils: While less productive agricultural land has often been managed less intensively and supports our most valued wildlife habitats, freely-draining brown earth soils have almost entirely been used for intensive agriculture (arable and improved grasslands and silage) at the expense of the wildlife habitats characteristic of these soils such as lowland neutral meadows, scrub and lowland oak woodlands.

Soil heath: Soils are under substantial pressure in Devon. Soils become degraded when:

1. They don’t receive enough organic matter (energy and nutrients) to maintain soil functions. In order to maintain soil health all soils need an adequate supply of organic matter, which provides the energy they need to function. This may come from a cover of living plants, crop residues or providing organic matter through manure, compost or other applications of organic materials. Although all organic matter is an energy source, a balance of carbon and other nutrients (such as nitrogen, phosphorous and iron) is necessary to build living biomassThe total quantity or weight of organisms in a given area or volume. and carry out ecosystem functions. For example, straw provides energy but does not provide all the nutrients needed to create a high biomass of decomposer organisms in the soil.

2. They are physically disturbed too much, for example by ploughing or trafficking (vehicles, livestock, people). Soils have largely evolved to function in undisturbed environments and are not adapted to disturbance.

3. They are exposed to potentially toxic elements such as agro-chemicals (such as pesticides, fertilisers and vet medicines) or land contamination.

All three factors lead to soils that are low in biological activity, which causes weak structure, poor nutrient cyclingThe process of nutrients being moved around and reused in the sand by animals and other organisms., limited pest control and poor retention of nutrients and water.

Devon’s wet climate and heavy rainfall interact with poor soil structure, putting soils at greater risk of compaction and soil loss. Devon’s wet and acidic soils are slow to recover from damage as they cannot easily develop a new healthy structure. Soil surveys show that poor soil structure is widespread in agricultural land. Compacted soils can also occur in habitats such as upland moors, heaths and woodlands. Where this is caused by poor management there may be a need to change practices to improve soil structure.

However, there is huge potential to restore degraded soils through nature-friendly farming on all agricultural land or by creating wildlife habitats, particularly on less agriculturally productive land.

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Soil biodiversity and invasive species

The ability of soils to support diverse communities above and below ground is an integral part of good soil health. Soil biodiversity has probably been significantly affected by widespread land use change and changes in agricultural practices over the last century. They may also be affected by invasive species such as Antipodean flatworms and landhoppers. In both cases we have a poor understanding of the impacts of these changes on soil biodiversity because the original state and composition of our soils’ communities was not well studied.

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Monitoring

Soils have in the past been poorly monitored. However, recent initiatives such as the England Ecosystem Survey are helping to establish a baseline understanding of the state of our soils, building on the sparser monitoring carried out by the Countryside Survey. Although there is no citizens’ science network assessing and collating soils data in a similar way to birds and butterflies, this information could be assembled based on land manager and public observations of soil properties and communities.

2. What we need to do and where

Priorities

Better (healthy) soils across Devon as part of wildlife-rich habitats and providing critical wider benefits such as agriculture, water resilience and carbon capture.

Better (wildlife-rich) geological habitats (such as caves, quarries, mines, cliffs and boulders) connected to a network of habitats across the county and benefiting Devon Special Species.

Actions

Geological habitats

Ensure that geological habitats such as caves, quarries, mines, boulders and cliffs are managed for wildlife by reducing recreational impacts, ensuring that any grills over entrances allow bats to pass through and maintaining open rocky habitats through scrub clearance. See Species pages for more information.

Maintain and restore soils by ensuring that they obtain sufficient organic matter and minimizing soil disturbance and impacts from chemicals.

Organic matter (energy and nutrients)

Ensure that soils have a sufficient supply of organic matter. Most wildlife habitats have continuous vegetation cover all year round and receive an adequate supply of energy and nutrients in the right balance to support ecosystem function. However, to ensure that agricultural soils are healthy, they must be fed through cover crops, grass leys, manure, compost or applications of organic materials. These organic materials need to give the soil energy and nutrients, such as nitrogen, phosphorous and iron.

Disturbance

Limit soil disturbance. This includes reducing the frequency and intensity of tillage and reducing traffic on soils. Cultivation, loosening and trafficking land should be avoided when soils are wet (a soil that goes squelch when you step on it is too wet for operations).
Do not cultivate old permanent pastures that have wildlife- and carbon-rich undisturbed soils (waxcap fungi can be a good indicator). Comply with the Environmental Impact Assessment for agriculture. Also see Wildlife-rich grassland and Fungi.
However, some disturbance is needed at the micro scale to provide habitats for species adapted to these conditions, such as patches of bare ground for basking Adders and burrowing bees. These habitats are best created by wild mammals and livestock. Rare arable plants require disturbance to germinate.
While physical disruption of compacted soils can temporarily reduce their density (especially in the short term), it will not provide a long-term fix on its own. To stimulate the biological processes that will repair the soil, it must be carried out in conjunction with increasing plant cover and organic matter and reducing disturbance such as trafficking or further cultivation.

Soil chemistry and hydrology

Avoid widespread use of pesticides and adopt an Integrated Pest Management approach to control problem species. This involves:
- monitoring the problem species (including plants and animals)
- setting tolerance targets
- exploring the use of cultural controls (such as land management, cutting, ploughing, livestock movement regimes and grazing)
- encouraging natural pest enemies such as predatory soil mites (through maintaining healthy soils)
- biological control such as introducing native nematodes to control slugs rather than using slug pellets
- targeted actions such as hand or mechanical weeding or, as a last resort, targeted applications of chemicals.
When restoring or recreating habitats the target habitat should reflect the natural chemistry of the soils. For example, calcareous grasslands on calcareous soils.
Soil chemistry is strongly influenced by the water in the soil. Target habitats should also reflect the natural hydrology of the soil, for example, creating wet mosaics in formerly drained valley bottoms.

Headline actions for broad soil groups

Brown earth soils: Where possible create wildlife habitats such as lowland meadows, scrub and lowland oak woodlands. Re-creation of these habitats can help to solve issues such as soil erosion, water and air pollution as well as helping with carbon sequestrationThe process of capturing and storing carbon. and creating recreational opportunities.

Gley soils: Match land use to the capability of soils with poor drainage. Gley soils are generally not suited to arable crops in Devon. especially in areas of high rainfall. Look for opportunities for land use change to wet acid habitats such as mires, wet heath, Purple moor-grass and rush pasture and wet woodland.

Podzol soils: Manage moors and heaths to avoid and reduce soil erosion along tracks and paths. Manage trees, scrub, bracken and stock to avoid soil compaction. Look for opportunities to expand and create heathland mosaics.

Deep peat soils: Block land drains, ditches and peat cuttings to raise the water table to protect and restore peat soils and bogs, store carbon and help flood control. Trap redeposited peat sedimentSmall pieces of rock, sand, mud, or organic material that settle at the bottom of rivers, lakes, or the sea. in areas where peat hags and gullies cannot be rewetted.

Shallow soils: Manage and create species-rich grasslands, rough grazing and woodlands.

Man-made soils: Protect or restore soils on building sites, especially by soil loosening. Allow mosaics of wildlife habitats to develop.

Invasives

In order to understand the impacts of land use change and invasive species on soil biodiversity we urgently need to study and characterize unaffected sites and compare these with affected sites.

Devon Special Soils

Identify, promote and protect Devon Special Soils (such as Crwbin and Torbay limestone grasslands or Hallsworth and Culm grasslands). Identify local networks where the soils can be easily accessed and understood and promote these through guided Soils Trails as an education resource.

Start to catalogue and evaluate a living database of sites that are good for accessing, viewing and understanding soils and telling their stories (such as formation, human use and wildlife habitats). Use these to help construct Soils Trails and identify and designate Devon’s best soil sites. Communicate Soils Trails using the Explore Devon website.

Monitoring and engagement

Contribute to and support the development of a national system which uses soil measurements from land managers to calculate a soil health metric, to indicate how well a soil is delivering the functions to which it is best suited. This system should provide insight into the current state of soil health and enable the collation of widespread information on the state of soil health in the future. If integrated with land management systems, this could provide a key resource to help us understand the impacts of land use and management change on soil health. It should be possible to calculate a soil health metric based on a small number of land manager-supplied data, or based on detailed national monitoring, to give comparable results.
Measurements supplied by land managers might include:
- simple visual soil assessments
- counting soil organisms such as earthworms
- measuring the percentage of soil organic matter and depth of peat and peaty soils.
- developing a suite of simple kitchen-science soil assessments to explore soil properties more deeply, such as soil aggregate stability, Tullgren funnel extracts of soil fauna or soil infiltrationThe natural passage of rain into the soil where it falls. rates.
Adopt and support emerging efforts and technologies to enable soil biological communities to be identified more quickly. These include supporting genetic bioblitzes, developing AI image recognition for soil fauna, supporting the development and use of identification resources and supporting networks of experts and trainees in recording soil biological data.

Where to focus action

Geological habitats:

High Opportunity Areas and Species Opportunity Areas include:

Bat Sustenance Zone. For example, around roosts in the caves at Beer, Berry Head, Chudleigh and mines near Tavistock and Hay Tor.
Teign Valley gorge spiders
Cliffs and slopes along the Coastal Wildbelts
Dartmoor: tors and clitter fields

Soils

All soils are important and actions are needed across Devon to maintain healthy soils and restore those that have been degraded. A detailed knowledge of soils and their capabilities should inform how we use and manage land and be the building blocks of a Devon Land Use Framework. In the future, a soil health metric (see above) should be used to help target actions and advice.

3. Inspiration

Case studies

Willey Farm

Willey Farm is a mixed farm near Dartmoor with arable cropping on difficult gley soils. Much of the wet land is drained with regular subsoiling. Crops are established by strip tillage and use of cover crops with a long-term aim to improve organic matter, soil structure and soil biodiversity.

Some of the land on the very wet soils with a high water table has been reverted to wetland and pond creation. Other land has recently been planted with longer-term cover crops for wildlife and to improve soil structure.

The farmer is keen to provide soil demonstration sites for education and awareness.

If you’re doing something to help nature thrive, please share it on the Devon Nature Recovery Delivery Map to inspire others to take action.

Where to visit

Always follow the Countryside Code and keep to footpaths and sites that are managed for public access.

The Geology in Devon booklet has lots of examples of where to go to see Devon’s amazing geology, including the Jurassic Coast World Heritage Site.

For more information on visiting other sites that are open to the public please see the Explore Devon website.

4. Find out more

Soils

Low-input farming advice for farmers and growers | Soil Association

The functions of soil biology | AHDB – for guidance on measuring soil biology

A Guide to Soils and Carbon in the Blackdown Hills

LandIS – Land Information System – Soilscapes soil types viewer

UK Soil Observatory – for national maps on soil biodiversity

thinksoils | AHDB – for guidance on assessing soil structure

New web tool for measuring health of soils | UK Centre for Ecology & Hydrology – for benchmarking soil health

CS Soils | UK Centre for Ecology & Hydrology – for access to Countryside Survey soil data

Take part in Waxcap Watch 2025 – Plantlife.

Changing uncultivated, semi-natural and rural land: when you need permission – GOV.UK.

Geology

The Devon County Council geological webpages have a wealth of information on Devon’s geology and links to other sites.

Geology Archives – Explore Devon

Welcome to the Jurassic Coast World Heritage Site

English Riviera Global Geopark – Homepage

Photo credits

Soil – Becky Halterman Robinson
Worm – Alexa Hunt
Soil – Richard Smith
Soil – Richard Smith