The Devon landscape: climate, geology and soils
he landscape of Devon reflects the complexity of interactions between climate, geology, soils and land use Tthat have combined to produce a wide range of plant environments. The diverse flora of the county has adapted to these environments, and continues to change in response to land use pressures and on-going and future climate change. This introduction to the climate, geology and soils of Devon provides an overview of broad edaphic patterns and relationships, thus explaining the essential controls on the diversity of flora that can be observed throughout the county.
Climate The climate of Devon varies widely from the low-lying coastal zones exposed to mild, maritime influences to the harsher upland environments of Dartmoor and Exmoor. The combination of altitude, exposure and distance from the ameliorating influences of the sea produces markedly contrasting climatic environments. This section gives a brief summary of key elements of the climate of Devon. For more detailed information, see Meteorological Office (2012).
Rainfall The topography of Devon exerts a strong influence on the distribution of rainfall. Figure 1 shows the mean annual average rainfall, recorded over the period 1981– 2010. The two elevated areas of moorland, Dartmoor and Exmoor, receive the highest annual rainfall total. Parts of northern Dartmoor lie 600 m above sea level
Figure 1. Annual average rainfall 1981–2010 (Crown Copyright, reproduced courtesy of Met Office, National Climate Information Centre).
A New Flora of Devon 11 The Devon landscape: climate, geology and soils
(asl), with the highest summits of High Willhays and Yes Tor reaching 620 m Annual rainfall on the northern slopes of Dartmoor ranges from 2,000–2,600 mm per annum (p.a.). The southern zone of Dartmoor attains somewhat lower altitudes, typically 400–500 m asl, resulting in annual rainfall totals in the range 1,800–2,200 mm. Exmoor rises to 520 m, with an annual average rainfall of just over 2,000 mm.
Annual rainfall declines rapidly as altitude declines, with gradients being most marked on the more sheltered, east facing slopes which lie in the rain shadow of these two moorland massifs. In consequence, rainfall falls to a minimum in the Exeter area, with the lowest 30 year annual mean of 760 mm occurring just east of Exeter. Within a distance of 40 km the annual rainfall falls to around 30% of the total on the highest slopes of Dartmoor. This marked rainfall gradient exerts a strong influence on local soil hydrology and edaphic conditions.
The pattern of rainfall varies throughout the year, with the months of May, June and July being consistently the driest, and November, December and January, when the sea is relatively warm and the Atlantic depressions most vigorous, being the wettest (Meteorological Office 2012). For example, the long term monthly average for Plymouth ranges from 45 mm in July to 125 mm in January.
Temperature Air temperatures in Devon are primarily controlled by solar radiation, modified by the land reflectivity (albedo), altitude and the influence of the sea. Devon lies at a latitude of 50 –51 ºN, which in combination with the maritime influence yields a long term average annual air temperature ranging from 7–9 ºC on Dartmoor and Exmoor to 11–12 ºC on the coastal fringes of the county (see Figure 2). Due to the northerly latitude, mean air temperatures tend to reach a maximum in the months of July and August, and a minimum in the months of January and February. For example, average air temperature at Teignmouth on the English Channel coast
Figure 2. Mean annual average air temperature 1981–2010 (Crown Copyright, reproduced courtesy of Met Office, National Climate Information Centre).
12 A New Flora of Devon The Devon landscape: climate, geology and soils
ranges from 6.4 ºC in January to 17.1 ºC in July. Princetown, situated in central Dartmoor at an elevation of 400 m asl is much cooler, with January and July average air temperatures of 3.4 ºC and 14.3 ºC respectively (Meteorological Office 2012).
Altitude and exposure also influence the number of frost-free days, another important factor that influences the distribution of more sensitive plants. In general the coastal zones are less frost prone, with the South Devon coast being particularly mild in that respect. On average, Teignmouth experiences 15 air frosts per year, while Princetown experiences 45 (Meteorological Office 2012). The north coast around Barnstaple also experiences earlier springs than other parts of Devon, due to the influence of the Gulf Stream. Local variations in the distribution of frosts will be controlled by aspect and topography, with lower lying, north facing valley bottoms being more vulnerable to damaging frosts.
Exposure Devon has coastlines that face south into the English Channel and north into the Bristol Channel and the Western Approaches. The prevailing westerly winds bring not only rain but also high winds and a significant salt burden, particularly during periods of prolonged cyclonic activity. Exposure to these influences can exert a strong influence on edaphic conditions. Marked local variations in microclimate can occur, dependent on aspect and exposure. For example, the cliffs and coastal fringes of the South Hams between Plymouth and Start Point are often exposed to salt-laden desiccating winds.
Plant water availability The regional climate exerts a controlling influence on plant water supply. The balance between rainfall input and evapotranspiration, driven by solar radiation and temperature, controls the amount of water available to be stored in soil for plants to transpire. Typically evapotranspiration rates exceed rainfall inputs in lowland Devon during the period April –September, which can lead to periods of water stress on the less water retentive loamy and sandy soils. Examples include the heathlands of East Devon and the Bovey Basin. This complex interplay of climate and soils further complicates the distribution of natural and semi-natural plants.
Solid and Superficial Geology The landscape and diverse plant communities of Devon are underlain by a complex pattern of rocks of varying ages and characteristics. The interaction between these geological materials and the climate has produced an equally varied range of soil materials that support the diverse flora of the county. The wide age range of the rocks, and their contrasting resistance to erosion, have dominated the landforms in the county. This section will describe the characteristics and age of key geological materials that outcrop in the county, and indicate their significance in controlling soil and landscape development. By convention, the solid or bedrock geology of an area is described in age sequence with oldest first, followed by successively younger rocks, and then finally the overlying superficial deposits which while more spatially variable, can be particularly significant in explaining contrasts in local soils and habitats. This chapter draws on the geological summary given in Ivimey-Cook (1984), and both have used Durrance and Laming’s (1982) detailed description of the geology of Devon, including a description of geological timescales. For a less detailed but nonetheless informative overview of Devon’s geology the reader is referred to Hesketh (2006). Detailed geological information at a range of scales of can be obtained from the British Geological Survey publications (BGS 2012).
Many of the major rock types are found in Devon, in a geological record that extends over 400 million years. While this represents less than one-tenth of the age of the Earth (4,500 my), a considerable diversity of rock types outcrop in the county. The three-fold classification of rocks is based on their genesis or mode of formation; igneous rocks such as granite and basalt are formed from molten liquids; sedimentary rocks such as sandstone and limestone are formed from accumulations of materials at the Earth’s surface and metamorphic rocks such as slate and marble are formed by changes in state of a former rock in the solid phase, due to elevated temperature or pressure, without becoming molten again. Examples of all these rocks are found in Devon.
A New Flora of Devon 13 The Devon landscape: climate, geology and soils
Figure 3. Simplified surface geology of Devon (redrawn from British Geological Survey data). Both solid and superficial geology are shown, to illustrate the dominant soil parent materials.
14 A New Flora of Devon The Devon landscape: climate, geology and soils
Geological materials can be dated by a range of techniques some of which are very sophisticated and rely on precise chemical analysis. Absolute dating is achieved using measurements of radioactive decay rates in selected minerals. Relative dating can be carried out using fossil evidence and relative position in the geological column. This combination of techniques allows geologists to construct a detailed picture of the geological evolution of an area, and can help to explain patterns of soil development and landscape evolution. The main periods represented in Devon’s geological record are the Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Tertiary and Quaternary. Key features of these rocks are described here, and presented in Figure 3.
Devonian The oldest rocks in the county date from the Devonian period, approximately 350–410 million years ago (mya), when much of central and northern Britain was part of a large continental land mass. A variety of rocks of Devonian age occur in Devon, and were first mapped and placed in stratigraphical context here, such that the county has given its name to this geological period. The oldest rocks in Devon are probably the green schists and mica schists (metamorphic rocks) that outcrop on the South Devon coastline between Start Point and Bolt Tail (Durrance and Laming 1982).
The Devonian rocks in North Devon, including Dartmoor, are made up of mudstones, shales, sandstones and occasional limestones, all deposited in shallow water. These rocks are often iron rich, indicative of deposition of the hot arid conditions prevailing in the sediment source areas to the north. The extensive sandstones that occur across the Exmoor plateau are typical of this period.
In South and East Devon, shallow water conditions dominated the Lower Devonian. During the Middle and Upper Devonian the seas became deeper, leading to the deposition of siltstones and mudstones. Locally, sheltered waters persisted, resulting in the formation of limestones such as those that outcrop in and around Plymouth, and these have been exploited extensively for building purposes. These rocks contain interbedded ash and basalt lavas, indicating that volcanic activity was occurring at this time. Some of these rocks have been subsequently metamorphosed during periods of mountain building, for example changing the mudstones into slate, known locally as shillet. Soils derived from these mudstones and slates extend across much of south Devon (see Figure 4), and tend to be of moderate fertility depending on local hydrological conditions.
Carboniferous The marine conditions that pervaded in the Devonian continued into the Carboniferous Period, leading to the deposition of an extensive range of sandstones, shales and mudstones. This period extended from approximately 350 to 290 mya. The occurrence of basalts, tuffs (formed from volcanic ash) and dolerites indicate that volcanic activity was widespread during this time. Shales, other argillaceous sediments and sandstones of Carboniferous age are widely distributed across mid-Devon, north of Dartmoor (Figure 3) and are known throughout Devon and north east Cornwall as the Culm Measures (Findlay et al. 1984). Where the Culm Measures outcrop, they give rise to clayey and silty, poorly structured soils with impeded drainage. If unimproved (that is of low nutrient status and not drained) these soils support nationally significant species- rich grasslands (Goodwin et al. 1998).
The end of the Carboniferous was marked by an extensive period of mountain building associated with the Variscan (or Hercynian) Orogeny. Many of the sediments deposited during the Devonian and Carboniferous were folded and faulted. The Crackington Formation on the North Devon coast near Hartland Point offers a classic exposure of these deformed interbedded sandstones and shales. At the same time the Devonian sediments of the South Hams were also metamorphosed, producing the more resistant, mica schists of the Start Point and Bolt Head complex. Today these rocks support a range of shallow soils with characteristic coastal plant communities.
The final stages of the Variscan Orogeny were marked by the intrusion of a large mass of granitic magma (290 mya) in the form of a subterranean batholith which now extends beneath much of Devon and Cornwall. As the molten magma cooled slowly from initial temperatures up to 1,000 ºC large crystals of feldspar, mica and
A New Flora of Devon 15 The Devon landscape: climate, geology and soils
Figure 4. Simplified soil map of Devon, based on the 1:250,000 National Soil Map. The map shows the distribution of ‘soilscapes’ which combine the detailed subdivisions of various soils into soil-landscape units.
16 A New Flora of Devon The Devon landscape: climate, geology and soils
quartz formed to give the characteristic coarse grained appearance of granite that we see today. However, the exposure of the granite from its original location as an intrusion in the heart of the Variscan mountains only occurred after erosion of the overlying sediments, several millions years into the Permian. Linked with the intrusion of the granite and the subsequent crustal disturbance was the thermal metamorphism and extensive mineralisation of the surrounding ‘country’ rocks. Hydrothermal fluids at temperatures of 200–600 ºC deposited a range of minerals including tourmaline and metal ores of tin, lead, copper and zinc. Limited mineralisation also took place in the Devonian and Carboniferous sediments that underlie Exmoor. Subsequent alteration of the granite itself also occurred, leading to the formation of china clay deposits, for example at Lee Moor on the southwest fringes of Dartmoor.
The significance of this late-Carboniferous geological activity to the evolution of the landscape of Devon cannot be overstated. The distinctive lithology of the granite, with few joints and a lack of alkaline mineral components has led to the development of the characteristic moorland landscape of tors, with acid, coarse textured, mineral poor soils and extensive peat deposits in the broad, elevated basins that can be seen across Dartmoor.
Permian and Triassic Following the geological disturbance and uplift associated with the Variscan Orogeny, the climate became semi-arid and sub-tropical. In these desert-like conditions thick sequences of iron-stained sandstones, conglomerates and breccias (coarse angular sediments) were deposited by periodic flash floods. Sharp unconformities can be seen where these sediments lie on older Devonian and Carboniferous rocks. Prominent exposures of these Permian sediments can be seen along the East Devon cliffs between Exmouth and Sidmouth. This so-called ‘New Red Sandstone’ period continued into the Triassic (250–200 mya) with a similar series of rocks, although tending to become finer in texture, as witnessed by the mudstones beds in East Devon. Invariably these rocks led to the formation of freely drained soils, often supporting heathland habitats such as Woodbury and Aylesbeare commons (see Fig. 4).
Jurassic and Cretaceous The extended period of continental conditions came to an end with a marine incursion at the beginning of the Jurassic period (200 mya). The Jurassic and Cretaceous periods were marked by gradual sea floor subsidence to allow the accumulation of a succession of sandstones, limestones and argillaceous rocks which again can be seen in section in the cliffs of East Devon (see Fig. 3). Lower Jurassic rocks (the Lias) notably consist of fossiliferous blue clays. Sedimentation continued in the sub-tropical shallow marine environment in the Cretaceous with glauconitic greensands, marls and ultimately chalk being deposited. These contrasting lithologies have led to a range of mostly freely drained soils in East Devon. Inland the more indurated greensand outcrops over the Blackdowns and Haldon Hill, allowing the development of considerable areas of heathland. The chalk soils in particular tend to support a calcicole flora, with the exception of the less freely draining acid/neutral clay-with-flint caps on the summits of chalk hills.
Paleogene and Neogene The Cretaceous/Paleogene boundary is marked by another period of crustal disturbance. Uplift caused the sea to retreat. The granite mass of Lundy was intruded in the mid-Paleogene. Aerial weathering and erosion removed much of the Jurassic and Cretaceous sediments, leaving residual flint deposits on Haldon Hill and to the east of Exeter. Faulting affected the eastern edge of the Dartmoor granite, leading to the formation of the Bovey Basin, where many thousands of metres of clays, sands and lignites have accumulated. Local subsidence on the NW–SE trending Sticklepath Fault north of Okehampton has allowed a small basin to collect similar sediments at Petrockstow. The Alpine Orogeny continued into the Neogene (20 –10 mya), further elevating the land surface and allowing the incision of major river networks.
Quaternary and Recent deposits The last two million years of geological history have been characterised by wide variations in climate which have left an indelible mark on the soils and landscape of Devon. For the most part the climate has been temperate, but influenced by the periodic glacial advances occurring across northern and central Britain. Evans
A New Flora of Devon 17 The Devon landscape: climate, geology and soils
et al. (2012) recently proposed that the higher parts of Dartmoor above 350 m sustained a small ice-cap during the Pleistocene, leaving some relic features such as moraine ridges and over-deepened valleys. The majority of Devon escaped the direct influence of glacial activity, but extensive periods of periglaciation occurred, resulting in periodic freezing and thawing of soils and loosely consolidated surface sediments. Downslope movement of these materials has led to extensive deposits of mixed solifluction deposits, known by the general term of ‘head’. Lithologically the character of head is closely related to the surrounding rocks, but will typically be composed of clays, sands and gravels, often in distinct layers which tend to be thicker towards the base of slopes. Movement of these materials is thought to be caused by instability following temporary summer thawing of frozen slope deposits. Locally these deposits are important in creating soils and habitats that can support distinctive flora, such as on the Start Point/East Prawle coastline of the South Hams, an area designated as an SSSI in part due to the Quaternary raised beach and head deposits. The formation of characteristic granite tors on Dartmoor is largely a product of this period of active weathering and slope movement.
Other ‘superficial’ deposits of significance shown on Figure 3 include river alluvium following the main river arteries, such as the Exe, Taw, Torridge, Dart and Tamar, and the blown sand deposits at the mouth of the Taw/Torridge Estuary. These soft recent deposits add significantly to the local soil and habitat variability.
Soils, plants and land use The geology and climate of Devon combine to produce a range of complex soils that support the varied plant communities seen throughout the county. Key soil types and characteristics are summarised in Figure 4, the soilscapes of Devon, and are described in detail by Findlay et al. (1984). The soilscapes distinguish patterns and characteristics based on soil texture (sandy, loamy, clayey or peaty), drainage status (wet, slowly permeable, impeded or freely draining) and chemistry (acid, neutral, lime-rich). These groupings of soils are particularly useful to understand the interaction between soils and flora. More recently, Harrod (2011) described the development of our understanding of the distribution of soil types throughout the county, and has summarised the contribution that soils have made to Devon’s biodiversity.
Soils provide not only a growing medium for plants and crops, but are also an integral part of a complex and active ecosystem. Soils act as a habitat to support a wide range and variety of micro- and macro-organisms that drive natural nutrient and carbon cycling processes. Today it is recognized that soils contribute to many key ‘ecosystem’ functions in addition to habitat support. These include flood regulation, maintenance of water quality and carbon sequestration (UK National Ecosystem Assessment 2011).
Soil development The interaction between climate and geology dominates the processes of soil formation. Local topography, vegetation and soil biota modify natural soil characteristics, and then human influences, particularly agricultural activity, have induced further changes to soil conditions.
The development of mature soil takes many thousands of years, over which time climate may change. Although Devon did not experience direct impact of glacial activity, the analysis of pollen records and other environmental data indicates that the climate of Devon was considerably cooler 20,000 years ago, with periglacial conditions leading to the formation of extensive head deposits. More recently the climate has fluctuated; for example a cooler, wetter period towards the end of the Bronze Age (2500–3000 years before present) led to the more extensive development of peats and other poorly drained soils reflecting the wetter hydrological conditions (Charman 2002). In the 11 th and 12 th centuries AD the climate was on average 1 –2 ºC warmer than today, which led to improvements in soil conditions. As a result, many moorland fringe soils were ‘improved’ by cultivation and manuring at that time.
As noted previously, topography varies widely across the county of Devon, which not only influences the climate, but also exerts a strong influence on soil formation and the development of plant communities. The primary influence is on soil hydrology, the zones of water storage and patterns of water movement. Local
18 A New Flora of Devon The Devon landscape: climate, geology and soils
ground slope controls water and nutrient runoff, leading to well drained, more acid soils being found in the steeper, mid-slope positions, with valley floor soils tending to be waterlogged if not artificially drained. Table 1 displays the key soilscapes of Devon, grouped according to key hydrological classes, with additional parent material, topography and habitat information. There are a diverse range of soilscapes, which have in turn led to the wide range and variety of habitats across the county.
Freely draining soils The dominant soils in Devon are the freely draining slightly acid loamy brown earth soils that occur extensively in the South Hams as well as in North Devon; these soils occur just under half (40%) of the total land area, and are used primarily to support arable and more intensive grassland production. Fig. 5 shows a profile of a typical Denbigh Association soil, which is a member of this soilscape. This soil, derived from Devonian slate, supports a range of neutral and slightly acid pastures, as well as some more intensively managed arable crops, notably cereals. The natural fertility of these soils tends to be low, but agricultural improvement by use of lime, manure and fertilizer has in many cases raised the fertility, and usually limits the botanical interest.
On the steeper slopes of Dartmoor and Exmoor these loamy soils become shallower and more acid, allowing the development of dry heath communities, often supporting a range of heath species such as Heather Calluna vulgaris , Bell Heather Erica cinerea and Cross-leaved Heath Erica tetralix , as well as Bilberry Vaccinium myrtillus and Western Gorse Ulex gallii . The soils tend to show more differentiated, podsolic profile characteristics, often with an iron pan, as is shown in Fig. 6. This Hexworthy Association soil, from the freely draining acid loamy soilscape on Dartmoor is derived from granite and is usually common grazing for cattle, sheep and ponies.
Figure 5. Denbigh Association brown earth soil type, from the freely draining slightly acid loamy soilscape (SX542612). This soil, derived from Devonian slaty mudstone and siltstone is found widely throughout the South Hams, and supports a range of neutral and slightly acid pastures, as well as some more intensively managed arable crops, notably cereals.
A New Flora of Devon 19 The Devon landscape: climate, geology and soils . s
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20 A New Flora of Devon The Devon landscape: climate, geology and soils
Soils with impeded drainage Occupying a quarter of the landscape of Devon, soils with impeded drainage occur in a range of locations, but predominantly in topographical positions that encourage the accumulation of water within the profile, enhanced by slowly permeable subsoil geology. Featuring prominently throughout North Devon are the slowly permeable seasonally wet acid or slightly acid soils of the Culm Measures. These Rhôs pastures include nationally important areas of Purple Moor-grass Molinia caerulea dominated mires, rush-pastures and wet heath communities. Agricultural improvement through the use of pipe- drainage systems and artificial fertilizers, particularly phosphate-based, has resulted in the loss of much of this formerly more extensive landscape (Goodwin et al. 1998). Without such improvement, orchids, including Heath Spotted-orchid Dactylorhiza maculata subsp. ericetorum and Lesser Butterfly- Orchid Platanthera bifolia , persist in fen-meadow communities with Meadow Thistle Cirsium dissectum , Saw-wort Serratula tinctoria and Sneezewort Achillea ptarmica . Whorled Caraway Carum verticillatum , the nationally scarce Wavy St John's-wort Hypericum undulatum and Petty Whin Genista anglica , near threatened on the British Red List, are almost entirely restricted to these soils in Devon. On marginally better drained soils, Devil's-bit Scabious Succisa pratensis , the larval food-plant of the Marsh Fritillary butterfly, may be locally common.
Naturally wet soils Although rather more limited in area (just 7% of Devon), the naturally wet soils of the county support some ecologically very significant habitats. On the high moor, the Blanket bog peat soils lie naturally wet due to the high rainfall (in excess of 2000 mm per year), low temperatures (and hence reduced evapotranspiration rates) and acidic, nutrient poor granite parent material. Although much altered by human interference, notably peat cutting, these soils
Figure 6. Hexworthy Association soil, from the freely draining acid loamy soilscape on Dartmoor (SX579683). Derived from granite, this soil supports a range of moorland grass, heather and bilberry dominated plant communities, often grazed by cattle, sheep and ponies, as can be seen across much of Dartmoor.
A New Flora of Devon 21 The Devon landscape: climate, geology and soils
support a range of plants adapted to oligotrophic conditions (Charman 2002). Sphagnum mosses enhance the water retention, allowing adapted plants such as Common Cottongrass Eriophorum angustifolium , Bog Asphodel Narthecium ossifragum and Round-leaved Sundew Drosera rotundifolia to grow.
Soils developed in lower lying areas, are naturally wet due to groundwater being present within the soil profile for much of the year. Fig. 7 illustrates an example of naturally wet soil, a member of the Ivybridge Association, from the loamy soils with naturally high groundwater soilscape (SX603600). Derived from Devonian slaty mudstone and siltstone, this soil underlies wet acid meadows and mixed deciduous woodland in the Cornwood and Lee Moor area to the north east of Plymouth. Being naturally wet and of low fertility, typical habitats include woodlands and acid meadows. The woodlands tend to be dominated by Oak Quercus spp., Birch Betula spp. and Alder Alnus glutinosa , with an abundant herb layer, often supporting Bluebells Hyacinthoides nonscripta and Wood Anemone Anemone nemorosa .
Highlighted in blue in Fig.4, the major river corridors, for example the Exe and Culm in East Devon, stand out as important landscape zones underlain by naturally wet, heavily gleyed soils. Grasslands with Crested Dog’s-tail Cynosurus cristatus, Red Fescue Festuca rubra and Yorkshire Holcus lanatus dominate, with Meadow Buttercup Ranunculus acris , Common Sorrel Rumex acetosa and Autumn Hawkbit Scorzoneroides autumnalis with Marsh Marigold Caltha palustris and Cuckooflower Cardamine pratense and Water Forget-me-not Myosotis scorpioides in wetter areas. River bank trees will include Willows Salix spp. and, very rarely, Black Poplar Populus nigra subsp. betulifolia .
Figure 7. Ivybridge Association soil, from the loamy soils with naturally high groundwater soilscape (SX603600). Derived from Devonian slaty mudstone and siltstone, this soil underlies wet acid meadows and mixed deciduous woodland in the Cornwood and Lee Moor area to the north east of Plymouth.
22 A New Flora of Devon The Devon landscape: climate, geology and soils
Natural Character Areas As can be seen from this brief description of the climate, geology and soils of the county, Devon has a wide range of landscapes reflecting the combined influence of these physical factors, on which human influences have been imprinted, notably through agricultural activity and development of urban areas. Natural England have classified ‘Natural Character Areas’ that reflect dominant landforms, soils and geological associations (Natural England 2013). Further, the dominant features that define the landscape of each area have been recorded, together with an explanation of the contrasts between areas, and a description of the character development. The key natural character areas of Devon include: Dartmoor Exmoor, the Devon Redlands, the Culm, the Blackdowns, South Devon and Lundy. Each character area description includes not only aspects of the development of the physical environment, but also extensive detail of the land use and landscape designations, as well an assessment of key habitats and biodiversity. Hence these character assessments are an important source of reference for those seeking a more detailed description of selected localities in Devon.
Rob Parkinson & Tim Farewell
A New Flora of Devon 23