Wealth of Wildlife - Plants of the Dunes

Hundreds of plants and animals, rarely found elsewhere in a county dominated by acidic, granite rock, thrive on Cornwall's sand dune systems.

The varied history of Cornwall's sand dunes has helped characterise the habitats and landscape we know today. Agriculture, sand extraction, tourism, mining and industrial activity on the dunes have had a huge impact on the habitats and landscape. Sand dunes are quick to adapt. For example, the National Explosives Factory on Upton Towans near Hayle ceased to operate just after the end of the First World War, and now the area supports a wealth of dune wildlife.  

Sand dunes develop when deep-rooting marram grass traps the windblown seashell sand, rich in calcium. In the shifting sands of the smaller and more mobile dunes backing the beach, specialist plants such as sea holly and sea spurge grow in the most extreme conditions. Further inland, more plants are able to colonise the sandy soil to create flower-rich dune grassland.

Plants that grow on the shell sand need to be able to tolerate the alkaline, calcareous soil. Consequently, many of the plants on the dunes are only found on this habitat and are rare in the rest of the county and Britain.

The gradual change from bare sand at the back of the beach to flower-rich dune grassland as you move inland and eventually scrub and woodland on a large sand dune system is known as natural succession. The youngest dunes are at the back of the beach and the oldest dunes, furthest inland. The dunes are effectively growing out to sea. However, they can only grow so far, because the sea will 'chop' off the front of the dunes.

With natural succession, the number and types of plants change as you move inland and the chemical and physical nature of the soil alters.  The number of different plant species generally increases as conditions become less harsh.
As you move inland the ground becomes:

  • Less salty (saline) as the influence of the sea air is reduced;
  • Damper as the increased numbers of plants and organic matter hold more water;
  • The amount of humus or organic matter increases;
  • The pH of the soil becomes more acidic due to increased humus and leaching by rainwater of calcium carbonate in the sandy soil and;
  • The area of exposed sand decreases and conversely, plant cover increases.

Typical sand dune succession is shown below. Variations to this model may occur due to the height of sand over-lying the rock base; historical alterations to the sand dunes by people; coastal squeeze with erosion on the seaward side and developments, golf courses or agriculture on the landward side.

BTCV 1991 The Field Studies Council produce an excellent Key to Plants Common on Sand Dunes. The field guide is a full colour, fold out, laminated pamphlet which can be used for plant identification on the sand dunes of Britain.

Factfile

  • The young dunes immediately behind the beach move inland at up to 7 metres/year depending on the local conditions.
  • An individual dune can take up to 50 years to reach it's maximum height.

Sand dunes are important largely due to the highly variable conditions within the dunes, forming a complex mosaic of habitats including the following:

  • Strandlines;
  • Embryo dunes;
  • Mobile foredunes;
  • Semi-fixed dunes;
  • Fixed dunes;
  • Calcareous grassland;
  • Dune slacks;
  • Scrub and;
  • Woodland.

Within each area of habitat there will be further subtle variations in conditions which increase the structural diversity allowing a higher number of plants and animals to flourish. Factors which can increase structural diversity include:

  • Grazing pressure;
  • Aspect (angle to the sun);
  • Human pressure;
  • Shelter from the wind;
  • Proximity to the water table and;
  • Soil conditions.

On many of the smaller Cornish dune systems, the whole range of dune habitats may not be present. On the smallest dunes such as Poldhu, Church Cove and Pendower, there may only be the mobile and semi-fixed dune habitats present.  The larger dunes such as the Towans and Penhale have the whole complement of dune habitats.

The strandline and embryo dunes are very bare, with just a few pioneer plants with special adaptations allowing them to grow in salty, dry, moving sand. These mostly annual plants will come and go from year to year and over the seasons and the young dunes continuously change shape. The habitat is very transient and vulnerable to human disturbance because the plants are only just clinging onto the sand.  Typical Cornish strandline/embryo dune plants include Sandwort, Rocket, Beet and Scentless Mayweed.

After the pioneer plants of the embryo dunes have started trapping more sand, a few other plant species are able to grow. One of the most important and common dune building plants is Marram Grass. The tall Marram leaves slow the wind- carrying sand and the network of deep roots bind the sand together

The mobile dunes are, as the name suggests, always moving around and changing shape. There is usually quite a lot of bare sand exposed and the wind can easily blow it around. The mobile dunes are very dynamic and typical Cornish examples include Marram Grass, Red Fescue, Sand Sedge, Sow Thistles, Traveller's Joy, Hawkbit, Sea Bindweed, Sea Holly, Sand Couch and Sea Spurge.
As the Marram Grass traps yet more sand and the soil conditions start to change lots more different plants can grow and the habitat looks more like a grassland, rather than a beach with a few plants growing. As the name suggests this habitat is still fairly mobile and there is still a lot of movement of sand, but the soil will have slightly more organic matter in it and may be slightly less alkali. There is still a lot of Marram Grass in this habitat.  Typical examples of Cornish semi-fixed dune plants include Marram Grass, Red Fescue Grass, Sand Sedge, Viper's Bugloss, Pyramidal Orchid, Wild Carrot, Sea Bindweed, Black Medick and Evening Primrose.

The fixed grey dunes are the richest in plant species as conditions are less harsh further inland. From a distance, the dunes appear grey due to the abundance of mosses and lichens, but close-up there is a mass of different flowers creating a colourful, flower-rich grassland, especially in May, June and July. The sand is fixed by the vegetation and the habitat receives little wind blown sand. Typical examples include Red Fescue Grass, Mosses and Lichens, Common Centuary, Carline Thistle, Kidney Vetch, Dove's Foot Cranesbill, Common Storksbill, Wild Thyme, Lady's Bedstraw, Hawkweed, Birds Foot Trefoil, Eyebrights, Cowslip, Stinking Iris etc.

 
Stinking Iris

Rabbit or livestock grazing creates a closely cropped, short grass sward, often in sheltered hollows whilst taller grasses and flowers thrive elsewhere. Marram is more scarce as shallow-rooting plants dominate, rapidly soaking up available rainfall.


Flower-rich dune grassland

Dune slacks form when the wind scours the sand until it reaches the water table,. These are wet or damp habitats and may be permanent ponds. More often they are only wet for the winter when rain is heaviest and the water table highest.

Plants which thrive in wetter conditions can be found here and are often very different from the surrounding dunes.

Dune slacks are mostly found on the larger dune systems. The best examples are found at Penhale Sands and include Silverweed, Creeping Willow, Adder's Tongue, Yellow Bartsia, Fleabane, Meadowsweet, Water Mint, Field Horsetail, Souther Marsh Orchid and Stonewarts.

Areas of isolated scrub are an important feature on sand dunes as rabbit warrens and shelter for birds, invertebrates and reptiles. However the frequency and extent of scrub needs to be carefully monitored and controlled.  Typical Cornish dune scrub plants include Hawthorne Bramble, Ivy Elder, Blackthorne Wild Privet and European Gorse.

Woodland is absent from most of Cornwall's dunes. It would normally be found on the landward section of the dunes, as the climax community of natural succession. In many places, dune woodland is unable to form due to developments or agriculture. Some small woods have been planted by people, with trees such as sycamore. Grey willow tends to be the dominant dune woodland species in Cornwall.  Typical woodland plants include Ivy, Grey Willow, Bramble, Sycamore and Ash.

Factfile

  • In the mobile sand dunes, immediately behind the beach only about 7 different plant species may be found.
  • In the fixed dune grassland at the inland area of the larger dune systems there may be as many as 75 different plant species.
  • About 300 different plant species can be found Cornwall's sand dunes - this represents one-fifth of all the plant species that can be found in Cornwall.
  • Calciphiles are calcium-loving plants.

Some of the many hundreds of plants found on sand dunes are very rare, both in Cornwall and Britain. For example a so-called, Red Data Book plant, may only be found in less than 15 places in the whole of Britain, so they are extremely vulnerable. Many have become rare in the last 50 years because of habitat loss or reduction in habitat quality due to:

  • Tourism developments, sand extraction and agriculture;
  • Human pressures through recreation and tourism;
  • Pollution of the water or air, from nearby agriculture or industry and;
  • Lack of management or grazing.
  • Autumn lady's tresses orchid
  • Autumn squill
  • Babington's leek
  • Balm-leaved figwort
  • Brackish water buttercup
  • Bulbous meadow grass
  • Dense silky-bent
  • Dune fescue
  • Early gentian
  • Galingale
  • Hairy-fruited cornsalad
  • Italian lords and ladies
  • Ivy broomrape
  • Least soft-brome
  • Sea radish
  • Fringed rupturewort 
  • Early meadow grass
  • Mountain st john's wort
  • Petalwort
  • Portland spurge
  • Slender spike rush
  • Scrambled egg lichen
  • Sharp rush
  • Shore dock
  • Subterranean clover
  • Tree mallow
  • Twiggy mullein
  • Variegated horsetail
  • Wild leek
  • Western clover
  • Yellow bartsia
  • Marsh helleborine


Early Gentian  

Probably the most important plant which assists in the formation of sand dunes is Marram Grass or Ammophila arenaria. Marram is specifically suited to growth in sandy conditions because it is:

  • Xerophytic or drought tolerant;
  • Halophytic or salt tolerant;
  • Capable of growing very deep roots , called rhizomes, in search of water;
  • Able of growing when sand blows onto it and thrives in these conditions and;
  • Has leaves which curl up during hot and dry weather to reduce water loss (transpiration) and have a corrugated surface on the inside.

These specialist adaptations allow Marram to thrive in extreme conditions where it can be found almost to the exclusion of all other plants. The Marram root network is vital in helping to trap the sand, allowing other plants to colonise.


Marram grass

Factfile

  • Scientific studies have demonstrated that Marram Grass can die if repeatedly walked over 10 times.
  • Marram roots can grow up to 7cm in 10 days.
  • Marram can survive when buried by 1 metre of sand/year.

Other adaptations for life on the seaside desert shown by Orache, Sea Holly, Sea Sandwort and Sea Rocket include: