Plant Succession :Psammoseres The Physical Core Biosphere

Important Plants are the key to the formation and character of sand dunes. If there were no plants and no plant colonisation, there would be no sand dunes. Plants are the key to the formation and character of sand dunes. If there were no plants and no plant colonisation, there would be no sand dunes. For pioneer plants however there are several obstacles to overcome

Obstacles for pioneer species Strong stormy high tides and the use of beaches by people can destroy plants and dunes. Strong stormy high tides and the use of beaches by people can destroy plants and dunes. Sand is a sterile environment often lacking humus and nutrients. Sand is a sterile environment often lacking humus and nutrients. Sand can be very dry due to the rapid drainage. Drought resistant plants are classified as xerophytic. Sand can be very dry due to the rapid drainage. Drought resistant plants are classified as xerophytic. Shelly fragments often create an alkaline environment. Shelly fragments often create an alkaline environment.

Model Sand Dune

Embryo, fore and mobile dunes Plants that occupy this area of a sand dune have to be xerophytic. Plants that occupy this area of a sand dune have to be xerophytic. They also have to have particular growth features. They also have to have particular growth features. Be resistant to salt water during spring tides Have foliage to trap the sand, causing it to drift over them. As they grow vertically and laterally, they bind the sand and build up embryo and foredunes. Sea rocket, sea lyme and couch grass

Sea rocket Couch grass Sea lyme

Yellow Dune Once the tops of dunes have grown well above the highest tide level, marram grass is able to colonise. Once the tops of dunes have grown well above the highest tide level, marram grass is able to colonise. This is the main pioneering plant. This is the main pioneering plant. Thanks to rhyzomes (long creeping underground roots) spreading vertically and laterally, the marram very effectively grows with fresh deposits of sand. Thanks to rhyzomes (long creeping underground roots) spreading vertically and laterally, the marram very effectively grows with fresh deposits of sand.

Marram Grass

Grey dunes On the landward more sheltered side of dunes more plant species establish themselves. On the landward more sheltered side of dunes more plant species establish themselves. Such fixed dunes are called grey dunes because of the increased humus content of the soil and the surface growth of lichens. Such fixed dunes are called grey dunes because of the increased humus content of the soil and the surface growth of lichens. As the distance from the shore increases, sand no longer accumulates and marram grass cannot compete with new colonising plants. As the distance from the shore increases, sand no longer accumulates and marram grass cannot compete with new colonising plants. Sand sedge, buttercups & dandelions.

Sand sedge buttercups dandelions

Older grey dunes Further inland, the older grey dunes support bushes such as sea blackthorn but more ‘ordinary’ plants are also present – gorse, broom, heather. Further inland, the older grey dunes support bushes such as sea blackthorn but more ‘ordinary’ plants are also present – gorse, broom, heather. One factor is that the soil is now more acidic. Any lime from the shells has been leached (washed out) and the amount of humus is now greater. One factor is that the soil is now more acidic. Any lime from the shells has been leached (washed out) and the amount of humus is now greater.

broom heather

Dune Slacks Other ‘ordinary’ species occupy the dune slacks. These damp, low lying hollows have a higher water table, especially in winter. Other ‘ordinary’ species occupy the dune slacks. These damp, low lying hollows have a higher water table, especially in winter. Hydrophytic (water tolerant) vegetation thrives: rushes, willows and alders are found here. Hydrophytic (water tolerant) vegetation thrives: rushes, willows and alders are found here.