Sand dunes Flashcards
(31 cards)
How does an embryo dune form?
Plants growing at the back of the beach cause the wind to drop locally.
Sand carried by the wind falls at these points and begins to build small sand piles
This forms another more substantial wind break, encouraging more and more sand to be deposited.
pH of an embryo dune?
Highly alkaline pH values(over 8) from the calcium carbonate in shell fragments
How tall are embryo dunes?
No higher than a metre
What species live in embryo dunes?
Sea twitch grass, sea rocket, sea couch grass
How do plants in the embryo dune help develop?
They are salt tolerant. The stabilise the dune and decay to provide humus for plants in the next stage
How do fore dunes form?
Embryo dunes that persist are colonised by sea couch grass and sea holly. The join together in a line to develop into fore dunes
How are conditions more favourable in fore dunes?
Lower alkalinity as levels of calcium carbonate fall. Grass from the previous stage decomposed and formed humus
How are plants in the fore dune adapted?
They are drought resistant. They can withstand burial by shifting sand and high salinity levels
What helps fore dunes reach 5 metres?
Plants grow and trap more sand. The root system of Marram grass stabilises the dune
What vegetation exists in yellow dunes?
Mostly marran grass. Others are mosses, lichens, sea holly and sea spurge
How tall are yellow dunes?
5-10 metres
Vegetation cover of grey dunes
Vegetation cover is almost 100% as moss and lichens fill spaces between plants while small shrubs such as brambles appear for the first time
- Humus darkens surface layers and a true soil forms
What is less common on grey dunes?
Marram grass as less sand is blown on the dune and there is competition from other plants
What plant takes advantage of the acidic soil in grey dunes?
Heathers
How tall are grey dunes?
10 metres
What is a dune slack?
They are found in between grey dunes and mature dunes where the water table reaches the surface and causes seasonal waterlogging and surface water
What plants live in dune slacks?
Cotton grass, creeping willow
How far away are mature dunes from the shore?
700 metres
How is the water content and humus in mature dunes different than in grey dunes?
Much higher water content here. It is very low in grey dunes. More humus. Plants here succeed previous vegetation
What plants are supported by the soil that develops on mature dunes?
Shrubs and trees including hawthorn.
Salinity of embryo dunes
High salinity from frequent immersion in seawater
Why is there a lack of nutrients in embryo dunes?
There is no humus
What causes a lot of salt spray on embryo dunes?
High wind speeds
Why is there rapid drainage on embryo dunes?
Sand doesn’t hold water well
