The Sand Dune Ecosystem

Succession is the act or process of following in order or sequence. In sand dune area the succession is the processes that the area goes through in order to change from a sand dune area into a climax community, deciduous woodland, which takes place over hundreds of years.

As a sand dune forms the conditions are extremely harsh; strong wind, high pH and extremely dry conditions are found. These conditions are less than ideal for plant growth and means that plants need to be specially adapted in order for them to live there. The first nutrients enter the soil from rotting sea weed being washed up by a storm onto the dune. As the sea weed breaks down the first humus, dead organic matter, is placed into the soil. Nutrients are vital to plant growth in any area, they are especially important I sand dune areas due to the various other factors that make the area such a difficult place to grow.

There are four different dunes in a sand dune ecosystem that relate to the seres.

* Embryo

* Fore

* Yellow

* Grey

Each of the seres shows differences due to their development thorough the succession process, however is can be hard to tell where each of the seres start due to their proximity to each other. The different seres all have individual properties with different types of vegetation, amounts of vegetation, types of wildlife and edaphic factors.

Embryo Dune

The species that grow here are determined by the abiotic factors which include wind, nutrient content, soil pH, soil salinity, soil humus and water content in the soil. This will vary in the different seasons.

The climatic factors here will be very windy which means sands will be blown away and also fresh sand could be deposited. Also, a lot of water will come off from the sea so the conditions could be quite wet. Also, due to sea water being present it means that the nutrient will be very low. However, even though humus content is very low, if it breaks down it releases nutrients. Also, when it breaks down it lowers the pH as it releases acids. It will also bind the soil together as it holds onto water and acts like a sponge. It means that the soil is very poor as there is very little humus.

An edaphic factor is the pH of the soil. Due to sea shells being made of calcium carbonate it means that the soil will be very alkaline.

Soil particle size has a huge impact due to the fact that the sand particles are quite large so water drains quickly meaning that it will be very dry. It will quite loose and aerated.

The sea spray makes the conditions very salty meaning high salinity levels so the conditions in the small pile of sand are very hostile. This means it is very unfavourable to living organisms and few plants can grow here. The plants have to specially adapted in order for the embryo dune to be its habitat.

The topography of this dune shows that it is very small and isolated. It has raised areas of sand with flat bits in between and alternates between sand and vegetation.

Fore Dune

The fore dunes are the second stage of the succession process and found on the leeward side.

The fore dunes have a much more stable environment than the embryo dune meaning that development can happen. The soil is held together much better in the fore dunes because of the amount of roots holding it together, and the increased amount of humus holding the particles. The humus brings added moisture to the dunes which enable plants which have not adapted quite as much to the dry conditions to be able to grow. The humus also allows more nutrients to be held in the soil, for uptake by the plants. These can be replaced much more easily due to the greater amounts of plants, which results in more plants dying to replace the lost nutrients.

The soil is deeper. This can cause leaching of the nutrients away from the plants. This means that the plants cannot develop as they should due to the greater competition found here. This means that there is competition.

The soil is much more stable as more roots are found holding it together due to the increased in denser vegetation coverage. The vegetation found starts to have to be less adapted to specific condition but still has to cope with quite harsh conditions. The pH is still very alkali due to the calcium carbonate found in the sea shells but the soil is made more acidic by the breakdown of plants.

The types of vegetation found on the fore dunes are sea couch, lyme grass, marram grass and variety of other grasses. Grass is adapted to the dry conditions by having leaves which are tightly rolled, protecting the stomata on the base of the leaf from loss of moisture. The leaf, once unrolled, can be seen to have a downy appearance which is the result of having fine hairs. These, and the grooves running lengthways along the leaf inside which the stomata are located, all help to reduce moisture loss through transpiration.

Yellow dune

The yellow dunes are the third sere of the succession process. The vegetation is very dense.

A greater amount of humus is found in the soil in the yellow dunes as the amount of dead organic matter is always increasing. As more plants inhabit an area more plants die resulting in humus being replaced, back into the soil, to be absorbed by other vegetation.

The pH of the yellow dunes starts to become acidic at this stage due to the fact there are no sea shells as it is on the leeward side.

The plants found on the yellow dunes are known as xerophytes which includes plants such as marram grass. Some traits of xerophytes are;

* Thick waxy cuticle.

* Stomata closure.

* Increased water storage.

* Reduction in size of transpiration surface (lower leaf only).

* Leaves covered with silvery hairs (creates wind break & light reflective surface).

* Deep taproots or wide spreading fibrous roots near the soil surface.

* Low growth form (reduces H2O loss from wind).

The yellow dunes suffer from problems that can affect plant growth. Rapid deposition of sand, lack of water and lack of nutrients in the soil all attribute to the plants that can survive.

Grey dune

On the grey dunes the humus level is quite high. With the higher amount of humus the conditions are very friendly to plant growth. The vegetation can grow and develop easily without needed to be adapted very much.

There is a lot more shelter and less salt is carried by the wind. With these better conditions the number and range of plants increases covering, in places, the entire sand surface. There is a lot of competition due to the huge amounts of plants and species.

The plants do not need to be specialised. The pH is abit acidic. The conditions are not specific to any particular species; however the most commonly found species are mosses, lichens, annuals and perennials.