Offwell Woodland & Wildlife Trust

Promoting the British Countryside

Home

About us Conservation Education Wildlife Habitats Maps Search Resources Sponsors


Primary Succession

An exposed quarried rock face.

Primary succession is the series of community changes which occur on an entirely new habitat which has never been colonized before.

Examples of such habitats would include newly exposed or deposited surfaces, such as landslips, volcanic lava and debris, elevated sand banks and dunes, quarried rock faces.

A number of stages (seres) will take place in which an initial or 'pioneer' community will gradually develop through a number of different seres, into a 'climax' community, which is the final stage.

 

Coastal Sand Dunes
An Example of Primary Succession

 

Sand dunes will build up at the back of a beach where prevailing winds are strong enough to pick up and transport dry sand.

With high wind speeds and  little sand, the wind will continually shift the sand from the top of the dune to the windward edge, causing the dune to move landwards - a mobile dune.

Where there is large supply of dry sand (for example, on a sandy beach exposed by the tide and heated by the sun), together with winds having a speed greater than 15 kph,  the sand will be picked up and blown by the wind.

Plants growing on the shore-line, together with flotsam and jetsam washed up by the tide, provide mini- wind breaks which slow the wind down in their immediate vicinity. If the wind is slowed sufficiently, it will drop some of its cargo of sand. A sand pile will begin to accumulate at this point, providing an ever increasing wind break. Eventually the sand pile will grow into a dune at the back of the beach.

With high wind speeds, the sand is continually pushed over the crest of the dune, falling down the steeper windward slope. This has the effect of causing the dune to move steadily inland. Pioneer plants will begin to colonize the dunes, gradually holding the sand in one place with their root networks. New sand dunes may build up behind the first dune, eventually forming a series of dunes from the seashore, inland.

New sand dunes have the following environmental features:

  • Continually moving sand.

    This covers up pioneer plants, provides no anchor points for roots and is very abrasive, damaging soft tissues.

  • Very little freely available freshwater.

    Because sand is fairly coarse-grained, any rainwater rapidly percolates down through a new dune. There is no humus or organic matter in the sand to help absorb and retain the water.

    There is also a lot of salt derived from sea spray in the sand which may dissolve in the water. This concentrated solution can make it physiologically difficult for plants to absorb water.

    However, some water is still available to plants colonizing the dunes.

    The pioneer species will often have very long vertical roots which can reach down to freshwater which has collected at the base of the dune. Freshwater is lighter than seawater and so will tend to float on top of any seawater which is also present.

    In addition, because the sand is very porous, with many air spaces, the sun heating the upper layers of the sand will cause the air in the upper air spaces to expand. This draws cooler, moister in air from the lower reaches of the dune. At night, as the air cools again, the moisture in the air will condense out, leaving droplets of water in the sand. Night dews will often also add water to the upper surface of the dune. This is enough for the pioneer plants to be able to survive.

  • Very few nutrients.

    The dune is made up of hard, inorganic grains of sand. In a young dune, there are few nutrients available because there is not yet any dead organic matter being recycled within the sand. Some dune pioneer plants are able to fix nitrogen in root nodules and so are able to partially overcome this problem.

 

Characteristics of Sand Dune Pioneer Plants

  • High vertical growth rates to keep up with continuous sand deposition.

  • Extensive lateral root or creeping shoot systems to bind the plants over a large area.

    Marram Grass roots exposed. Note the long vertical roots, as well as the horizontal network.

  • Deep vertical root systems to aid with accessing water in the water table below.

  • Xerophytic adaptations to decrease water loss or increase water storage capacity.

    Examples include, small or rolled leaves which decrease the surface area
    for transpiration, a waxy cuticle which prevents water loss
    and succulent tissues which can store water.

    Physiological adaptations to high salt content in the environment.

 

Continue to

Sand Dune Stages

If you are not on Broadband, this next page may take longer
to download because it includes many images.
 

 

Succession Contents

 

 

 

Copyright Offwell Woodland & Wildlife Trust 1998/9 & 2000/1/2/3/4 http://www.offwell.info

All the information including images, charts, movies and sounds is provided copyright free, only for educational use by: schools, colleges and universities unless you are making a charge. If you wish to use information or any part of this site for commercial purposes or for any purpose where a charge is made then you must get permission, so make sure you contact us first. Remember, if you are not a school, college or university you must obtain permission to use any part of this website. Note that company logos are reproduced with permission and remain copyright of their respective owners.