An experiment to investigate how the water content of soil within a system of sand dunes affect zonation and succession.
Abstract
The water content of soil is a major factor that will determine what sort of plants are able to grow, and when considering a system of sand dunes will have considerable effects on the zonation and succession of that environment. In order to investigate this, trial experiments were initially carried out in order to determine the most effective method of assessing a section of the dunes and obtaining results. Once these results had been obtained, adjustments to the original method were made, and the process of gaining results took place.
After tabulating the results, and drawing appropriate graphs, I concluded that within a system of sand dunes, zonation and succession of plant species is present, and as the distance from the strand line increases, so too does the water content of the soil. I also concluded that the water content of the soil is affected by the aspect of its position as well, which relates directly to its exposure.
Planning
Aim
An experiment to investigate how the water content of soil within a system of sand dunes affect zonation and succession.
Introduction
This investigation will take place on the southern coast of the Gower Peninsula, at Oxwich Bay where an extensive system of sand dunes is present. In order to complete a successful experiment with accurate results, the investigation must be carefully planned out.
The complex structure and ecosystem of sand dunes must firstly be researched and studied, drawing conclusions and predictions from any information gained. Selecting the appropriate variables must also be considered, while taking into consideration the relevant information gained from the background information, and results from trial experiments.
Biological Knowledge
The following biological knowledge is all directly related to this investigation and is essential for predicting trends, and being able to give some sort of explanations for what is seen.
Community Ecology And Succession
A community is a group of interacting populations living in any given area representing the living part of an ecosystem. The formation of any community takes time, and building up a complex structure of organisms occurs through a process of ecological succession.
An example that shows the development of a community is the colonisation of bare rock. Algae and lichens initially colonize such areas, forming what is known as the pioneer community. The gradual build up of dead and decomposing material leads to the accumulation of enough soil to support larger plant species such as ferns and mosses, which are ultimately replaced by larger seed bearing plants. Some of these will include grasses, shrubs, and trees.
This type of replacement of species by others over long periods of time is a process known as ecological succession and this will ultimately lead to the climax community. This is the state of an environment which is the most productive to sustain and throughout most of the low-lying areas of Britain, deciduous forest is the climax community.
There are also different types of succession that can occur; the first of which is described above, whereby there is a colonisation of an area lacking organic soil, where vegetation has never grown previously. This type of succession is known as primary succession.
Secondary succession occurs where vegetation has grown, but has since been destroyed by fire, farming or flood for example. Seeds and spores of vegetative reproduction may already be present in the soil, and thus influence the succession.
Zonation
Within any habitat, there are very distinctive changes in the types and numbers of organisms that are present. These changes are caused by an environmental gradient, temperature for example, and this distribution of different species, according to any number of environmental factors, is known as zonation.
The boundaries between different zones are called transition zones and these often contain populations of animals and plants specially adapted for life in the transition zone. There will also be present species that are characteristic of the two major communities, existing at the limits of their tolerance range.
Zonation and Succession Within A Typical System Of Sand Dunes
A typical dune system has a basic structure and will show zonation and succession of vegetation. The vegetation of a dune system is not particularly tolerable to saline conditions (not halophytic), accept near to the seaward margin, but instead shows adaptations typical to plants found in areas of water shortage.
Dune systems can be divided up into different areas or zones, each of which will show different types of vegetation present. The types of vegetation found in each zone will be typical of that area, as ...
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Zonation and Succession Within A Typical System Of Sand Dunes
A typical dune system has a basic structure and will show zonation and succession of vegetation. The vegetation of a dune system is not particularly tolerable to saline conditions (not halophytic), accept near to the seaward margin, but instead shows adaptations typical to plants found in areas of water shortage.
Dune systems can be divided up into different areas or zones, each of which will show different types of vegetation present. The types of vegetation found in each zone will be typical of that area, as each section of the dune system will have its own, slightly different environment. Therefore the vegetation found in these zones will be adapted to cope with the various conditions that are characteristic of each area.
The diagram below shows the basic structure and profile of a dune habitat, and shows clearly the different zones that are found.
As can be seen from the diagram, the dune habitat can be broken down into five main zones or regions.
Beach And Shingle Ridge
The shingle ridge is the first zone that can be seen on the diagram, and is very important when considering the origins of the dune system. It is here where the first fragments of humus develop; it is the presence of this organic material in the soil that is essential for the healthy growth of vegetation. There are a number of sources that result in the build up of humus, some of which include, bird droppings, pieces of dead sea life (e.g. seaweed, crabs), the occasional dead chic or small mammal etc. All of this material adds up to the total amount of organic material that forms in the soil.
The moisture that is required for the growth of plants is required by the underlying shingle, a reliable source of fresh water. When these rocks are cooled, often during night, condensation forms on the surfaces of these rocks, and this provides just enough moisture for well adapted plant species to gain a hold.
Embryo Dunes
The next zone shown in the diagram is known as the embryo dunes and it is here where the first signs of vegetation can be seen, and this is in form of pioneer plants. Being so close to the sea salt, the pioneer plants of the embryo dunes must be able to retain their fresh water supplies very effectively. Sea Couch and Sea Sandwort can be found in this zone, and as they become established, reproduce and decay, they make way for the less demanding species of pioneer grasses.
Yellow Dunes
These less demanding species make up what is known as the yellow dunes and include species such as Lyme Grass and Sand Couch. However, perhaps the best adapted of these grasses is the Marram plant (Ammophila), and although Marram Grass cannot tolerate being covered by the sea, it has an amazing unlimited vertical and horizontal growth by means of rhizomes. The Marram plant grows taller and more extensive as the dune itself builds up, and because the outer-most part of the plant becomes further and further away from the water below the surface, the Marram Grass has become well adapted to survive in arid conditions.
A feature typical to Lyme Grass, Sea Couch and Marram Grass is the rolling of their leaves, forming long tubes with a hollow center. Consequently, the stomata of the leaves end up on the inside of the tube, and not only does this greatly reduce water loss through transpiration, but it also acts as a cavity that is capable of trapping and holding moist air.
The constant movement of sand is essential to the pioneer plants such as Marram Grass as this stimulates new growth producing fresh shoots.
Grey dunes
As you move still further back along the dune system, you begin to see the next zone of succession known as the Grey Dunes. These were formed over hundreds of years, and unlike the Yellow dunes, the sand/soil is well packed and firm, containing much higher levels of humus. Here mosses and lichens can be seen growing, along with clover., dandelions, erect grasses and a host of ordinary inland species.
Dune Slack
The final zone that can be identified, known as the dune slack, is situated in between the ridges of the dune hills where there are a number of relatively sheltered hollows. In these hollows that are more or less insulated from the wind and sea, a constant deposition of animal and vegetation humus occurs. This allows the soil to hold much more water, and the levels soon build up allowing the development of general aquatic and marsh plants. Some of the species present include Meadow Buttercups, Purple Orchids, mosses and Liverworts.
Species That Are Commonly Found In Sand Dunes Environments
The following tables below show give lists of species that are typical to the various zones within a sand dune system.
Strand Line
Binomial Name
Common Name
Characteristics
Cakile Maritima
Sea Rocket
4-petalled pale to deep lilac flowers; greyish, fleshy leaves that are deeply lobed
Honkenya Peploides
Sea Sandwort
5-petalled greenish flowers; grows just above the strand line
Salsola Kali
Prickly Saltwort
Prickly spines on tops of leaves which are sharp narrow and fleshy
Yellow Dunes
Binomial Name
Common Name
Characteristics
Ammophila Arenaria
Marram Grass
Rolled, sharp tipped cylindrical leaves; clumps together
Leymus Arenarius
Lyme Grass
Broad, hairy leaves, often found growing in close proximity to Marram grass
Elymus Farctus
Sand Couch
A bluish plant, rarely over 50cm in height, with hairy leaves.
Carex Arenaria
Sand sedge
Creeping rhizomes several cm under the surface of the sand are present, sending up a few stiff and channeled leaves.
Eryngium Maritimum
Sea Holly
Spiny Greyish leaves, with pale blue flowers.
Senecio Jacobaea
Common Ragwort
Dark green leaves, and daisy-like leaves
Festuca Rubra
Red Fescue
Reddish leaf sheath, panicles-used for lawn grass.
Grey Dunes
Binomial Name
Common Name
Characteristics
Arenaria Serpyllifolia
Thyme-leaved Sandwort
Grey leaves, and flowers with small white petals.No more than 2-3 inches in height.
Ononis Repens
Restharrow
Trailing stems, rooting at intervals near the base.
Rosa Pimpernelifolia
Burnet Rose
An upright, spiny, bushy plant; creamy white flowers and hairless leaves.
Sedum Acre
Biting Stonecrop
Short stalks with some bearing flowers, and others with overlapping leaves tipped with crimson.
Hypothesis
After conducting research and gaining relevant background information concerning sand dune ecology, I can hypothesis on certain matters. Firstly, I expect to see zonation and succession occurring clearly as I move further from the strand line. I expect to find species that are well adapted to arid conditions in those areas closer to the strand line, and those which require more shelter and soils capable of holding greater volumes of water, further inland. I also expect to see a direct relationship between the aspect of a dune, and the water content of the soil at that point.
Predictions
The first and most obvious prediction to make is that within the system of sand dunes at Oxwich Burrows, I will see clear patterns of zonation and succession. I also predict that as I move away from the strand line, the water content of the soil will increase.
However, due to the varying height and shape of the dunes, within each separate dune hill, the water content of the soil will vary depending on whether it is the seaward or leeward side. This is because I would expect the top of the seaward side of a dune, to be much more exposed to the coastal environment than the bottom of the leeward side. Therefore I would expect the former to have a much lower soil water content than the former.
Variables
My initial aim was very 'open-ended' leaving many possibilities and details that have to be considered in more detail. The nature of this investigation means that there are many variables that have to be looked at in order to conduct a successful investigation.
The following list shows the variables that will be considered during the planning of this investigation. It must be decided which of the possible vaiables are to be varied, which of them are to be kept constant, and those which do not have any great relevance to this investigation.
- Distance from the strand line
- Aspect
- Percentage cover of vegetation
- Species Diversity
- Height above sea level
- Humus content of soil
- Water content of soil
- pH of soil
- Air temperature
- Humidity of air
- Light intensity
- Distance between transect poles
- Position in quadrat of soil sample taken
- Depth of soil sample taken
The list above shows all of the possible variables, and factors that could be considered when undertaking this investigation. However, it is clear that all of these cannot be included in this investigation and therefore the most important should be discussed.
Key Variables
These are the variables which will play a major part in my investigation and therefore have to be explained in further detail. These variables will either be controlled, and varied in a regular pattern (e.g. distance from the stand line), or they are those variables which cannot be controlled, but the way in which they vary will be the basis behind this investigation.
Distance From the Strand Line
The whole of this investigation will be based around this variable, as areas of land will be investigated at different distances from the strand line. As I intend to look at succession within the sand dunes, this is clearly an essential factor to consider.
Therefore the distance from the strand line will be varied, but the increase in distance from the strand line will be kept constant, i.e. the distance between the transect poles will be kept constant.
Water Content of Soil
Within my initial aim it was made clear that the water content of the soil would be investigated. The water content of the soil is an essential factor that effects the vegetation; therefore I would expect to see a clear pattern between this, and the types of plants growing in the dunes. However, although this factor is a variable that must be considered, it is clearly one that cannot be controlled and will hopefully show patterns similar to what has been predicted.
Variation In Vegetation
Rather than looking at the number or percentage cover of vegetation, I am interested in looking at the types of species found in the dunes. By looking at how the different species vary throughout the dune system, I will be able to consider the different zones, and also look at succession.
Aspect
The aspect of different parts of the dune is something that will obviously vary quite substantially. The aspect of a particular part of the dune will have an effect on how exposed that area is, and thus will effect the water content of the soil, and ultimately what will grow there.
* The rest of the variables that were mentioned do not need to be considered further because they will not play a part in this investigation. Whether or not they can be controlled or not, isn't important as they will not have an effect in the final outcome.
Initial Problems To Be Considered
After conducting research into sand dune ecology and considering the variables that should be controlled or varied etc., I have identified a number of problems that must be addressed before planning any trial or main experiments.
. Due to the fact that a dune system can stretch back from the strand line a considerable distance, and there is only a certain amount of time available to conduct practical work, I should not expect to see the full process of succession that ultimately results in the climax community. I would expect to see much of the dune slack zone, but hope to see zonation as far as the grey dunes.
2. As indicated in the aim of this investigation, a major section of the actual experiment is the process of identifying various different species of plants and vegetation. However, due to the fact that my knowledge of botany is limited, I should expect to come across species that I am unable to identify. If this occurs then the plants should still be recorded, even if it is not eventually compared to other data. Any species that are found which I am not able to identify will be allotted a letter instead and this will used instead of its official name.
Trial Experiment
The aim of conducting a trial experiment is to be become well equainted with the method being used, and identify any further problems with the method itself or generally. I will also conduct a trial experiment to insure that the transect line chosen takes a path that shows a fair representation of the dunes, and does not pass through any major obstructions.
Once I have conducted a trial experiment I can analyze the results and make any modifications that are necessary; this will enable me to gain accurate results when conducting the actual investigation.
Apparatus
* Clinometer
* Ranging Poles (x2)
* Tape measure
* Quadrat (0.5m )
* Trowel
* Identifying books
* Compass
* Sticky labels
* Plastic bags
Method
A ranging pole was placed into the ground at a point along the strand line. A quadrat was then placed down next to the pole in such a way that two of its sides were parallel with the strand line, and the bottom left hand corner was in contact with the pole.
The aspect of the quadrat was recorded using the compass, and a soil sample was taken. The quadrat was then examined, recording any vegetation that was present.
Once the quadrat had been examined, the next ranging pole was placed down, 10m from the first, in a line perpendicular to the strand line. The tape measure was used to measure the distance. At this stage, a clinometer was used to measure the angle from the top of the first pole, to the top of the second pole.
N.B. this method will obviously not show every change in the profile of the dune, however it should give an accurate estimate for this investigation.
At the point where the second ranging pole was placed into the ground, a quadrat was also placed down in exactly the same way as before.
This procedure was carried out for a total distance of 30m and if any of the plants found within a quadrat could not be identified a small sample was taken and labeled.
Results
Quadrat Letter
Distance From Strand Line (M)
Aspect (?)
Species Record
A
0
28
None
B
0
30
Marram Grass
Sea Sandwort
C
20
40
Marram Grass
CommonRestharrow
Dune Fescue
D
30
34
Marram Grass
Sand Sedge
Dune Fescue
Moss
Plant A
Plant B
Plant C
Analysis of Results
After conducting a trial experiment and testing my proposed method, I can now identify the problems that arose, and modify my procedures accordingly.
The actual procedure of taking the transect line proved to be successful, and I found that the method being used was easy to perfect. As I am happy with the results shown in the table above, I have decided to use these in the actual experiment, and when I begin to conduct the main investigation I will begin from where I finished in the trial experiment; from the 30m mark.
However, recording the species that are present is only one part of the investigation as the second part of the method involves taking a soil sample and measuring its water content. A problem arose in that I was not sure where and at what depth to take the soil sample from and it soon became aware to me that this should be perhaps kept constant for each quadrat, in order to give accurate and reliable results. Therefore there were no soil water contents recorded, and this needs to be repeated in the main investigation.
