The most mature dunes are found several hundred metres from the shore. Left undisturbed these dunes will develop a soil which is able to support shrubs and trees including hawthorn, ash and birch. Eventually oak climax vegetation may develop.
As conditions change further along the succession, more species arrive and biodiversity increases. This leads to greater species diversity.
Several abiotic factors will change during the succession. These include salinity, soil moisture, organic matter, pH and nitrate levels. Further more, the profile of the sand dune system shows changes in height above sea level.
Background information:
The sand dune succession is show clearly in these pictures taken from the website :
Humus is the organic material in lending it a dark brown or black colouration. It is organic matter that has reached a point of stability.
This picture taken from the website shows the nitrogen cycle and its importance to plants. The humus levels of the soil depend on the nutrition in the soil. The decomposers in the soil, anaerobic and aerobic bacteria and fungi, increase the level of ammonium ions in the soil which is absorbed by the roots of plants. Ammonium compounds produce nitrates and nitrates which are also absorbed by plants.
As stated in the website, , Xerophytes are s which are able to survive in an ecosystem with very little water available. It is these xerophytic adaptations that allow plants such as marram grass to survive in such harsh conditions where water is minimal. Marram grass, when covered by sand, has stems which can elongate allowing the grass to re-emerge. The long roots that spread deep into the ground help search for water.
Preliminary work:
I carried out a preliminary investigation at Winterton sand dunes. I had to consider certain factors when carrying out the experiment. To discover the optimum quadrat size I implemented the quadrat size exercise on an area with good biodiversity, the mature dunes. In the preliminary investigation I found the optimum quadrat size to be 100 x 100 metres. This provided me with the best quadrat size to use for the experiment that will produce more reliable results. Another factor that needed to be considered was the length of the transect line or interrupted belt transect. To produce enough data for a potential statistical analysis and kite diagrams the length chosen was 600 metres. This provided enough length for data to show a clear trend. The transect will be at intervals so that the experiment is more time efficient and data can be collected over a relatively large area. To gather enough data that will emphasise a trend 15 quadrat repeats will be performed along the transect line, each at roughly 40 metres from each other. By taking 15 samples, a sample at each quadrat, a wide range of area is covered which will provide accurate data to work with.15 samples are enough data to draw a reliable conclusion from.
The method of quadrat sampling was also taken into consideration. Point quadrat sampling is repeatable however there is the possibility that the point may keep missing important organisms. Subjective elimination was eliminated due to the disadvantage of human error. Percentage cover was considered the best method for quadrat sampling. Although it is not repeatable it is does take into account the size of the organism and is a useful compromise between the speed of percentage frequency and the accuracy of species density. To eliminate the problem of not being able to repeat the percentage cover, transect repeats could be done to gather more data and increase the reliability of trends shown. This could be done by other students and the results could be shared between the classes.
There are a lot of abiotic factors to consider in this experiment however I have decided to look more closely at the levels of pH and humus in the surface layers of the dunes aswell as the plant diversity. I feel these factors will produce reliable and precise results that will show clear trends when analysed by using a plant species identification card, the reliability of results is greatly improved as the data of each species present is most likely to be accurate.
Measuring Succession:
It is possible to use the distance along a sand dune to study changes over time. As you travel away from the sea you will go from young to old dunes. A transect is the best technique to use for the study of dune succession. By using a quadrat, vegetation and soil can be sampled at intervals along the line. This is known as an interrupted belt transect.
Prediction:
I predict that as you go inland from the sea, species diversity will increase and more varieties of plants will be seen. Further more, several abiotic factors will change during succession. The humus level of surface layers will increase due to an increase in plant species as you travel away from the shoreline. As the species die and biodegrade, humus levels increase. Humus levels will also rise as animals such as rabbits may add their droppings which will enrich the developing soil. I also predict that the pH of the soil will decrease in value as you travel way from the see.
Factors to take into account:
Method:
At the sand dunes
- Using the metre rulers, form a quadrat, and determine the optimum quadrat size for this experiment. You may use the table below to help you. The optimum quadrat size should be determined towards the middle of the transect.
- Create a quadrat of 25 x 25 cm using four metre sticks.
- Count the number of different species in the quadrat.
- Increase the quadrat size to 25 x 50 cm and count the number of new species found in the increased area.
- Continue in this way, doubling the quadrat size each time.
Plot a graph of the data recorded. The optimum quadrat size is where the point where the line begins to level off and no new species can be found.
- Using the 30m tape, produce a transect line from near the shore line towards the upper marsh area.
- Place your quadrat at the first sampling point of 0 metres.
- Estimate the percentage cover of each plant species that you can find and using the plant species identification card name all the species in the quadrat.
- Using the trowel, collect a soil sample and seal it in a labelled plastic bag reading the metres it is from the start of the transect.
- Move the quadrat to the next sampling point, 2 metres, and again measure and record the percentage cover of each species. Also collect a sample of soil and seal this in a separately labelled bag.
- Move the quadrat to the next sampling point, 4 metres, and continue until you have completed 15 quadrats and have 15 soil samples each in separate bags.
In the laboratory
Humus content:
-
Weigh an empty crucible and record the mass (x).
- Fill half the crucible with some of the soil sample keeping enough spare for finding the pH later.
-
Find the new mass and record it (y).
- Calculate the mass of wet soil:
-
Mass of wet soil = y – x = a
-
Place the crucible in the preheated oven set at 110oC and heat for at least 6 hours.
- Heat in the oven for a further hour and reweigh. If the mass is less than previous, repeat step 5 until there is no further loss in mass.
- Heat the dry soil sample over a roaring Bunsen flame for 30 minutes.
-
Allow cooling until safe to handle and weigh to find the mass of burnt soil (p).
-
Heat for a further 10 minutes and reweigh. If the mass is less than (p) repeat this step until there is no further loss in mass.
- Calculate the percentage of humus in the soil as follows:
- Mass of humus = mass of wet soil – mass of burnt soil.
= a – p = q
-
Percentage of humus in soil =_mass of humus_ x 100
mass of wet soil
= q x 100
= a
12. Repeat this for each sample collected recording the results in a table like the one below.
Soil pH:
- Add soil to a depth of 1 cm to a clean test tube.
- Add water to a depth of 5 cm.
- Shake thoroughly and leave to settle for at least 10 minutes.
- Add universal indicator, a few drops, until you can see a colour sufficiently well enough to compare with the colour chart.
- Record the pH value in a table like the one below.
- Repeat for each of the soil samples.
Safety:
When at the sand dunes be careful of your footing as the dune system is very fragile and could collapse in certain areas. Wildlife such as adders should be taken into consideration. Stay to the footpaths to minimise risks.
In the laboratory were heat proof gloves when handling hot crucibles or operating the oven. Beware of the Bunsen burner and its open flame. Perform the experiment from arms length.
Presentation of results:
Data should be displayed in a suitable table where the results can be seen clearly. Graphs should be drawn using the data to show trends in the abiotic factors. Calculations that will be used in the analysis are finding the humus content and wet soil mass.
Bibliography:
Pictures taken from website –
The Sands of Time –
Xerophytes information –