Investigating Succession in a Sand Dune System

Investigating succession in a sand dune system

Aims

In this activity, you will study the colonisation of the dunes by pioneer species and follow the succession through to the climax community. At each stage in the succession, certain species change the environment so that other species can survive. As the succession progresses, there are changes in the abiotic environment which result in a less hostile environment and thus increase the diversity of organisms that can survive.

A dune system can be extensive and your sampling technique needs to be adapted to the morphological features, such as the dune ridges (the highest points) and the dune slacks or hollows. It would be too time-consuming to sample at regular, fixed points along the transect, so you can choose to sample along the strandline, the embryo dune, the first dune ridge, the first dune hollow and so on. This type of transect is called an interrupted belt transect.

If the apparatus is available, and time permits, it could be useful to have a profile of the dune system.

Safety

n Follow local rules for fieldwork. Do not damage the sensitive environment. Treat organisms with care and respect.

Equipment

n Measuring tapes

n Quadrat frames/point quadrats

n Notebook and pencil

n Prepared species lists

n Anemometer for measuring wind speed

n Light meter for measuring light intensity

n Thermometer for measuring soil temperature

n Trowel

n Plastic bags

n Soil testing kit for measuring pH

n Hygrometer for measuring humidity

Method

1 When you get to the dune system, stand near the drift line with your back to the sea and decide on the line of your transect. It is best to look for a landmark or fixed point, so that each time you move your tape you can keep in line. Fix your tape at the shore end and run it out as far as it will go inland.

2 At each place you sample the vegetation, you need to measure and record the abiotic factors, so:

n Use the thermometer to measure and record the soil temperature in °C.

n Use the hygrometer to measure the relative humidity.

n Use the anemometer to measure and record the wind speed, taking care that your readings are taken at the same height above ground level each time.

n Use the soil testing kit to test the pH. This test can be done in the field or back in the laboratory, using soil collected at each site.

3 Take a small sample of soil, place it in a plastic bag, label it with the site number and take it back to the laboratory to determine the moisture content and the humus content.

4 Record the vegetation by estimating percentage cover, either by using a subdivided quadrat or a point quadrat. Bear in mind that you are not likely to find a large number of different species in the young dunes, but it is likely that the number will increase as you move towards the bigger dunes and the hollows between them. Place your quadrat at the starting point of your transect on the shore around the high drift line and record your measurements.

5 Continue to sample at 5m intervals until you reach the first dune ridge.

6 After the first dune ridge, proceed to the first dune hollow, recording the distance from the last sampling point. Sample the abiotic factors and the vegetation in the dune hollow.

7 Continue working your way inland, measuring the distance between each sampling point and recording the abiotic and biotic factors.

8 Your transect will end when you reach the dune scrub community, where there are likely to be bushes and small trees.

9 Back in the laboratory, if necessary, find the pH of each soil sample using the soil testing kit or a pH meter.

10 Determine the percentage moisture content of each soil sample by the drying method described in an earlier practical.

11 To determine the percentage humus content of each soil sample, burn the dried sample (you will know its mass) in a furnace at 450 °C for 2 hours, cool in a desiccator and then reweigh. Ideally, each sample should be re-heated in the furnace, cooled and reweighed to constant mass. If there is not a furnace available, a rough estimate of the humus content can be made by heating the dry sample, in a crucible, over a Bunsen burner and burning off the organic matter. This has to be done carefully: the organic matter catches fire and may spark.

12 Tabulate all your results and consider how you can present the information to show the succession from the shore to the dune scrub.

Questions

1 Do you think that there are other factors, biotic or abiotic, that it would be useful to record? Is there evidence of animal activity in any parts of the dune system?

2 Are there any abiotic factors which do not change as you proceed from the shore inland?

Results

n The information about the abiotic factors is probably best recorded and displayed in a table. It is then easy to see how the factors change along the dune transects and you will be able to compare and correlate the results.

n A bar chart can be used. The species can be listed and the percentage cover at each sampling point recorded. The distance between the sampling points should be indicated and, if possible, a profile of the dune system should be added so that dunes and hollows can be shown.

Discussion

1 Discuss the influence of the abiotic factors on the vegetation. In your opinion, does the environment become less hostile as you move inland?

2 How important are the colonising or pioneer plants? Which plants changed the environment and how did they change it?

This resource sheet may have been changed from the original.