Temperature was simply measured using an alcohol thermometer or temperature probe. The reading should be taken only about 15cm from the ground as this the temperature where the plants grow. The number was then either read off the gauge on the thermometer or simply recorded from the screen on the temperature probe.
Infiltration rate was also recorded. This calculated the rate at which water filters through various soil types. A 250cm3 measuring cylinder was pushed into the ground so that the 20cm3 line was level with the ground. The cylinder was filled with water and a stopwatch was started as the level of water crossed the 250cm3 mark. The clock was then stopped when the water fell to 100cm3 (so the time was recorded for the infiltration of 150cm3 into the soil)
Volume (i.e. 150cm3) ∕ Time (decimal) = cm3/min-1
Wind speed was measured using an anemometer, it was held out above the sand surface and the maximum gust speed was recorded. The units of measurement are wind speed/ 1ms-1. Each type of variable was measured in the same way i.e. the exact same height above the ground or the same amount of time etc. There are many variables that can greatly affect the results so these have to be recorded accurately as they may help explain the results.
Some plants on the dunes are poisonous such as ragwort so extra care was given while handling these plants. The universal indicator used in the pH test was also handled with great care and disposed of appropriately as it is poisonous and can affect the plants.
A clinometer was used to measure the morphology of the land by measuring angles of significant difference in dune height using meter rules.
NULL HYPOTHISIS = There will be no significant difference between the abundance and distribution of marram grass and other plant species between the fixed and mobile dunes. This is due to the fact mobile and fixed dunes are so close to each other that there cannot be such a significant difference change in environment that will affect plant growth greatly.
Results
Optimum quadrat size
Abiotic factors
Mobile dune
Fixed dune
To decide if the differences in the set of samples were of true statistically significance or just purely by chance an x2 test was carried out on the number of species found in each area studied. This measures the difference between observed and expected results and allows s to decide if the difference is significant or not.
Chi2 = sum of (Observed data – Expected data)2
Expected data
X2 = ∑ = 10.46
In biological statistical tests of this nature a significance of 5% is usually chosen.
To calculate degrees of freedom, it is always one less than the total number of groups of data so as there was 2 in this example there is only 1 degree of freedom, so the critical value that corresponds to 5% probability with 1 degree of freedom is 3.841
The critical value is lower than the calculated value so the null hypothesis is rejected. It is now acceptable to say the difference cannot simply be due to chance.
Conclusion
There was a significant difference in the distribution of marram grass between the mobile and fixed dunes. Much less of the total vegetation cover was marram in the fixed dunes. The mobile dunes had less than a third of the species found in the fixed dunes. The null hypothesis was rejected using chi2.
In the mobile dunes the conditions are much harsher with the pH being very alkali due to calcium carbonate from the break down of shells of sea creatures and there is little or no humus in the soil, there are many air pockets in the sand which all lead to high infiltration rates, as was shown in the bar chart showing the large infiltration rate difference between the two sites. There is also not much protection from sand blasting & sea spray. The dunes are also slowly moving hence their name.
Marram is perfectly adapted to surviving on the mobile dunes its small surface area to prevent water loss, thick cuticle to decrease evaporation and deep root system that can reach water tables metres under ground are just a few of its features that have made this arguably the best adapted plant on the dunes.
Far from the shore in the fixed dunes the pH of the soil is now more neutral if not slightly acidic and due to dead organic matter there is some humus so infiltration rates are not as high. The dunes & plants create protection so other species start to grow. The ground may also become boggy due to the water table, this means the calcium may leech out creating amore neutral area. These conditions are suited to a much larger species diversity and marram is easily out competed as it is not as specially adapted to these areas. Marram still exists here in relative large amounts but not in the same quantity as on the mobile dunes
Evaluation
Even though the results of the investigation seem to prove marram was mainly distributed on the mobile dunes, being a field experiment there were several faults and limitations of the investigation.
Only 1 mobile and 1 fixed dune area was researched these areas may not have been a true representation of the entire dune ecosystem. A fixed dune further back from coast will probably have less marram and a mobile dune closer to the shore will probably have more marram etc. At least 10 quadrats were used at each site, they all gave similar results i.e. more species found in the fixed which improves the data’s reliability. However frame quadrats were used which can only measure sessile organisms; do not provide data about height of vegetation or overlapping vegetation. Some plants form in clumps, so by using quadrats some species may be missed out and inaccurate results recorded.
Such limitations could seriously change the results for example lots of smaller plants grow in the mobile dunes close to the marram as they use it as protection from the harsh environment, these may not be recorded making the mobile dunes look less fertile than they actually are. The same could be said about the fixed dunes as there are so many plants in this area some could easily be hidden under plants etc. So this may make the difference between the areas even greater or perhaps less.
The wind changes all the time, the wind will of probably of changed speed as the day progressed. The wind varies so much, it is impossible to measure in such a small time. The % cover was judged by humans and there judgement is never 100% correct and varies between people. Getting more time to study the plants, or having a plant expert in each group would make sure all the species were recorded correctly in each transect.
The pH and wind speed difference between the two areas was only small, this difference is so small it cannot possibly be causing the huge vegetation difference between the two areas.
Perhaps the change in the environment between the two areas is not greatly affected by any one variable, but is due to all the small differences in all the variables. My data would suggest this as there is no great difference in the factors I have recorded except infiltration rates. There may be a variable such as sunlight or CO2 levels that I have not recorded that affects these areas also.
Other variables not accounted for include human activity such as tourists and walkers trampling on the vegetation. This can cause huge damage to the ecosystem, as do rabbits burrowing holes in the sand. Both these factors can cause huge blow-outs where little vegetation can survive.