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Wasim's Transect Experiment
In the experiment, I intended to observe the distribution of various plant populations in a small grassy area to the rear of the sports hall of Camp Hill, whilst taking into account various abiotic factors, such as light intensity, soil pH and soil temperature. This was done using a variety of techniques and equipment (e.g. quadrats and light meters), the details of which are explained in the method. The results were collated to observe if any trend took place.
Firstly, a location was generated randomly in the grassy area, and a 0.5m x 0.5m quadrat was placed at the start of the transect. Once this had been done, the species of plant likely to be encountered during the experiment (i.e. along the proposed transect) were noted. An estimate of the coverage of each plant species for the first quadrat was carried out in the form of a percentage. This was followed by measuring the light intensity, using a light meter, then the soil pH (by adding pH paper to a soil/distilled water mixture) and soil temperature (using a temperature probe). The results were collected and the quadrat was flipped over twice, before the results for that quadrat were collected in the same method. This was repeated until 10 quadrat samples were obtained.
The light intensity was measured by using a lightmeter in each quadrat. This consisted of a simple voltmeter connected with a photocell. This equipment was faced upwards, and the value was allowed to stabilise before being noted down.
To measure the soil pH, first a cork borer was placed into the ground in the quadrat space, and a set amount of soil was extracted for each quadrat sample. This was added to a test tube along with approximately 5ml of distilled water. This mixture was thoroughly shaken and pH paper was added. The colour was noted and, using a chart, this corresponded to a particular pH value, for instance if the paper was green, the pH value was 5.0.
To measure the soil temperature a digital thermometer with a temperature probe was used. The probe was placed into the ground (at the same depth for each sample) and the reading on the display was allowed to settle, before being noted. The probe was placed approximately in the middle of the quadrat, although this was not essential.
The results show a variety of notable trends with regards to abiotic factors. Many of the plant species are distributed following the idea of inter-specific competition. Inter-specific competition occurs when 2 or more species rely on similar limiting resources. In this case, you can see that some species, such as grass, have been outcompeted by ivy and bramble the deeper you go into the transect. We can see from the results that as the distance along the transect increases, the less grass coverage there is, and the more it leans towards ivy, bramble, and even nettles.
With regards to light intensity, there is a clear decrease as you increase the distance along the transect. This is clear, on account that with more larger plants coming into fruition, and even trees being part of the transect at some stage, light intensity from the sun will decrease, and shady areas will increase. The progressively shady areas may be the reason that the grass became a subject to "Competitive Exclusion". Gause's 1934 study illustrated how a population can't get any higher due to limiting factors in certain situations. In this case, one could say the factors are light and space. On this principle, you could say that the ivy and bramble are better competitors than the grass and that is the reason for their relative distributions.
The soil temperature also shows a steady decrease as the distance along the transect increases. This could be attributed to the fact that there are a lot more larger plant species along the transect, which create a more shady and cooler environment, leading to lower temperatures of the soil. Again, this could have a bearing on the transpiration streams of certain species, such as teh bramble etc, with a cooler, more humid environment favouring water retention. Grass, on the other hand, does not require as vast a supply of water and this could be the reason it is found in the drier, less humid regions along the transect.
With regards to soil pH, our experiment ended up showing that the pH of the soil remained at a constant value of 5.0 throughout. This shows that certain areas are not exposed to more acidic conditions, and that the plants all cope with the same pHs.
Use the data you collected for the abiotic factors and the idea of interspecific competition to offer explanations for the zonation of the plant species along your transect.
I think the results and conclusion are reliable considering the small nature of the experiment. The experiment was only designed to be a small sample of an enclosed area behind a wood, and considering these limitations, the results are quite worthy of analysis. Also, if you look at the broader picture, collectively, 10 different transects were used, which allowed a much more vast comparison to be drawn between different areas. The results are reliable in a way, because accurate instruments were used to record data, such as photoelectric cells, and temperature probes. These gave very specific values and allowed us to obtain numerical averages. However, the estimation of percentage coverage of each species was far too vague and involved human judgement, which in some cases may have been wildly inaccurate. Thus some coverages of species may be way off, and could alter the conclusions with regards to Competitive Exclusion Principle.
Also, a major flaw was that the results were taken at different times, on 2 different days. The light intensity would have been different at these 2 times and the temperature may also have fluctuated uncontrollably. This may have led to serious unreliability in the experiment, but it was the only method available. Also, it was evident that the area being studied had been influenced in a negative manner by the presence of man, i.e. there was excessive trampling. This may have ruined some of the occupation of some species.
To increase reliability, a longer belt transect could be used. This does not just mean that the distance in which the quadrats are placed be increased, but a more scientific approach would be to take into account the space above the ground level that the quadrat occupies. Also, much more temperature and light readings could be taken at different areas of the quadrat, to obtain a more accurate average for that particular quadrat. In an ideal situation, the results would be carried out at the same time on the same day, giving more objective and reliable data. Also, the area where the experiment is conducted could be done in a place without any trampling etc.
How reliable do you think your results and conlusion are?
What could you do to increase reliability?
How could you use your quadrats to collect more
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