I will be investigating two areas approximately 200 meters from each other in Brundholme Woods (Lake District grid ref:31,25). Site one is a majority oak filled woodland also containing birch tress, the trees are there due to natural succession in the climax community stage of self replicating trees. Site two mainly contains larch trees brought to the woodland by Victorians, making it semi-natural.
I am going to be investigating a well known fern called bracken (pteridium aquilinum), it is mainly found in areas such as woodland, heath and grassland. It tends to grow best on slight acidic soil. They generally grow to no more than 180cm but in the right conditions could get slightly higher. Observations: Oak trees tend to cover a larger area giving greater canopy cover to the shrub layer in comparison to larch trees, which have a smaller canopy cover.
Aims: To investigate the height difference in bracken in an area of majority oak woodland and compare the findings with bracken measured in majority larch woodland. I hope to then relate the findings to abiotic factors. Variables: There are a number of abiotic factors which could effect my results and therefore I plan to measure these factors to take note of any significant differences in the two areas being studied.
pH: From my research about bracken I have discovered that it prefers to grow on slightly acidic soil, therefore this could effect the amount and height which grows in the areas. I will therefore systematically measure the pH levels in every 5th quadrat taken in each site. This will be done by taking soil samples from the centre of each quadrat and then analysing the soil once back at the lab by using barium sulphate, deionised water and universal indicator.
Slope and Aspect: As the sites I will be working on are situated on hillside I will take the aspect and slop readings (using a compass and clinometer). In doing so I can try and work on similar slopes to make sure that it is not effecting my results. Temperature: Temperature of the soil could affect things such as the water and mineral content of the soil and also the rate at which the plants photosynthesise, therefore the height at which they grow. I will systematically measure the temperature (every 5th quadrat) using a temperature probe. It will be placed in the centre of the quadrat and the reading taken after 60 seconds, giving time for a stable reading to be shown.
Light intensity: This will be my key variable for this experiment as I am particularly interested in finding out whether the amount of canopy coverage (and therefore light intensity) affects the rate at which the bracken will grow. The light readings will be taken with a light meter at each quadrat placed in each site. Hypothesis: In the oak woodland light intensity on the shrub layer will be lower therefore the height of the bracken will be lower than that of the bracken which grows in the larch woodland with higher light intensity.
Also make sure that you do not trample on any of the bracken you are going to measure and be careful not to disturb or harm wildlife in the area. Implementation: From the results gathered for light intensity and height of bracken I calculated a running mean and produced 2 graphs showing both for both sites. As you can see from the graphs (graph 1 and graph 2) my results began to taper as the number of quadrats studies increased, this brings me to the conclusion that I took enough results to have a thorough and accurate experiment. Obviously there were some time limits but I think that the amount of bracken studied gives a good representation of the two areas.
The measurements for pH obtained from the soil samples showed that there was a 0.5 pH difference between the soil pH for each site. However every sample taken at each site remained the same which means that there was a consistency in each site. The slope and aspect for each site were very similar. At site 1 the aspect was 24, whereas at site 2 the aspect was 25 and the slope was 174�. Although again I could not control the angle of the slope they are quite close and should not have affected the results too much.
Analysis: I have produced 2 bar charts one showing the mean height of bracken in both sites and one showing the mean light intensity in both sites. Both bar charts contain error bars which show the margin of error. For graph 3 the error is +or- 0.5 cm because I noted the height of the bracken to with in 0.5 cm. For graph 4 which shows light intensity the margin of error shown is + or – 10% because the light meter had a tendency to fluctuate quite a lot. Graph 3 shows that the mean height of bracken in site 2 is higher than the mean height of bracken in site 1, there is no overlapping between the error bars which leads me to believe there is a significant difference between the bracken growth in both sites.
Graph 4 shows the mean light intensity in site 2 is higher than the mean light intensity for site 1, again there is no overlapping of error bars which leads me to believe that there is a significant difference between the two areas. I have decided to carry out some statistical tests from the results which I have obtained because I believe there is a significant difference in the results from each site. The statistical test I will use will be a student t test. A student t test is best suited to the sample size I did because it is better for showing correlations within larger sample sizes. I will do this for both my light intensity and mean height of bracken results.