The amount of light pervading through the canopy was measured with a light meter at each site. These measurements were recorded at five metre intervals along the transect lines. As well as light meter readings at every five metres general observations of plant species within three metres north and south of each transect line were made. Also, every five metres at each site a soil sample were collected for pH measurement; this was to be investigated in the laboratory. Photographs of any unidentified species were taken to aid further investigation.
Results
The data collected gave the following sets of results: ten sets of data for species identity and percentage cover, and five sets of data for pH, light and species diversity adjacent to the transect lines, for both sites. The raw data for this experiment is contained in Appendix ‘B’; this raw data was interpreted into the following results. Charts 1 and 2 show the composition of the growth along the transect line. These show the average amount of bare ground at the old site to be 87.5% and to be 34.5% at the new site. They also show similarity in the amount of species found in the quadrats, three species at the old site and four at the new site
Chart 1.
Chart 2.
Tables 1 and 2 show the particular species to be found in the direct vicinity of each transect line at five metre increments. Frequencies rated as trace are for species where only one sapling individual was found for that species. As can be seen in Table 1, three species dominate the old site (Oak, Holly and Ivy), whereas Table 2 shows the increased diversity of the new site. The new site is widely populated by four species, (Silver Birch, Oak, Bracken and Bramble), but also has more individual species than the old site (eleven at the new site compared to seven at the old).
Table 1.
Species coverage at old site.
Table 2
Species coverage at new site
In Chart 3 the estimated heights of various growth is displayed. This shows that at the old site there was very little ground cover, and average of just 10 cm; whereas at the new site the ground cover average was 84 cm. It shows very little difference in overall structure apart from ground cover and the starting heights of any sub canopy (this was an average of 1m at the new site and 2.3m at the old site.
Chart 3.
Table 3 shows the pH values gained from samples at both sites. The average pH at the old site was 4, and at the new site it was 3.9, suggesting that soil pH for both sites was the same.
Table 3.
Average pH along transect lines
Table 4 shows the light readings taken at the different points along each transect line. This gave an average light reading of 4.7 at the old site, and an average of 15.8 at the new site. This clearly displays the increased amount of light available at the new site compared to the little light available at the old site.
Table 4.
Light meter readings
Discussion
In overall height both sites were very similar, as displayed by Chart 3. However, the coverage of the top canopy at the old site was very different to that of the new site. The top canopy of the old site had nearly total coverage, very little light pervaded through it, and the lack of floor growth reflects upon how poor the growing conditions are under the canopy of the old site. Any spaces in this canopy were filled by a high sub-canopy that was growing between two and eight metres in height from the floor. This sub canopy was predominantly ivy covered Holly. This indicated that opportunist plants quickly take up any chance for new growth in this environment. Both Ivy and Holly were observed everywhere along the old site transect line: as shade loving plants they are suited to the gloomy conditions under the canopy, and grow a lot quicker than the Oaks. The lack of light under the canopy is probably also responsible for the fewer species found along the old site transect line.
In contrast the new site top canopy had less than fifty percent coverage, and consequently far more floor growth than the old site. Indeed, any floor growth found at the old site was less than ten centimetres high, compared to being between fifteen and one hundred and eighty centimetres high at the new site. This also allowed more growth in the sub canopy, and far more sapling trees were present at the new site. Also the improved light conditions allowed more diversity of plant species: eleven species found at the new site compared to seven at the old site. Furthermore, two of the species found at the start of the old site transect were individual saplings; no more individuals of either species were found at the old site.
The oak trees, with the holly and the ivy being the only valid competitors for any space and light, dominated the old site. In contrast there was a variety of species competing for space and light at the new site, with no one species easily dominating, although Silver Birch was the most numerous species. One other significant observation was the presence of three different species of fungi at the new site, and none at the old site. This suggests that there is more decomposition occurring at the new site than the old site. As the bracket fungi were observed on mature Silver Birch this could well be the case: compared to Oak the Silver Birch is a short lived tree and so a faster rate of decomposition would exist at the new site.
In regard to conservation it would seem that the age of a patch of woodland does not confer any special benefit in this instance. The results gained suggest that the new site has more diversity, and a more varied environment; making it more favourable as a habitat for a wider selection of flora and fauna than the old site.
The hypothesis that the old site would reveal less diversity than the new site, because of its’ dominating canopy, proved correct. Also there was only one tree dominating the canopy at the old site, oak; whereas at the new site there were at least four tree species in the canopy.
The method used in this experiment was not entirely successful in gathering accurate information. The transect line did not intersect any trees on either site, nor were the girth of trees or number of trees accounted. No method was devised to assess the volume of floor space used by trees in relation to shrubs and other plants. The use of a tape for the transect line actually encouraged members of the group to look down more than up: so the depth, vibrancy and variation of the canopy were overlooked. The photographs taken by Alex were excellent and proved very helpful in later classifying species that were unidentified in the field. The surveying of several five-metre squares at both sites would probably generate more accurate results than of those gained by the method employed in this experiment.
References:
Hubbard, C.E. (1989) GRASSES: A guide to their structure, identification, uses, and distribution in the British Isles, 3rd Edn. Penguin Books Ltd.
Keble Martin, W. (1982) The New Concise British Flora. The Rainbird Publishing Group Ltd.
Polunin, O. (1977) Trees and Bushes of Britain and Europe. Oxford University Press.
Aas, G. & Riedmiller, A. (2001) Trees of Britain & Europe. HarperCollinsPublishers.
Bremness, L. (1995) The Complete Book of Herbs. BCA.
southampton.gov.uk/leisure/hort_rec/lesdev/hort/commons.htm
