Conclusion and Evaluation
In my experiment I investigated the effect of mowing on petiole heights of white clover, by sampling petiole heights in unmown and mown areas.
From my results I can infer that mowing had a significant effect on the petiole height of white clove. The mean petiole heights of the unmown areas was considerably higher at 103cm than the mean petiole heights in unmown areas at 43cm. This indicates that mowing does cause a decrease in petiole height.
My data was imprecise as indicated by the large standard deviation/error bars. Because our sample size was 50 our results were reliable and it is more likely that this impreciseness is cause by the fact that height is a continuous measurement and is usually normally distributed in relation to organisms, therefore there will be some plants with petiole heights which vary greatly from the average which will have affected our error bars these outliers though naturally occurring, like the unmown petiole of 330cm, become more frequent with some natural factors which I shall explore in my evaluation. Although this does explain the inconsistency of my original samples, yet the subsequent mean calculations and t test ensures that the integrity of the data is intact. In spite of this there was a difference in the size of error bars between the mown and unmown areas, with the unmown area having a much greater standard deviation of 62. This indicates to me that there must have been some systematic errors within my experiment otherwise I would expect the error bars to be similar.
My results are easily explained by science, in all subterranean clover, like the white clover, petiole length is important due to the plants prostrate growth nature, while still allowing for photosynthesis. Our experiments indicate that petiole length responded rapidly to being cut during mowing and became “more prostrate and smaller leaved under grazing”¹. This is because the shorter petioles keep a greater proportion of leaflets below the grazing/mowing horizon. In this case the mowing has acted as a selection pressure, removing petioles over a certain height while the smaller ones survived. With consistent mowing the clover plant with the stolen which produces shorter petioles is more likely to survive and grow, passing on its genetic material though reproduction, eventually the mown area will become populated with prostrate clover. While the unmown clover also has to compete with other plants for light, which isn’t a problem for the mown clover as the grass is also being mown. In the unmown clover it is favourable to have tall petioles as this allows for greater light access and more effective photosynthesis which directly increases the survival rate of the plant, therefore tall clover in the unmown areas is more likely to survive and grow, passing on its genetic material though reproduction, eventually the mown area will become populated with tall clover. Therefore allowing for the petiole height differences seen in my results between the mown and unmown clover samples.
However my results are reflected by these other experiments such as the one a found online which directly measured the difference of petiole height in hard-grazed and lax-grazed areas. Their results are shown in the table below.
The findings though not as extreme were very similar to my own, as the heavily grazed grass has a shorter petiole than the less heavily grazed grass. Therefore I can conclude that my findings and my explanation is correct as it is confirmed by an outside source.
2) Competition and Succession in Pastures edited by P. G. Tow, Alec Lazenby