Clover Abundance And Proximity To Tree Life Biology Essay

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White Clover Trifolium repens is a familiar weedy herbaceous plant with sprawling stems that is native or naturalized across most of the temperate regions of the world. The white or pinkish flowers are produced in heads consisting of dozens of flowers. It is a perennial and an insect-pollinated, obligate outcrosser; plants also spread vegetatively by stolons (Olsen et al. 2008). Like other plants in the Fabaceae (legume family), White Clover harbors microbes in its root system that are capable of fixing nitrogen, i.e., converting atmospheric nitrogen into a form that is usable by plants. White Clover is one of the three-leafleted clover species that occasionally produces a leaf with four (or more) leaflets, i.e., a "four-leafed clover". 

Rationale

Ecological studies such as this are becoming ever more important in adding to our knowledge of the Plantae kingdom. For instance the International Seed Bank, an organisation entirely focused on preserving the seeds of our planet in case of a world disaster (5). However Seed Bank has to preserve knowledge of growing conditions so that if the post tragedy climate is different they can be confident that there are other conditions in which said plant will grow. The trifolium repense and trifolium pratense are one of the greatest natural fertilisers due to their natural tendency to remove nitrogen from the air (2), and with the environment changing at such a rapid rate and as there are many threats to the natural world it is obvious why this study as well as others are necessary.

Light intensity

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With the proximity to a tree being considered, light intensity varies for two reasons: Competition from other plants and amount of canopy coverage.

Trifolium repense and Trifolium pratense both remove nitrogen from the air using nodules on their roots, this means that they can survive in soil containing low nitrogen and can turn it into an area of higher nitrogen content (2), which can attract other plants to said areas. However unlike most Plantae Clover are able to survive in areas that are regularly mown.

Tree canopy can affect the light intensity in contact with any clover under the extent of the trees canopy; this can vary depending on distance from the tree. For instance any clover located one meter from said tree will have a fairly constant light intensity level, whereas any clover located at the outskirts of the canopy will have widely varying intensities of light due to a variety of factors: wind moving branches, seasonal changes to the leaves, older branches falling exposing more clover to direct sunlight(2).

Soil moisture

Clover tends to grow best in 56-60% soil moisture (3). As the clovers in this study are within close proximity to a Tree the soil moisture varies at different distances from said tree as the roots of trees remove large amounts of moisture from surrounding areas of soil. In a study it was found that the standard deviation in soil moisture between areas with trees and areas without was on average 1.6, this shows that a tree's presence can remove considerable amounts of moisture from the soil (4), which considering the previously suggested growing conditions for clover, means that Clover are likely to suffer in environments populated by trees.

Summary http://upload.wikimedia.org/wikipedia/commons/thumb/2/25/Four-leaf_clover.jpg/175px-Four-leaf_clover.jpg

The observations suggest that Clover will be more abundant in areas further away from trees, clover however have adapted to live in areas with low levels of nitrogen and so are suited to areas in which they can outlive competition. This can be seen as an evolutionary advantage when choosing an area in which to grow. While underneath a tree the Clover have restricted light, however there is a general lacking in competition for the available light as the clover are among the only Plantae able to live in the low nitrogen conditions and so are able to grow at a constant rate.

Hypothesis

my hypothesis is that due to its ability to live in mown areas (of which Nettlecombe is mowed every two weeks) and its ability to live in areas of low nitrogen; that where there is less light intensity, there will be a lower abundance of clover. As such I believe that proximity to tree life does cause variance in abundance of clover.

Site map

The Red lines in this picture are the 15 meter transects, 50cm apart

The black lines that are parallel are the start and end points of the transects

The black outline is of the tree I used in this test

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Planning

Dependent variable: Clover abundance

Independent variable: distance from tree

The following are variables that may have affected the dependent variable

Time of day

Light levels

Position of tree

Soil richness (moisture/nutrients)

Time of year

Weather

The location of my experiment was Nettlecombe court, in Somerset England, the area of my experiment will stay constant (Tree located next to graveyard)

Process of Data collection:

Place three stakes 50cm away from each other along the tree base (do not place stakes in tree roots, place in soil)

Attaching a tape measure to each stake walk fifteen meters away and place another stake in the ground (both ends of the tape measure should now be attached to a stake)

Repeat the above step with stakes 2 and 3 while keeping all three transects completely parallel.

At 1 meter intervals measure the clover abundance using a 1 meter (100 square) quadrat, place the bottom left edge of the quadrat to the right of the measuring tape at the meter point. If one square contain any clover it means there is a 1% clover abundance, if all of the squares of the quadrat contain any clover there is 100% abundance of clover. Do this at all sixteen intervals (starting at 0 and ending at 15) and repeat for transects two and three.

At 1 meter intervals measure the light intensity using a light meter. To do this you must stand on the transect line with your heels at the meter mark and the light meter held by your chest. When you have the number (in lux) record it. Perform this at all sixteen intervals (starting at 0 and ending at 15) and repeat for transects two and three.

At 0, 7.5 and 15 meters measure the soil moisture by removing a core sample using a borer, place the borer into the soil directly to the right of the 0 (meter), 7.5 (meter) and 15 (meter) intervals. Place each soil sample in containers and label A to C. repeat

At transects two and three. Take soil sample A and place in a crucible (weight crucible before and after soil is put in), put into microwave alongside similar crucible half filled with water, microwave until all water is gone. Now weigh the crucible that contains the soil and calculate the difference in weight.

Statistical test the statistical test that I will use to evaluate my Data will be the Spearman's Rank test.

Risk assessment

While the area in which I performed my study are not inherently dangerous, the equipment that I used in collecting my results were potential hazards. These risks can be avoided or minimized if the appropriate precautions are made.

Risk

Steps taken to avoid/minimize the risk

Likelihood of risk occurring

Hazard rating

Tripping over transect

Make sure to avoid crossing the transect on regular basis, and ensure feet are clear of the line when crossing does occur

High

5

falling on soil borer

Ensure that soil borer is placed carefully out of harm's way when not in use and has the sharp end placed to some degree in the soil

Low

10

Tripping on tree roots

Make sure to avoid walking over the tree roots as you are able to walk around them

High

3

Falling branches

Always be aware of the stability of the trees above, if they look weak then avoid them.

Low

8

Hurting self on metal stakes

Careful when handling and stepping over stakes. Pay attention

Low

8

Nettles/thorns

Wear clothing that protects all areas of

the body

High

6

Pilot Study Results

Test

Distance from tree in meters (M)

0

2

4

6

8

10

12

14

16

18

20

Abundance of clover (1)

0

0

1

2

10

10

12

16

7

17

18

Abundance of clover (2)

0

0

0

1

1

3

14

16

9

12

11

Light intensity (LUX) 1

36

51

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24

32

82

151

346

389

408

426

453

Light intensity (LUX) 2

14

14

17

17

40

96

254

364

408

421

451

Soil moisture

Dry

Moist

Moist

Modifications of pilot study (1): The investigation will use three transects instead of the previous two, so I can accumulate more precise averages. In my pilot I found that there where many anomalous results for the abundance test, but not for the light intensity test. I will use 1 meter intervals in my final study along a fifteen metre transect so as to document the increase in abundance closer. Another reason for making the transect fifteen metres instead of twenty is due to the lack of grassy areas, this way I can study a larger area due to the addition of a third transect, which will hopefully solidify the results I attain in my final study. I changed my method of soil moisture level collection, instead of using a simple moisture metre I will instead use a soil borer to remove soil samples at three different sections of the transect and will then calculate the moisture levels by performing tests in the soil lab.

Summary of change in method

15 meter transect with 1 meter intervals

Three transects

Taking soil samples to measure soil moisture in the lab

Observing and Recording

Distance from tree in meters and sample number

Abundance of clover

Light intensity (LUX)

Moisture levels

1

2

3

Average

1

2

3

Average

0

0

0

0

0

36

48

46

43.3

19.8

1

0

0

0

0

57

61

59

59

2

1

0

2

1

59

64

60

61

3

2

4

2

2

34

72

69

58.3

4

44

41

44

43

89

84

85

86

5

43

37

46

42

198

134

141

157.6

6

42

39

40

40.3

985

248

316

516.3

7

63

65

62

63.3

1190

590

720

833.3

32.1

8

64

61

69

64.7

1305

836

918

1019.7

9

68

70

71

69.7

1409

1124

1030

1187.7

10

71

76

73

73.3

1544

1060

1254

1286

11

83

85

86

84.7

1541

1002

1382

1308.3

12

89

86

88

87.7

1612

1045

1509

1388.7

13

91

89

92

90.7

1664

1262

1616

1514

14

96

91

94

93.7

1669

1180

1648

1499

15

95

87

94

92

1712

1264

1648

1541.3

26.4

From these results several conclusions can be made, the abundance of trifolium repense and trifolium pratense increases as distance from the tree increases apart from few anomalous results that will be excluded when plotting a graph of results

The results show that light intensity increases as distance from the tree increases, with the only exceptions being sample numbers 3 and 14, this variance in results is most likely due to a change the cloud cover causing the light intensity to alter slightly. I noticed such anomalies while doing the tests but decided that I could not counter this other than doing more experiments along the three transects.

It is shown from the results that the soil moisture levels have no real correlation and this could have been countered if I had taken more results and removed any anomalous results.

Stats test

My choice of Stats test is the Spearman's rank correlation coefficient as it is used to assess the strength of a correlation or relationship between two continuous variables that are able to be ranked

Number of pairs (n)

Distance

Rank (R1)

Abundance of clover

Rank (R2)

Difference (R1-R2)

Difference2 (D2)

1

0

1

0

1.5

- 0.5

0.25

2

1

2

0

1.5

+ 0.5

0.25

3

2

3

1

3

0

0

4

3

4

2

4

0

0

5

4

5

43

7

-2

4

6

5

6

42

6

0

0

7

6

7

40.3

5

2

4

8

7

8

63.3

8

0

0

9

8

9

64.7

9

0

0

10

9

10

69.7

10

0

0

11

10

11

73.3

11

0

0

12

11

12

84.7

12

0

0

13

12

13

87.7

13

0

0

14

13

14

90.7

14

0

0

15

14

15

93.7

16

-1

1

16

15

16

92

15

1

1

Calculating my significance level

∑ D2 = 10.5

Calculating Rs

(6 x 10.5 = 63) divided by (16 x 16 x 16 - 16 = 4080) = 0.0154411764705882

1 - 0.0154411764705882 = 0.9845

Rs = 0.9845

My calculated Rs value is greater than the critical value 0.665 for 16 pairs of data. This means that I am able to reject my null hypothesis that there is no correlation and accept my hypothesis. I am able to do this because my results when altered in the stats test show that there is 99% chance that there is a positive correlation.

Conclusion

From this statistical test it becomes evident that there is a positive correlation between the abundance of clover and the distance from a tree. These results have proven my hypothesis that as distance from a tree increases clover abundance increases to the high 1% significance level. The few results that didn't fit the trend are relatively easy to explain due to the conditions in which they were being taken. The results were taken over a 3 meter by 15 meter area, with such a width the light intensity is shown to vary widely over the three transects on which the results were taken. For instance transect one had 737 LUX more light intensity than transect two for sample 6, this shows that the light intensity can vary wildly in areas only one meter apart and because of this the abundance can change vastly despite the distance from the tree.

On a whole this study was without many anomalies, however this is most probably due to the fact that the growth patterns of Clover are an absolute and so there isn't much room for variance, clovers require light moisture and nutrients to grow, and it is likely that these amenities are likely to be more abundant in areas away from a much larger plant which will use the same resources with the benefit of being larger and therefore outcompetes the clover close by.

Evaluation

Aspects of my results such as the soil moisture study are not reliable, for this test I should have obtained many more soil samples from different areas, if this problem was rectified it would be possible for me to observe where the anomalous results are and discard them, as I only collected three results I must conclude that there is no direct correlation for soil moisture due to a larger value of 32% in the middle of the transect when the first reading from the base of the tree was which I believe to be inaccurate as it does not fit the general trend for moisture levels, as Matthew Campbell-Ellis shows in his study of moisture levels when around trees (4) I could have rectified this if I had had time to obtain more soil samples. If I had improved my study in this way I would have increased the reliability, validity and accuracy of this section of the study and my study as a whole.

Although the abundance of clover should increase as the ideal conditions become more readily available (as distance from a tree increases) it can vary due to the many other variables that can affect how colonies of clover grow. For instance the centre where I performed my study (Nettlecombe) has its fields (including the area where I placed transects) mown every two weeks and so although clover do have an ability to survive under such conditions, it is likely that certain areas will have more clover removed than others and this I believed caused the random errors, which in turn caused the varying results shown above.

The study as a whole in my eyes was a success as it was of the highest significance level achievable, and although the results varied slightly in different areas, there still remained a positive correlation. I believe the results of my study can help gardeners know where to sow the seeds so that the fertilising properties of the clovers. If able to extend my study I would investigate the PH levels as it is a factor that affects the growing efficiency of both trifolium repense and trifolium pratense, meaning I could ensure the validity of this study further.