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Soil Moisture at Different Heights up the Slope and the Length of the Longest Leaf of a Bracken Fern Essay Sample

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Soil Moisture at Different Heights up the Slope and the Length of the Longest Leaf of a Bracken Fern Essay Sample

Introduction: Slapton Wood, situated in the North-western corner of the reserve, is an Ancient Woodland (an area that has been wooded since 1600AD – Slapton Wood is mentioned in the Domesday Book), and as a result has very little active management. In practise what this means is that the only work that goes on in Slapton Wood is to maintain the network of footpaths and steps, which includes the clearing of dead, dying or dangerous trees when they pose a threat to public safety. The wood itself is a National Nature Reserve and is mostly composed of Sweet Chestnut and Oak, with a reasonable amount of Ash and Beech also present. An understory of Hazel and Holly can be found throughout most of the wood.

Hypothesis: I think that there will be a correlation between the length of the longest leaf of a Bracken Fern and soil moisture at different heights up the slope. This is because soil moisture will decrease up the slope as the soil gets further and further away from the river, at the bottom of the slope. The importance of the river is that some of the water it contains is absorbed by the soil, thus meaning moisture levels in the soil closest to the river would be higher than soil anywhere else. Furthermore, when it rains, the rainfall would flow down the slope due to gravity and the slope angle.

This results in the soil closer to the bottom of the slope being exposed to more water as the rainwater collects at the bottom of the slope, thus meaning that soil moisture would be higher here (at the bottom of the slope) than it would at the top of the slope as rainwater doesn’t collect here and the soil is therefore not in contact with the water for as long as the soil lower down the slope is. Therefore, as soil moisture decreases up the slope, the Bracken Fern up the slope will be progressively smaller as there is less water available in the soil for growth, thus resulting with the largest Bracken Fern consisting at the bottom of the slope. Due to this, I therefore predict that the length of the longest leaf would decrease up the slope as the Bracken Fern get smaller, because if the plant is smaller, its leaves should also reduce in length. We will determine whether this hypothesis was correct using Spearman’s rank because we are measuring the correlation between the soil moisture and the longest leaf, and whenever correlation is measured, spearman’s rank is used. This experiment will be carried out in Slapton Wood in June.

Null Hypothesis: There will be no correlation between the length of the longest leaf of a Bracken Fern and soil moisture at different heights up the slope.

Independent variable: Soil moisture at different heights up the slope up the slope is our abiotic factor and therefore our independent variable. The independent variable being the variable that is changed in order to deduce whether there is a correlation between soil moisture and Bracken Fern leaf length. The soil moisture will be measured with the soil moisture probe, where it’s inserted into the soil of each of the 7 Bracken Ferns being used, every 5 metres along the transect starting at 0 metres and finishing at 30 metres, for 30 seconds (in order to allow the reading to stabilise). A measurement is then taken after the 30 seconds. This measurement will be repeated three times in order to guarantee a reliable reading. In Ecology we can’t control our independent variable because for example in this case, the value of the soil moisture in the forest is always changing due to different weather and different seasons. However, by measuring and changing the area at which it’s being measured, we’re able to control it to an extent because we are deciding where it’s being measured and we’re also making the measurements along the same 30 metre transect, in the same part of the wood, along the same section of the valley, so we therefore know that the results should be concordant. This is our method of controlling the independent variable and why we’re controlling it.

Dependent variable: Length of the longest leaf of the Bracken Fern is our biotic factor and is therefore our dependent variable. This will be measured using a metre ruler from the start of the Bracken Fern leaf, from where the stem branches off into the leaf, until the tip of the leaf (the last possible point of the leaf at which a measurement can be taken). In order to determine the longest leaf, all leaves must be measured because if they’re not all measured, our recording is therefore based upon perspective which is unreliable as everyone’s perceptive of what may be the longest leaf may be different. Therefore by measuring each leaf there would be no debate as to which leaf is longest. The leaf with the longest length should then be recorded. We must ensure that this measurement is done carefully and precisely in order to guarantee a reliable reading. The measurement is made to identify if leaf length is affected by soil moisture and therefore if there is a correlation between the two.

Variable

How is it controlled?

Why is it controlled?

Light intensity

Measured with a Light Metre.

The light metre should be held at the same height as that of the leaf you are recording the longest length of. This should be done for 30 seconds (in order for the reading to stabilise). This recording should be made at the site of every Bracken Fern that is measured and should be repeated 3 times, in order to guarantee a reliable reading.

Light intensity is not the abiotic factor we are recording and we therefore want to keep it constant. However, because the light intensity during the day is constantly changing we therefore cannot control it. By measuring it we are therefore able to determine whether there is a significant difference in light intensity at every Bracken Fern being recorded and therefore work out whether it affects the correlation between soil moisture and the longest leaf. We know that light intensity affects the rate of photosynthesis of plants and can thus affect growth; however, we are controlling the light intensity to an extent because we’re recording the data in the same part of the wood, along the same section of the valley. Therefore by doing so, we’re able to predict that the light intensity shouldn’t affect our experiment because the area being measured will be shaded by the same trees and hence, light intensity should remain the constant throughout the experiment.

Soil Temperature

Digital Thermometer

The digital thermometer is relevant here because it’s more precise than a regular thermometer. The thermometer should be inserted into the soil for 30 seconds (in order for the reading to stabilise), at the site of every Bracken Fern that is measured and should be repeated 3 times in order to guarantee a reliable reading.

Soil temperature is not the abiotic factor we are recording and we therefore want to keep it constant. However, because soil temperature constantly changes throughout the day, we therefore cannot fully control it. By measuring it we are therefore able to determine whether there is a significant difference in soil temperature at every Bracken Fern being recorded and therefore work out whether it affects the correlation between soil moisture and the longest leaf. Furthermore, we are controlling the soil temperature to an extent as we’re recording the data in the same part of the wood, along the same section of the valley and therefore the conditions the soil is exposed to (e.g. gaps in the canopy layer where extra sunlight increases soil temperature) are relatively similar throughout the area of measurement. Due to this we can therefore predict that temperature should be constant throughout our experiment and therefore shouldn’t affect our dependent variable.

Humidity

Measured with a whirling hydrometer

Firstly some water should be inserted into the water cap inside the hydrometer. The hydrometer should then be spun around in the air, at the same height as that of the leaf you are recording the longest length of, for 30 seconds (in order for the reading to stabilise). This recording should be made at the site of every Bracken Fern that is measured and should be repeated 3 times, in order to guarantee a reliable reading.

Humidity is not the abiotic factor we are recording and we therefore want to keep it constant. However, because Humidity constantly changes throughout the day, we therefore cannot fully control it. By measuring it we are therefore able to determine whether there is a significant difference in humidity at every Bracken Fern being recorded and therefore work out whether it affects the correlation between soil moisture and the longest leaf. Furthermore, we are controlling the Humidity to an extent as we’re recording the data in the same part of the wood, along the same section of the valley and therefore the conditions the air is exposed to should be relatively constant throughout the area of measurement. Due to this we can therefore predict that Humidity should be constant throughout our experiment and therefore shouldn’t affect our dependent variable.

Soil PH

Measured with a PH probe

The PH probe should be inserted into the soil for 30 seconds (in order for the reading to stabilise). This recording should be made at the site of every Bracken Fern that is measured and should be repeated 3 times, in order to guarantee a reliable reading.

Soil PH is not the abiotic factor we are recording and we therefore want to keep it constant. However, because Soil PH is constantly changing due to different factors like increased rainfall which makes soil PH more acidic, we therefore cannot fully control it. By measuring it we are therefore showing that we acknowledge its value and presence and the effects it can have on my final result as well as allowing us to determine whether there is a significant difference in soil PH at every Bracken Fern being recorded and therefore work out whether it affects the correlation between soil moisture and the longest leaf. Furthermore, we are controlling the Soil PH to an extent as we’re recording the data in the same part of the wood, along the same section of the valley and therefore the conditions the soil is exposed to should be relatively constant throughout the area of measurement. Due to this we can therefore predict that Soil PH should be constant throughout our experiment and therefore shouldn’t affect our dependent variable.

Wind Speed

With an Anemometer

The Anemometer should be held at the same height as that of the leaf you are recording the longest length of, for 30 seconds (in order for the reading to stabilise). This recording should be made at the site of every Bracken Fern that is measured and should be repeated 3 times, in order to guarantee a reliable reading.

Wind Speed is not the abiotic factor we are recording and we therefore want to keep it constant. However, because wind speed is constantly changing throughout the day, we therefore cannot fully control it. By measuring it we are therefore showing that we acknowledge its value and presence and the effects it can have on my final result as well as identifying any significant changes in wind speed values that may therefore affect our experiment. However, this should not be a problem because we’re controlling Wind speed to an extent, as we’re recording the data in the same part of the wood, along the same section of the valley and therefore the conditions the Ferns are exposed to should be relatively constant throughout the area of measurement. Due to this we can therefore predict that Soil PH should be constant throughout our experiment and therefore shouldn’t affect our dependent variable.

Slope Angle

Measured with an inclinometer

The slope angle should firstly be focused by looking into the inclinometer and focusing on one fixed point. After doing this the slope angle can then be measured at the site of every Bracken Fern that is being measured with the focus being kept on this one fixed point. It should be repeated 3 times, in order to guarantee a reliable reading.

Slope angle is not the abiotic factor we are recording and we therefore want to keep it constant. It’s also extremely important in our experiment because slope angle affects the rate at which water flows down a slope. However, due to environmental and ecological changes that occur in a forest, the slope angle is always changing and we are therefore unable to fully control the slope angle. However, by measuring it we are therefore showing that we acknowledge its value and presence and the effects it can have on my final result as well as allowing us to determine whether there is a significant difference in slope angle at every Bracken Fern being recorded and therefore allowing us to work out whether it affects the correlation between soil moisture and the longest leaf. To an extent, we are controlling the slope angle by taking our measurements in the same part of the wood, along the same section of the valley and therefore the conditions the Ferns are exposed to should be relatively constant throughout the area of measurement. Due to this we can therefore predict that Slope angle should be constant throughout our experiment and therefore shouldn’t affect our dependent variable.

There are other possible control variables; however, these are the variables that I’ve identified as being most important to the data I’m collecting.

Apparatus:

* Digital thermometer

* Soil moisture probe

* Soil PH probe

* Inclinometer

* Whirling Hydrometer

* Anemometer

* Metre Ruler

* 30 metre measuring tape for transect

* Bottle of water (for Whirling Hydrometer)

* Pen and paper to record results

* Towel/cloth (for cleaning soil moisture probe)

Method:

1) From the river lay out a 30 metre transect up the slope using the measuring tape. This should be done by leaving one end of the measuring tape at the bottom of the slope. Then with the other end of the measuring tape, walk up the slope (against the gradient) in a straight line, ensuring that that you are always moving up in a vertical direction and therefore are not drifting to any one side. Starting from 0 metres at the bottom of the slope, carefully measure out 30 metres. When 30 metres has been measured out, looking from the 30 metre mark down the slope, ensure that the transect laid out is straight and flat along the slope. If this is not the case, correct the transect so that it is straight and flat along the soil of the slope. This experiments sampling technique is systematic as a transect is laid out.

2) We will firstly record the length of the longest leaf of the Bracken Ferns along the transect. Starting at 0 metres, locate a Bracken Fern that occurs on the transect line. If there is no Bracken Fern that features along the transect at 0 metres, make a horizontal contour along that 0 metre point to the nearest Bracken Fern. Once this Bracken Fern has been identified, measure the length of each leaf on the Bracken Fern because if they’re not all measured, our recording is therefore based upon perspective which is unreliable as everyone’s perceptive of what may be the longest leaf may be different. Therefore by measuring each leaf there would be no debate as to which leaf is longest. This measurement should be made using a metre ruler from the start of the Bracken Fern leaf, from where the stem branches off into the leaf, until the tip of the leaf (the last possible point of the leaf at which a measurement can be taken). This measurement must be taken very carefully and precisely in order to guarantee a reliable reading. No repeats are therefore required as the reading would be the same each time.

3) This step for measuring the longest leaf should be carried out every 5 metres up until 30 metres. There should thus be 7 readings taken for the longest leaf.

4) Our independent Variable, soil moisture, should be measured after the longest leaf of a Bracken Fern has been found, but before the next reading of the longest Fern leaf, 5 metres along the transect. These readings should be made in the soil of the roots of each the 7 Bracken Ferns used for the experiment. The soil moisture should therefore be measured by inserting the soil moisture probe into the soil of the roots of each of the 7 Bracken Ferns. The soil moisture probe must be left in the soil for at least 30 seconds in order to allow the reading to stop fluctuating. The reading on the probe should thus then be recorded at 30 seconds. This measurement should be repeated 3 times in the exact same place so that an average for the soil moisture at each of the 7 locations can be deduced. We should make sure the probe is dried before every use as any residue on the probe may affect results.

5) Using the Digital Thermometer, take a reading for the soil temperature by inserting it into the soil of the roots of each of the 7 Bracken Ferns. The digital thermometer must be left in the soil for at least 30 seconds in order to allow the reading to stop fluctuating. The reading on the probe should thus then be recorded at 30 seconds. This measurement should be repeated 3 times in the exact same place so that an average for the temperature at each of the 7 locations can be deduced.

6) Using the light metre, take a reading for the light intensity by placing the light metre at the same height as that of the leaf you are recording the longest length of. This recording should be taken for 30 seconds in order to allow the reading to stop fluctuating. The reading on the light metre should thus then be recorded at 30 seconds. This measurement should be repeated 3 times in the exact same place so that an average for the light intensity at each of the 7 locations can be deduced.

7) For humidity, firstly some water should be inserted into the water cap inside the hydrometer. The hydrometer should then be spun around in the air, at the same height as that of the leaf you are recording the longest length of, for 30 seconds in order to allow the reading to stop fluctuating. The reading on the hydrometer should thus then be recorded at 30 seconds. This measurement should be repeated 3 times in the exact same place so that an average for the humidity at each of the 7 locations can be deduced.

8) Using the PH probe, take a reading for the soil PH by inserting it into the soil of the roots of each of the 7 Bracken Ferns. The PH probe must be left in the soil for at least 30 seconds in order to allow the reading to stop fluctuating. The reading on the probe should thus then be recorded at 30 seconds. This measurement should be repeated 3 times in the exact same place so that an average for the Soil PH at each of the 7 locations can be deduced.

9) Using an Anemometer, hold it at the same height as that of the leaf you are recording the longest length of, for 30 seconds in order to allow the reading to stop fluctuating. The reading on the Anemometer should thus then be recorded at 30 seconds. This measurement should be repeated 3 times in the exact same place so that an average for the Anemometer at each of the 7 locations can be deduced.

10) Using an inclinometer, the slope angle should firstly be focused by looking into the inclinometer and focusing on one fixed point. After doing this the slope angle can then be measured at the site of every Bracken Fern that is being measured with the focus being kept on this one fixed point. At each Bracken Fern, the inclinometer should be held at the same height as that of the leaf you are recording the longest length of. The recording should be repeated 3 times, in order to guarantee a reliable reading.

11) Using a calculator, first calculate the average value of soil moisture at each of the 7 sites. Then find the averages of the all the controlled variables (Wind speed, Soil PH, Soil Temperature, Slope Angle, Humidity, Light intensity) at each of the 7 sites.

12) Using Spearman’s Rank, calculate if there is a correlation between the length of the longest leaf of a Bracken Fern and soil moisture at different heights up the slope and therefore if the hypothesis was correct.

The Raw data can be displayed like this:

Independent Variable:

Location:

1st reading of Soil Moisture:

2nd reading of Soil Moisture:

3rd reading of Soil Moisture:

Average soil Moisture:

0 metres from river

5 metre from river

10 metres from river

15 metres from river

20 metres from river

25 metres from river

30 metres from river

Dependent Variable:

Location:

1st reading of the Length of the longest leaf of a Bracken Fern:

2nd reading of the Length of the longest leaf of a Bracken Fern:

3rd reading of the Length of the longest leaf of a Bracken Fern:

Average Length of the longest leaf of a Fern:

0 metres from river

5 metre from river

10 metres from river

15 metres from river

20 metres from river

25 metres from river

30 metres from river

Risk Assessment

Risk Assessment

Precautions

Ticks (Biting insects)

Apply insect repellent to all exposed parts of the body and then check yourself thoroughly after the experiment for any bites, especially the more moist areas of the body (this is where Ticks normally reside).

Hypothermia

Ensure warm clothes are packed as well as a towel.

Vicious Plants

Take a skin healing cream (e.g. savlon) and suitable medication for anyone with allergies.

Sun Burn

Apply sun tan lotion before going out to carry out the experiment.

Slip trip fall

Be careful of where you’re walking and always be aware of your surroundings. Don’t run to minimize the chance of falling over and ensure that someone in your group has a first aid kit before setting out.

Drowning in river

Pair up to ensure that there is always someone to help if you do fall into the river. Also be careful of where you’re walking and always be aware of your surrounding and don’t run to minimize the chance of falling into the river.

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