Comparison of numbers of organisms In Coniferous And Deciduous Woodlands
COMPARISON OF NUMBERS OF ORGANISMS IN CONIFEROUS AND DECIDUOUS WOODLANDS
ABSTRACT
Hypotheses
Null Hypothesis (Ho) - there was no difference in the number of organisms in the two soils.
Alternative Hypothesis (H1) - there was a difference in the number of organisms in the two soils.
An experiment was done to find out whether there was a difference in the number of organisms in the coniferous and deciduous woodlands. A quadrat of 10m by 10m was used and co-ordinates 5,1 5,2 5,3 5,4 5,5 5,6 5,7 5,8 5,9 5,10 were used because these were exactly in the middle of the quadrat area. Ten samples of leaf litter and ten samples of humus was obtained from each woodland.
In the laboratory tullgren funnels were set up, the samples were tested and the organisms were collected. A results table was made to record the numbers of organisms in. The results were displayed in graphs and tables. The graphs show the average number of each organism and the actual number of each organism in each of the woodlands. In the third graph five significant organisms have been picked out. This is because they have significant values and reasons for these values.
The tullgren funnel was set up using a certain amount of the leaf litter that acted as a sieve that the organisms could fall through from the humus that was placed on top of the leaf litter. 20g of humus and 10g of leaf litter was used in the tullgren funnel because only a small amount was needed. A 100w bulb was used in both experiments (for each woodland). The organisms were driven, by the drying effect of the bulb, down the tullgren funnel and eventually they fell into the 30cm3 of ethanol. The organisms died but their bodies were preserved so that at the end of five days the different organisms in the ethanol and the larger organisms in the dried up leaf litter could be identified and recorded using a microscope and a dichotomous key.
This method was used because it was the most reliable, and ensured that all organisms present were removed from the sample in the tullgren funnel. Some very small organisms that were not affected by the drying effect of the bulb were not counted. During the experiment predation between organisms were occurring, this was not accounted for.
The average test and the t-test were used, because two averages were being compared and there were less than 25 unmatched organisms in each sample. The value of t = 5.524 was greater than the value given for 22 points of freedom so that the Ho (null hypothesis) was rejected and the alternative hypothesis was accepted.
Therefore the assumption, that the number of organisms are greater in the deciduous woodland, can be made. So the number of organisms did differ in the deciduous and coniferous woodland.
The decomposition rate in the deciduous woodland is faster because organisms such as the earthworm can survive in this environment, because this environment is more alkaline than the coniferous woodland, which is more acidic. If conditions are less acidic then organisms such as the earthworm can survive and continue the fast decomposition, keeping the surrounding environment more alkaline. This is a negative feedback effect. So the number of species was greater deciduous woodland, with the exception of Springtails and small spiders. This is because these organisms have adapted to the acidic conditions of the coniferous woodland.
PLAN
Hypotheses
Null Hypothesis (Ho) - there was no difference in the number of organisms in the two soils.
Alternative Hypothesis (H1) - there was a difference in the number of organisms in the two soils.
The Aim
The aim of this investigation is to compare the difference in numbers of invertebrates in the coniferous and deciduous woodlands when samples are taken from each. The samples taken will be tested, recorded and evaluations will be made.
Prediction
The data collected will show that a coniferous woodland will contain fewer of the organisms that have been selected for study than in the deciduous woodland, and also that the depth of leaf litter will be considerably more in the coniferous woodland than in the deciduous woodland.
Evidence
In the deciduous woodland where the experiment was done, many different species of trees were growing. These trees have large, thin green leaves, to absorb the maximum amount of sunlight available. When these leaves fall off the trees to the ground, detritivores such as the worm, start the chain of decomposition. Without the detritivores the saprophytes (bacteria) cannot continue the process, after the detritivores, of breaking down the complicated organic matter.
These leaves have a large surface area for detritivores to start the process of decomposition. Decomposition occurs relatively quickly therefore the layer of leaf litter will be thinner.
However, in the coniferous woodland where the experiment took place there was only one species of tree and that was the pine. The pine needles are long and thin which are thought to increase the surface area for the absorption of sunlight.
This surface area is also where, when the pine needles fall to the ground, the detritivores start the process of decomposition. Because of the conditions in the coniferous woodland the detritivores take longer to decompose the leaf litter. Therefore if the rate of decomposition is slow, and the rate of the pine needles falling are fast, then there will be more leaf litter on the ground of the coniferous woodland than on the floor of the deciduous woodland.
The exotic conifer grows at a faster rate than the native broardleaves. Because the conifer is exotic, there are few insects and birds associated with it and so the exotic conifer is useless for use by native organisms. Because conifers are planted as a monoculture they are easy to manage (i.e. planting, weeding, fertilising, etc). But each tree needs exactly the same amount of nutrients and water because they are of the same species. This causes a deficiency of nutrients in the soil and so fertilisers have to be used. This could eventually lead to pest epidemics and so pesticides may also be needed. When a monoculture is planted, all the trees are of the same age and so are easily managed because there is little variation in height. The conifer woodlands and forests are planted in straight lines and are therefore easier to manage. However, this arrangement looks odd and unnatural because trees in a deciduous woodland are not planted in this way. If the conifers are planted densely then this ensures reduced side branch growth and increased height (therefore increasing the value of the timber). If all the trees are removed at the same time there will be a drastic change of the landscape which may result in a large amount of soil erosion.
Variables
* Light intensity in the coniferous woodland = 3.5
* Light intensity in the deciduous woodland = <3.5
* Temperature in the coniferous woodland = 28oC
* Temperature in the deciduous woodland = 27oC
Syllabus Areas
Climate (i.e. local and micro climates, vegetation, landuse, topography).
The Lithosphere (i.e. soils, nutrients, acidity).
Ecological Relationships (i.e. ecosystems).
Soil (i.e. conservation, cultivation techniques).
Mathematical Skills (i.e. plotting graphs, understanding graphs, etc).
INTRODUCTION
Hypotheses
Null Hypothesis (Ho) - there was no difference in the number of organisms in the two soils.
Alternative Hypothesis (H1) - there was a difference in the number of organisms in the two soils.
...
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* Temperature in the coniferous woodland = 28oC
* Temperature in the deciduous woodland = 27oC
Syllabus Areas
Climate (i.e. local and micro climates, vegetation, landuse, topography).
The Lithosphere (i.e. soils, nutrients, acidity).
Ecological Relationships (i.e. ecosystems).
Soil (i.e. conservation, cultivation techniques).
Mathematical Skills (i.e. plotting graphs, understanding graphs, etc).
INTRODUCTION
Hypotheses
Null Hypothesis (Ho) - there was no difference in the number of organisms in the two soils.
Alternative Hypothesis (H1) - there was a difference in the number of organisms in the two soils.
The Aim
The aim of this investigation is to compare the difference in the numbers of invertebrates in the coniferous and deciduous woodlands when samples are taken from each. The samples taken will be tested, recorded and evaluations will be made.
Coniferous woodlands develop from podsoil by extreme leaching and breakdown of clay minerals by organic acids and have a bleached topsoil (situated beneath the surface organic layers). The leached clay develops into an impermeable layer that decreases drainage rate and results in waterlogging of upper soil layers. Conifers are exotic plants (i.e. don't grow naturally in Britain).
Deciduous woodlands develop from brown earth soils. There is a thick leaf litter layer, and many organisms in the humus layer break down the leaf litter. The brown earth soil also consists of a well mixed mineral and organic horizon (i.e. topsoil).
Variables
* Light intensity in the coniferous woodland = 3.5
* Light intensity in the deciduous woodland = <3.5
* Temperature in the coniferous woodland = 28oC
* Temperature in the deciduous woodland = 27oC
* Nutrient content in the coniferous woodland and in the deciduous woodland.
* Water content of soil in the coniferous woodland and in the deciduous woodland.
There are also other factors that need to be considered such as...
* The abiotic factors such as the environment.
* The biotic factors such as the trees and invertebrates in the soils.
* The exposure to climate.
* The management of the woodlands.
* The depth of soil.
* The type of woodland.
* The exposure to pests.
* The area that will be used for the experiment will be 10m by 10m quadrat. A list of ten co-ordinates will be used. They are 5,1 5,2 5,3 5,4 5,5 5,6 5,7 5,8 5,9 and 5,10. These are selected because they are exactly in the middle of the quadrat. These co-ordinates will be used in both woodlands. So that the experiment is fair and reliable results can be obtained.
* The experiment will be completed as quickly as possible so that the variables that cannot be controlled (such as the above) will not change too much, so that the experiment will remain fair so accurate results can again be obtained.
Eventually all the data collected will be taken to the laboratory and the amount of organisms in each sample will be calculated.
Apparatus
Auger
40 Plastic bags
4 Gradient poles
2 Paper funnel
Clinometer
Ethanol
2 Tape measures
2 Conical flasks
2 Clamp stands
Source of heat (e.g. 2 Light bulbs - 100w each)
Syllabus Areas
Climate (i.e. local and micro climates, vegetation, landuse, topography).
The Lithosphere (i.e. soils, nutrients, acidity).
Ecological Relationships (i.e. ecosystems).
Soil (i.e. conservation, cultivation techniques).
Mathematical Skills (i.e. plotting graphs, understanding graphs, etc).
Scientific Background
Banks, Sir Joseph (1743-1820), British naturalist, born in London and educated at Christ Church College, University of Oxford. Banks encouraged the transfer of exotic plants from the colonies to Europe and the development of the Kew Royal Botanic Gardens in London.
Tull, Jethro (1674-1741), English agriculturist, born in Basildon, Berkshire, and educated at the University of Oxford. He became a farmer, and in 1701 he invented a machine drill that sowed seeds in rows, permitting cultivation between the rows and reducing the need for fallowing. The rotary mechanism in the invention was the foundation of all subsequent sowing implements. Tull placed great emphasis on the importance of pulverising soil so that air and moisture could reach the roots of growing plants.
(ENCARTA 1995)
Background Information
Humus (ENCARTA 1995)
Humus is the decaying organic matter found in soil and made from dead animals and plants. During early decomposition, some of the carbon, hydrogen, oxygen, and nitrogen are quickly dissipated as water, carbon dioxide, methane, and ammonia, but the other constituents decompose slowly and remain as humus. The chemical composition of humus varies, because it depends on the action of living soil organisms, such as bacteria, protozoa, fungi, and certain kinds of beetles, but usually it contains varying amounts of proteins and certain uronic acids combined with lignin's and their derivatives. Humus is a homogeneous, amorphous, dark-coloured, and practically odourless material. The end products of the decomposition of humus are mineral salts, carbon dioxide, and ammonia.
As humus decomposes, plant residues are converted into stable forms that are stored in the soil and are useable by plants as food. The amount of humus in soil also affects such important physical properties of the soil as structure, colour, texture, and moisture-holding capacity.
Detritus, Soil Organisms, Humus and Topsoil (Wright 1993)
The accumulation of dead leaves, roots and other detritus on and in the soil supports a complex food web, including numerous species of bacteria, fungi, protozoa's, mites, insects, millipedes, spiders, centipedes, earthworms, snails, slugs, moles, and other burrowing animals. As these organisms feed, the bulk of the detritus is consumed through their cell respiration, and carbon dioxide, water and mineral nutrients are released as by-products. However, each organism leaves a certain portion undigested - that is a certain portion resists breakdown by the organism's digestive enzymes. This residue of organic matter that remains for a time after most of the feeding and digestion have occurred is called humus.
The activity of soil organisms integrates humus with mineral particles to create soil structure. For example, earthworms feet on detritus, they ingest inorganic soil particles as well. As the mineral particles go through the gut, they become thoroughly mixed and "glued" together with the non-digestible humus compounds. Thus, the sand, silt and clay particles are bound together with humus into larger clumps and aggregates. The burrowing activity of organisms keeps the lumps loose. This loose, clumpy characteristic is referred to as soil structure.
Humus forms and soil structure develops mainly in the upper 10 to 30 cm of the soil, the zone in which soil organisms are active. Thus, a layer of dark-coloured soil with a clumpy, aggregate structure develops on top of the lighter coloured, humus-poor, compacted soil. This layer of humus-rich soil is called topsoil; the soil below it is called sub-soil. A careful cut through a natural, undisturbed soil is called the soil profile.
Humus has a phenomenal holding capacity for both water and nutrients, as much as 100-fold greater than clay on the basis of weight. The clumpy aggregate structure of top-soil greatly enhances infiltration, aeration and workability. Regardless of soil texture, then, attributes are enhanced with humus and the soil structure it imparts. Sandy soils may be given significant water holding capacity, clayey soils may be given sufficient aeration and infiltration, and loamy and silty soils may be enhanced in all regards.
DIAGRAM
A Map Showing Aberystwyth
METHOD
How the site was selected
The coniferous and deciduous woodlands that the experiments will take place in, were at Aberystwyth in Wales. It was made sure that the sites were in the same geographical area. The two forests had to be close together in order to keep the uncontrollable variations such as the soil, temperature and micro climates approximately the same.
Both sites were near the sea. The weather on the day of the experiment was very warm and moist with a slight breeze from the sea coming over on to the land.
On approaching the coniferous woodland, which was uphill, the experiment was done on a slope.
On approaching the deciduous woodland, a steep hill had to be climbed but the experiment was done on fairly flat ground.
Collecting the data in the coniferous woodland
In the coniferous woodland, a quadrat of 10m by 10m will be measured with a tape measure. The gradient should be measured by pushing a gradient pole in to the ground at 0m (the bottom) and pushing another gradient pole into the ground at 10m (up the hill). The clinometer is used to measure the gradient.
The co-ordinates 5,1 5,2 5,3 5,4 5,5 5,6 5,7 5,8 5,9 5,10 are going to be used because they are exactly in the middle of the selected area. At all of the co-ordinates (above) a sample of leaf litter (one handful only) should be taken and put into a plastic sample bag. Only one handful is needed for the experiment. The bag should be labelled with the co-ordinate number from which the sample has been taken. In the same place at the same point, an auger should be used to take a sample of humus. The auger is pushed in to the ground, about 30cm deep. The sample needed should be secured and the auger should then be bought up to the surface. The layer of humus in the soil seen should be measured with a ruler and then recorded. The sample taken should be placed in a plastic sampling bag. The bag should be labelled as the same co-ordinates on the bag with the leaf litter sample. This must be done at the ten different co-ordinates. The light intensity in the coniferous woodland must be measured and recorded and can then be taken into account.
Notes
It was noticed that the smaller trees seemed to be hollow, they seemed to crumble at the touch.
The distance between five trees was also measured. It was noted that the coniferous forest had only one species of tree, which was the pine tree. It was also noted that the trees were planted 1.5 meters apart and that one row of trees was cleared (bracken now grows here). This was probably because the trees are all the same species and so need the same amount of nutrients from the soil, and the trees were also planted close together because it restricts the growth of the side branches so all the energy goes into growing higher.
The number of errors were minimised by measuring how far the auger was put down into the ground. The amount of leaf litter taken was also taken carefully (only one handful for each sample because only one was needed).
Collecting data in the deciduous woodland
(The same procedure as above).
Notes
It was noticed that the trees were planted randomly, over the area. There were many different species amongst them. The gradient of the ground was fairly flat. A few shrubs were also growing there, amongst the various species of tree.
The number of errors were minimised by measuring how far the auger was put down into the ground. The amount of leaf litter taken was also taken carefully (only one handful for each sample).
The auger used on both occasions was used so that the depth and width of the soil sample taken would be the same as the other soil samples.
The laboratory experiment - number of organisms
In the laboratory, a tullgren funnel should be set up so that the number of organisms living in the leaf litter and humus can be recorded.
The tullgren funnel consists of a conical flask, filled up to 30cm3 with ethanol. A paper funnel should be put into it so that it is about 3 cm above the ethanol. Into this, first put 10g of leaf litter from the coniferous woodland, then on top of the leaf litter 20g of humus from the coniferous woodland. A 100w bulb must be placed at a distance of 5cm above the funnel. The bulb is held by a clamp and stand. The light should be turned on and left for 5 days. The organisms in the soil and leaf litter are driven down the funnel because of the drying effect of the lamp on the soil. The organisms eventually fall into the ethanol and died but, the bodies are preserved so that the organisms can be distinguished from one another. This is done using a microscope and dichotomous key.
Another tullgren funnel was set up in exactly the same way but the sample of leaf litter and humus used, was from the deciduous woodland.
Justification Of Method
This method is used because of the reliability of the results. If a random co-ordination is picked and is different for each woodland then the experiment is unfair and therefore the results are unreliable.
The materials used are reliable and give accurate measurements. The quadrat of 10m by 10m was used
because this allowed a specific area to be studied. The auger that was placed into the ground at 30cm was used to measure the exact depth of the humus in each woodland allowing a reliable measurement to be obtained.
RESULTS
A table to show the abundance of organisms from a random sample of a coniferous woodland.
Random sample site edge - central point.
ORGANISM
2
3
4
5
6
7
8
9
0
SUM
AVERAGE
Adult beetles
0
0
0
0
0
0
0
0
0
0
0
0
Large earthworms
0
0
0
0
0
0
0
0
0
0
0
0
Millipedes
0
0
0
0
0
0
0
0
0
0
0
0
Fly larvae
0
0
0
0
0
0
0
0
0
0.1
Slugs
0
0
2
0
0
0
0
0
0
0
2
0.2
Woodlice
2
0
0
0
0
0
0
0
0
3
0.3
Spiders (large)
0
0
0
0
0
2
0
0
2
0
4
0.4
Small earthworms
0
0
0
0
0
0
0
0
0
0
0
0
Centipedes
2
0
0
4
6
0
9
3
2
27
2.7
Beetle larvae
6
0
0
0
2
0
0
0
0
9
0.9
Spiders (small)
2
2
4
0
0
0
2
6
8
8
72
7.2
Oligocheatic Worms
0
3
3
2
6
2
1
6
35
3.5
Mites
3
3
5
3
8
3
7
9
5
4
50
5
Springtails
0
0
0
6
0
8
1
9
4
0
78
7.8
Totals
9
26
4
24
36
36
35
29
42
20
281
28.1
A table to show the abundance of organisms from a random sample of a deciduous woodland.
Random sample site edge - central point.
ORGANISM
2
3
4
5
6
7
8
9
0
SUM
AVERAGE
Adult beetles
0
2
0
0
0
0
0
0
0
0
2
0.2
Beetle larvae
0
0
0
5
4
5
0
0
7
6
27
2.7
Fly larvae
0
0
0
0
0
0
0
5
3
9
0.9
Millipedes
0
0
0
7
0
0
0
0
3
1
.1
Spiders (large)
0
0
0
0
0
0
7
0
0
0
7
0.7
Large earthworms
6
2
0
0
0
4
0
4
0
0
6
.6
Small Earthworms
0
0
0
0
0
0
3
0
5
0.5
Spiders (small)
0
0
0
5
3
2
0
4
6
.6
Slugs
0
0
0
0
3
4
5
2
2
7
.7
Woodlice
0
0
4
0
0
0
0
3
0
8
0.8
Centipedes
20
0
0
5
2
2
0
0
8
38
3.8
Mites
0
20
2
2
4
2
2
3
0
5
50
5
Springtails
3
8
3
2
5
5
2
3
33
3.3
Oligocheatic worms
3
5
3
2
3
7
2
2
4
3
44
4.4
Totals
43
39
4
27
30
27
9
24
7
31
283
28.3
Calculating the Average (Stats Test)
H0 - there is no significant difference between the averages of the organisms from the two woodlands, and any differences are down to chance.
H1 - There is a significant difference between the averages of the organisms from the two woodlands.
CONIFEROUS
DECIDUOUS
ORGANISM
SUM
AVERAGE
SUM
AVERAGE
Adult beetles
0
0
2
0.2
Large earthworms
0
0
6
.6
Millipedes
0
0
1
.1
Fly larvae
0.1
9
0.9
Slugs
2
0.2
7
.7
Woodlice
3
0.3
8
0.8
Spiders (large)
4
0.4
7
0.7
Small earthworms
0
0
5
0.5
Centipedes
27
2.7
38
3.8
Beetle larvae
9
0.9
27
2.7
Spiders (small)
72
7.2
6
.6
Oligocheatic Worms
35
3.5
44
4.4
Mites
50
5
50
5
Springtails
78
7.8
33
3.3
Totals
281
28.1
283
28.3
ORGANISM
AVERAGE
AVERAGE
. Adult beetles
0
0.2
2. Large earthworms
0
.6
3. Millipedes
0
.1
4. Fly larvae
0.1
0.9
5. Slugs
0.2
.7
6. Woodlice
0.3
0.8
7. Spiders (large)
0.4
0.7
8. Small earthworms
0
0.5
9. Centipedes
2.7
3.8
0. Beetle larvae
0.9
2.7
1. Spiders (small)
7.2
.6
2. Oligocheatic Worms
3.5
4.4
3. Mites
5
5
4. Springtails
0
3.3
Totals
30.3
28.3
The t-test
This test is used when two averages are being compared. There have to be fewer than 25 measurements in each unmatched sample.
CONIFEROUS
WOODLAND
DECIDUOUS
WOODLAND
ORGANISM
?A
?A2
?B
?B2
Adult beetles
0
0
2
4
Large earthworms
0
0
6
256
Millipedes
0
0
1
21
Fly larvae
9
81
Slugs
2
4
7
289
Woodlice
3
9
8
64
Spiders (large)
4
6
7
49
Small earthworms
0
0
5
25
Centipedes
27
729
38
444
Beetle larvae
9
81
27
729
Spiders (small)
72
5184
6
256
Oligocheatic Worms
35
225
44
936
Mites
50
2500
50
2500
Springtails
78
6084
33
089
Totals
Sample Size
[GSP1]??A=281
?A=10
A2=15833
B=283
?B =14
B2=8843
A = 281 ??B = 283
?A = 10 ?B = 14
(A = 28.1 (B = 20.2143
(??A)2 = 2812 (??B)2 = 2832
= 78961 = 80089
A2/?A = 78961/10 ??B2/?B = 80089/14
= 7896.1 = 5720.6429
A2-(??A)2/?A ??B2-(??B)2/?B
= 15833 - 7896.1 = 8843 - 5720.6429
= 7936.9 = 3122.3571
Sample variances
7936.9 3122.3571
10 - 1 14 - 1
SA2 = 881.87778 SB2 = 240.18132
SC2 = (?A-1) SA2 + (?B-1) SB2
(?A-1) + (?B-1)
SC2 = (9 x 881.87778) + (13 x 240.18132)
(10 - 1) + (14 - 1)
SC2 = 793.69 + 3122.3572
22
SC2 = 178.00215
Estimated standard error
SED = S C2 + S C2
? ?A ?B
SED = 178.00215 + 178.00215
? 10 14
SED = ?17.800215 + 12.714439
SED = 5.524
No of degrees of freedom
= (?A-1) + (?B-1) =(10-1) + (14-1)
= 22
5% significance level = 2.074
H0 is therefore rejected because it is larger than all the significance level values.
There is a significant change in the average numbers of organisms in the results.
A table showing the depth of leaf litter in each woodland.
Sample
Deciduous
Woodland
Coniferous
Woodland
5.1
2.3 cm
6.8 cm
5.2
2.4 cm
6.9 cm
5.3
2.6 cm
6.5 cm
5,4
2.9 cm
7.0 cm
5.5
2.8 cm
7.1 cm
5.6
2.7 cm
7.2 cm
5.7
2.3 cm
7.6 cm
5.8
.2 cm
6.1 cm
5.9
.1 cm
6.1 cm
5.10
.8 cm
6.8 cm
CONCLUSION
The aim of this investigation was to compare the differences in and numbers of invertebrates in the coniferous and deciduous woodlands when samples were taken from each. The samples taken were tested, recorded and evaluations were made.
The results from the t-test showed that the numbers of invertebrates in the deciduous woodland was greater than in the coniferous woodland.
Because coniferous woodlands developed from podsoils, and have extreme leaching and breakdown of clay minerals by organic acids they have more acidic soils.
The deciduous woodlands developed from brown earth soils and because there was a thick leaf litter layer, many organisms that lived in the humus layer broke down the leaf litter.
Light intensity, temperature and nutrient content varied in both the deciduous woodland and the coniferous woodland and were therefore variables that affected the results. The water content of soil, the abiotic factors such as the environment, the biotic factors such as the trees and invertebrates in the soils were variables that could not be controlled. The exposure to climate, the management of the woodlands, the depth of soil, the type of woodland, the exposure to pests were also variables that could not be controlled.
The experiment was completed as quickly as possible so that the variables that could not be controlled (such as the above) did not change too much, so the experiment remained fair and accurate results were obtained.
The data collected showed that the coniferous woodland contained fewer of the invertebrates selected for study than in the deciduous woodland also that the depth of leaf litter was considerably more in the coniferous woodland than in the deciduous woodland because of the slower decomposition rate in the coniferous woodland.
In the deciduous woodland where the experiment was done, many different species of trees were growing. These trees had large, thin green leaves, to absorb the maximum amount of sunlight available. When these leaves fell off the trees to the ground, detritivores such as the worm, started the chain of decomposition. These leaves had a large surface area for detritivores to start the process of decomposition. Decomposition occurs relatively quickly because of the alkaline conditions of the soil and the number of earthworms that were present, therefore the layer of leaf litter was thinner.
However, in the coniferous woodland where the experiment took place there was only one species of tree and that was the pine. The pine needles were long and thin which increases the surface area for the absorption of sunlight. When the pine needles fell to the ground, the detritivores started the process of decomposition. Because of the acidic conditions in the coniferous woodland there were not many detritivores, such as the earthworm, and therefore it would take longer to decompose the leaf litter. Therefore if the rate of decomposition was slow, and the rate of the pine needles falling was fast, then there was more leaf litter on the ground of the coniferous woodland than on the floor of the deciduous woodland.
The numbers of organisms was greater in the deciduous woodland as shown in graph 2 of the results. The invertebrates that decomposed leaf litter in the coniferous woodland would have had to have adapted to the harsh acidic conditions. Therefore there is decreased competition for the leaf litter between organisms.
If there is decreased number of organisms, then there is decreased competition for food and space. With this it can be assumed that if there was enough food and space for each organism in the deciduous woodland, then the numbers of each invertebrate would be higher still than the numbers of the invertebrates in the coniferous woodland.
Because the coniferous woodlands are man-made, each tree is planted very close to the next tree. Because of this, less light is allowed to penetrate through the canopy, this will therefore reduce the number of organisms and therefore, as in the coniferous woodland decrease decomposition rate.
EVALUATION
In this investigation there were some limitations.
The investigation in general was too vague. Only the number of invertebrates and the depth of leaf litter were measured, whereas another factor that was not measured could have been limiting. If more factors were considered then the experiment could have been made fairer. An example would be to put an auger in to the soil up to 1 meter and measure the length of each horizon. Then each horizon could be placed in to separate bags and then the invertebrates could be collected and counted.
The organic content and inorganic content of the soil could have also been measured. The different ions and salts in each of the two soils could have affected the organic content of the soil.
A limitation was that the environment was not accounted for. The concentrations of SO2 and CO2 in the microclimate around each of the woodlands could have been measured and correlated with the pH of the soil in both woodlands. The acid rain could infiltrate into the soil and an increase in concentrations of iron and aluminium may allow the pH to decrease.
Because conifers are planted as a monoculture they are easy to manage (i.e. planting, weeding, fertilising, etc). But each tree needs exactly the same amount of nutrients and water because they are of the same species. This could cause a deficiency of nutrients in the soil and so fertilisers would have to be used. This could firstly lead to pest epidemics and so pesticides may be needed but also may cause and increase in the acidity of the soil.
Because conifers are planted as monocultures, all the trees are of the same age and so are easily managed because there is little variation in height. This could allow the investigation of the differences in height in the two woodlands.
One possible extension could be to collect data at different times of the year, so a wide variety of results can be obtained. But because there is all year round needles on the coniferous trees the amount of organisms in the coniferous woodland soil sample may not vary too much. Because the depth of leaf litter is continually changing in the deciduous woodland, the numbers of invertebrates are also changing, with the change corresponding to the change in the amount of leaf litter.
Another extension could be to do the investigation at different altitudes (heights), or in different parts of the country. The country has differences in land shape and vegetation cover which may influence the organic content or the numbers of invertebrates in the soil.
When samples are taken and tested the test should be repeated several times so that an accurate and fair average can be worked out. Also the number of samples taken from each woodland were too small and were only taken from a small selected area (the quadrat). The number of samples taken could be increased significantly and the area over which the samples could be taken could be larger so that a more accurate number of species can be calculated.
After samples had been taken and placed into plastic bags, predation may have occurred and was not accounted for and therefore is a limitation.
Because there was a limited number of plastic bags, only ten samples of soil and ten samples of leaf litter were taken from each woodland, so this was another limitation.
As the invertebrates feed, most of the detritus is consumed through cell respiration, and carbon dioxide, water and mineral nutrients are released as by-products.
Because soil organisms move about, the humus is combined with mineral particles to create soil structure. The sand, silt and clay particles are glued together with the humus into big clumps. The burrowing activity of organisms keeps the lumps loose. This is soil structure.
Because this is known, types of soils can be identified and the types of organisms in them could also be identified and recorded. This is another possible extension.
APPENDIX
Water Content for 10g soil sample.
Deciduous
Coniferous
3
.37
2
3.1
.35
3
3.2
.35
) Start of forest
2) Middle quadrat area
3) Final quadrat area
More samples would have been done but there was a limitation - no more plastic sampling bags
Their was no positive correlation between the species which prefer high levels of water - so these results were disregarded.
Organic Content for 10g soil sample.
Deciduous
Coniferous
4
2
2
3.84
2.5
3
3.85
.8
The organic content is synonymous with the number of organisms.
These results are also disregarded because there is no positive correlation.
Water Retention for 20g of soil
Deciduous
Coniferous
0.5
20
35
22
35
.5
22
35
2
22
36
2.5
22
37
3
22
38
3.5
22
38
4
22
38
4.5
22
39
5
22
38
Invertebrates lives are purely dependant on how much water the soil retains.
The above data for the other variables investigated apart from pH from the soil samples.
These values were made relevant to see whether these also effect the numbers of species significantly or not.
Chi-squared data was used to see the significance levels. As proved pH was more significant.
REFERENCES
ENVIRONMENTAL SCIENCE : WRIGHT . N (1993)
ENCARTA 1995
[GSP1]