Introduction
Elephants are huge animals that have the ability to change entire habitats and ecosystems through their feeding habits of felling trees. When elephants push trees over, they benefit other plants by eliminating competition and by exposing smaller plants under the trees to sunlight. They benefit animals by providing food to the animals that cannot reach the leaves on the tops of trees. They also benefit much smaller organisms by providing them with a habitat in which to live. (Tiller, 2012).
An experiment will be conducted in the Kruger National Park in the Nkuhlu area (24,9958”S, 31,5919”E). This area receives about 553mm of rainfall annually.
Figure 1. An aerial photograph of the Nkuhlu area
It is extremely hot in the summer months, but much cooler in winter. The dense woody vegetation is dominated by Acacia nigrescens. (Anon., 2016).
This research will only go as far as establishing whether or not elephants can benefit other plants by pushing trees over and exposing those plants (that were in the shade of the tree) to sunlight.
A limiting factor of the experiment is that the experiment cannot be repeated because there will not be another opportunity to go back to the Kruger National Park in order to get more accurate results. Another limiting factor is that there is a drought and this could affect the results because the plants may not have enough water to grow despite being exposed to sunlight.
This research is being conducted in order to prove that elephants are more helpful to the environment and plants in the ecosystem than destructive; this will break the common misconception that elephants are catastrophic.
The aim of the experiment is to determine whether or not elephants benefit plants growing under trees in the savannah biome by pushing trees over and exposing the plants under them to sunlight.
The Acacia nigrescens and the plants that grow in its shade will be studied in order to answer the question, do elephants benefit plants growing under trees in the savanna biome by pushing trees over which exposes the plants under them to sunlight?
The number of plants, the grass percentage and the number of different plant species growing around Acacia nigrescens trees that are unaffected by elephants will be studied and compared to the number of those growing around Acacia Nigrescens trees that have been pushed over by elephants.
The hypothesis of this research is that elephants do benefit plants growing under trees in the savanna biome by pushing trees over and exposing the plants under to sunlight.
Literature review
Elephants are a keystone species meaning that they play a vital role in keeping the balance of all the species in the ecosystem. They do this in a number of ways.
Elephants have the ability to change an entire habitat by pushing over trees and by stripping bark off trees. Elephants can transform thickets into open savannahs, creating grazing opportunities for all animals and helping animals to get to the leaves they cannot usually reach at the tops of trees. Once the elephants move on, the habitat can change back to what it was initially. The pushing over of trees not only benefits other animals, it benefits plants as well; especially in forests. When elephants push trees over, they create a gap in the thick forest canopy and allow light to filter through to the forest floor. The plants on the forest floor now receive sun light in order to photosynthesise and grow. The diversity and abundance of plants on the forest floor increases, therefore allowing a greater diversity in the ground animals. (Tiller, 2012).
When breaking branches and pushing over trees, elephants not only lower the browse line, they also assist seedlings by making space for them to germinate and allow them to grow without the shade of their parent plants or other plants. (Sheldrick, 1992).
Roots of trees absorb the nutrients in soil and over a long period of time, these nutrients are locked up in the wood of plants. When elephants push trees over, they play an important role in releasing and recycling the important nutrients trapped in the wood of trees. These nutrients are now available to all other organisms, including other plants. (Sheldrick, 1992).
The debris from trees that have been pushed over by elephants can act as protection to pioneer grasses and shrubs as the debris prevents these plants from being trampled. Following the pioneer grasses and shrubs are the perennial grasses with deep roots. With this vegetation change, the number of grazers increases while that of browsers decreases. The elephant numbers then fall and a thicket starts to regenerate. As the woodlands begin to take over, the elephant numbers rise again. These events continue in a cycle. (Sheldrick, 1992).
The types of plants species in a community change gradually over time in a predictable pattern after a disturbance. This is known as ecological succession. There are two main types of succession namely primary succession and secondary succession. Primary succession occurs on areas that have not been inhabited by plants previously. These sites include larva flows, bare rocks and various other sites. Secondary succession occurs on sites where there has been a disturbance that has removed all or some of the plant species. The soil, however, remains. The disturbances can be caused by climate change, physical disasters like floods and/or human or animals like elephants. These disturbances are beneficial as they give new species the opportunity to develop in that area. These new species create an environment that is ideal to other newer species by changing the character of the community. (Grogan & Suter, 2015).
Three stages occur in ecological succession: the pioneer species stage, the intermediate species stage and the climax stage. Pioneer plant species grow first as areas with limited competition for space and resources are ideal conditions. Pioneer species, like grass, grow in the sun, not shade. These plants are robust and sturdy in order to withstand the varying environment. Pioneer plants, like lichens, grow slowly but manage to establish rather quickly. The pioneer species reproduce using spores or seeds. Pioneer species prepare the environment for later plant species as they make the soil more fertile and provide shade, thereby changing the amount of light that is available. The pioneer plant species of secondary succession are herbs and weeds, followed by grasses and perennials. (Grogan & Suter, 2015).
In the intermediated stage of ecological succession, more organisms begin to inhabit the area because the soil is richer and there is more shade which is provided by the pioneer plants. The soil builds up further due to the increase in number of organisms in the area. The buildup in soil allows sturdy woody plants to take over from the non-woody herbaceous plants. The small woody plants then give way to slower growing but bigger woody shrubs and bushes. An important thing to note is that the grass remains in the area. (Grogan & Suter, 2015).
The final stage of ecological succession is the climax stage. In the savannah biome, the climax community consists of grasses and acacia trees. Future disturbances will cause the plant species in the community to change. (Grogan & Suter, 2015).
Out of all the food that elephants eat, only about half of it is properly digested, leaving the dung rich in minerals, nutrients and fibres and acting as a great fertilizer. Elephant dung, due to its nutritious properties, provides a suitable environment for the germination of seeds; it is also a source of food for many smaller organisms. (Tiller, 2012).
As the elephant population increases, they become more and more destructive. An area can only handle a restricted number of elephants, once the elephant number passes this, the elephants become destructive instead of useful. Due to their large appetites, elephants uproot, trample and destroy many plants while they roam around. Some ecologists are concerned that all this plant destruction may lead to loss of biodiversity. (Rodrigues, n.d.).
As with all animals, when confined to specific areas, elephants do cause habitat destruction. Elephants can change woodlands into bush and scrub by destroying plants and they may even prevent the regeneration of the woodland biome because they enjoy feeding on young shoots and saplings.This is bad because it changes the biodiversity and the animals which live in woodland areas and which depend on trees for survival will start to disappear and decrease in abundance. Smaller reserves suffer more severely from the destruction of woodland habitat because there are fewer places of refuge for woodland animals. However, elephants cannot be blamed for this destruction because it is likely that they would not cause destruction if they were not restricted to reserves and if their habitat was not destroyed by human influence. (Anon., n.d.).
All plants require sunlight in order to photosynthesise and therefore grow and survive. There are several factors of light that influence the growth of plants; these include light quality, light intensity and light duration. The less light a plant receives, the less it will photosynthesise and vice versa. The leaves of plants that normally grow in low light will easily become sun scorched when exposed to bright light; as time passes the cuticle thickens and the plant becomes more resistant to the sun. Different plants require different light intensities and some plants thrive in shade while others thrive in full sun. Temperature, however, also affects light intensity and some plants need shade in order to escape the heat. The amount of time that a plant receives sunlight for, light duration, also has an effect on the photosynthetic and growth rate of the plant. Plants that are exposed to sunlight for a long time will photosynthesise a lot, but plants cannot tolerate receiving sunlight for 24 consecutive hours. (Whiting, et al., 2016).
Although plants require sunlight, too much sunlight can be damaging. When receiving too much sunlight, plants become flaccid and begin to wilt. The colour of the flowers begins to dull, the leaves of the plant as well as the flower petals begin to dry out. If plants are shade plants and are used to growing in shade, they will not cope well if their source of shade is taken away and they are exposed to full sun. (Frowine, n.d.).
Assessment of sources:
(Tiller, 2012) is a blog that informs people about elephants and the numerous beneficial roles which they play in the environment. The information was posted in the year 2012 which is not that recent but the blog is valid and useful in terms of the research because it is all about elephants and the environment and the major role which they play which benefits plants. The blog is based on facts and several others sources were found which had the same information, the blog is therefore reliable. A limitation of this source is that it discusses how elephants benefit plants in a forest biome but not in a savannah biome which is the question and aim of the research.
(Sheldrick, 1992) is a conservation website that discusses numerous different things about elephants. It discusses the elephant debate about culling, the negatives of culling, the benefits of elephants and numerous other things. This source is valid and useful because it discusses the numerous different ways in which elephants benefit surrounding plants when they push trees over. The source is reliable because it gives examples from past studies in order to substantiate what has been said.
(Grogan & Suter, 2015) is an IEB matric textbook. This section of the textbook is useful and valid because it discusses ecological succession and the different stages thereof. Ecological succession is vital in this research in order to reach a conclusion as it all about which plants occur in which stages after a disturbance. A limitation to the source is that it does not link ecological succession with animals and the effect which animals have on the succession. The source is reliable because it is factual and is used by schools all over the country. Several websites also contain the same information as this textbook and it is therefore reliable.
(Rodrigues, n.d.) is a newspaper article stating the pros and cons of culling elephants. The article gives both viewpoints on the debate giving reasons as to why elephants should be culled and why they should not. The source states that elephants become destructive when their population increases to more than the environment can sustain. The source is valid and useful because it has information which contrasts the purpose of this investigation and this information can be used if the hypothesis is disproved. The source is reliable as it gives both sides of the argument and it backs up the information with quotes from officials and conservationists. A limitation of this source is that it focuses on the question of culling but does not mention the roles which elephants play and the disadvantages of elephants.
(Anon., n.d.) is a source that discusses the negative impact that elephants have on plants and the negative consequences that this has on the environment and other organisms. The source, however, does not entirely blame elephants and states that this destruction is unlikely to happen if elephants are not confined to small areas. The source is very useful and valid as it gives information about the negatives of elephants instead of positives. The source, however, is unreliable as both the author and date that the information was posted is unknown. The information in the source is also not supported by any figures or examples.
(Whiting, et al., 2016) is a gardening website that discusses the correct amount of sunlight that plants should receive. The source explains that different plants require different amounts of sunlight. The information is valid and useful to the investigation as it discusses the fact that some plants prefer shade and others sun. This helps discuss the data gathered and helps reach a conclusion. Figures are used in order to substantiate the facts and the source is therefore reliable. A limitation of the website is that it is more about garden plants than about plants in the natural savannah biome.
(Frowine, n.d.) is a book that states the effects of plants not receiving the correct amounts of sunlight. The book is useful and valid in terms of the research for the same reasons given for the above research. The source is reliable as it is based on facts and other sources contain the same information. As with the previous source, a limiting factor is that the website discusses garden plants and not wild plants in the savannah biome.
Gathering of Data
Apparatus
‘ Tape measure
‘ 4 beacons
‘ Clipboard, pen and paper
Methodology
1. Locate an Acacia nigrescens no shorter than 5 metres that has been pushed over by an African Elephant, Loxodonta Africana, (how long ago the tree was pushed over does not matter)
2. Using a tape measure, measure a 3 metre radius around the base of the tree where it has been pushed over (figure 2)
Figure 2. Measuring a 3m radius around the base of a tree where it has been pushed over
3. Place 4 markers/beacons around the tree on the 3 metre radius (divide the circle into quarters)
4. Count the number of plants taller than 30 centimetres (not including grass) in each quarter of the circle and add them together to find the total number of plants in the whole circle (figure 3 and 4)
Figure 3. Measuring plants to ensure they are taller than 30cm.
Figure 4. Counting the number of plants and different plant species.
5. Estimate the percentage of grass in each quarter
6. Add up the percentages of grass in each quarter and divide this number by 400 and then multiply by 100 to find the total grass percentage in the circle
7. Count the number of different species of plants above 30 centimetres (not including grass)
8. Record the results in a table (figure 5)
9. Repeat these steps for 4 other Acacia nigrescens that have been pushed over by elephant and for 5 Acacia nigrescens that are unaffected by elephant
Ethical issues for the experiment include large numbers of people walking in the bush in order to gather data. The ethical issue here is that if something were to go wrong and an animal were to charge, the animal would inevitably be shot.
Figure 5. Recording the results in a table.
Results
Table 1 showing the number of plants taller than 30cm, the number of different plant species taller than 30cm and the grass percentage growing within a 3m radius of Acacia nigrescens trees that were pushed over by elephant
Tree Number of plants taller than 30cm Number of different plant species taller than 30cm Grass percentage
1 14 9 15
2 13 4 20
3 7 5 25
4 11 5 18.75
5 11 5 22.5
Average 11 6 20.25
Table 2 showing the number of plants taller than 30cm, the number of different plant species taller than 30cm and the grass percentage growing within a 3m radius of Acacia nigrescens trees that are unaffected by elephant
Tree Number of plants taller than 30cm Number of different plant species taller than 30cm Grass percentage
1 28 8 24
2 24 6 30
3 12 4 10
4 18 9 8.75
5 11 6 13.75
Average 19 7 17.3
Bar graph 1 comparing the average number of plants taller than 30cm and the average number of different plant species taller than 30cm within a 3m radius of Acacia nigrescens trees that were pushed over by elephants and Acacia nigrescens trees that were unaffected by elephants
Bar graph 2 comparing the average grass percentage within a 3m radius of Acacia nigrescens trees that have been pushed over by elephants and Acacia nigrescens trees that are unaffected by elephants
Discussion
Elephants have the ability to change biomes from thickets to savannahs (pg.5, par.2), from the results, we can see this is true. Graph 1 (pg.15) shows that there are 8 more plants and 1 more different plant species growing in the shade of Acacia nigrescens trees that are unaffected by elephants than there are growing near the same species of trees that have been pushed over by elephants. Tables 1 and 2 (pg.14) shows that there is 14,54% more grass growing around the trees that have been pushed over by elephants than there is growing in the shade of the trees that are unaffected by the elephants. These results illustrate that the elephants are allowing more grass to grow and less plants and trees to grow when they push trees over thereby transforming the habitat from thicket to savanna. In this way, the elephants are benefiting the grass but not other plants.
Elephants assist seedlings by creating space for them to grow when they push trees over and also by allowing the seedlings to grow without the shade of other trees and plants (pg.5 par.3). Looking at the results (pg.14 and 15), it can be said that the elephants assist grasses in this way but not shrubs, trees and other plants. There is an average of 19 plants growing in the shade around tress that are unaffected by elephants, but there are only 11 plants taller than 30cm growing in the sun around a tree that has been pushed over by elephants. However, there is 20,25% grass covering around trees that have been pushed over by elephants compared to the 17,3% grass covering under trees that are still standing and are unaffected by elephants.
The debris caused by elephants pushing over trees assists pioneer grasses and shrubs by allowing them to grow without being trampled on (pg.5 par.5). Graph 2 (pg.15) shows this. We see that there is more grass (20,25% grass covering) growing in the area around the tree that has been pushed over by elephants than there is under the tree that is unaffected by elephants (17,3% grass covering), showing that it could be true that the debris protects the pioneer grasses and shrubs. These results, however, were not taken from an area that has been entirely destroyed by elephants and where there is lots of debris lying around, but from areas within a 3m radius of single trees that have been pushed over. Around these trees, there is not much debris, if any, and so the results cannot be used to prove this point.
Secondary plant succession occurs when there has been a disturbance in an area that has life (pg.6 par.2). This disturbance could be anything like a herd of elephants pushing trees over and destroying the area. The experiment conducted examines disturbance on a very small scale by only looking at a 3m radius around a single tree that has been pushed over by elephants. In secondary succession, the growth of annual herbs, shrubs and grasses begins in the pioneer stage (pg.6 par.3). This can be seen in graph 2 (pg.15) and tables 1 and 2 (pg.14) of the results where there is much more grass growing within a 3m radius of Acacia nigrescens trees that have been pushed over by elephants than within a 3m radius of the same type of tree that is still standing and is unaffected by elephants. There is a difference of 14,54% grass coverage between the two areas. In this way, elephants are beneficial to plants as they create a disturbance allowing new species to grow in that area. In the results it is also seen that the grass remains throughout the succession, not like other pioneer species (pg.6 par.3).
Graph 1 (pg.15) shows that there are 8 more plants taller than 30cm growing within a 3m radius of trees that are unaffected by elephants than there are growing around trees that have been pushed over. This could be because the elephants trample and destroy the smaller plants under the tree while pushing the tree over (pg.7 par.3). In this way, elephants are more destructive than beneficial to the plants.
Different plants require different intensities of sunlight for different durations of time in order to thrive. If plants are exposed to too much sunlight for too long, they become scorched and die. If not exposed to enough sunlight, they cannot photosynthesise sufficiently and will not thrive (pg.7 par.5). From both graphs (pg.15) in the results, it is clear to see that grass most likely prefers to grow in full sun as there is more grass (20,25% grass covering around pushed over trees, 17,3% grass covering around unaffected trees) with no shade around the trees that have been pushed over by elephants. Plants other than grass seem to prefer growing in partial shade under trees that have been unaffected by elephants. This is seen in the results where there are 8 more plants growing in the shade of trees than around trees that have been pushed over by elephants.
Temperature has an effect on light intensity and some plants require shade in order to escape the heat (pg.8 par.1). These results were captured during a drought when temperatures were high so plants that normally prefer growing without the shade of other trees may have required this shade in order to escape the heat. This could be a reason as to why more plants taller than 30cm (19 plants) were growing within the shade of a 3m radius of trees that were unaffected by elephants than there were growing without shade (11 plants) within a 3m radius of trees that had been pushed over by elephants (graph 1 pg.12). This could also be a reason as to why more different species (7 different species) were found growing in the shade of trees than around trees that had been pushed over (6 different species) by elephants (graph 1 pg.12). In the shade of the unaffected trees, there may have been plants growing that usually thrive in shade as well as those that normally grow in full sun but are using the shade to escape the full heat and intensity of the sun. In this incident, elephants are not beneficial to plants as they are removing shade that the plants may desperately require in order to survive in high temperatures.
In forests, elephants are beneficial to smaller plants and trees that are trying to grow because these smaller plants are completely shaded by the taller trees and receive no sunlight. They therefore cannot photosynthesise. Elephants push forest trees over and create a gap in the forest canopy where sunlight can penetrate. The smaller plants are then able to receive sunlight and thrive (pg.5 par.2). In graph 1 (pg.12), we see that this is not the case for plants in the savannah biome where there are 19 plants growing in the shade of other trees but only 11 growing in the sun around trees that have been pushed over by elephants. In the forest, smaller plants receive no sunlight at all, in the savannah biome, however, even in the shade of other trees, the plants still receive some sunlight. In the savanna biome, these smaller plants are not completely surrounded by trees so they do, at some point during the day receive sunlight. Due to this fact, when trees are pushed over, plants that were growing in partial shade now receive full sun for the entire day. This sunlight is most likely too much for the plants and they wilt and die (pg.8 par.2).
Conclusion
In the savannah biome, elephants are beneficial to grasses but are not beneficial to other plants when they push trees over and expose the plants in their shade to direct sunlight. The hypothesis is partially accepted as elephants benefit grasses but not plants taller than 30cm when they push trees over in the savannah biome in the Nkuhlu area in the Kruger National Park.
Graphs 1 and 2 (pg.12) show that there are more plants and more plant species growing in the shade within a 3m radius of Acacia nigrescens trees that are still standing than there are growing without shade within a 3m radius of Acacia nigrescens trees that have been pushed over by elephants. There is, however, a greater percentage of grass growing around the pushed over trees than in the shade of the unaffected trees. These results show that the elephants assist the grasses by creating more space for them to grow without the shade of trees. The elephants do not assist other plants as these plants require shade to escape the intense heat of the sun and also so they do not receive too much sunlight for too long; elephants remove the shade that these plants require when they push trees over.
Limitations to the experiment are that it was only conducted once, in one area, using only one species of tree, during a drought and only in one season. A small sample size was also a limitation.
In order to improve the experiment, it should be repeated several times and in different areas but all areas should be savannah biome. The area that the experiment is conducted in has an effect on the results because various factors such as the soil and how nutrient-rich the soil is and how much water is available in the soil affect the growth of plants.
The experiment should also be done using a bigger sample size. More trees should be looked and an average of the results should be calculated. Doing this will make the experiment more reliable.
The experiment should also be conducted at a different time when there is no drought. The experiment should be conducted in stable environmental conditions so the results are not affected by droughts or floods.
The experiment can also be carried out at different temperatures and in different seasons. The average of these results should be used in order to get reliable results.
Another way to improve the experiment is to conduct the whole experiment several times but using different species of trees. This could have an effect on the results as some tree species create deeper shade than others. Once again, an average of these results should be used.