Ecological Disturbance and its Effects - Research Paper Example

Ecological effects of disturbance Introduction Ecological disturbance is generally regarded as the disruption of the flora, fauna and land by external forces such as flood, drought, fire and cyclones. Such disturbances are major factors that have the potential to transform the structure of the ecosystem and biological communities (Gutschick and BassiriRad 2003). The impacts may be adverse or beneficial for the ecosystem, depending on the characteristics of the disturbance. This paper examines the ecological effects of disturbances such as fire, drought and cyclones on biotic communities in the Australasian region. The paper focuses on three case studies of the impacts of fire, drought and cyclone on the Australian ecosystem in particular, and, thereafter, analyses these impacts in detail, focusing on their impact on the biodiversity, flora, fauna and landscape of the Australian region. Before this discussion is undertaken, it is important to establish what is meant by the term ‘disturbances.’ Literature review There are several definitions that have been developed by scholars and environmentalists to define what is entailed in an ecological disturbance. The most acceptable definition is that ecological disturbances are temporary but significant changes in the environment that impact on the ecology of an ecosystem (Gutschick and BassiriRad 2003). Disturbance can either result from natural causes or human activities (Simkin and Baker 2008). Due to various changes that come about as a result of disturbances, there can be many alterations in the biodiversity and community life of an area. These changes that take place at either a micro level or at the macro level and often alter the ecology of the region (Gutschick and BassiriRad 2003). For instance, a fire can cause displacement of certain species from the area and force relocation of them to a distinct region, thereby altering the characteristics of the region (Franklin 2010). The disturbances that occur at the micro level usually affect the community life in small but significant ways. For example, if there is lighting, that might strike a tree or specific area. This can be of great significance to a localised flora/fauna community especially where there is a thick coverage of vegetation, such as in Australian rain forests (Flematti, Ghisalberti, Dixon and Trengove 2004). Under such circumstances the falling of the tree will allow sunlight to enter into the ecosystem which is not prone to it. Macro level ecological disturbance is usually high and the impact of the disturbance has more significant impact on larger and more diverse elements in the ecosystem. Macro ecological disturbances are usually connected with the occurrence of various extreme incidents and events such as extreme variance in temperature, floods, cyclones, wildfires. Although, such extreme events might be rare, their occurrence plays a key role in the shaping of the ecology (Gutschick and BassiriRad 2003). The following case studies investigate the impacts of fire, drought and cyclone on the Australian ecosystem. Thereafter, the ecological affects of each of the disturbances are investigated by focusing on their impact on the biodiversity, flora, fauna and landscape of the Australasian region. Case study 1: Fire Wild fires are usually highly destructive in nature, especially to the biodiversity that is present in an area. Wild fires can be described as a chemical disturbance which is caused by the rapid combustion of the biomass, usually the plants in the area, and it often causes mortality of the most dominant species that are present in an ecosystem such as the trees that are dominant in the area (Agee 1993). There are a number of causes that contribute to the phenomenon of wild fires in an ecosystem. These can be natural causes or man made. One of the most noticeable causes of wild fires is that of lightning, especially in the cases of those forests which are situated in the dry regions, as wood in these regions is especially dry (Flematti, Ghisalberti, Dixon and Trengove 2004). Fires can also be made artificially by humans. In the case of human made fires, they are sometimes lit by rangers to ensure that they can demarcate the forest areas (Egan and Holland 2009). They are also undertaken for security purposes or to enhance the agricultural functioning in an area. Australia is known as the most fire-prone country that has unique fire-adapted flora and islands consisting of vegetation that are sensitive to fire (Bowman 2000). Due to wildfire, many species such as Acacia aneura and Callitris glaucophylla found in rangelands suffer heavy mortality (Griffin and Friedel 1984; Noble 1997). However, it is interesting to note that much of Australian biodiversity is also the result of wildfire. But, due to the ending of the Aboriginal fire management system, the survival of many of these natural habitats is being threatened. For instance, E.diversicolor is a huge tree that is related to the Eucalyptus species, whose regeneration is dependent on disturbance, especially fire (Brooker 2000). It has been seen that in most cases wildfire is conceived to have negative impact on the biodiversity, due to the high mortality rate of animals during a wildfire. However, in reality, research indicates that animals and plants are much more tolerant to fire than perceived. It is difficult to provide a general picture about the impact of fire on biodiversity as some species might be impacted negatively due to fire, while others often derive benefits out of it (Griffin and Friedel 1984) In the case of flora, it has been found that most vegetation survives even during wildfire. This is mostly due to the fact that most native Australian vegetation has developed mechanisms to protect tissue against the heat. Features such as thickness of the bark, re-sprouting above the ground level, strong roots and stem systems also strengthens the fire resistance mechanism in these plants and trees (Griffin and Friedel 1984). A case in point is the Eucalyptus tree. This tree can vegetatively regenerate from the epicormic buds that are found in the bark of the tree. These buds are protected by the thick bark and the branches are re-sprouted even if they are damaged during the fire (Burrows 2002). However, this is a difference between the responses of vegetation to fire in Southern and Northern Australia. In the Southern part of Australia, the Eucalyptus found promotes the spread of fire due to the presence of highly flammable materials such as bark and leaves. However, in Northern Australia, the Eucalyptus does not display such characteristics and in fact are resistant to fire and recover quickly from a wildfire (Brooker 2000). The fauna found in Australia is relatively tolerant of wild fire due to their highly developed senses. Native animals have developed a capacity of escaping fire by moving to places that are not affected by fire or by making a pit in the soil and burrowing under it to escape from the heat (Griffin and Friedel 1984). Research has found that the mortality rate due to fire is commonly low as the animals evacuate the place as soon as a fire breaks out (Griffin and Friedel 1984). However, mortality rates have been found quite high in invertebrates that cannot fly as well as insects in their larval stages. Fire also results in changing the physical environment and the natural habitat of the fauna living in the forest. It leads to alteration in food quality and quantity (Gutschick and BassiriRad 2003). For instance, birds are able to feed on dead insects or herbivores can eat nutritious new grass. Further, post-fire, the ground temperature and the moisture found in the soil also alters comprehensively. This also leads to changes in the habitat of the fauna population (Bowman 2000). Wildfires may also impact the atmosphere and landscape and change the biogeochemical cycles as well. Horwitz et al (1999) believe that fire results in influencing the nutrient cycle and helps in redistributing nutrients in the environment. It has been found that due to fire, nutrients such as potassium, manganese and calcium are circulated in the atmosphere. However, it also results in the loss of nitrogen in large quantities as well. As per Horwitz et al (1999), the soil in Australia is found to be lacking in phosphorus and nitrogen. This is being linked to the occurrence of wildfire in the country. Further, due to repeated fire incidents, the soil organic matter in Australia is also in decline. The soil in the area that is being burnt is found to crust more easily than that not burnt. This is due to the fact that the humus content in such soils is very low, which results in the dispersion of clay. This results in disturbance to the ecosystem as the infiltration of water may get affected (Horwitz et al 1999). The most typical effect of wildfire is the emission of greenhouse gasses such as methane, carbon dioxide and nitrous oxide, resulting in air pollution and depletion of ozone layer (Bowman 2000) Case study 2: Drought Australia is a country that has variable rainfall climates. The fluctuations have varied causes; one of the strongest reasons for the variation in Australia’s rainfall climate is the Southern Oscillation. This is seen to have air pressure shifts in the east Pacific and Asian regions. It is also known as El Niño (Bond et al 2008). It has been argued there can be little possibility for the entire Australian continent to be drought hit in the same period. It has been witnessed that some drought conditions are prolonged for a longer time creating severe impacts on the community;, while some droughts only last for a shorter period of time. Further, some drought conditions are restricted to one region while other parts of the country receive rain. As some of the regional droughts may not be related to El Niño; therefore, it is difficult to predict the nature of such droughts (McBride and Nicholls 1983). The average rainfall received in the country varies considerably across the region. While the large areas receive rainfall of around 600-1,500 millimetres (mm) on an average, this is compared or similar to North American and European averages. On the other hand, most parts or half of the region receives an average rainfall of less than 300 mm annually. In the past years, parts of Australia such as south-east of the continent, the Murray-Darling Basin, southern Queensland, have experienced severe drought conditions. This has consequently lowered the water levels in the region (Bond et al 2008). During the twelve months of September 2008 to August 2009, populated areas of Victoria and New South Wales, including the Murray-Darling Basin were under severe stress and received below average rainfall. Parts of south-east Australia have been very dry and other parts i.e. the north-east have been seen as normally wet (Bond et al 2008). Figure 1: Rainfall anomalies: September 1, 2008 – August 31, 2009 Source: Australian Bureau of Meteorology Figure 2: Rainfall anomalies: September 1, 2007 – August 31, 2009 Source: Australian Bureau of Meteorology The above rainfall anomaly maps showcase the changes or digression in the annual average rainfall. As per the Bureau of Meteorology, the rainfall received has been below average in parts of south-east and south-west Australia in 1997. On the other hand, the Murray-Darling Basin has experienced below average rainfall since 2002. This is considered to be the most productive agricultural areas of Australia. Therefore, the Murray-Darling Basin has remained under severe drought like conditions, while the north-eastern part of the country received adequate rainfall. This is an excellent case of ecological disturbance, wherein the uneven distribution of rainfall results in a drought-like situation in one place and sufficient rainfall in another (Bond et al 2008). It is a common knowledge that water is on of the most critical factors for sustaining life. It also serves as an important input for the Australian ecosystem as well as the economy, especially for the agricultural sector. The country has not only seen floods but also sever drought conditions, which has given rise to the fact that taking out too much water from the rivers and groundwater results in negative impacts on the ecology of the country. It may further impact on biodiversity and results in the decrease of local plant and animal populations as well as agricultural produce (Bond et al 2008). Droughts not only adversely affect the economy of the country by disrupting the crops but also cause serious damage to the environment, especially related to the loss of vegetation and soil erosion. The quality of water also is impacted as algae outbreak may take place in drought-hit areas. Drought often results into dust-storms and bush fires due to extreme dry conditions and lack of moisture (Bond et al 2008). It is considered that drought has adverse effects on the aquatic ecosystem. However, it has also resulted in the formation of some of the most unique bio-systems due to the environmental conditions prevalent in Australia. Freshwater fauna and flora in Australia are found to be well adapted to drought and flood conditions and have developed their recovery mechanisms over centuries of evolution (Boulton 2003). With the outbreak of drought, organic materials and sediments are also being flushed downstream. This result in providing nutrients and huge food quantity to fish and insects, which are in turn are consumed by water birds (Humphries and Baldwin 2003). However, it may take many decades for the ecosystem to re-establish itself in its former order. It may be seen that native fish may take years before regaining their previous habitat (Matthews and Marsh-Matthews 2003). However, research still needs to be undertaken to find out the impact of drought on fishes, especially those dwelling in a river system that is not being affected by drought. Further, the recovery rate may also vary significantly as it would depend directly on factors such as using of the fresh water after the drought for farm development or river regulation (Matthews and Marsh-Matthews 2003). Also, the extinction of species that were found abundantly before the drought may also result in changing the structure of aquatic ecosystem (Humphries and Baldwin 2003). Case study 3 – Cyclones Many parts of Australia are prone to often severe tropical cyclones. On average each year around six cyclones hit Australian coasts, especially in the northern regions of the Continental landmass (Emmanuel 2005). The range of a cyclone’s intensity is from range 1, where wind gusts reach around 125 kilometers per hour, up to a range of 5, where the gusts reach more than 280 kilometers per hour. The cyclone season in Australia usually reaches from November to April. This occurs in the region of Perth, WA coasts and in the Northern Territory. In general, areas above the Tropic of Capricorn are also vulnerable (Emmanuel 2005). Two deadly cyclones that have hit Australia are Cyclone Tracy and Cyclone Mahina. In the year 1899 (March), Cyclone Mahina hit Cape Melville, Queensland. This storm killed around 400 people in the region. It also completely devastated the pearling fleet. In the month of December 1974, Cyclone Tracy hit Darwin, and around 195 mm of rainfall fell in the span of 8.5 hours and killed 65 people (Emmanuel 2005). Cyclones are considered to be the worst ecological disasters Australia’s environment suffers. Diverse regions in Australia suffer from cyclones every year. On an average during the cyclone season around 10 cyclones develop in and around Australian waters. Scientists have also proven the occurrence of El Niño increases the cyclone activity. Also, the La Niña phenomenon also provokes the formation of cyclones in the Pacific (Grove et al 2000). The following chart indicates the occurrence of cyclones that affect parts of Australia yearly. Since the 1970s, cyclonic conditions have been aggravated in Australia with high winds impacting the vegetation and animals in those parts of the country susceptible to cyclonic impacts (Emmanuel 2005). Studies have found that cyclones may affect the growth of vegetation, structure of forests, composition of the animal community, patterns of evolution and even the height of the canopies (Hopkins 1990; Clarke and Kerrigan 2000; de Gouvenain and Silander 2003). One of the most devastating disturbances of cyclones in Australia is destruction of coral reefs. As per a survey by Fabricius et al (2008), the coral reefs at the Far Northern Great Barrier Reef suffered considerable damage due to the impact of Cyclone Ingrid in 2005. The study found that the offshore reefs suffered the most damage, while the inshore reefs witnessed the breaking away of the coral shoals. The cyclone reduced the density of the coral by as much as 30 per cent. Thus, cyclones can have devastating impact on the coral reefs of Australia (Fabricius et al 2008). Cyclones often wreck havoc in the rain forests of Australia as well (Grove et al 2000). The high winds results in breaking of branches and the falling of trees, which causes penetration of light into the floor of the rainforest, which is normally shaded by the branches (Turton 1992). This leads to the growth of dormant plants that are unable to germinate due to the non-availability of sunlight. The major fallout of this phenomenon is the uncontrolled growth of weeds (Chazdon 1988). Australian rainforests are mainly vulnerable to the influence of cyclones. Conclusion The paper has found that ecological disturbances have an immense impact on the ecosystem and biotic communities of Australia. For instance, in the case of fire and drought, it has been found that most flora and fauna have the ability to regenerate and recover quickly. However, in case of cyclonic disruption, the impact on the ecosystem is far-reaching and often permanent. In the case of fire especially, it was found that although being perceived to be harmful to the flora and fauna, the Australian vegetation and animals have developed survival mechanisms. Trees, especially the Eucalyptus species, have the ability to re-sprout its branches from the epicormic buds that are found in the bark of the tree, which are well-protected from the heat due to the thickness of the bark (Burrows 2002). Similarly, animals have developed behaviour to protect themselves from wildfires by evacuating the area or by burying themselves into the soil to escape heat. However, fire also has negative impacts, especially due to its influence on the nutrient cycle. Wildfire has resulted in the lack of phosphorus and nitrogen in the Australian soil. Further, repeated fires has also given rise to greenhouse gases such as methane, carbon dioxide and nitrous oxide, which augment air pollution and depletion of ozone layer in the region. Drought has severe impact on the livelihood of human beings, as it impacts the survival of vegetation and crops. Further, it results in soil erosion, water pollution and even bush-fires. However, it is interesting to note that freshwater fauna and flora in Australia are well adapted to drought conditions. They have natural mechanisms that help them to regenerate. Although, significant studies have yet to be undertaken to understand the regeneration strategies adopted by these flora and fauna; insufficient studies have been undertaken to understand if such mechanisms are being developed in the organisms dwelling in healthy rivers that have not seen a drought situation. The paper has found that cyclones are the most devastating of the range of ecological disturbances as they impact the ecosystem without providing sustainable scope for regeneration. Cyclones have particularly wrecked havoc in the Australian rainforests and coral reefs of the Far Northern Great Barrier Reef. References: Agee, J 1993, "Fire ecology of Pacific Northwest forests", Washington, DC, USA, Island Press. Bond, Nicholas R. Lake, P. S. and Arthington, Angela H. 2008, “The impacts of drought on freshwater ecosystems: an Australian perspective”, Hydrobiologia 600(1). Boulton, A.J. 2003, “Parallels and contrasts in the effects of drought on stream macroinvertebrate assemblages”, Freshwater Biology, 48, 1173–1185. Bowman, D. 2000, “Rainforests and Flame Forests: the Great Australian Forest Dichotomy”, Australian Geographical Studies, 38(3), 327-331. Brooker, M. 2000, “A new classification of the genus Eucalyptus L’He´r. (Myrtaceae)”, Australian Systematic Botany 13, 79–148. Chazdon, R. L. 1988, “Sunflecks and their importance to forest understorey plants”, Advances in Ecological Research 18, 2–63. Clarke, P.J. and Kerrigan, R.A. 2000, “Do forest gaps influence the population structure and species composition of mangrove stands in northern Australia”, Biotropica 32, 642–652. De Gouvenain, R.C. and Silander, J.A. Jr. 2003, “Do tropical storm regimes influence the structure of tropical lowland rain forests”, Biotropica 35,166–180. Egan, Carmel and Holland, Steve 2009, “Inferno terrorizes communities as it rages out of control”, Herald Sun, March 2009. Emmanuel, K.A. 2005, “Increasing destructiveness of cyclones over the past 30 years”, Nature 436, 686–688. Fabricius KE, De’ath G, Poutinen ML, Done T, Cooper TF, Burgess SC 2008, “Disturbance gradients on inshore and offshore coral reefs caused by a severe tropical cyclone”, Limnology and Oceanography 53, 690–704. Flematti GR, Ghisalberti EL, Dixon KW and Trengove RD, 2004, “A compound from smoke that promotes seed germination. Science. 2004; 305 (5686):977 Franklin, J 2010, "Mapping Species Distributions: Spatial Inference and Prediction (Ecology, Biodiversity and Conservation), New York, Cambridge University Press. Griffin, G.F. and Friedel, M.H. 1984, “Effects of fire on central Australian rangelands: Changes in tree and shrub populations,” Australian Journal of Ecology 9, 395–403. Grove, S. J., Turton, S. M. and Siegenthaler, D. T. 2000, “Mosaics of canopy openness induced by tropical cyclones in lowland rain forests with contrasting management histories in northeastern Australia,” Journal of Tropical Ecology 15, 883–894. Gutschick, V. P., and BassiriRad, H. 2003, “Extreme events as shaping physiology, ecology, and evolution of plants: toward a unified definition and evaluation of their consequences,” New Phytologist 160, 21–42. Hopkins, M.S. 1990, “Disturbance – the forest transformer”, In: Australian tropical rainforests: science – values – meaning—Webb LJ, Kikkawa J, eds. (1990) East Melbourne: CSIRO, 40–52. Horwitz, P., Pemberton, M. and Ryder, D.1999, “Catastrophic loss of organic carbon from a management fire in a peatland in southwestern Australia”, In McComb, A.J. and Davis, J.A. (eds) Wetlands for the Future, Gleneagles Publishing, Adelaide, 487–501. Humphries, P. and Baldwin, D. 2003, “Drought and aquatic ecosystems: an introduction”, Freshwater Biology 48, 1141–1146. Matthews, W.J. and Marsh-Matthews, E. 2003, “Effects of drought on fish across axes of space, time and ecological complexity”, Freshwater Biology, 48, 1233–1255. McBride, J. L. and Nicholls, N. 1983, “Seasonal relationships between Australian rainfall and the Southern Oscillation”, Mon. Wea. Rev., 111, 1998-2004. Noble, J.C. 1997, “The delicate and noxious scrub: CSIRO studies on native tree and shrub proliferation in the semi-arid woodlands of eastern Australia”, CSIRO: Canberra. Simkin, R & Baker, P.J. 2008, Disturbance history and stand dynamics in tall open forest and riparian rainforest in the Central Highlands of Victoria, Austral Ecology, vol. 33, pp. 747-760. Turon, S. M. 1992, “Understorey light environments in a north-east Australian rain forest before and after a tropical cyclone,” Journal of Tropical Ecology 8, 241–252. Read More

The following case studies investigate the impacts of fire, drought and cyclone on the Australian ecosystem. Thereafter, the ecological affects of each of the disturbances are investigated by focusing on their impact on the biodiversity, flora, fauna and landscape of the Australasian region. Case study 1: Fire Wild fires are usually highly destructive in nature, especially to the biodiversity that is present in an area. Wild fires can be described as a chemical disturbance which is caused by the rapid combustion of the biomass, usually the plants in the area, and it often causes mortality of the most dominant species that are present in an ecosystem such as the trees that are dominant in the area (Agee 1993).

There are a number of causes that contribute to the phenomenon of wild fires in an ecosystem. These can be natural causes or man made. One of the most noticeable causes of wild fires is that of lightning, especially in the cases of those forests which are situated in the dry regions, as wood in these regions is especially dry (Flematti, Ghisalberti, Dixon and Trengove 2004). Fires can also be made artificially by humans. In the case of human made fires, they are sometimes lit by rangers to ensure that they can demarcate the forest areas (Egan and Holland 2009).

They are also undertaken for security purposes or to enhance the agricultural functioning in an area. Australia is known as the most fire-prone country that has unique fire-adapted flora and islands consisting of vegetation that are sensitive to fire (Bowman 2000). Due to wildfire, many species such as Acacia aneura and Callitris glaucophylla found in rangelands suffer heavy mortality (Griffin and Friedel 1984; Noble 1997). However, it is interesting to note that much of Australian biodiversity is also the result of wildfire.

But, due to the ending of the Aboriginal fire management system, the survival of many of these natural habitats is being threatened. For instance, E.diversicolor is a huge tree that is related to the Eucalyptus species, whose regeneration is dependent on disturbance, especially fire (Brooker 2000). It has been seen that in most cases wildfire is conceived to have negative impact on the biodiversity, due to the high mortality rate of animals during a wildfire. However, in reality, research indicates that animals and plants are much more tolerant to fire than perceived.

It is difficult to provide a general picture about the impact of fire on biodiversity as some species might be impacted negatively due to fire, while others often derive benefits out of it (Griffin and Friedel 1984) In the case of flora, it has been found that most vegetation survives even during wildfire. This is mostly due to the fact that most native Australian vegetation has developed mechanisms to protect tissue against the heat. Features such as thickness of the bark, re-sprouting above the ground level, strong roots and stem systems also strengthens the fire resistance mechanism in these plants and trees (Griffin and Friedel 1984).

A case in point is the Eucalyptus tree. This tree can vegetatively regenerate from the epicormic buds that are found in the bark of the tree. These buds are protected by the thick bark and the branches are re-sprouted even if they are damaged during the fire (Burrows 2002). However, this is a difference between the responses of vegetation to fire in Southern and Northern Australia. In the Southern part of Australia, the Eucalyptus found promotes the spread of fire due to the presence of highly flammable materials such as bark and leaves.

However, in Northern Australia, the Eucalyptus does not display such characteristics and in fact are resistant to fire and recover quickly from a wildfire (Brooker 2000). The fauna found in Australia is relatively tolerant of wild fire due to their highly developed senses. Native animals have developed a capacity of escaping fire by moving to places that are not affected by fire or by making a pit in the soil and burrowing under it to escape from the heat (Griffin and Friedel 1984).

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