THE SURVIVAL OF THE GREY MANGROVE IN SPITE OF URBANIZATION AND POPULATION PRESSURE AT THE SALT PAN CREEK

Posted: August 25th, 2021

THE SURVIVAL OF THE GREY MANGROVE IN SPITE OF URBANIZATION AND POPULATION PRESSURE AT THE SALT PAN CREEK

                                                                                    By

The Name of the Class (Course)

Professor (Tutor)

The Name of the School (University)

The City and State where it is located

The Date

The survival of the Grey Mangrove In Spite of Urbanization and Population Pressure at the Salt Pan Creek

Introduction

            Estuaries are good marine environments for the growth of mangrove forests. The forests usually grow in the tropical tidal areas with the largest concentration of mangrove forests being the areas between 5 degrees to the north and south of the equator. The largest concentration of mangrove forests is found in Indonesia. Australia ranks number 5 in terms of the size of mangrove forests. Mangrove forests are rich ecosystems since very many species of plants and animals depend on them for survival. Research estimates that 35% of all mangrove forests have disappeared secondary to climate change and human activities (Valiela, Brown and York, 2001).  Most people view the forests as unproductive lands and end up clearing them for human settlements, agriculture, and aquaculture. In addition, mangrove trees provide a rich source of timber, firewood, animal fodder, and charcoal. Consequently, the trees are constantly harvested to provide raw materials. The forests’ existence has also been threatened by climate change which destroys coral reefs which often act as shields against strong tides from the ocean. Therefore, the threats against the mangrove forests in many parts of the world are evident.

            One of the factors that have affected mangrove ecosystems in Australia is climate change. However, the effect of climate change has not been well studied due to the presence of confounding factors such as human population pressure. Most of the remaining mangrove tress that makesgood areas of study include protected environments such as national parks. If one wants to study the prevalence and growth of the grey mangroves in areas where human activities are happening, such protected areas would not form good grounds of study. Urbanized areas such as the Salt Pan Creek provide a good environment to study the mangrove trees while at the same drawing insights on the effects of human activity on these forests.

            Mangrove species are found in different parts of Australia along the creeks, rivers, and estuaries. The Salt Pan Creek area is one such area which although threatened by human pressure, the mangrove trees have continued to exhibit their resilience. As an urban water catchment area, one would expect urbanization to have taken the toll over the areas resulting in diminishing number of trees. The area has several of the endangered tree species that are impossible or rare to find in many other parts of Australia. One species of such trees that have been the object of study by many ecologists is the Grey Mangrove whose botanical name is Avicennia marina. The grey mangrove grows well along with the tropical climates. The distribution of this species is, therefore, under the influence of many factors that range from biotic, physiographic, and climatic. In Australian estuaries such as the Salt Creek Pan, dense growths of mangrove trees are common phenomena. Areas such as these often receive high quantities of rainfall per annum. The physiological activities of different species of mangrove species tend to differ. As it has been shown in many studies, other species of mangrove trees present in Australia include Aegiceras corniculatum, commonly known as the river mangrove and Sarcocornia quinquefolia(Alongi 2002). The grey mangrove, in particular, thrives in areas with high solar radiation and hypersaline water.

             The most common mangrove on the coast of Australia is the grey mangrove. It is characterized by its ability to withstand the colder climates of Australia as compared to other mangrove trees which grow well in areas around the equator. The trees have been shown to grow to heights of 25 meters. However, most of the common trees found along the Australian coastline grows to heights of between 10 and 15 meters under conditions that favor them. They have a fissured bark and wide leaves. The most common measurement for the leaves is 8cm for the length and 5cm for the width. The characteristic color of the leaves is glossy green with some of the trees being distinctively pale. They also have pencil-like pneumatophores that grow horizontally to allow the plant to breathe in hypersaline conditions. During the flowering period, they produce yellow flowers that grow in clusters. The trees are widely known for their tolerance of extremely salty conditions (Department of Agriculture and Fisheries, 2013). Although they can withstand waterlogging for the duration of about 2 weeks, they often die when exposed to waters with low salinity. As has been mentioned previously, the grey mangrove is very sensitive to changing climatic conditions as well as human activity. Through a study of the height of the grey mangroves along the Salt Pan Creek, it is possible to determine the extent to which the grey mangrove has been affected by the above-mentioned factors. The presence of more tall trees than short ones would imply that the mangrove forests have suffered little or no effect due to human intervention and climate change. However, a reverse situation would imply that the species is threatened by the factors that form the basis of this study.

Methods

Study site

             The area of this study was the Salt Pan Creek Catchment area which is a tributary of Georges River. It is located in Sydney in Australia. The size of the area of study was approximately 7 kilometers although the creek itself covers an area of about 26 kilometers. It is an area that is rich in vegetation that comprises the indigenous species of mangrove trees. The most dominant species is the grey mangrove. The tidal flow in the area influences the kind of vegetation in the area to a great extent. Mudflats that have been formed through the processes of inundation dominate the coastline providing good habitats for the growth of the estuarine vegetation. Land clearing activities by man have, however, destroyed most of the vegetation.That notwithstanding, there still remain great biodiversity which provides a good environment for researchers to understand the effects of human activities on estuarine vegetation.

             The mangrove study was conducted along the creek in the mangrove forests. It is a town simmering with tourist activities who visit the area to observe biodiversity within an urbanized coastal region. There are several areas for people to engage in leisure activities such as nature walks. In addition to the plant species present, the area is also rich in fauna that is mainly dependent on the plant species for survival. It is clear from the outset that most of the tall trees have been cut down in human clearing activities. In addition to the estuarine vegetation, one can find many pockets of sandstone vegetation as they move along the creek. The upper sides of the creek are not as rich in vegetation as the lower sides. In fact, most of the upper side is barren. Native vegetation is, however, widespread as on moves towards the lower reaches along Cantebury road. The increase in vegetation as one move closer to the sea is attributed to increasing salinity of the soil. The rise in the sea level also appears to have adversely affected the growth of mangroves with most of the vegetation appearing to be receding inland. Climate change has also brought changes to the nature of the trees present making it a very important area of study.

Species

            The species that formed the basis of my study was Avicennia marina. As the most widespread form of vegetation along the Creek, it provided a good ground for understanding the effects of human activities on estuarine vegetation. Human interference in estuarine environments has been shown to have significantly affected the structure of the mangrove forests In Australia. Consequently, trees do not grow as tall they used to grow in the past. Using the discrepancies in the heights of the trees sampled, one can estimate the extent to which human activities have interfered with the mangrove forest ecosystems. Some of the ways in which humans have caused a disturbance in the forests include the practices of tree harvesting, clearing of land for urban settlements, construction of roads and reaction activities, and activities geared to promoting the fishing industry.

            The grey mangrove has also been affected by the changes in sea level because of its tendency to grow in hypersaline soils. This has brought a landward scenario of growth in the mangrove forests of Australia. The shape of the estuaries has also affected the growth of the mangroves. Shapes that allow waterlogging for prolonged durations lead to the death of the plants. The elevation of the surface on which the trees grow also determines their ability to survive changing sea levels. Other natural phenomena such as winds and tides influence the rate of growth. In spite of the effects of human activities and climate changes the grey mangrove has continued to be the most widespread kind of vegetation on the coastline of Australia. The aim of the study can, therefore, be fulfilled by studying one parameter of the size of the trees which is height.

Experimental Designs and Methods

            The aim of the study was to understand whether human activities and climate change had any impact on the population of grey mangrove on the Salt Pan Creek in Australia. To do this, it was important to develop an experimental design that reduced sampling bias as it was not possible to count all the trees in the whole mangrove forest in the area.  The study entailed the drawing of three-line transects of variable lengths between 3 and 15 meters. The total distance between the line transects was 32meters. Transect A was 3 meters in width and was mainly in an area with very sparse vegetation. Transect B which was in an area of dense vegetation was 14 meters. Transect C measured 15meters and was the closest to the Salt Pan Creek. The number of trees in the transects was counted based on the height categories assigned in the study design. The design was informed by the information in the available literature that the grey mangroves seldom grow taller than 25 meters. As such the categories of mangrove trees sampled were less than 10cm, 10-15cm, 15-30cm, 30-55cm, 1-3 meters, 3-10 meters and those above 10 meters. In spite of the varying lengths of the transects, the area in which the trees were sampled were all 0.5 meters wide. The total number of grey mangroves was recorded with respect to the categories developed in the study design for further analysis and presentation. As it had been discussed earlier, the size of the trees would be a clear indication of the impact of climatic concerns and human activities on the size of the mangrove trees on the Salt Pan Creek.

Statistical Analysis

            The categories for the heights of the trees were developed as part of the study designs from the very outset. The number of trees based on the height was the most important variable and not the number of trees counted in each of the transects. The focus was on one species of trees which was the grey mangrove. Furthermore, it is the most abundant vegetation on the Salt Pan Creek. The plan was to run statistical analysis of the data collected before its presentation. The data seemed to suggest that human activities had interfered significantly with the size of the trees as evidenced by the low number of 10 meters. At the beginning of the analysis, it was important to draw the frequency tables for the categories of heights developed in the study design. Subsequently, a statistical analysis was done using the Fisher exact test. The role of the statistical analysis was to determine whether there was a correlation between the variables under study. The study entailed the testing of the null and the tentative hypotheses which were stated as follows.

Null hypothesis- There is no statistical relationship between human activity and the height of grey mangrove trees along the Salt Pan Creek.

Tentative hypothesis- There is a statistical relationship between human activity and the height of grey mangrove trees along the Salt Pan Creek.

The significance level of 0.05 was adopted for the study giving a confidence interval of 95%.

Literature review

            A lot of studies have conducted on reducing mangrove forest cover due to human activities such as deforestation. Although the quality of data varies significantly between the various studies, the most reliable show that about 35% of these forests have been cleared. According to Valiela et al., (2001), the largest loss in the mangrove forest cover was the period before 2000. In addition, the forests have been decreasing at an annual rate of about 1%. This is an alarming rate that threatens the very survival of these forests. The rate of forest loss has reduced in the recent past, secondary to conservation efforts by governments and non-governmental organizations.

            Primavera (2006) attributes the largest losses of mangrove trees to efforts aimed at improving aquaculture. The author argues that in spite of the many benefits that aquaculture brings to mankind it has led to environmental degradation through the reduction in mangrove forest cover. The importance of this study is that it lays emphasis on the conservation of estuarine ecosystems through advocating for a change in the government policies of many countries. According to UNEP, aquaculture has continued to contribute significantly to the depletion of forests. The situation has been replicated in many parts of the world according to most of the other studies conducted in many countries.

            Polidoro et al., (2010) explores the state of mangrove forests in the planet and argues that most of the species of mangrove species are threatened by extinction. The authors compile data on the different species drawing from studies conducted previously. One of the points they raise is that the areas that are most affected lie in the coastlines of the Atlantic and Pacific oceans. They explain that the main reason for this trend is human encroachment on marine ecosystems. In their assessment, approximately 44% of the world population can be found along the coastline. Their conclusion, therefore, is that human population pressure is contributing to the decline in the biodiversity in the mangrove forests. At the current rate of exploitation, they estimate that all mangrove forests could be lost in 100 years. They argue that in spite of the reduction in the mangrove forest cover, the loss of individual species of mangrove trees remains the most worrying trend. However, data on this trend is not easily forthcoming as there are more than 70 documented species of mangrove vegetation. In addition, the loss of some of these species leads to economic losses for some of the communities that depend on the forest ecosystems for their livelihoods. They also postulate that the loss of biodiversity occasioned by the reduced forest cover reduces the emission of important gases on which several organisms in the aquatic environments depend. Therefore, the loss of these plants has severe economic and ecological consequences.

             Other studies have explored the immense benefits of mangrove ecosystems thus providing an explanation of the losses attributed to the declining mangrove forest cover. It has been shown that these forests act as barriers preventing the toxic waste from land reaching the deep waters of the ocean damaging the marine ecosystems. Their location between land and the sea has biogeochemical importance. They play the role of nutrient processing before transporting them into aquatic environments. In addition to being habitats for many organisms, the economic uses of the trees are something that many researchers have discussed at length. Studies have also demonstrated that farming activities in the maritime environment have been the greatest contributor to the loss of mangrove forests.

            The number of studies exploring the impact of environmental changes on the mangrove ecosystems has grown over the last few years. However, the challenge has mainly the availability of areas which are protected from human intervention. National parks have in this sense provided good grounds for studying the effects of climate change on mangrove forests. McKee, Cahoo and Feller,( 2007) have explored the effects of sea rising levels on the mangrove forests of the Caribbean. Although their study focused mainly on the red mangrove(Rhizophora mangle), the findings are stillsignificant in understanding the effects of rising sea levels on grey mangroves which is the species under study. The rising sea levels bring additional nutrients and as long as the levels do not submerge the trees, they are catalysts for growth. In a similar approach is adopted by Roger, Wilton, and Saintilan (2006), in their study in the estuaries of southeast Australia. The latter study is especially significant to the current study due to the similarities between this environment and that of Salt Pan Creek. In the latter study, the researchers found an increase in landward encroachment of mangrove forests. Saintilan et al., (2014) bears a close resemblance to the current study since the researchers are mainly interested in the effects of rising sea levels on the grey mangrove. They argue that the rise in sea levels have resulted due to global warming. Therefore, temperature towards the polar region has increased. This has been followed by grey mangrove growth pattern that extends towards the polar region. Sediment accretion has been shown to be the next important determiner of the ability of mangrove species to adapt to rising sea levels. Where this does not keep pace with the rise in the sea levels, it results in the destruction of the available mangrove forests. Studies in the pacific islands have demonstrated the effects of rising sea levels without accompanying sediment accretion (Mackay, 2008).

Results and Discussion

            The total number of trees counted was 845. Figure 1.1 illustrates the number of trees counted in each of the categories discussed in the experimental design section.

Figure 1.1 The height of grey mangrove trees in each category.

Figure 1.1 demonstrates the trend in the size of trees counted in the area sampled for the study. It is important to point out that the process of sampling tried to minimize bias as much as possible. Consequently, the area selected was largely representative of the larger Salt Pan Creek. The trend shows that the largest number of trees belonged to the category of 10-15 cm. These are very young trees. The smallest number was the tall tree beyond 10 meters. In the sampling area, only 4 trees were counted. The picture presented speaks a lot about the impact of human activity on the structure of mangrove forests along the Salt Pan Creek. The reduced numbers of tall trees is a clear indication that human activities have led to the clearing of forests along the coastline. However, the number of young trees is rising because of the favorable climatic conditions and government policies geared towards environmental conservation. These findings are in line with most of the published papers which attribute the increase in the number of young trees to rising sea levels.

            The other data set collected aimed to demonstrate the effects of pollution on the rate of growth of the grey mangrove along the coast of Australia. The number of trees counted in the three transects was as demonstrated in figure 1.2 below.

Figure 1.2 The number of trees counted in each of the transects

            The study area was located in an area that is highly urbanized. Consequently, there was litter observed lying along the selected sample area. The largest concentration of litter was in transect B. Coincidentally, this was the area with the largest concentration of grey mangrove trees. The conclusion drawn from this finding is that the level of land pollution does not have a bearing on the growth rate of the mangrove trees. The results of this study indicate a statistical relationship between human activity and the rate of growth of mangrove trees along the coastline of Australia. Thus, the tentative hypothesis of the study is adopted and the null hypothesis rejected.

Conclusion

            Human activities have emerged as a strong force shaping the nature of mangrove forests of the Salt Pan Creek. The particular species under study was the grey mangrove trees. The reduced number of tall trees implies the heavy toll that human activities that these human activities have exerted on the forest. A large number of young trees is, however, an indication of the resilience of this species. Therefore, efforts aimed at conservation through the introduction of protected forest areas would go a long way in the conservation of the species. Further research on the impact of climatic conditions on the state of mangrove forests along the Salt Pan Creek is recommended.

References

Alongi, D.M., 2002. Present state and future of the world’s mangrove forests. Environmental       conservation, 29(3), pp.331-349.

Department of Agriculture and Fisheries. (2013, October 17). Grey mangrove. Retrieved from https://www.daf.qld.gov.au/business-priorities/fisheries/habitats/marine-plants-including-mangroves/common-mangroves/grey-mangrove

Mackay, A., 2008. Climate change 2007: impacts, adaptation and vulnerability. Contribution of   working group II to the fourth assessment report of the intergovernmental panel on    climate change. Journal of Environmental Quality, 37(6), p.2407.

McKee, K.L., Cahoon, D.R. and Feller, I.C., 2007. Caribbean mangroves adjust to rising sea        level through biotic controls on change in soil elevation. Global Ecology and      Biogeography, 16(5), pp.545-556.

Polidoro, B.A., Carpenter, K.E., Collins, L., Duke, N.C., Ellison, A.M., Ellison, J.C.,        Farnsworth, E.J., Fernando, E.S., Kathiresan, K., Koedam, N.E. and Livingstone, S.R.,         2010. The loss of species: mangrove extinction risk and geographic areas of global            concern. PloS one, 5(4), p.e10095.

Primavera, J.H., 2006. Overcoming the impacts of aquaculture on the coastal zone. Ocean &         Coastal Management, 49(9-10), pp.531-545.

Rogers, K., Wilton, K.M. and Saintilan, N., 2006. Vegetation change and surface elevation          dynamics in estuarine wetlands of southeast Australia. Estuarine, Coastal and Shelf       Science, 66(3-4), pp.559-569.

Saintilan, N., Wilson, N.C., Rogers, K., Rajkaran, A. and Krauss, K.W., 2014. Mangrove expansion and salt marsh decline at mangrove poleward limits. Global change biology,           20(1), pp.147-157.

Valiela, I., Bowen, J.L. and York, J.K., 2001. Mangrove Forests: One of the World’s threatened   major tropical environments: At least 35% of the area of mangrove forests has been lost   in the past two decades, losses that exceed those for tropical rain forests and coral reefs,            two other well-known threatened environments. Bioscience, 51(10), pp.807-815.