Mangrove biodiversity survey south of the Onilahy River - Frontier ...

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Results Figure 30 shows a detailed map of the Mangoro mangal including the position of the creeks. This can be used to work out that the total surface area of tree covered mangal is ~710ha. Figure 31 shows the mean height of an individual of each species. Figure 30. Map depicting the modern layout of the Mangoro mangal. 37
1000 900 800 700 Height (cm) 600 500 400 300 200 100 0 R. mucronata S. alba A. marina C. tagal B. gymnorrhiza Figure 31. Graph to show the mean height of an adult of each species in the Mangoro mangal. Error bars = 95% confidence interval. It was also noted that the dense areas of forest around the creeks primarily consisted of Rhizophora mucronata, with scattered individuals of each other species. In the tannes, Avicennia marina was dominant. Discussion When comparing Figure 29 and Figure 30 it can be seen that the borders of the Mangoro mangal have not changed significantly over the last five years. It has however been noted that the system is under socio-economic pressures (Frontier-Madagascar, unpublished data). With little information as to the density and age structures of the individual populations it is difficult to make further inferences as to their health. The methods used for this mangal were unsuitable for these calculations, those end results not being what was initially desired from this survey. As the aims of the overall study developed this became a priority and thus the methods were refined for the other two mangals. What was noted in this mangal was the definite zonation between the dense forest and the tannes. The zonation was as expected with A. marina being dominant in areas of extreme salinity change and R. mucronata being dominant close to the creek where it is regularly flooded and has an influx of lower salinity water. Zonation is apparent in this mangal due to its larger size. As shown by Figure 31 Sonneratia alba has the average tallest height of an adult of all the species in the mangal with a mean height of 5.5m. R. mucronata had a mean height of 4.8, A. marina had a mean height of 4.3m, Bruguiera gymnorrhiza had a mean height of 3.8m and Ceriops tagal had a mean height of 2.4m. None of these species have reached their potential height. The trees can reach 12m, 20m, 13m, 18m, and 7m respectively (Semesi, 1996). The low average heights achieved in this mangal could be attributed to the fact that the mangal is under socio-economic pressures (Frontier-Madagascar, unpublished data). The forests of A. marina, believed by Lebigre (1997) to be characteristic of a population on the verge of disappearing, seem to be in this cataleptic state almost entirely as a result of overgrazing. These old trees are highly fecund, producing an enormous number of seeds, many of which germinate successfully. However, the complete absence of saplings throughout the duration of the 38
Page 1 and 2: Frontier Madagascar Environmental R
Page 3 and 4: Suggested Technical Paper citation:
Page 5 and 6: TABLE OF CONTENTS: List of Tables:
Page 7 and 8: LIST OF FIGURES Figure 1. Showing a
Page 9 and 10: EXECUTIVE SUMMARY Madagascar posses
Page 11 and 12: Miller, Ms. Sophie Miller, Mr. Thom
Page 13 and 14: Where zonation of species does occu
Page 15 and 16: CHAPTER TWO: THE LAVADANORA MANGAL
Page 17 and 18: Other • All environmental damage
Page 19 and 20: The densities of each species in ea
Page 21 and 22: No. of trees / ha Area of mangal (h
Page 23 and 24: 1400 1200 1000 Height (cm) 800 600
Page 25 and 26: Discussion Figure 4 shows a detaile
Page 27 and 28: Results Figure 16 shows a detailed
Page 29 and 30: Density (m² per hectare) 200 180 1
Page 31 and 32: Figure 20. Graph to show the densit
Page 33 and 34: Figure 22 shows the dominance of A.
Page 35 and 36: 100% 80% Percentage 60% 40% Seedlin
Page 37 and 38: 120 Percentage of species present 1
Page 39 and 40: throughout this mangal (see Figure
Page 41: Methods The surveys were carried ou
Page 45 and 46: CHAPTER FIVE: CONCLUSIONS Compariso
Page 47 and 48: 1400 1200 1000 Height (cm) 800 600
Page 49 and 50: REFERENCES Battistini R., Jouannic

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