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

Frontier Madagascar Environmental Research 

REPORT 9 

Mangrove biodiversity survey south of the 

Onilahy River 

Lavadanora, Lovokampy and Mangoro systems 

Frontier-Madagascar 

2003

Frontier Madagascar Environmental Research 

Report 9 

Mangrove biodiversity survey south of the 

Onilahy River 

Lavadanora, Lovokampy and Mangoro systems 

Woods-Ballard, A.J., Rix, C.E., & Fanning, E. (eds) 


University of Toliara 

The Marine Sciences Institute 

Madagascar 

The Society for Environmental 

Exploration 

UK 

Toliara 

2003 

1

Suggested Technical Paper citation: 

Frontier-Madagascar (2003) Mangrove biodiversity survey south of the Onilahy River: Lavadanora, Lovokampy 

and Mangoro systems. Frontier-Madagascar Environmental Research Report 9. Society for Environmental 

Exploration, UK and the Institute of Marine Sciences, University of Toliara, Madagascar. 

Suggested Section citations: 

Woods-Ballard A.J., Rix C.E. and Webster C.L. (2002) Chapter 1: General Introduction to the Mangroves of Southwest 

Madgascar. In: Mangrove biodiversity survey south of the Onilahy River: Lavadanora, Lovokampy and Mangoro 

systems. pp. 10-15. Frontier Madagascar Environmental Research report 9. Society for Environmental Exploration, UK 

and the Institute of Marine Sciences, University ofToliara, Madagascar. 

Rix C.E., Woods-Ballard A.J. and Webster C.L. (2002) Chapter 2: The Lavadanora Mangal. In: Mangrove 

biodiversity survey south of the Onilahy River: Lavadanora, Lovokampy and Mangoro systems. pp. 15-30. Frontier 

Madagascar Environmental Research report 9. Society for Environmental Exploration, UK and the Institute of Marine 

Sciences, University ofToliara, Madagascar. 

Rix C.E., Woods-Ballard A.J. and Webster C.L. (2002) Chapter 3: The Lovokampy Mangal. In Mangrove biodiversity 

survey south of the Onilahy River: Lavadanora, Lovokampy and Mangoro systems. pp. 30-45. Frontier Madagascar 

Environmental Research report 9. Society for Environmental Exploration, UK and the Institute of Marine Sciences, 

University ofToliara, Madagascar. 

Woods-Ballard A.J., Rix C.E., Clubb G. and Verma L. (2002) Chapter 4: The Mangoro Mangal. In: Mangrove 


Madagascar Environmental Research Report 9. Society for Environmental Exploration, UK and the Institute of Marine 


Woods-Ballard A.J., Rix C.E. and Webster C.L. (2002) Chapter 5: Summary and Conclusions. In: Mangrove 


Madagascar Environmental Research Report 9. Society for Environmental Exploration, UK and the Institute of Marine 


This report series was created in 2005 and incorporated previous reports published by Frontier-Madagascar. The 

previous citation for this report was: 

Frontier-Madagascar (2003) Woods-Ballard A.J and Fanning E. (eds) Mangrove biodiversity survey south of the 

Onilahy River: Lavadanora, Lovokampy and Mangoro systems. Frontier Madagascar Environmental Research 

report 9. ISSN 1479-120X Society for Environmental Exploration, UK and Institute of Marine Sciences, Toliara. 

The Frontier -Madagascar Environmental Research Report Series is published by: 

The Society for Environmental Exploration 

50-52 Rivington Street, 

London, EC2A 3QP 

United Kingdom 

Tel: +44 (0)20 7613 3061 E-mail: research@frontier.ac.uk 

Fax: +44 (0)20 7613 2992 Web Page: www.frontier.ac.uk 

ISSN 1479-120X (Print) 

ISSN 1748-3719 (Online) 

ISSN 1748-5126 (CD-ROM) 

© Frontier-Madagascar 2003, 2005 

2


Madagascar, the fourth largest Island on the planet is renowned for its high biological 

and ecological diversity, characterised by its high abundance of endemic species. 

Madagascar is one of the poorest nations in the world and very dependent on the 

resources the natural environment provides. As a result conservation and development 

work is of paramount importance as efforts are made to preserve an environment under 

pressure from non-sustainable exploitation. Frontier Madagascar is in the process of 

carrying out baseline survey work in the southwest coastal region of Madagascar in an 

effort to provide biological and resource utilisation data for the preparation of 

sustainable management initiatives for the region. 

Institute of Marine Sciences (IHSM) 

The Institute Halieautique et des Sciences Marines (IHSM) is part of the University of 

Toliara, in Madagascar. IHSM is a university centre of learning in the field of marine 

sciences and runs courses for both undergraduate and postgraduate students. IHSM also 

provides consultations to government institutions, NGOs and individuals. 

The Society for Environmental Exploration (SEE) 

The Society is a non-profit making company limited by guarantee and was formed in 

1989. The Society’s objectives are to advance field research into environmental issues 

and implement practical projects contributing to the conservation of natural resources. 

Projects organised by The Society are joint initiatives developed in collaboration with 

national research agencies in co-operating countries. 

FOR MORE INFORMATION 

Frontier -Madagascar 

BP41, Antsiranana, 201 

MADAGASCAR 

Tel/Fax: +261 (0) 20 82 23117 

E-mail: frontier@wanadoo.mg 

L’Insitute Halieautique et des Sciences 

Marine (IHSM) 

Zone Portuaire, BP 141, 

Tulear 601 

MADAGASCAR 

Tel: +261 (0) 20 94 43552 

Fax: +261 (0) 20 94 43434 

E-mail: ihsm@wanadoo.mg 

Society for Environmental Exploration 

50-52 Rivington Street, 

London, EC2A 3QP. U.K. 

Tel: +44 (0) 20 7613 3061 

Fax: +44 (0) 20 7613 2992 

E-mail: research@frontier.ac.uk 

Internet: www.frontier.ac.uk 

3

TABLE OF CONTENTS: 

List of Tables: 1 

List of Figures: 2 

Executive Summary: 4 

Acknowledgments: 5 

Chapter 1: General Introduction to the Mangroves of Southwest Madagascar. 7 

Introduction 7 

Aims and Objectives 9 

Chapter Two: The Lavadanora Mangal 10 


Methods 11 

Mapping 11 

Tree density and height measurements 11 

Salinity 11 

Other 12 

Results 12 

Discussion 20 

Chapter Three: The Lovokampy mangal 21 


Methods 21 

Results 22 

Discussion 33 

Chapter Four: The Mangoro 35 


Methods 36 

Results 37 

Discussion 38 

Chapter Five: Conclusions 40 

Comparison of the three mangals 40 

Summary of results. 42 

Conclusions and recommendations 43 

References 44

LIST OF TABLES 

Table 1. Showing the mangrove species surveyed during the Frontier-Madagascar surveys of 

the West coast mangroves South of the Onilahy river, Madagascar (after Schatz, 

2001). 7 

Table 2. Showing the number of quadrats completed per transect. 12 

Table 3. Showing the maximum density of each species within a surveyed quadrat. 15 

Table 4. Showing the number of trees per hectare. This figure was multiplied by the total 

area of the mangal excluding creeks to give the total number of trees in the mangal 

per species. ± 95% confidence interval. 16 

Table 5. Showing the soil salinity in parts per thousand (ppt) for each quadrat sampled. 18 

Table 6. Showing the number of quadrats completed per transect. 23 

Table 7. Showing the maximum density of each species within a surveyed quadrat. 28 

Table 8. Showing the number of trees per hectare. This figure was multiplied by the total 

area of the mangal excluding creeks to give the total number of trees in the mangal 

per species. ± 95% confidence interval. 28 

Table 9. Showing the soil salinity in ppt for each quadrat sampled. 31 

Table 10. Showing Simpson’s and Shannon’s diversity indices for the four mangals surveyed. 40 

Table 11. Showing the average basal area (m²) for an individual of each species in each 

mangal. 41 

Table 12. Showing the average height (cm) for an individual adult of each species in each 

mangal. 42 

1

LIST OF FIGURES 

Figure 1. Showing a typical zonation in an Indo-Pacific mangrove system (Chapman, 1977). 8 

Figure 2. Map depicting the location of the three mangrove systems focussed on for this 

report. 9 

Figure 3. Map depicting an historic layout of the Lavadanora mangal (Lebigre, 1997). 10 

Figure 4. Map depicting the layout of the Lavadanora mangrove as it is today. 13 

Figure 5. Graph to show the density of X. granatum in each transect in the Lavadanora 

mangal. Where more than one quadrat was sampled the results are displayed from 

left to right for each transect. Error bars = 95% confidence interval. 14 

Figure 6. Graph to show the density of A. marina in each transect in the Lavadanora mangal. 

Where more than one quadrat was sampled the results are displayed from left to 

right for each transect. Error bars = 95% confidence interval. 14 

Figure 7. Graph to show the density of B. gymnorrhiza in each transect in the Lavadanora 



Figure 8 Graph to show the density of R. mucronata in each transect in the Lavadanora 



Figure 9 Graph to show the density of L. racemosa in each transect in the Lavadanora 



Figure 10. Graph to show the comparative density of each tree species in each quadrat in the 

Lavadanora mangal. Error bars = 95% confidence interval. 15 

Figure 11. Graph to show the total number of adults, saplings and seedlings of each species 

per hectare in the Lavadanora mangal. Error bars = 95% confidence interval. 17 

Figure 12. Graph to show the age structure of the populations of each species. 17 

Figure 13. Graph to show the mean height of an adult of each species in the Lavadanora 

mangal. Error bars = 95% confidence interval. 18 

Figure 14. Scatter graph to show the density of each species in m² per hectare against salinity 

in ppt. 19 

Figure 15. Scatter graph to show the proportions of each species present against salinity in 

ppt. 19 

Figure 16. Map depicting the layout of the Lovokampy mangal as it is today with the creel 

leading to the sea to the Northwest.. 22 

Figure 17. Graph to show the density of A. marina in each transect in the Lovokampy 



Figure 18. Graph to show the density of B. gymnorrhiza in each transect in the Lovokampy 



Figure 19. Graph to show the density of R. mucronata in each transect in the Lovokampy 

mangal. Where more than one quadrat as sampled the results are displayed from 


Figure 20. Graph to show the density of C. tagal in each transect in the Lovokampy mangal. 

Where more than one quadrat was sampled the results are displayed from left to 

right for each transect. Error bars = 95% confidence interval. There is no 95% 

interval on quadrat 2 in transect 12, this was removed for clarity as the figure was 

17.93. 26 

2

Figure 21. Graph to show the density of L. racemosa in each transect in the Lovokampy 



Figure 22. Graph to show the density of each tree species in each quadrat in the Lovokampy 

mangal, transects 1 to 13. Error bars = 95% confidence interval. 27 

Figure 23. Graph to show the total number of adults, saplings and seedlings of each species 

per hectare in the Lovokampy mangal. Error bars = 95% confidence interval. 29 

Figure 24. Graph to show the total number of adults, saplings and seedlings of B. 

gymnorrhiza, R. mucronata, L. racemosa and X. granatum per hectare in the 

Lovokampy mangal. Error bars = 95% confidence interval. 29 

Figure 25. Graph to show the age structure of the population of each species. 30 

Figure 26. Graph to show the mean height of an adult of each species in the Lovokampy 


Figure 27. Scatter graph to show the density of each species in m² per hectare against salinity 

in ppt. 31 

Figure 28. Scatter graph to show the proportions of each species present against salinity in 

ppt. 32 

Figure 29. Map depicting the historic layout and position of the Mangoro mangal (Lebigre, 

1997). 35 

Figure 30. Map depicting the modern layout of the Mangoro mangal. 37 

Figure 31. Graph to show the mean height of an adult of each species in the Mangoro 


Figure 32. Graph showing the average basal area (m²) for an individual of each species in 

each mangal. 40 

Figure 33. Graph showing the average basal area (m²) for an individual of each species in 

each mangal, with the exception of the Mangoro for clarity. 41 

Figure 34. Graph showing the average height (cm) for an individual adult of each species in 

each mangal. 42 

3

EXECUTIVE SUMMARY 

Madagascar possesses over half of the mangroves found within the East-African region. 

Mangrove forests are recognised initially for their crucial ecological role and economic value. Although 

work on the mangrove forests of Madagascar have been carried out in recent history very little has been 

published. 

Frontier-Madagascar focussed on three mangals for this study all situated South of Toliara and the Onilahy 

river in Southwest Madagascar. The three mangals (Lavadanova, Lovokampy and Magoro) are important for 

study in that they either have unusual species composition or have been suggested as core zones for a 

proposed Biosphere reserve. 

The aim of study was to map mangrove diversity and surface area within each of the mangals. 

The mangals were mapped using GPS, and subsequently used to set out transects. 10x10 quadrats were 

placed at the start of each transect and then every 50m until the edge of the mangal was reached. Various 

data were collected within each quadrat, including total numbers of adults, saplings and seedlings for each 

species present, tree height, salinity via soil samples and any environmental damage. 

The results from the studies of each mangal were also compared to determine the differences between the 

mangals. Species composition of the three mangals were shown to differ with X. granatum dominating the 

Lavadanora mangal, A. marina being dominant in Lovokampy and in the tannes of Magoro, and R. 

mucronata dominating in the dense forests of Mangoro. 

Recommendations stemming from this study include the local village of Lovokampy dredging the creek in 

order to link it to the sea preventing further mangal loss within the area. The continuation of further work 

combining satellite imagery, GIS, socio-economic studies and continued biological surveys is also 

recommended in order to establish a sustainable management plan and monitoring scheme. 

Key to maps of the mangals 

Creek within the mangal 

Water outside the mangal 

Mangrove forest 

Other vegetation 

Transect line 

4

ACKNOWLEDGMENTS 

This report is the culmination of the advice, co-operation, hard work and expertise of many people. In 

particular acknowledgements are due to the following: 

L’INSTITUT HALIEUTIQUE ET DES SCIENCES MARINE (IHSM) 

F-M Co-ordinators: 

Dr. Man Wai Rabenevanana 

Dr. Mara Edouard Remanevy 

SOCIETY FOR ENVIRONMENTAL EXPLORATION 

Managing Director: 

Development Programme Manager: 

Research Programme Manager: 

Programme Manager 

Operations Manager 

Assistant Operations Manager: 

Ms. Eibleis Fanning 

Ms. Elizabeth Humphreys 

Dr. Damon Stanwell-Smith 

Ms. Nicola Beharrell 

Mr. Matthew Willson 

Mr. Alessandro Badalotti 

FRONTIER-MADAGASCAR 

Country Co-ordinator 

Project Co-ordinator: 

Marine Research Co-ordinators: 

Assistant Marine Research Co-ordinators: 

Logistics Managers: 

Diving Officers: 

Research Assistants 

Ms. Elouise Andrieux, Mr. John Bennett, Mr. 

Matthew Brennand Roper, Ms. Yvonne 

Charras, Ms. Louisa Coleman, Mr. Thomas 

Cuthbert, Ms. Charlene Davies, Ms. Jessica, 

Fedak, Mr. Rory Fraser, Ms. Juliet Gush, Ms. 

Elizabeth Jackson, Mr. Christopher Jones, 

Mr. Will Noel, Mr. Thomas Porter, Ms. Lucy 

Rushton, Ms. Martina Spada, Ms. Charlotte 

Sumner, Ms. Ailsa Taylor, Mr. Russel 

Thorne, Ms. Linda Torbet, Mr. James Traer, 

Mr. Graham Walker, Ms. Laura Webb, Mr. 

Jonathan Whicher, Ms. Elinor Ames, Ms. 

Roslalind Buckley, Ms. Katherine Burton, 

Ms. Julie Bygraves, Ms. Jillyan Drummond, 

Mr. Edward Eastward, Ms. Elizabeth 

Gutteridge, Ms. Hanning, Ms. Franseca 

Hinman, Mr. Luke McMillan, Piyawan 

Ms. Jemima Stancombe 

Ms. Chloë Webster 

Mr. Ryan Walker, 

Mr. Andy Woods-Ballard 

Mr. Luca Chiaroni, 

Mr. Gareth Clubb, 

Ms. Gwenaël Hemery, 

Mr. Angus Mc Vean, 

Ms. Charlotte Rix, 

Ms. Lucy Verma 

Ms. Sarah de Mowbray, 

Ms. Emily Roberts 

Mr. Duncan Ayling, 

Mr. Stuart Cheesman, 

Mr. Sander den Haring 

Mr. Mathieu, Mr. Tim Burns, Ms. Marios 

Cleovoulou, Ms. Hannah Davis, Ms. Anna 

Franson, Ms. Emma Gray, Ms, Barbara 

Hadrill, Mr. Roderick Haines, Ms. Cathleen 

Hallett, Mr. Joel Janco, Mr. Sam Page, Mr. 

Phil Preston, Mr. James Rounce, Mr. Daniel 

Sakai, Mr. Jonathon Starr, Ms. Laura 

Stevenson, Mr. Ben Tapley, Ms. Helen 

Watts, Ms. Alexandra Willis, Ms. Philine zu 

Ermgassen, Mr. Martin Meynell, Ms. Erica 

Planer, Mr. Luke Teague, Mr. Mattew 

Moore, Ms. Flora Bagenal, Ms. Natalie 

Blagg, Mr. Ryan Carpenter, Ms. Rachel 

Colman, Ms. Michelle Cooper, Mr. Tristan 

Gutteridge, Mr. Alex Hawkins, Mr.Tom 

Herbstein, Ms. Catherine Haywood, Mr. 

Daniel Jukes, Ms. Hannah Kew, Mr. John 

Leach, Mr. Edward Mannsaker, Ms. Claire 

Murray, Ms. Pippa Pledger, Ms. Helena 

5

Miller, Ms. Sophie Miller, Mr. Thomas 

Monk, Ms. Jennifer Pope, Ms. Hannah Prior, 

Ms. Samantha Rex, Ms. Gemma Rowley, 

Ms. Jennifer Watts, Ms. Rebecca Weeks, Ms. 

Stephanie Whybrow, Mr. Samuel Yates, 

Reinardy, Mr. Daniel Ridler, Ms. Candace 

Rose-Taylor, Mr. Philip Ryder, Mr. 

Christopher White, Ms. Yvonne Appleyard, 

Mr. Michael Bloom, Ms. Rhiannnon Cottrell, 

Mr. John Da Mina, Ms. Aisha Dasgupta, Ms. 

Marie Day, Ms. Rebecca Eastman, Mr. 

Stefab Hatvany, Sandor Hatvany, Mr. 

Thomas Jeffcoate, Mr. Richard Lee, Ms. 

Georgina Oliver, Ms. Catherine Prentice, Ms. 

Roxanne Smee, Ms. Katie Tuite-Dalton, Mr. 

Tavis Walker, Ms. Catorina Watts, Oliver 

Wyatt. 

6

CHAPTER 1: GENERAL INTRODUCTION TO THE MANGROVES OF 

SOUTHWEST MADAGASCAR 

Introduction 

Mangrove forests are important components of coastal tropical habitats, spanning the terrestrial and 

marine biotopes and recognised worldwide for their crucial ecological role and diversified 

economic value. These salt-tolerant evergreen trees are typically located at or above the mid-tide 

level in low-energy environments along estuaries and coastal lagoons, and show richest 

development where freshwater percolates the system (Semesi and Howell, 1989). Mangroves are 

found in the tropical regions and can be divided into three broad regional categories, Madagascar 

being part of the Indo-Pacific region (Nybakken 2001). 

Madagascar possess approximately 320,000ha (Gabrié et al., 2000) of the world’s 24 million ha 

(Clark, 1996). This represents over half of the mangroves found in the Eastern African region 

(excluding Somalia due to lack of data) (Semesi and Howell, 1989), with 99% situated on the West 

coast (Lebigre, 1990). This relatively high abundance compared with other countries can be partly 

explained by the lack of general large-scale economic exploitation, whilst the West coast 

predominance is due to ideal conditions for mangrove formation. 

Some of the most extensive research into the mangrove biodiversity in Madagascar was conducted 

during the 1960s (Deijard, 1965; Weiss, 1966a and 1966b) and 1970s (Weiss, 1972a and 1972b) 

with very little else completed until the 1990s (Lebigre, 1990; 1997 and 1999 and Edmond and 

Grepin, 1999). Work since this period has been conducted although little has been published 

leaving the data inaccessible to the public domain and present studies aim to build upon the work 

already completed, updating the knowledge of the status of each mangal into the present millennia. 

The mangals studied in this report are amongst the most Southerly in Madagascar. Table 1 shows 

the mangrove species surveyed during the Frontier-Madagascar research. 

Family 

No. of species in No. of species in Species surveyed 

genera 

genera in Madagascar 

ACANTHACEAE 12 1 Avicennia marina 

RHIZOPHORACEAE 6 1 Bruguiera gymnorrhiza 

RHIZOPHORACEAE 2 1 Ceriops tagal 

COMBRETACEAE 2 1 Lumnitzera racemosa 

RHIZOPHORACEAE 6 1 Rhizophora mucronata 

LYTHRACEAE 5-7 1 Sonneratia alba 

MELIACEAE 3 2 Xylocarpus granatum 

Table 1. Showing the mangrove species surveyed during the Frontier-Madagascar surveys of the West coast mangroves 

South of the Onilahy river, Madagascar (after Schatz, 2001). 

The different species of mangroves have developed a number of xerophyllic specialisations that 

enable them to tolerate ranges of salty or brackish environments broadly uninhabited by 

angiosperms. Most species show the typical adaptations of waxy cuticles and sunken stomata to 

reduce evapotranspirative water loss along with pneumatophores. Pneumatophores allow gas 

exchange above the sediment, which is often anoxic. Due to the lack of pneumatophores, X. 

granatum is classed as an associate mangrove species. Other specialisations include the active 

excretion of excess salt into leaves that will be discarded when salinity becomes toxic and 

selectively permeable membranes that exclude salt ions from root systems (Semesi and Howell, 

1989). 

7

Where zonation of species does occur, it is manifested in relation to a number of factors, including: 

pH, salinity; soil composition (Lebigre, 1997); duration of tidal inundation (Semesi and Howell, 

1989); gradient of the land (Dando et al., 1996); and sedimentation (Semesi, 1997). Often, zonation 

is negligible or absent due to the number of factors affecting the mangal (Lebigre, 1997). This is 

especially noticeable in the smaller mangroves typifying the region south of Toliara in the 

Southwest. A typical zonation is represented in Figure 1. 

Figure 1. Showing a typical zonation in an Indo-Pacific mangrove system (Chapman, 1977). 

Mangrove ecosystems are thought to recycle and conserve nutrients through a close link with a 

microbial community (Holguin et al., 2001). This performs an important function, recycling the 

nutrients of the nearshore area. Mangroves also provide an important habitat for a diverse fauna, 

whilst stabilising and protecting the shore from physical disturbances such as storms and erosion, 

and providing for low-level non-consumptive uses such as ecotourism (Semesi and Howell, 1989 

and Zheng et al., 1995). 

The three mangals focussed upon for this report (Lavadanora, Lovokampy and Mangoro, from 

North to South) are all situated south of Toliara and the Onilahy river in Southwest Madagascar (see 

Figure 2). They are all affected to varying degrees by outflow from the Onilahy River, which 

derives its input from a drainage basin of around 30,000km 2 (Lebigre, 1997) and has a flow rate of 

between 10-1000m 3 s -1 (Battistini et al., 1975). Despite the large drainage basin there is no delta 

formation at the mouth of the estuary due to the submarine canyon submerging to 1-2km within 2- 

10km of the shore (Batistini et al., 1975 and Lebigre, 1997). On top of the large volumes of 

terrigeneous sediments flowing from the estuary, the mangals are subject to heavy socio-economic 

pressures (Frontier-Madagascar, unpublished data). Finally these mangals are important for study 

as they are all either unusual in their species composition or location and/or have been suggested as 

core zones for the proposed Biosphere reserve in the Toliara region (Cellule Environnement Marin 

et Côtier (Office National pour l’Environnement), 2001). This will allow their value to be assessed 

and monitored with regard to potential management regimes. 

8

Figure 2. Map depicting the location of the three mangrove systems focussed on for this report. 

Aims and Objectives 

Broadly, the aims of this study were to map the mangrove diversity and surface area within each of 

the mangals. 

9

CHAPTER TWO: THE LAVADANORA MANGAL 

Introduction 

Although the Lavadanora mangal has been studied extensively in the past (Lebigre, 1997), there has 

been little recent work and it is apparent from casual observations that the structure of the mangal 

would appear to have changed over recent years. Figure 3 shows an historic zonation map with 

creeks. The mangal is situated approximately 1km west of the village of Lavenombato on the south 

side of the Onilahy river (see Figure 2). As with the other mangals in the area, it is impacted on by 

various factors including human exploitation, environmental degradation and grazing of livestock 

(Frontier-Madagascar, unpublished data), but as one of the core zones in the proposed Man and 

Biosphere Reserve for the Toliara region (Cellule Environnement Marin et Côtier (Office National 

pour l’Environnement), 2001) it is important that up-to-date information is available. This 

mangrove is unusual in Madagascar, being one of the few to contain Xylocarpus granatum, 

probably due to the high levels of freshwater input owing to its estuarine nature. The latter also 

results in reduced wave pressure. 

Figure 3. Map depicting an historic layout of the Lavadanora mangal (Lebigre, 1997). 

10

Methods 

Surveys were undertaken in the Lavadanora mangal between November 2001 and February 2002. 

Methods were revised from English et al. (1994) as appropriate for this mangal and are outlined 

below. 

Mapping 

• First the mangal was mapped using a GPS (WGS 84 Projection dd°mm.mmm’, Southings 23°, 

Eastings 043°). The mapping included the edges of the creeks at high tide and the extent of the 

mangal. Edges being defined as where the tree density fell to below one per 100m 2 . Important 

points were noted, such as fresh water sources. This map was then used to set out transects. Due 

to poor GPS coverage resulting from the proximity of the cliffs at this mangal, compasses and 

distance estimation were also used. 

Tree density and height measurements 

• Transects were conducted at approximately 200m intervals on either side of the creek 

perpendicularly to the angle of the creek. The perceived lack of different species zonation in this 

mangal making more frequent measurements unnecessary. 

• A 10m x 10m quadrat was placed at the beginning of each transect and then every 50m until the 

edge of the mangal was reached. 

• Within the quadrat the total number of adults, saplings and seedlings for each species present 

was recorded. Adults were classified as having a girth at breast height (GHB) greater than 4cm. 

Saplings were classified as having a height greater than 1m and a GBH less than 4cm, and 

seedlings as having a height less than 1m and a GBH less than 4cm. 

• The GBH and the height of the trees were recorded for three adults of each species present. 

• The trees closest to the Southwest corner of the quadrats if North of the creek or the Northwest 

corner of the quadrat South of the creek were measured. If the stem forked below breast height 

each branch was measured as a separate stem. 

• The height was measured using a clinometer in addition to being visually estimated. If the trees 

were small enough then a measuring tape was used to further increase the accuracy of the results. 

Salinity 

• Soil salinity is a more accurate measure than water salinity in the creeks, as it is not as tide 

dependent. In accordance with this, the salinity of the soil in each of the 35 quadrats sampled 

was measured using the following method. 

• Soil samples were taken at low tide when the substratum was uncovered. 

• They were taken from the middle of each quadrat. 

• In the region of 20g of soil was taken from 10cm below the surface to avoid problems associated 

with high salinity due to evaporation. 

• This was placed into a plastic bag with a piece of waterproof paper with the transect and quadrat 

number recorded on it in pencil. 

• The bag was then sealed to ensure it was airtight. 

• Analyses were carried out within two to three hours to minimise errors associated with 

evaporation and condensation. 

• The soil was analysed by putting it into a 60cc syringe previously prepared with a piece of filter 

paper placed in the bottom of the barrel. 

• Water was then squeezed through the filter using the plunger to extract 3-4 drops. 

• The drops were analysed for salinity using a refractometer before all the equipment being 

cleaned in preparation for the next sample. 

11

Other 

• All environmental damage was noted in each quadrat. 

Results 

Figure 4 shows a detailed map of the Lavadanora mangal including the transects completed and the 

position of the creeks. 

Eighteen transects were completed with a total of 35 quadrats. See Table 2 for breakdown of the 

number of quadrats in each transect and Figure 4 shows their locations. 

Transect No. No. of Quadrats 

1 1 

2 2 

3 4 

4 3 

5 3 

6 2 

7 1 

8 1 

9 3 

10 3 

11 3 

12 1 

13 3 

14 1 

15 1 

16 1 

17 1 

18 1 

Table 2. Showing the number of quadrats completed per transect. 

Six species of mangrove tree were found in the Lavadanora mangrove. These were Xylocarpus 

granatum, Avicennia marina, Bruguiera gymnorrhiza, Rhizophora mucronata, Lumnitzera 

racemosa, and Sonneratia alba. Of the six species all but S. alba were present in the quadrats 

sampled. 

12

Figure 4. Map depicting the layout of the Lavadanora mangrove as it is today. 

13

The densities of each species in each quadrat are described in Figure 5 to Figure 9. These are then 

summarised in Figure 10, which clearly shows the dominance of X. granatum throughout the 

mangal. 

Density (m² per hectare) 

4 

3 

2 

1 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 

Figure 5. Graph to show the 

density of X. granatum in each 

transect in the Lavadanora 

mangal. Where more than one 

quadrat was sampled the results 

are displayed from left to right 

for each transect. Error bars = 

95% confidence interval. 

Transect number 


0.8 

0.6 

0.4 

0.2 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 


density of A. marina in each 









0.25 

0.20 

0.15 

0.10 

0.05 

0.00 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 


density of B. gymnorrhiza in 

each transect in the Lavadanora 








0.1 

0.08 

0.06 

0.04 

0.02 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 

Figure 8 Graph to show the 

density of R. mucronata in each 








14


0.005 

0.004 

0.003 

0.002 

0.001 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 

Figure 9 Graph to show the 

density of L. racemosa in each 








4 

3.5 

3 


2.5 

2 

1.5 

X. granatum 

A. marina 

B. gymnorrhiza 

R. mucronata 

L. racemosa 

1 

0.5 

0 

T1Q1 

T2Q1 

T2Q2 

T3Q1 

T3Q2 

T3Q3 

T3Q4 

T4Q1 

T4Q2 

T4Q3 

T5Q1 

T5Q2 

T5Q3 

T6Q1 

T6Q2 

T7Q1 

T8Q1 

T9Q1 

T9Q2 

T9Q3 

T10Q1 

T10Q2 

T10Q3 

T11Q1 

T11Q2 

T11Q3 

T12Q1 

T13Q1 

T13Q2 

T13Q3 

T14Q1 

T15Q1 

T16Q1 

T17Q1 

T18Q1 

Transect and Quadrat numbers 

Figure 10. Graph to show the comparative density of each tree species in each quadrat in the Lavadanora mangal. Error 

bars = 95% confidence interval. 

In addition to X. granatum accounting for the greatest basal area and density in the mangal it also 

has the maximum density of any species within a surveyed quadrat (see Table 3). 

Species 

Maximum density (m²/ha) 

X. granatum 1.764 

A. marina 0.419 

B. gymnorrhiza 0.079 

R. mucronata 0.078 

L. racemosa 0.003 

Table 3. Showing the maximum density of each species within a surveyed quadrat. 

15

No. of trees / ha Area of mangal (ha) Total number of trees 

X. granatum 

Adults 1,620 ± 347 80 129,600 ± 27,760 

Saplings 1,011 ± 479 80 80,880 ± 38,320 

Seedlings 574 ± 184 80 45,920 ± 14,720 

Adults 229 ± 101 80 18,320 ± 8,080 

A. marina 


R. mucronata 

Saplings 20 ± 21 80 1,600 ± 1,680 

Seedlings 34 ± 38 80 2,720 ± 3,040 

Adults 83 ± 77 80 6,640 ± 6,160 

Saplings 94 ± 60 80 7,520 ± 4,800 

Seedlings 611 ± 472 80 48,880 ± 37,760 

Adults 11 ± 11 80 880 ± 880 

Saplings 0 80 0 

Seedlings 0 80 0 

Adults 9 ± 12 80 720 ± 960 

L. racemosa 

Saplings 6 ± 11 80 480 ± 880 

Seedlings 3 ± 6 80 240 ± 480 

Table 4. Showing the number of trees per hectare. This figure was multiplied by the total area of the mangal excluding 

creeks to give the total number of trees in the mangal per species. ± 95% confidence interval. 

Table 4 shows an average number of trees per hectare for each of the species surveyed in this 

mangal. By multiplying this by the area of the mangal (~80ha) an assessment of the total number of 

trees in the mangal can be made. X. granatum was the most abundant species in the mangal with a 

total number of 256,400 ± 80,800 trees including adults saplings and seedlings, followed by B. 

gymnorrhiza with 63,040 ± 48,720 trees, A. marina had 22,640 ± 12,800 trees, L. racemosa had 

1,440 ± 2,320 trees, and the least abundant species in the mangal was R. mucronata with 880 ± 880 

trees. This is also depicted in Figure 11. 

16

2500 

2000 

Number of trees 

1500 

1000 

Adults 

Saplings 

Seedlings 

500 

0 

X. granatum 

A. marina 


R. mucronata 

L. racemosa 

Figure 11. Graph to show the total number of adults, saplings and seedlings of each species per hectare in the 

Lavadanora mangal. Error bars = 95% confidence interval. 

Figure 12 shows how the proportion of adults, saplings and seedlings varies between the species 

surveyed. 

100% 

80% 

Percentage 

60% 

40% 

Seedlings 

Saplings 

Adults 

20% 

0% 

R. mucronata 

A. marina 

X. granatum 

Species 

Figure 12. Graph to show the age structure of the populations of each species. 

Figure 11 and Figure 12 show the age structure for the mangrove while Figure 13 shows the 

average height of each species in this mangal. 

L. racemosa 


17

1400 

1200 

1000 

Height (cm) 

800 

600 

400 

200 

0 

X. granatum A. marina B. gymnorrhiza R. mucronata L. racemosa 

Figure 13. Graph to show the mean height of an adult of each species in the Lavadanora mangal. Error bars = 95% 

confidence interval. 

Table 5 shows the breakdown of the salinity samples taken in this mangal, these were then plotted 

against density of each species (see Figure 14) and proportion of each species (see Figure 15). 

Soil Salinity ‰ 

Transect number Quadrat 1 Quadrat 2 Quadrat 3 Quadrat 4 

1 18 N/A N/A N/A 

2 17 16 N/A N/A 

3 22 20 18 20 

4 16 19 18 N/A 

5 18 9 18 N/A 

6 10 22 N/A N/A 

7 4 N/A N/A N/A 

8 26 N/A N/A N/A 

9 14 14 18 N/A 

10 26 20 10 N/A 

11 26 21 18 N/A 

12 12 N/A N/A N/A 

13 25 24 20 N/A 

14 10 N/A N/A N/A 

15 20 N/A N/A N/A 

16 22 N/A N/A N/A 

17 23 N/A N/A N/A 

18 22 N/A N/A N/A 

Table 5. Showing the soil salinity in parts per thousand (ppt) for each quadrat sampled. 

18

Density (m 2 per hectare) 

2 

1.8 

1.6 

1.4 

1.2 

1 

0.8 

0.6 

0.4 

0.2 

0 

0 5 10 15 20 25 30 

Salinity ‰ 

X. granatum 

A. marina 


R. mucronata 

L. racemosa 

Figure 14. Scatter graph to show the density of each species in m² per hectare against salinity in ppt. 

120 

Percentage of species present 

100 

80 

60 

40 

20 

X. granatum 

A. marina 


R. mucronata 

L. racemosa 

0 

0 5 10 15 20 25 30 

Salinity ‰ 

Figure 15. Scatter graph to show the proportions of each species present against salinity in ppt. 

The salinity of the soil samples taken from each quadrat is shown in Table 5. A positive correlation 

is shown between the density of X. granatum and salinity at the 95% confidence level using the 

Spearman Rank correlation (see Figure 14). There was no significant correlation between the 

densities of the other species and salinity. Figure 15 showing the relationship between the 

percentage of species present and salinity, appears to demonstrate a positive correlation between the 

percentage of A. marina and salinity, however this relationship is not significant according to the 

Spearman Rank correlation. Similarly there is no significant correlation between the percentage of 

the other species and salinity. 

19

Discussion 

Figure 4 shows a detailed map of the Lavadanora mangal including the transects completed and the 

position of the creeks. The map of the mangrove has changed slightly from that completed by 

Lebigre in 1997 (see Figure 3). Lebigre depicts the main creek with two secondary creeks flowing 

out of it, whereas 7 secondary and tertiary creeks were recorded off the main creek during this 

study. Lebigre’s map has also simplified the positions of the trees into A. marina and X. granatum 

stands. This is in contrast to how it is in this day where although X. granatum and A. marina are 

still the most dominant species present they are intermingled with each other and with B. 

gymnorrhiza, L. racemosa and R. mucronata. Observations do show however, that A. marina has a 

slight dominance in the West of the mangal, and X granatum in the middle to East. 

All species with the exception of B. gymnorrhiza had more adults than seedlings (see Figure 12). 

This could indicate that the adults of B. gymnorrhiza have been chopped and utilised by the local 

village, however there is little evidence that this is the case (Frontier-Madagascar, unpublished 

data). This species has several uses, which include firewood, fish smoking, fishing stakes, building 

poles and telephone poles (Frontier-Madagascar, unpublished data; Semesi and Howell, 1989). As 

there are a relatively large number of seedlings it would appear that there is the potential for 

regeneration. Both R. mucronata and A. marina have a markedly lower percentage of juveniles 

(seedlings and saplings), which would suggest that regeneration is unlikely. X. granatum and L. 

racemosa however, had a similar percentage of juvenile and adult trees suggesting a healthy 

population. 

As shown by Figure 13 A. marina has the average tallest height of an adult of all the species in the 

mangal with a mean height of 10.6m. X. granatum had a mean height of 9.1m, R. mucronata had a 

mean height of 7.1m, B. gymnorrhiza had a mean height of 3.6m, and L. racemosa had a mean 

height of 3.1m. Populations of X. granatum, A. marina and L. racemosa appear to be healthy in 

terms of their height as the individual species can grow to 10m, 13m, and 3m respectively (Semesi, 

1996), which is approximately what they have achieved in this mangal. Individuals of B. 

gymnorrhiza and R. mucronata however, have not reached their potential fully grown height, which 

can be 18m and 20m respectively (Semesi 1996). Casual observations during the survey showed 

that B. gymnorrhiza and A. marina were heavily grazed and cut with many stumps being observed, 

again indicating that these species are heavily utilised by the local population. 

The overall low soil salinity of the mangal in general (4-26ppt), due to its estuarine as opposed to 

coastal nature, is a contributing factor to the dominance of X. granatum as this species is most often 

found where there is a freshwater influence (Semesi and Howell, 1989) and has a lack of 

xerophyllic adaptations (Semesi, 1996). A positive correlation was shown between the density of 

this species and salinity. Semesi and Howell (1989) state that A. marina can tolerate high ranges of 

salinity and as a result is the most widely distributed species in the East African region. As can be 

seen from Figure 10 it is the second most dominant species in the mangal. No significant 

correlation was found between A. marina and salinity. B. gymnorrhiza can tolerate mixed salinity 

and is often found with R. mucronata, while L. racemosa is always found as landward mangrove 

where there is an influence of freshwater (Semesi, 1996). English et al. (1994) state that the 

majority of mangrove species grow best in low to moderate salinities (25ppt). The highest salinity 

found in Lavadanora mangal was 26ppt possibly accounting for the low density of these three 

species. However, as this small mangal has such low densities of B. gymnorrhiza, R. mucronata, 

and L. racemosa inferences cannot be made as to their zonation, and no significant correlation was 

found between these species and salinity. Finally it was noted that erosion is a particular problem 

for this mangal as trees were seen to be falling into the river. 

20

CHAPTER THREE: THE LOVOKAMPY MANGAL 

Introduction 

This mangal is one of the core zones for the proposed Man and Biosphere Reserve for the Toliara 

region (Cellule Environnement Marin et Côtier (Office National pour l’Environnement), 2001) 

however there has been very little research published to date as to its biodiversity or cartography. It 

is situated between the village of Soalara and the Onilahy river, Southwest Madagascar (see Figure 

2) and is subject to human exploitation for firewood and building materials. It is also grazed by 

livestock from the nearby village of Lovokampy (Frontier-Madagascar, unpublished data). This 

mangal, although it has a creek is likely to have an unusual or absent zonation pattern due to the 

creek having been being blocked from 1990-1995 an occurrence that appears to be repeated 

intermittently over the years (Frontier-Madagascar, unpublished data). The fresh water source 

appears to emanate from the cliffs surrounding this mangal, however it does not become a creek 

until further into the mangal. This mangal is protected from wave action due to its position, set 

back from the mean high water mark by approximately 70m. All these factors make this zone ill 

suited to mangal formation. 

Methods 

Surveys carried out in the Lovokampy mangal between May and June 2002 were conducted using 

methods similar to those used for Lavadanora with three exceptions. 

1. All mapping was completed using a GPS. 

2. Transect lines were marked out approximately every 100m as this mangal has not been surveyed 

previously and dominance was less obvious. 

3. As the creek ended before the edge of the mangal a bearing was taken from the end to the 

freshwater source in the cliffs and the transects continued as before along this imaginary 

freshwater gradient. This ensured that the entirety of the mangal was represented in the surveys. 

21

Results 

Figure 16 shows a detailed map of the Lovokampy mangal including the transects completed and 

the position of the creeks. 

Figure 16. Map depicting the layout of the Lovokampy mangal as it is today with the creel leading to the sea to the 

Northwest. 

Twenty-six transects were completed with a total of 81 quadrats in the Lovokampy mangal. Table 

6 shows a breakdown of the number of quadrats in each transect, and Figure 16 shows their 

locations. 

22

Transect No. No. of Quadrats 

1 1 

2 1 

3 2 

4 3 

5 2 

6 2 

7 3 

8 4 

9 4 

10 5 

11 6 

12 4 

13 5 

14 4 

15 4 

16 7 

17 4 

18 3 

19 2 

20 1 

21 1 

22 1 

23 2 

24 4 

25 3 

26 3 

Table 6. Showing the number of quadrats completed per transect. 

Six species of mangrove tree were found in the Lovokampy mangal. These included Avicennia 

marina, Bruguiera gymnorrhiza, Rhizophora mucronata, Ceriops tagal, Lumnitzera racemosa and 

Xylocarpus granatum. Their densities in each quadrat are displayed in Figure 22. 

Figure 17 to Figure 22 (the final figure is split for clarity) show that A. marina has the greatest basal 

area of the six different species in the mangal. C. tagal accounts for the next highest basal area, 

followed by R. mucronata, B. gymnorrhiza and L. racemosa. X. granatum does not have a basal 

area calculated for it. There was no GBH reading taken due to its height of 1.1m (see below). 

23


200 

180 

160 

140 

120 

100 

80 

60 

40 

20 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 


Figure 17. Graph to show the density of A. marina in each transect in the Lovokampy mangal. Where more than one quadrat was sampled the results are displayed from left to right 

for each transect. Error bars = 95% confidence interval. 

0.025 


0.02 

0.015 

0.01 

0.005 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 


24

Figure 18. Graph to show the density of B. gymnorrhiza in each transect in the Lovokampy mangal. Where more than one quadrat was sampled the results are displayed from left to 

right for each transect. Error bars = 95% confidence interval. 

25 


20 

15 

10 

5 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 


Figure 19. Graph to show the density of R. mucronata in each transect in the Lovokampy mangal. Where more than one quadrat as sampled the results are displayed from left to 


1.2 


1 

0.8 

0.6 

0.4 

0.2 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 


25

Figure 20. Graph to show the density of C. tagal in each transect in the Lovokampy mangal. Where more than one quadrat was sampled the results are displayed from left to right 

for each transect. Error bars = 95% confidence interval. There is no 95% interval on quadrat 2 in transect 12, this was removed for clarity as the figure was 17.93. 

0.004 


0.0035 

0.003 

0.0025 

0.002 

0.0015 

0.001 

0.0005 

0 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 


Figure 21. Graph to show the density of L. racemosa in each transect in the Lovokampy mangal. Where more than one quadrat was sampled the results are displayed from left to 


26


180 

160 

140 

120 

100 

80 

60 

40 

20 

0 

A. marina 


R. mucronata 

C. tagal 

L. racemosa 

X. granatum 


Figure 22a. Graph to show the density of each tree species in each quadrat in the Lovokampy mangal, transects 1 to 13. Error bars = 95% confidence interval. 


180 

160 

140 

120 

100 

80 

60 

40 

20 

0 

A. marina 


R. mucronata 

C. tagal 

L. racemosa 

X. granatum 


Figure 22b. Graph to show the density of tree species in each quadrat in Lovokampy mangal, transects 3 to 26. Error bars = 95% confidence interval. 

27

Figure 22 shows the dominance of A. marina throughout the mangal and Table 7 shows that A. 

marina accounts for the highest density of any of the species in one quadrat. 

Species Maximum density (m²/ha) 

A. marina 63.63 

B. gymnorrhiza 0.017 

R. mucronata 11.101 

C. tagal 0.717 

L. racemosa 0.003 

Table 7. Showing the maximum density of each species within a surveyed quadrat. 

Table 8 shows an average number of trees per hectare for each of the species surveyed in this 

mangal. By multiplying this by the area of the mangal (~90ha) an assessment of the total number of 

trees in the mangal can be made. A. marina was the most abundant species in the mangal with an 

estimated number of 1,051,110 ± 381,780 trees including adults, saplings and seedlings, followed 

by C. tagal with 244,530 ± 140,760 trees. R. mucronata had 2,250 ± 3,420 trees, B. gymnorrhiza 

had 540 ± 720 trees, L. racemosa had 180 ± 270 trees and X. granatum was the least abundant 

species in the mangal with only 1 tree count. These results are shown in Figure 23 to Figure 25 and 

Table 8. 

A. marina 


R. mucronata 

No. of trees / ha Area of mangal (ha) Total number of trees 

Adults 2,599 ± 634 90 233,910 ± 57,060 

Saplings 737 ± 280 90 66,330 ± 25,200 

Seedlings 8,343 ± 3,328 90 750,870 ± 299,520 

Adults 4 ± 5 90 360 ± 450 


Seedlings 2 ± 3 90 180 ± 270 

Adults 18 ± 25 90 1,620 ± 2,250 

Saplings 5 ± 8 90 450 ± 720 

Seedlings 2 ± 5 90 180 ± 450 

Adults 749 ± 440 90 67,410 ± 39,600 

C. tagal 

Saplings 63 ± 50 90 5,670 ± 4,500 

Seedlings 1,905 ± 1,074 90 171,450 ± 96,660 

Adults 2 ± 3 90 180 ± 270 

L. racemosa 


Seedlings 0 90 0 

Table 8. Showing the number of trees per hectare. This figure was multiplied by the total area of the mangal excluding 

creeks to give the total number of trees in the mangal per species. ± 95% confidence interval. 

Figure 23 to Figure 25 show the age structure for the mangal, while Figure 26 shows the mean 

height of an adult individual of each species. 

28

Number of trees per hectare 

14000 

12000 


10000 

8000 

6000 

Adults 

Saplings 

Seedlings 

4000 

2000 

0 

A. marina 


R. mucronata 

Species 

Figure 23. Graph to show the total number of adults, saplings and seedlings of each species per hectare in the 

Lovokampy mangal. Error bars = 95% confidence interval. 

C. tagal 

L. racemosa 

X. granatum 

45 

40 

35 

30 


25 

20 

15 

Adults 

Saplings 

Seedlings 

10 

5 

0 

B. gymnorrhiza R. mucronata L. racemosa X. granatum 

Figure 24. Graph to show the total number of adults, saplings and seedlings of B. gymnorrhiza, R. mucronata, L. 

racemosa and X. granatum per hectare in the Lovokampy mangal. Error bars = 95% confidence interval. 

29

100% 

80% 

Percentage 

60% 

40% 

Seedlings 

Saplings 

Adults 

20% 

0% 

L. racemosa 

X. granatum 

R. mucronata 


C. tagal 

A. marina 

Figure 25. Graph to show the age structure of the population of each species. 

500 

450 

400 

350 

Height (cm) 

300 

250 

200 

150 

100 

50 

0 

A. marina B. gymnorrhiza R. mucronata C. tagal L. racemosa X. granatum 

Figure 26. Graph to show the mean height of an adult of each species in the Lovokampy mangal. Error bars = 95% 


Table 9 shows the breakdown of the salinity samples taken in this mangal, these were then plotted 

against density of each species (see Figure 27) and proportion of each species (see Figure 28). 

Soil Salinity ‰ 

Transect Quadrat 1 Quadrat 2 Quadrat 3 Quadrat 4 Quadrat 5 Quadrat 6 Quadrat 7 Quadrat 8 

1 55 N/A N/A N/A N/A N/A N/A N/A 


3 108 109 N/A N/A N/A N/A N/A N/A 

4 55 46 * * * N/A N/A N/A 

5 50 * N/A N/A N/A N/A N/A N/A 

6 153 83 N/A N/A N/A N/A N/A N/A 

7 68 * * * > 96 N/A N/A 

30

8 42 115 38 35 N/A N/A N/A N/A 

9 52 91 45 100 N/A N/A N/A N/A 

10 37 42 85 81 102 N/A N/A N/A 

11 46 155 124 78 148 * * N/A 

12 64 70 108 N/A N/A N/A N/A N/A 

13 * 42 120 104 * N/A N/A N/A 

14 39 60 * * N/A N/A N/A N/A 

15 38 30 134 * N/A N/A N/A N/A 

16 40 66 65 54 78 65 162 46 

17 63 82 125 * N/A N/A N/A N/A 

18 22 53 * N/A N/A N/A N/A N/A 

19 98 174 N/A N/A N/A N/A N/A N/A 

20 * N/A N/A N/A N/A N/A N/A N/A 



23 > * 157 N/A N/A N/A N/A N/A 

24 148 40 26 58 N/A N/A N/A N/A 

25 40 20 54 N/A N/A N/A N/A N/A 

26 56 16 * N/A N/A N/A N/A N/A 

Table 9. Showing the soil salinity in ppt for each quadrat sampled. 

(* soil sample too dry for analysis, > salinity reading above capacity of refractometer (180ppt), N/A not applicable). 

70 

60 


50 

40 

30 

20 

A. marina 


R. mucronata 

C. tagal 

L. racemosa 

X. granatum 

10 

0 

0 20 40 60 80 100 120 140 160 180 200 

Salinity ‰ 

Figure 27. Scatter graph to show the density of each species in m² per hectare against salinity in ppt. 

31

120 

Percentage of species present 

100 

80 

60 

40 

20 

A. marina 


R. mucronata 

C. tagal 

L. racemosa 

X. granatum 

0 

0 20 40 60 80 100 120 140 160 180 200 

Salinity ‰ 

Figure 28. Scatter graph to show the proportions of each species present against salinity in ppt. 

The salinity of the soil samples taken from each quadrat is shown in Table 9. A negative 

correlation is shown between the density of A. marina and salinity and R. mucronata and salinity at 

the 99% confidence level using the Spearman Rank correlation (see Figure 27). There was no 

significant correlation between the densities of the other species and salinity. There was also a 

positive correlation between the proportion of R. mucronata and salinity at the 99% confidence 

level using the Spearman Rank correlation (see Figure 28). The other species showed no significant 

correlation between the proportion of species and salinity. 

32

Discussion 

As the Lovokampy mangal has not been studied previously there is no map to compare it to but 

residents of the local village stated that approximately five years ago the mouth to the creek became 

blocked thus allowing no water flow through the mangal. This considerably changed the shape, the 

mangal decreasing a lot in surface area as it became much drier (Frontier-Madagascar, unpublished 

data). The creek opened up again and was open during the visits to the mangal in May and June 

2002. However a recent visit to the mangal in November 2002 revealed that the creek had again 

become blocked, and little seawater was entering the mangal. 

Both A. marina and C. tagal had a higher number of seedlings than adults. B. gymnorrhiza, R. 

mucronata, L. racemosa and X. granatum all had more adults than saplings and seedlings. This is 

shown in Figure 23 to Figure 25 and Table 8. 

The local people, both from the village of Lovokampy and from surrounding villages use the 

mangrove trees for a variety of uses including firewood and fencing materials (Frontier- 

Madagascar, unpublished data). Semesi and Howell (1989) state that both A. marina and C. tagal 

are often used for these purposes and this could account for the low proportion of adults in relation 

to the seedlings for these two species. As there was such a high percentage of seedlings it would 

seem that regeneration of both A. marina and C. tagal is possible. 

The percentage of adult B. gymnorrhiza is only slightly greater than that of juveniles (saplings and 

seedlings) suggesting a healthy population. While the populations of L. racemosa, and R. 

mucronata have a much lower percentage of juveniles which would indicate that regeneration is 

unlikely. Only one adult of X. granatum was observed so the future of this species in the mangal 

seems very unlikely, especially when considered in conjunction with the high salinity of the mangal 

(see below). It seems likely that this individual was seeded from the Lavadanora mangal. 

As shown by Figure 26 A. marina has the average tallest height of an adult of all the species in the 

mangal with a mean height of 4.0m. R. mucronata had a mean height of 2.8m, L. racemosa had a 

mean height of 1.7m, C. tagal had a mean height of 1.6m, B. gymnorrhiza had a mean height of 

1.4m while the X. granatum tree had a height of 1.1m. None of these species have reached their 

potential height. The trees can reach 13m, 20m, 3m, 7m, 18m and 10m respectively (Semesi, 

1996). The low average heights achieved in this mangal could be attributed to the fact that the 

mangal was cut off from inflow of seawater for a significant amount of time, therefore stunting the 

mangrove trees. For example C. tagal occurs as short stunted trees in very saline environments. In 

addition to this A. marina, the dominant species present is extremely suitable for coppice (regular 

cutting to form new shoots) (Semesi, 1996), which the locals regularly chop for use as firewood and 

building materials (Frontier-Madagascar, unpublished data) contributing to the general low height 

of this species. Casual observations during the survey showed that A. marina was utilised both in 

terms of grazing and chopping. Chopping appeared to be spread throughout the mangal rather than 

concentrated in one area, with two exceptions of extensively cleared areas on the outskirts of the 

mangal where many stumps were observed. Trees chosen for harvest tended to be those that had 

died after the creek blocking (1990-1995) (Frontier-Madagascar, unpublished data). 

The Lovokampy mangal has an overall high soil salinity, which varies between 4 and 155+ ppt as 

shown in Table 9. The quadrats, which had low soil salinity measurements were near the 

freshwater source that emerges from the bottom of the cliff. The rest of the mangal, less influenced 

by this freshwater had much higher salinity. An explanation for this is most likely to be the mouth 

of the creek being blocked at intervals throughout the years (Frontier-Madagascar, unpublished 

data), culminating in high soil salinity due to evaporation. A. marina is dominant and widespread 

33

throughout this mangal (see Figure 17 and Figure 22), and a positive correlation was shown 

between the density of this species and salinity. This could be attributed to the fact that it tolerates 

high salinity and varied flooding regimes (Semesi, 1996). L. racemosa is typically found as 

landward mangrove where there is an influence of freshwater (Semesi, 1996) which is true of this 

mangal. Semesi (1996) also states that B. gymnorrhiza can tolerate mixed salinity and is often 

found in stands mixed with or between stands of R. mucronata and C. tagal but B. gymnorrhiza is 

usually present in areas less inundated with salt water than R. mucronata (Schatz, 2001). Such low 

densities of L. racemosa, B. gymnorrhiza and R.mucronata species exist in this mangal that it is 

very difficult to make inferences, however the high salinity of the mangal most probably accounts 

for the low densities of these species along with their inability to tolerate variation over time. 

English et al (1994) state that the majority of mangrove species grow best in low to moderate 

salinity’s (25ppt), which this mangal generally exceeds. There was a positive correlation between 

R. mucronata and salinity but again there was such a low density of this species in the mangal no 

inference can be made. X. granatum almost certainly is an exceptional occurrence in the mangal 

due to the extreme high salinity experienced here as this species has a lack of xerophyllic 

adaptations, most obviously its lack of pneumatophores and is most often found where there is a 

significant freshwater influence (Semesi and Howell, 1989). Finally C. tagal appeared to be 

distributed mostly around the edge of the mangal. 

34

CHAPTER FOUR: THE MANGORO 

Introduction 

This mangal is situated approximately 40km south of Toliara (see Figure 2). It has been the subject 

of study in the past, but with no recent published work as to the arboreal biodiversity. Once again 

the geographical positioning of the Mangoro mangal is not ideal for its formation, subject to 

considerable wave action at high spring tides, but protected from the seasonal prevailing swells 

from the West and Southwest. This mangal is again one of the core zones in the proposed Man and 

Biosphere Reserve for the Toliara region (Cellule Environnement Marin et Côtier (Office National 

pour l’Environnement), 2001) making baseline information important for future management. 

Figure 29. Map depicting the historic layout and position of the Mangoro mangal (Lebigre, 1997). 

35

Methods 

The surveys were carried out in the Mangoro mangal between November 2000 and February 2001. 

The methods used for this mangal were similar to those used for Lavadanora with three exceptions. 

1. The transect line plots were completed in a similar manner as described above to calculate the 

individual tree density and height measurements with a few changes. Transect lines were 

established from the seaward margin of the forest, at right angles to the edge of the mangrove 

forest. 

2. In the dense forest the quadrats used were 5x5m, and 10x10m quadrats were used elsewhere in 

the mangal due to the sparser nature of the trees. However these were not used to work out the 

tree density within this mangal. 

3. Soil salinity samples were not taken in this mangal. 

36

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% 


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

study suggests that no seedling grows beyond two seasons, while the absence of ‘young’ (narrowgirthed) 

adults suggests that no seedling has succeeded in reaching adulthood for perhaps twenty 

years or more. The presence of numerous stunted trees (all shrub-like and less than 30cm in height) 

is further evidence of severe grazing pressure. Although Lebigre (1997) states that livestock graze 

tanne plants, they remain exclusively untouched in Mangoro mangal, at the expense of all stages of 

the life cycle of A. marina. Only those trees that are greater than zebu or goat height survive in a 

non-stunted form. Other factors may contribute to the stunted nature of the trees including the 

extreme environmental conditions of one of Madagascar’s most Southerly mangals. 

In this mangal, C. tagal appears not to be harvested (perhaps because it is regarded as being a 

juvenile form of other species), whereas ample evidence exists to show the coppicing or complete 

harvesting of individuals of B. gymnorrhiza and R. mucronata. The harvesting appears to be spread 

throughout the forest, and not performed in a clear-felling manner that would clearly be more 

efficient for the gatherers. 

Lebigre (1990) suggests that summer groundwater perfusion may be sufficient to meet the 

freshwater requirements of the trees. Without this, he believes that it is difficult to explain the 

presence of B. gymnorrhiza at the edge of the tannes, without calling into question the normal 

requirement of this species for a salinity below that of seawater. However, incidental salinity 

measurements taken at random points throughout the creek (Frontier-Madagascar, unpublished 

data) concurring with the supposition of the local people that there is no freshwater in the system 

refute this suggestion that the mangroves are supplied with groundwater. Throughout the duration 

of this study, there was no evidence of freshwater input other than through direct precipitation. It 

could be concluded that this ecosystem relies on seawater, frequently hypersaline, supplemented by 

freshwater derived from precipitation (rainfall and dew). Any groundwater influx is either 

negligible, or it was undetected; further study would help identify more precisely the actuality. 

39

CHAPTER FIVE: CONCLUSIONS 

Comparison of the three mangals 

Study of the three mangals will stand alone, however it is interesting to compare the three different 

populations. With this in mind, the results were further analysed. First, the diversity of each 

mangal was calculated using Simpson’s and Shannon’s diversity indices. Results from these 

calculations are displayed in Table 10 and would indicate the Mangoro to be the most species 

diverse of the mangals studied as expected due to it’s larger size. As standard, the Simpson 

diversity index is displayed as 1/D, the resulting figure being higher if the population is more 

diverse. When interpreting the Shannon diversity index, natural communities generally fall in the 

range of H 1.5-3.5. Thus all of the populations in Table 10 would seem to be heavily disturbed. 

Diversity Index Lavadanora Lovokampy Mangoro 

Simpson 1/D 1.702049 1.426824 2.234069 

Ed 0.283675 0.237804 0.446814 

Shannon H 0.770064 0.488792 1.010764 

Eh 0.429781 0.2728 0.628023 

Table 10. Showing Simpson’s and Shannon’s diversity indices for the four mangals surveyed. 

In Figure 32 the average basal area of a tree from each species surveyed in each mangal is 

displayed. These values are very difficult to interpret due to the significantly larger average basal 

areas of the trees in the Mangoro mangal, consequently this value was taken out for easy 

interpretation of the remaining two mangals (see Figure 33). For further information the results are 

also displayed in Table 11. 

1.00E-01 

9.00E-02 

Average Basal Area (m²) 

8.00E-02 

7.00E-02 

6.00E-02 

5.00E-02 

4.00E-02 

3.00E-02 

2.00E-02 

1.00E-02 

Lavadanora 

Lovokampy 

Mangoro 

0.00E+00 

A. marina 

B. 

gymnorrhiza 

R. mucronata 

C. tagal 

L. racemosa 

X. granatum 

S. alba 

Figure 32. Graph showing the average basal area (m²) for an individual of each species in each mangal. 

40

1.20E-02 

Average Basal Area (m²) 

1.00E-02 

8.00E-03 

6.00E-03 

4.00E-03 

2.00E-03 

Lavadanora 

Lovokampy 

0.00E+00 

A. marina 

B. 

gymnorrhiza 

R. mucronata 

C. tagal 

L. racemosa 

X. granatum 

S. alba 

Figure 33. Graph showing the average basal area (m²) for an individual of each species in each mangal, with the 

exception of the Mangoro for clarity. 

Lavadanora Lovokampy Mangoro 

A. marina 5.16*10 -4 ± 1.06*10 -4 0.00288 ± 8.11*10 -4 0.0107 ± 0.00534 

B. gymnorrhiza 4.47*10 -5 ± 4.46*10 -5 8.46*10 -5 ± 2.53*10 -5 0.00676 ± 0.00231 

R. mucronata 2.5*10 -4 ± 3.49*10 -4 4.90*10 -3 ± 5.93*10 -3 0.0106 ± 0.00188 

C. tagal N/A 1.37*10 -4 ± 7.32*10 -5 1.62*10 -4 ± 4.05*10 -5 

L. racemosa 1.66*10 -5 ± 9.97*10 -6 3.40*10 -3 N/A 

X. granatum 3.87*10 -4 ± 8.38*10 -5 N/A N/A 

S. alba N/A N/A 0.0501 ± 0.0417 

Table 11. Showing the average basal area (m²) for an individual of each species in each mangal. 

Figure 34 shows the average height of an adult tree of each species in each mangal, broken down in 

Table 12. These values can be used to make various inferences as to the general health of the 

individual populations, which agree with those conclusions drawn from the diversity indices 

calculations. 

41

1400 

1200 

1000 

Height (cm) 

800 

600 

400 

Lavadanora 

Lovokampy 

Mangoro 

200 

0 

A. marina 

B. 

gymnorrhiza 

R. mucronata 

C.tagal 

L. racemosa 

X. granaum 

S. alba 

Figure 34. Graph showing the average height (cm) for an individual adult of each species in each mangal. 

Lavadanora Lovokampy Mangoro 

A. marina 1055.22 ± 151.19 397.79 ± 45.72 429.43 ± 66.89 

B. gymnorrhiza 364.80 ± 129.03 137.33 ± 31.12 383.36 ± 45.08 

R. mucronata 713.16 ± 537.43 277.05 ± 110.87 482.37 ± 41.95 

C. tagal N/A 158.02 ± 15.36 243.33 ± 13.07 

L. racemosa 308.52 ± 59.63 174.07 ± 125.59 N/A 

X. granatum 909.57 ± 122.26 110 ± N/A 

S. alba N/A N/A 545 ± 334.63 

Table 12. Showing the average height (cm) for an individual adult of each species in each mangal. 

Summary of results. 

• X. granatum was dominant in the Lavadanora mangal 

• A. marina was dominant in the Lovokampy mangal 

• R. mucronata was dominant in the dense forests of the Mangoro mangal and A. marina in the 

tannes. 

• A. marina has a significantly taller adult population at the Lavadanora mangal, however the 

trees are of a significantly larger girth at both Lovokampy and more so, the Mangoro. 

• Both R. mucronata and B. gymnorrhiza had significantly larger average basal areas at the 

Mangoro mangal, however the individuals of B. gymnorrhiza were no taller than those of 

Lavadanora. 

• The trees of Lovokampy tended to have larger basal areas than Lavadanora. 

• S. alba and X.granatum, although being present, were only found at one each of the mangals. 

• L. racemosa and C. tagal were only found in very small numbers during the surveys, which 

were unlikely to be representative of healthy populations. 

• Damage was observed in all three of the mangals, but it was not considered to be extensive. 

• The Mangoro was the largest of the mangals at ~710ha, followed by Lovokampy at ~90ha and 

Lavadanora at ~80ha. 

42

Conclusions and recommendations 

Mangrove trees are used for firewood and for making charcoal. In the East Africa region, many 

mangrove forests (particularly those close to urban areas) have been subject to indiscriminate 

cutting and the destruction of entire mangrove habitats (Semesi, 1996). Mangroves to the North of 

Madagascar have been progressively exploited for firewood, with recent incursions into the 

mangroves at Songoritelo being noted by Vasseur (1997), shrimp farming and salt extraction. 

Although the pressure on the mangrove forests for charcoal remains small in this area due to the 

local preference for xerophilic (terrestrial) timber (Lebigre, 1997), there is a local preference for A. 

marina as a fuelwood (Frontier-Madagascar, unpublished data). Where mangroves are common 

and close to centres of population (e.g. Toliara), they are subject to considerable felling activity. In 

fact Salomon (1981) showed that the charcoal requirements of Toliara result in the clearance of 

5,000ha of (terrestrial) forests annually; the natural xerophilic vegetation now covers only 27% of 

the southwest of the country (Lebigre, 1997). As this terrestrial vegetation becomes exhausted, the 

resources of the mangroves are more likely to come under threat. 

Semesi and Howell (1989) state that the most destructive activities affecting mangroves are clearfelling 

for rice cultivation, salt and charcoal production, aquaculture, or for firewood; whereas 

selective felling for export and local construction purposes is not a major threat if adequately 

controlled. Rice culture is not possible in this area (the driest in Madagascar), and can be 

discounted as a threat to the mangroves. Traditional fishing in Western Madagascar relies 

extensively on forest products, much of which originate from readily accessible mangroves 

(Rasolofo, 1997), but there is little use of smaller mangroves for this purpose. Nor is salt 

production a real concern for the tannes, since despite the favourable climate (Hamilton and 

Snedacker, 1984), the dune-derived relief and access difficulties are probably enough of a logistical 

barrier to discourage any large-scale operation. The major problems facing mangroves to the North 

(poor agricultural practises, tree felling, salt production, and shrimp fishing and aquaculture (Iltis, 

1997)) are largely absent from this section of the coastline, although the first two are present and are 

likely to become increasingly important factors influencing the local environment. 

The cutting of any mangrove tree technically requires a permit in Madagascar, but there is no 

enforcement of this edict (Cooke et al., 2000). Mangrove wood is highly dense, an attribute that 

confers resistance to fungi and termites (Semesi, 1996). For construction purposes the 

Rhizophoraceae are most prized, as they most often have the forked trunk preferred for wooden 

domiciles. Good management of mangrove forests has been demonstrated in Belo-sur-Mer, where 

local people have exploited the resource in a sustainable manner for many decades (Henry Chartier 

and Henry, 1997), and we conclude that the people living near these mangals are likewise already 

engaged in an element of stewardship of their mangrove forest. With this in mind, a 

recommendation can be made to the local village that the creek is dredged in order to link it with 

the sea to prevent further mangal loss in Lovokampy. 

The three mangals are far from a pristine condition and if they are to be conserved into the future 

then management of their current diversity and restoration of a fuller diversity need to be the 

priorities. These three mangals are all important sites for the proposed Man and Biosphere reserve 

yet they are in a generally poor state of health being exploited by local populations and under threat 

from environmental factors. Future work combining satellite imagery, GIS techniques, 

hydrological, chemical and socio-economic studies, and continued biological survey work are 

essential to production of a suitable management plan and monitoring scheme. 

43

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