nvestigating the influences of tidal inundation and surface elevation on the establishment and early development of mangroves for application in understanding mangrove rehabilitation techniques 1

INVESTIGATING THE INFLUENCES OF TIDAL INUNDATION AND SURFACE ELEVATION ON THE ESTABLISHMENT AND EARLY DEVELOPMENT OF MANGROVES: FOR APPLICATION IN UNDERSTANDING MANGROVE REHABILITATION

INVESTIGATING THE INFLUENCES OF TIDAL INUNDATION AND SURFACE ELEVATION ON THE ESTABLISHMENT AND EARLY DEVELOPMENT

OF MANGROVES: FOR APPLICATION IN

UNDERSTANDING MANGROVE REHABILITATION

TECHNIQUES

OH RUI YING, RACHEL

(B Sc (Hons.), NUS)

A THESIS SUBMITTED FOR THE DEGREE OF

MASTER OF SOCIAL SCIENCES DEPARTMENT OF GEOGRAPHY NATIONAL UNIVERSITY OF SINGAPORE

2015

Declaration

I hereby declare that this thesis is my original work and it has been written by me in its entirety I have duly acknowledged all the sources of information which have been used in the thesis

This thesis has also not been submitted for any degree in any university previously

Oh Rui Ying, Rachel

23 January 2015

Acknowledgements

To my supervisor, Dr Daniel Friess – I would like to express my deepest gratitude for the guidance received and for sharing the countless opportunities that allowed me to learn from and communicate with other academics and like-minded people The academic and personal growth gleaned has been invaluable

Deepest appreciation to my academic inspirations – Dr Edward L Webb for strengthening my natural inclinations towards ecological research and Dr Roman Carrasco, for incepting a love and appreciation for statistical methods

Many thanks also, to Benjamin Brown, Dominic Wodehouse and a third who wish to remain anonymous, for the precious time and effort for academic discussions with this greenhorn Your dedication, passion and in-depth knowledge have been most inspiring

Working in the mangroves is not for the faint-hearted I am genuinely thankful for those who have mucked around in the mud with me – Akhzan Nur Iman, Andi Darmawansyah, Ikhsan Ismail, Regista Rapa, Rio Ahmad, Sardis Andis, Suwardi, Teguh Nagir, Yusran Nurdin, Benjamin Lee Chengfa, Lee Bee Yan, Leong Mun Kidd and Tan Bo Hui I am humbled also, through working with my team of Bengali bhai (Bengali: brother) and Indian ahney (Tamil: brothers)

To Derek Yap (Camphora Pte Ltd) and Salad Dressing Architecture Company – deepest appreciations for sharing the collaborative opportunity in setting up the mesocosm experiment

I am forever grateful to the Mangrove Lab team and my friends for being my pillars of support Special mention goes to Serene Ng, my comrade-in-arms, for being a constant companion on this academic journey with her encouragement and sweet nature, over our many cups of juice and chai

Finally, I am eternally indebted to my family, for their unwavering faith, patience and unconditional support

Table of Contents

1.2.2 A lack of mangrove rehabilitation success 3

2.2.1 The evolution of coastal wetlands restoration 9 2.2.2 Approaches in coastal wetland restoration 11 2.3 Adopting the Ecological Mangrove Rehabilitation (EMR)

approach

11

2.4 The importance of surface elevation and inundation hydroperiod for mangrove rehabilitation success

15

2.4.1 Field studies relating surface elevation and mangrove distributions

16

2.4.2 Experimental studies relating seedling responses to inundation

18

2.4.3 Experimental studies relating propagule establishment to inundation

20

Chapter 3 – Surface elevation is an important factor in achieving mangrove rehabilitation success

24

3.2.3 Post-rehabilitation vegetation survey in aquaculture ponds and reference mangrove forests

29

3.2.4 Genera-specific surface elevation envelopes and prediction maps

30

3.3.1 Vegetation established in aquaculture ponds and reference mangrove forests

31

3.3.2 Genera-specific surface elevation envelopes and prediction maps of mature mangrove trees in aquaculture ponds

34

3.4.1 Surface elevation affects propagule establishment and seedling development

40

3.4.2 Low surface elevations hinder propagule establishment: mid-corrective actions are required in approaching successful re-vegetation at rehabilitation site

43

3.4.3 Using surface elevation data to predict future establishment

45

Chapter 4 – Interspecific variations in survival and growth responses of

mangrove seedlings to three contrasting inundation durations

47

4.3.3 Root length of Rhizophora seedlings 57

4.4.1 Impacts of prolonged inundation on seedling survival 58 4.4.2 Impacts of prolonged inundation on seedling growth 61 4.4.3 Interactions between inundation and other physical

factors that affect seedling growth

63

5.1.1 Effects of surface elevation on mangrove establishment 66 5.1.2 Effects of prolonged inundation on seedling survival and development

67

5.2 A synthesis: Reconciling a field study and a mesocosm

experiment

68

5.4 Recommendations

5.4.1 Identifying disturbance-free periods that favour establishment and colonisation

73

5.4.3 Long-term monitoring of recovery trajectory 74

Summary

Human exploitation and conversion of natural mangrove ecosystems is causing widespread ecosystem degradation and loss Yet, mangroves have the potential to recover functionality through secondary succession Human-mediated mangrove rehabilitation projects have been implemented in response to mitigating such losses However, projects vary in success rates, most of which could be attributed to the lack

of identifying site-specific cause(s) of mangrove degradation, and/or the barriers and stressors that have prevented natural recovery via secondary succession The aim of this thesis is to contribute to the understanding of hydrologic management in the success of mangrove rehabilitation projects The focus is on how tidal inundation and surface elevations influences the establishment, survival and development of mangroves in early developmental stages This was achieved via a field study and a mesocosm experiment Overall, analyses suggested that (a) establishment of mangroves were restricted to specific surface elevations in rehabilitation site (-1.511 m

≤ x ≤ 0.228 m WGS 84) , and (b) Avicennia seedlings were incapable of tolerating

prolonged inundation durations beyond 5 hours (diurnal regime) compared to

Rhizophora seedlings This highlight that there are species-specific thresholds beyond

which mangrove establishment is impeded, and where early development is constraint Taken together, the results suggest that surface elevation is potentially a key influence

on the successful establishment and development of mangroves as it controls inundation hydroperiod It highlights also, the need for rehabilitation planners and practitioners to include consideration of altering surface elevation in degraded sites to favour natural colonisation and establishment in achieving rehabilitation success

Chapter 1 provides an introduction to the issues facing mangrove rehabilitation It outlines some of the potential reasons why certain mangrove rehabilitation projects

aimed at reversing mangrove losses have ended in failure It introduces the EMR approach, which has been applied in achieving reforestation success in coastal wetlands, and the aims and objectives of this thesis in contributing to this set of rehabilitation knowledge Chapter 2 starts with an introduction and review of literature regarding coastal wetland ecosystems restoration The chapter progresses with how this knowledge has been applied to the rehabilitation of mangroves, as encapsulated in the Ecological Mangrove Rehabilitation (EMR) approach To create a foundation and link to subsequent empirical chapters, Chapter 2 concludes with an in-depth summary

of studies that investigated the effect of prolonged inundation on seedling survival and growth, and a discussion on the contributing physiological processes that were proposed to explain the observed effects Chapters 3 and 4 will discuss the two objectives outlined above: the large scale rehabilitation project and the controlled mesocosm experiment Each chapter is self-contained and consists of a short introduction, methods, results and a discussion of the observed results The final chapter, Chapter 5, provides a synthesis of the findings and the implications of this study for future mangrove rehabilitation efforts, recommendations for further research

466 Words

List of Tables

CHAPTER 2

2.1: Watson inundation classification and the related Southeast Asian

mangrove species Source: Watson, 1928

17

CHAPTER 3

3.1: Number of seedlings/saplings and trees surveyed across aquaculture

ponds and reference forests

32

3.2: Minimum, interquartile range and maximum surface elevation of

established trees surveyed in reference forest sites, based on WGS 84 datum

35

CHAPTER 4

4.1: Performance matrix of the GLM models fitted 55 4.2: Performance matrix of the mixed-effects models fitted 57

CHAPTER 5

5.1: A summary of the EMR rehabilitation techniques employed across eight mangrove rehabilitation projects in achieving successful reforestation (Lewis

& Brown, 2014)

71

List of Figures

CHAPTER 2

2.1: A traditional view of restoration options for a degraded system,

illustrating the idea that the system may proceed along different trajectories

and that the goal of restoration is to guide the trajectory towards some

desired state Source: Hobbs & Norton, 1996

10

2.2 The 6-step EMR approach (Lewis & Brown, 2014) 13

2.3: Schematic representation using an Avicennia alba propagule to illustrate

the three thresholds to be surpassed before establishment (1) The propagule

first has to acquire a minimum root length during an inundation-free period

to resistant against floating up during tidal inundation (2) Then, roots have

to be long enough to resist hydrodynamics by waves and currents (3) Rooted

seedling may still be dislodged via mixing or erosion of surface sediments

Source: Balke et al., 2011

23

CHAPTER 3

3.1: (a) Regional setting of Makassar (black box), South Sulawesi,

Indonesia; (b) former aquaculture ponds at Kuri Caddi and reference forests

at both Kuri Caddi and Kuri Lompo; and (c) broken lines delineate the

disused aquaculture ponds in Kuri Caddi, extracted from Google Earth

(dated February 2014)

27

3.2: (a) Dike walls that have undergone strategic breaching, and (b)

regrading of selective dike walls to produce substrate at lower surface

elevations (foreground) Red arrows point to existing dike walls

29

3.3: The interquartile range represents surface elevation envelopes per

species of seedling/saplings surveyed in (a) aquaculture ponds and (b)

reference forests Whiskers indicate maximum and minimum values and

empty circles indicate outliers

34

3.4: The interquartile range represents surface elevation envelopes per genus

(i.e Avicennia spp., Excoecaria spp., Rhizophora spp and Sonneratia spp.,

surveyed in reference forest sites Whiskers indicate maximum and minimum

values and empty circles indicate outliers

35

3.5: Map of aquaculture ponds showing surface elevation changes (i.e grade

down, grade up), location of pile of broken branches and established

vegetation where each green triangle represents an established individual

(surveyed in June 2014)

36

3.6: (a) Each green triangle represents one established vegetation individual

(surveyed in June 2014) Predicted elevation ranges where (b) Avicennia

spp., (c) Rhizophora spp and (d) Sonneratia spp might establish in the

future as trees are represented as green areas

39

CHAPTER 4

4.1: (a) Aerial view of experimental set-up, (b) side and (c) aerial view of

each pair of reservoir and experimental tank

49

4.2: Photographs of (a) the actual mesocosm set-up and the experimental

pots with (b) Rhizophora and (c) Avicennia seedlings

50

4.3: Proportion of seedlings alive per inundation treatment (A = Avicennia

spp.; R = Rhizophora spp.; 5, 7 and 9 represent the number of inundation

hours)

54

4.4: Cumulative stem height of both Rhizophora (top row) and Avicennia

seedlings (bottom row), segregated by inundation treatment, across weeks 1

to 11 Standard errors are indicated by whiskers

56

4.5: Barplot of (a) mean stem height and (b) mean root length of Rhizophora

seedlings across three Inundation Treatments (R5, R7 and R9) Standard

errors are indicated by whiskers

58