Regeneration mechanisms in Swamp Paperbark (Melaleuca ericifolia Sm.) and their implications for wetland rehabilitation



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Regeneration mechanisms in Swamp 
Paperbark (Melaleuca ericifolia Sm.) 
and their implications for wetland 
rehabilitation  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Randall Robinson 
School of Biomedical Sciences 
Institute of Sustainability and Innovation 
Victoria University 
St Albans Victoria 
Australia 
June 2007 
 

 
II
 
Declaration 
 
 
I, Randall William Robinson, declare that the PhD thesis entitled Regeneration 
mechanisms in Swamp Paperbark (Melaleuca ericifolia Sm.) and their implications 
for wetland rehabilitation is no more than 100,000 words in length including quotes 
and exclusive of tables, figures, appendices, bibliography, references and footnotes. 
This thesis contains no material that has been submitted previously, in whole or in 
part, for the award of any other academic degree or diploma. Except where otherwise 
indicated, this thesis is my own work 
 
 
 
Randall William Robinson 
28 August 2007 
 
 
 
 
 
 
 
 

 
III
Table of Contents 
 
Summary 
 
 
 
 
 
 
 
 
 

 
1.0 Introduction 
 
 
 
 
 
 
 
 

 
 
1.1 General ecological background to the project 
 
 
 

  1.1.1 
Melaleuca 
 
 
 
 
 
 

  1.1.2 
Adaptations 
to 
soils 
and 
climate    9 
  1.1.3 
Vegetative 
growth 
     10 
  1.1.4 
Genetic 
diversity      12 
  1.1.5 
Sexual 
reproduction 
     15 
  1.1.6 
Rehabilitation 
approaches 
    17 
 
1.2 
Aims 
of 
this 
project 
      18 
 
2.0 The study site 
 
 
 
 
 
 
 
 
21 
 
 2.1 
Introduction        21 
 2.2 
History 
of 
Dowd 
Morass 
      23 
  2.2.1 
Water 
levels 
over 
past 
∼ 
three 
decades 
   26 
 
 
2.2.2 Salinity regimes over past 
∼ three decades 
 
 
29 
 2.3 
Water 
quality 
in 
Dowd 
Morass 
     30 
  2.3.1 
        31 
 2.4 
Sediment 
quality 
in 
Dowd 
Morass     34 

 
IV
 
 
2.4.1 Carbon, nitrogen and phosphorus 
contents 
  34 
  2.4.2 
Soil 
salinity 
      35 
 
 
2.4.3 Soil pH and the presence of acid-sulfate soils   
 
36 
  2.4.4 
Heavy 
metals 
      39 
 2.5 
Vegetation 
of 
Dowd 
Morass 
     40 
 
3.0 Clonality in Melaleuca: a study of population structure and dynamics using 
molecular analyses and historical aerial photographs 
  44 
 
Abstract 
 
 
 
 
 
 
 
 
44 
3.1 
Introduction        45 
3.2 
Methods 
        50 
 
 
3.2.1 Sample collection and molecular analysis 
 
 
52 
   DNA 
isolation 
      57 
 
 
 
Primer screening 
 
 
 
 
 
57 
   DNA 
amplification 
     57 
 
 
 
Data analysis   
 
 
 
 
 
58 
  3.2.2 
Analysis 
of 
aerial 
photographs 
    60 
   Determination 
of 
growth 
rates and longevity based on  
    Aerial 
photography 
interpretation 
  61 
 3.3 
Results 
        64 
  3.3.1 
Vegetative 
reproduction 
     64 
  3.3.2 
ISSR 
analysis 
      66 
 
 
3.3.3 Growth rates and longevity, determined from  
   aerial 
photographs. 
 
     70 

 
V
 3.4 
Discussion 
        75 
  3.4.1 
Clone 
size 
and 
growth 
type. 
    75 
  3.4.2 
Implications 
for 
revegetation. 
 
    77 
 
4.0 Comparison of two contrasting life forms of Melaleuca in south-eastern 
 Australia
 
 
 
 
 
 
 
 
80 
 
 
Abstract 
 
 
 
 
 
 
 
 
80 
 4.1 
Introduction        81 
 4.2 
Methods 
        84 
  4.2.1 
Seed 
collection 
      84 
  4.2.2 
Seed 
viability 
      86 
 4.3 
Results 
        88 
  4.3.1 
M. ericifolia 
 
 
 
 
 
 
88 
  4.3.2 
Melaleuca parvistaminea 
 
 
 
 
91 
  4.3.3 
Comparison 
of 
M. ericifolia and M. parvistaminea.    
91 
 4.4 
Discussion 
        93 
 
 
4.4.1 Trade-offs between sexual and nonsexual reproduction 
93 
  4.4.2 
Other 
factors 
influencing sexual reproduction in 
 
 
 
M. ericifolia.    
 
 
 
 
 
94 
 4.5 
Conclusions        98 
 
 
 
 

 
VI
 
5 .0 Germination characteristics of Melaleuca ericifolia Sm. 
 (Swamp Paperbark)  
 
 
 
 
 
 99 
 
 
Abstract 
 
 
 
 
 
 
 
 
99 
 5.1 
Introduction        100 
 5.2 
Materials 
and 
Methods 
      103 
  5.2.1 
Seed 
collection 
      103 
  5.2.2 
Seed 
viability 
      103 
 
 
5.2.3 Interactive effects of salinity, light and  
temperature 
on 
germination 
 
    104 
 
 
5.2.4 Effects of preliminary exposure to salt on germination  
106 
 
 
5.2.5 Effects of seed burial and substrate type on germination 
106 
  5.2.6 
Statistical 
analysis 
     107 
 5.3 
Results 
        108 
  5.3.1 
Viability 
       108 
 
 
5.3.2 Interactive effects of salinity, light and  
temperature 
on 
germination 
    108 
  5.3.3 Effects of preliminary exposure to salt on germination  
112 
 
 
5.3.4 Effects of seed burial and substrate type 
 
 
115 
 5.4 
Discussion 
        116 
 
 
5.4.1 Poor seed viability and its causes 
 
 
 
116 
 
 
5.4.2 Effects of chronic and acute exposure to salt   
 
118 
 
 
5.4.3 Effects of environmental variables on germination 
 
120 
 
 
5.4.4 Effects of seed burial and substrate type 
 
 
121 

 
VII
 
 
5.4.5 Implications for rehabilitation of coastal wetlands 
 
122 
 
6.0 Hypocotyl hairs and their importance for recruitment success in  
seedlings of Melaleuca ericifolia Sm. (Swamp Paperbark). 
 
124 
 
Abstract         124 
 6.1 
Introduction        125 
 6.2 
Methods 
        129 
  6.2.1 
Field 
site 
       129 
 
 
6.2.2 Life history of M. ericifolia 
    131 
  6.2.3 
Seed 
collection 
      132 
 
 
6.2.4 Effect of surface sterilisation on hypocotyl hair  
development 
      132 
  6.2.5 
Hypocotyl 
hair 
structure     132 
 
 
6.2.5 Effect of water availability on hypocotyl hair development 
133 
 
 
6.2.7 Effect of salinity, light and temperature on hypocotyl  
hairs 
       134 
 
 
6.2.8 
Data 
analysis 
      136 
 6.3 
Results 
        137 
  6.3.1 
Effect 
of 
surface 
sterilisation 
 
    137 
  6.3.2 
Origin 
and 
characteristics of hypocotyl hairs   
 
138 
 
 
6.3.3 Hypocotyl hairs and seedling development 
 
 
141 
6.3.4 Effect of water availability on hypocotyl hair development 
141 
 
 
6.3.4 Effect of salinity, light and temperature on hypocotyl  
hair, root hair and secondary root development 
 
143 

 
VIII
 
6.4 
Discussion 
        149 
 
 
6.4.1 Functions of hypocotyl hairs in M. ericifolia 
  149 
 
 
6.4.2 Effects of environmental variables on hypocotyl hair 
   Development 
      150 
 
 
6.4.3 Implications for seedling establishment and plant  
   Recruitment 
in 
the 
field 
    152 
 
7.0 Historical recruitment events of Melaleuca ericifolia at Dowd Morass 
155 
 
 
Abstract         155 
 7.1 
Introduction        156 
 7.2 
Methods 
        159 
  7.2.1 
Historical 
aerial 
photographs 
    159 
  7.2.2 
Climatic 
and 
salinity 
data 
    159 
 7.3 
Results 
        161 
 
 
7.3.1 Recruitment events determined using aerial photographs 
161 
  7.3.2 
Climate 
data 
 
      163 
   Rainfall       163 
   Temperature 
      169 
  7.3.3 
Salinity 
data 
      170 
 7.4 
Discussion 
        172 
  7.4.1 
Aerial 
photographs 
     172 
  7.4.2 
Climate 
       173 
 
 

 
IX
8.0 Safe sites for recruitment of M. ericifolia in Dowd Morass   
 
175 
 
 Abstract         175 
 8.1 
Introduction        176 
 8.2 
Methods 
        180 
 
 
8.2.1 Recruitment sites in Dowd Morass 
 
 
 
180 
  8.2.2 
Statistical 
analysis 
     183 
 8.3 
Results 
        184 
  8.3.1 
Recruitment 
sites 
determined in field inspections 
 
184 
 8.4 
Discussion 
        190 
  8.4.1 
Recruitment 
sites      190 
 

General 
Discussion 
        194 
 
 
9.1 Clonality in M. ericifolia 
      196 
 
9.2 Trade-off between sexual and asexual recruitment and impacts 
  on 
germinability 
      199 
 
9.3 Environmental requirements for seedling establishment   
 
201 
  9.3.1 
Germination 
      201 
  9.3.2 
Hypocotyl 
hairs 
      202 
 
9.4 Safe sites for germination in M. ericifolia    204 
  9.4.1 
Temporal 
requirements: 
climatic 
conditions 
  204 
 
 
9.4.2 Spatial requirements: the importance of hummocks 
 
205 
 
9.5 Implications of plant and germination characteristics for 
  management 
of 
brackish 
wetlands 
    207 
References 
         211 
 

 
X
Figures 
 
1.1 Distribution of Melaleuca forests and woodlands in Australia.    
 

2.1 Map of the Gippsland Lakes, Victoria.   
 
 
 
 
22 
2.2 Dowd Morass, showing the location of internal levees.   
 
 
26 
2.3 Recent (since 1991) patterns in water levels in various sections  
of Dowd Morass. 
 
 
 
 
 
 
 
28 
2.4 Recent (since 1991) salinity patterns in various sections of Dowd Morass. 
30 
2.5 Rookery in Area B of Dowd Morass in mid 2006.  
 
 
 
33 
2.6 Algal bloom in Area B (the rookery) at Dowd Morass.    
 
 
34 
2.7 Location of the four sites used for a complete sulfidic analysis of 
 Dowd 
Morass 
sediments. 
 
      39 
2.8 Stands of Swamp Paperbark, M. ericifolia.  
 
 
 
 
42 
2.9 Dense swards of Common Reed, Phragmites australis
 
   42 
2.10 Aerial photograph of a section of Dowd Morass, showing areas of  
Common Reed (DR) and Swamp Paperbark 
(SP). 
 
   44 
3.1 Exposed root system of a mature patch of M. ericifolia.   
 
 
50 
3.2 Individual patch of M. ericifolia at Wilson’s Promontory National Park, 
 
Victoria.  
 
 
 
 
 
 
 
 
51 
3.3 Location of sampled patches of M. ericifolia at Dowd Morass.    
 
53 
 3.3a 
M. ericifolia patch A1 showing sample points.   
 
 
54 
 3.3b 
M. ericifolia patch A2 showing sample points.   
 
 
55 
 3.3c 
Doughnut-shaped 
M. ericifolia patches showing  
  sample 
points. 
       56 
3.4 Exposed edge of a patch of M. ericifolia showing the depth of the  

 
XI
 
extensive network of roots, Narawntapu National Park, Tasmania.   
65 
3.5 Two large patches of M. ericifolia showing individual genets (1-5) 
 determined 
by 
ISSR. 
 
       67 
3.6 ISSR DNA profiles for all samples using primer 814.    
 
 
68 
3.7 Visual differentiation of phenotypes.  
 
 
 
 
 
70 
3.8 Historical aerial photographs of a section of Dowd Morass.  
 
 
72 
3.9 Mean expansion rates of individual M. ericifolia clones at Dowd Morass.  
73 
3.10 Mean expansion rates of all clones of M. ericifolia
 
   74 
4.1 Distribution of M. ericifolia 
in 
Australia. 
     82 
4.2 Distribution of M. parvistaminea 
in 
Australia. 
 
    82 
4.3 Linear regression of seed weight versus germination rate for  
M. ericifolia.   
 
 
 
 
 
 
 
90 
4.4 Germination rate for various population sized of M. ericifolia 
 in 
Victoria 
and 
Tasmania. 
 
      90 
4.5 Comparison of germination rates and seed weights of various 
populations of M. parvistaminea and M. ericifolia
 
   92 
5.1 Effects of temperature, salinity and light regime on the germination  
of M. ericifolia 
seeds. 
       111 
5.2 Effects of prior exposure to saline conditions for up to 16 days, followed  
by exposure to freshwater conditions, on the germination of  
M. ericifolia 
seeds. 
       114 
6.1 Percentage germination and presence of hypocotyl hairs 22 days after 
 soaking with sodium hypochlorite (30 sec to 30 min soaking) and  
de-ionized 
water 
(5 
to 
30 
min 
soaking). 
    138 
6.2 Microscopy images of seedling without and with hypocotyl hairs. 
 
140 

 
XII
6.3 Development of hypocotyl hairs on seedlings grown on substrates 
  
made up with various concentrations 
of 
agar.    143 
6.4 Percentage of seedlings exhibiting positive geotropism when grown  
on substrates made up with four different concentrations of agar.   
144 
6.5 Percentage of seedlings showing hypocotyl hair development  
at 
various 
salinities. 
       146 
6.6 Hypocotyl hair and root development in M. ericifolia in  
response to various salinity concentrations over 14 days. 
 
 
148 
7.1 Photos of a single section of Dowd Morass at six time periods from 1957  
2003. 
         162 
7.2 Dendrogram from the hierarchical 
cluster 
analysis. 
   164 
7.3 Rainfall data from the 5 outlier cases from the hierarchical cluster 
analysis. 
        168 
7.4 Mean monthly temperature levels from East Sale weather station, 
Sale, Victoria from July 1943 to June 2005.   
 
 
 
169 
7.9 Mean monthly salinity levels of surface waters in Lake Wellington,  
Sale, Victoria from July 1968 to June 1975.   
 
 
 
171 
7.1 Sample sites for identification of possible recent recruitment of 
 
 
M. ericifolia 
in 
Dowd 
Morass.     181 
8.2 View of reed community at the western end of Dowd Morass.   
 
184 
8.3 close up of juvenile M. ericifolia recruit on a hummock.  
 
 
185 
8.4 Moisture content of substrata. 
      188 
8.5 
Salinity 
of 
substrata. 
       188 
8.6 
pH 
of 
substrata. 
        189 
8.7 
Organic 
matter 
content. 
       189 

 
XIII
Tables 
 
2.1 Summary of water quality data for Dowd Morass. 
 
 
 
31 
2.2 Water-column nutrient data for four areas at Dowd Morass. 
 
 
32 
2.3 Carbon, nitrogen and phosphorus content of sediments in four areas at  
 
Dowd Morass.  
 
 
 
 
 
 
 
35 
2.4 Soil moisture, electrical conductivity and in situ soil salinity for sediments 
 
in three zones of Dowd Morass from 2003 to 2006.   
 
 
36 
2.5 Tritatable peroxide activity (TPA) results for 12 sediment samples from 
 
Dowd Morass.  
 
 
 
 
 
 
 
38 
2.6 Concentrations of heavy metals in two areas of Dowd Morass.   
 
40 
3.1 Source and Characteristics of aerial photographs used in this study.  
 
62 
3.2 Probability of observed phenotypes occurring based on allele frequencies.  
69 
3.3 Size of 18 individual clones of M. ericifolia
 
    71 
4.1 Populations and location of seed collection sites for M. ericifolia  
 across 
southern 
Australia. 
 
      85 
4.2 Populations and locations of seed collection sites for M. parvistaminea 
 
in 
South 
Gippsland, 
Victoria. 
      85 
4.3 Classification of population size of M. ericifolia across  
 southern 
Australia. 
 
       86 
4.4 Population size, seed weight and viability of various populations of 
 
M. ericifolia in Victoria and Tasmania, 
Australia. 
 
   89 
4.5 Population size, seed weight and viability of various populations of  
 
M. parvistaminea in South Gippsland, Victoria, 
Australia. 
 
  91 
5.1Results of three-way ANOVA of primary and interactive effects of  

 
XIV
salinity, light and temperature on the germination of M. ericifolia seeds. 
110 
7.1 Specific rainfall events identified from years identified as potential  
recruitment periods for M. ericifolia at Dowd Morass. 
 
 
167 
8.1 Contingency table of potential recruitment sites for M. ericifolia.  
 
187 
 
 
 
 
 
 
 

 
XV
Acknowledgements 
 
 
I would like to acknowledge and personally thank a large number of people who, in 
their own way’ have assisted me to complete this work. The people that I have come 
into contact with in researching this project have, to a person, been enthusiastic and 
helpful, sometimes inspiring new ideas and directions that have made this work much 
more valuable than my original proposal.  
 
Professor Paul Boon provided a well-timed opportunity to join his team. As my 
supervisor he provided clear guidance and the inspiration to go well beyond my 
perceived personal limits. Our regular and intellectually lively meetings considerably 
broadened my understanding of scientific, ecological and academic processes. I am 
particularly grateful that he was willing to answer my every question even if the 
timing was not always convenient to his schedules.  On a more personal note, Paul 
has become a true friend. I look forward to a long and fruitful professional and 
personal relationship.    
 
The opportunity to work with and be part of the Wetland Ecology Group at Monash 
University allowed me to put my work into a practical framework and make practical 
and intellectual contribution to the overall project being carried out by the group. 
Involvement in the group also provided me with valuable information and a sounding 
board to help clarify my project. I gratefully acknowledge the help of Elisa Raulings, 
Michael Roache, Kay Morris, Jacquie Salter, Ni Luh Watiniasih, Matt Hatton, Dr. 
Paul Bailey and all of the other students and staff.  

 
XVI
 
The difficult task of making a transition from private business to academic life was 
assisted greatly by the staff and students at Victoria University. I thank them all for 
providing a stimulating academic environment and making the transition to academia 
relatively smooth and enjoyable. Special thanks to Professor Paul Boon, Dr. Bronwen 
Scott, Professor David Greenwood and Dr. Russ Swan who helped me so greatly by 
providing considerable assistance in reading drafts, proposing corrections and 
providing me with teaching opportunities to assist my academic development and 
financial stability.  My fellow students provided continuing feedback and assistance in 
the finer points of university and academic life and the particular needs of my trials, 
statistics and preparation of a thesis. Thank you, Matt Hatton, Megan O’Shea, 
Rachael Keefe, Mark Scarr, Davide Coppolino, Mark Toomey and Bram Mason. Lab 
work was made an absolute delight with the assistance of Heather Altamari, and all of 
the other lab technicians.  
 
Parks Victoria kindly provided access to the field study sites, assisting field 
arrangements and providing all the necessary permits. Special thanks go to Andrew 
Schulz, Jasmin Aly and the rest of the staff at Parks Victoria (Sale).  
 
The staff of the Royal Botanic Gardens Melbourne, in particular Elizabeth Smith, 
Nina Sawtell and Rob Cross contributed significantly to the section on clonality and 
hypocotyl hairs. Their knowledge and understanding of DNA analysis and plant 
physiology was freely shared.  I would especially like to thank Bruce Abaloz, 
University of Melbourne for his generous advice and assistance with the histology. 
 

 
XVII
The Department of Primary Industry provided access to aerial photography and 
negotiated the potentially difficult area of copyright with ease and speed, thank you 
George.  
 
Most of all I would like to thank my partner, Dale Kruse, who put up with me and 
supported me though the years of my study. I look forward to spending a lot more 
time together. Maybe we can even take that holiday we have been talking about for 
years. Special thanks to Edwina Wright, Barry Kaufmann, Darcy Duggan, Liz 
Connelly, Patricia Reynolds, Patrick Vaughan and all my other friends, for keeping 
me sane and just being there. Special thanks also to Lois Robinson for always 
believing in me and teaching me the skills that have carried me through life.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Summary 
 
This study investigated three aspects of the life history of Swamp Paperbark 
(Melaleuca ericifolia Sm.) that have implications for the ecology, management and 
restoration of wetlands occupied by the species: i) seed germination responses and 
tolerances; ii) clonal growth characteristics; and iii) safe sites for recruitment.  
 
Laboratory studies included the responses and tolerances of seed to three key 
environmental factors: light; temperature; salinity; and the potential interactions they 
may have on germination. Germination percentages were used as indicators of 
success. Darkness, moderate temperatures (~ 20
0
C) and low salinity levels (< 2 gL
-1

were found to be the most ideal germination conditions. Additional studies were 
carried out on secondary structures, hypocotyl hairs, which were shown to influence 
establishment success of seedlings. The conditions found ideal for germination proved 
to be suitable for hypocotyl hair formation.  
 
Field and laboratory studies were carried out to determine the allocation of resources 
to reproductive effort and seed production in M. ericifolia. Comparative studies were 
carried out between two sympatric Melaleuca species with contrasting life histories 
and reproductive strategies (clonal vs. non-clonal) to determine if there were 
differences in reproductive capacity and commitment of resources to either sexual or 
asexual reproductive effort. There was low germinability of the clonal species M. 
ericifolia (< 40%) when compared to the non-clonal M. parvistaminea (> 70%). 
Germinability of M. ericifolia was reduced as population size decreased and distance 
to nearest population and degree of disturbance increased.  

 
2
 
Laboratory and field studies were undertaken to investigate the growth characteristics 
and ecological significance of the clonal growth form. Genetic methods were used to 
determine the genetic diversity and clonal intermingling in existing populations. 
Individual genets were found to contain thousands of stems and cover areas greater 
than 3,000 m
2
. Intermingling of the genets was not found. Air-photograph 
interpretation and structural analysis of individual clones were used to determine 
colonisation rates, longevity and time since recruitment. Lateral growth rates were 
generally found to be rapid, up to 0.5m per year. The largest plants found (3,274 m
2
), 
were determined to be approximately 52 years old.  
 
Safe sites for germination and recruitment were determined using historical aerial 
photographs and climate data combined with on-ground confirmation and 
characterisation of conditions. Microtopographical relief provided by hummocks 
within the wetland provided suitable safe sites for recruitment by modifying light, 
salinity and moisture levels to a range suitable for germination and hypocotyl hair 
production. Recruitment was however, restricted to a limited range of climatic 
conditions that diluted salinity levels but did not inundate newly germinated 
seedlings:  flood conditions in spring followed by average rainfall in summer.   
 
Recommendations for landscape-scale rehabilitation of wetlands using M. ericifolia 
were formulated. The implications of the findings of this study on current ecological 
restoration theory and practice are discussed. Germination from seed in the highly 
modified conditions found in many wetlands in South-eastern Australia is problematic 
due to the specific climatic and on-ground conditions needed for successful 

 
3
recruitment. The findings of the growth and genetic studies of M. ericifolia indicate 
that planting of nursery grown stock is possible and even preferable if the growth 
characteristics of the plant are taken into consideration. Present planting methods used 
for non-clonal terrestrial species, hand planting large numbers of seedlings at close 
spacings, is inappropriate for M. ericifolia. A planting method that carefully selects 
planting sites, uses smaller numbers of plants and factors in clonality and lateral 
growth rates (time) would reduce restoration costs and improve long-term survival of 
planted stock.   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
4
Chapter 1  
Introduction 
 
 
Swamp Paperbark (Melaleuca ericifolia Sm.) is a colony-forming clonal tree species 
that grows in near-coastal wetlands in south-eastern Australia.  The distribution and 
abundance of this species has decreased markedly with the clearing or draining of 
many of the wetlands in which it formerly occurred (Bowkett and Kirkpatrick 2003). 
Community groups, non-government organisations and government authorities are 
committing considerable effort and finances to the restoration of M. ericifolia and the 
wetlands in which it occurs. Closely related species, occurring in similar situations 
throughout Australia and overseas, are also the subjects of large-scale restoration 
efforts (Turner and Lewis 1997; de Jong 1997; de Jong 2000).    
 
Assisted regeneration of M. ericifolia and related species is, at present, totally reliant 
on the use of manually planted nursery-raised seedlings. Conventional plantings of M. 
ericifolia follow terrestrial planting schemes for non-clonal species, using high 
numbers of individuals planted on 2-3 m spacings or closer (de Jong 2000; Greening 
Australia 2003). The process of natural regeneration, the preferred ideal in the long-
term, is not well understood and alternative techniques have not been developed or 
tested to improve planting success. In the short – medium-term reliance on manual 
planting remains a reality although it is by no means the preferred option (Cole 1998; 
Van der Valk 1998; de Jong 2000).  A full characterisation of the life history 
attributes of the species, including regeneration mechanisms such as seed germination 

 
5
establishment and clonal lateral spread is necessary if more naturalistic regeneration 
methods are to be attempted.  
 
The evolution of the clonal growth form (vegetative outgrowths sprouting at a 
distance from the original plant) is usually attributed to the high natural variability of 
the wetland habitat and severely limited resources (Fischer and van Kluenen 2001). 
Clonality confers two advantages to wetland plants. Firstly, the clonal growth form 
allows plants to circumvent sexual reproduction in an environment where seedling 
recruitment events may be extremely rare or risky. Second, as many stems in an 
individual clone of M. ericifolia remain connected, they retain their ability to transfer 
air, nutrients and water between stems. Stems growing in ideal conditions have the 
theoretical ability to support stems growing in otherwise unsuitable conditions, 
conferring an ecological fitness not available to non-clonal plants (Hutchings 1999).  
 
The allocation of resources to asexual versus sexual reproduction has been linked to 
the heterogeneity of the environment or limited resources (Cain et al. 1996) leading to 
a delay in reproductive maturity. In extremely resource-limited environments, such as 
wetlands and deserts, the clonal life form is particularly well developed (Song and 
Dong 2002; van Groenendael et al. 1997) and plant longevity may be extreme (Vasek 
1980). Several clonal and non-clonal Melaleuca species are co-extensive in southern 
Australia and provide an opportunity to undertake comparative studies. 
 
Development of the clonal growth form allows efficient capturing of resources and 
great longevity in some plants, but may lead to a disadvantage in regard to sexual 
reproduction and severely reduced genetic diversity within a population (Wherry 

 
6
1972). Novel or infrequent ecological challenges may arise that result in senescence 
of existing individuals leading to further erosion of genetic diversity or even local 
extinction. Decisions in relation to the conservation of M. ericifolia are limited by a 
lack of knowledge regarding the genetic diversity and number of individuals within 
existing populations. The clonal life form in M. ericifolia, and the potentially large 
number of individual stems contained in a genet, may lead to unwise seed collection 
or propagation techniques. Seed production between genets can vary considerably but 
may be relatively uniform within the genet (pers obs.). Not understanding the 
underlying clonal nature of the species and the potentially large area covered by a 
genet may lead seed collectors to deduce that they are dealing with a genetically 
diverse colony instead of one genetically uniform plant.  
 
This study questions the appropriateness of presently used methods for regeneration 
of  M. ericifolia and, by extension, similar swamp-growing clonal species. It would 
appear that present assisted regeneration is not based on knowledge of the species 
used or the basic ecology of the system being restored (Van der Valk 1998). Existing 
restoration of brackish wetlands is based on horticultural principles, is expensive and 
is applicable to the small scale only and likely to be unsuccessful (Mitsch 1998; 
Mitsch and Wilson 1996). Two major questions identified in preliminary work on M. 
ericifolia (de Jong 2000; Van der Walk 1998) relate to: 
•  the ecological fitness of the plants established through present manual planting 
techniques and; 
•  the relevance of present planting techniques to a clonal species such as M. 
ericifolia.  
 

 
7
1.1 General Ecological Background to the Project  
 
 
1.1.1 Melaleuca 
 
Melaleuca is one of several large and diverse genera of shrubs and trees including 
Eucalyptus, Leptospermum and Callistemon that make up the family Myrtaceae. 
Australia contains seventy-five native genera and over 1,400 species of Myrtaceae, 
which is nearly half the total number of species in the world (Jeanes 1996). Forests 
and woodlands dominated by Melaleuca cover nearly 90,513 km
2
 in Australia 
(National Land and Water Resource Audit (2001) (Figure 1.1).  
 
 
 
Figure 1.1 Distribution of Melaleuca woodlands and forests in Australia. Adapted 
from National Land and Water Resource Audit (2001).      Woodlands,   Forests 

 
8
Swamp Paperbark (Melaleuca ericifolia), the species under investigationis one of a 
genus of approximately 240 species of trees and shrubs with a primary distribution in 
Australia but represented in New Guinea through to South-east Asia (Spencer 1996). 
Many Melaleuca species are associated with wetlands or areas with impeded 
drainage. All Melaleuca species have seed stored in woody capsules on the plants. 
Only a few of the species found in eastern Australia produce lateral vegetative growth 
by suckering from the roots (Byrnes 1984) and these species occur in seasonally 
inundated situations (swamps).  
 
The most primitive species of Melaleuca occur in inundated tropical lowlands with 
Melaleuca generally replacing Eucalyptus as the dominant tree species (Barlow 
1988). This suggests a warm climate derivation of Melaleuca.  There is a record of M. 
ericifolia in southern Australia from a fossilised forest in western Tasmania dating 
from the late Pleistocene (1.2 million years before present) (Rowell et al. 2001) and 
an even earlier possible record from the Mid Cenozoic (25 million years before 
present) (Lange 1978) when temperatures in this area were approximately 1-1.5
0

higher than present. 
 
The genera Melaleuca, Callistemon and Eucalyptus are part of a larger flora that has 
evolved within Australia (Australian element) and have adapted to changing climate, 
particularly decreasing temperatures, increasing aridity and seasonality (Hill et al. 
1999) and decreasing soil fertility. These factors have lead to increasing habitat 
differentiation and speciation with most of the present broad vegetation formations 
and many genera well established by the Late Cenozoic (Hill et al. 1999).  
 

 
9
1.1.2 Adaptations to soils and climate 
 
Scleromorphy, characterised by small, hard leaves, short internodes and small plant 
size, is a characteristic of M. ericifolia. Evolution of scleromorphy in Melaleuca and 
other genera in the Australian element of the Australian flora, is a specific adaptation 
to low nutrient levels in the soil (Specht 1972; Johnson and Briggs 1981) and in 
particular, low soil phosphorus levels (Beadle 1968) and not an adaptation to aridity 
as originally assumed. Xeromorphy (morphological adaptation to aridity) is a 
secondary trait conferred by plant adaptations to low nutrient status soils.  
 
Most species of Melaleuca have woody capsules that release seed after the parent 
branch is killed, either by fire or other means. The development of serotinous fruits 
(woody, late-opening capsules) in Melaleuca and similar genera is generally viewed 
as an adaptation to and protection from fire (Specht 1981). Gill (1993) clearly reports, 
however, that the greatest richness of woody fruits is more closely related to mineral-
poor soils. Many of the species that produce serotinous fruits do not have other seed 
dormancy factors and are relatively short-lived in the soil seed bank (Ashton 1985; 
Gill 1993). There is some evidence that fire may temporarily increase soil nutrients to 
allow germination and survival of woody-fruited species (Specht et al. 1958; Ashton 
1976) but this is not conclusive.  
 
A second competitive advantage conferred by serotiny is predator satiation (Silverton 
and Charlesworth 2001).  The predator satiation hypothesis is usually applied to trees 
that produce mast (large seed crops, followed by small or non-existent seed crops), 
flooding the system with copious amounts of seed and therefore overwhelming the 

 
10
ability of predators to harvest all seed. This strategy ensures that at least some seed 
and seedlings survive.  A similar effect is achieved post-fire in Australian species that 
have woody persistent fruits that are held in the canopy and released en masse after 
fire (Ashton 1979).  While some annual seed rain takes place in Melaleuca, through 
the death of stems, this may not be of sufficient magnitude to outpace the harvesting 
rate by granivores (ants).  
 
 
1.1.3 Vegetative growth 
 
A particularly noticeable feature of M. ericifolia is its clonal growth form, with 
individual plants able to cover large areas and produce numerous stems. In 
evolutionary terms, the clonal growth form is very ancient and occurs in a wide range 
of plants (Mogie and Hutchings 1990). van Groenendael et al. (1997) and Hatton 
(2005) estimated that well over two-thirds of wetland plants exhibit the clonal growth 
habit.  
 
The clonal growth form, based on lateral vegetative reproduction, is highly mobile, 
allowing for wide-ranging utilisation of nutrients, space and other resources without 
going through sexual reproduction in potentially inhospitable sites (Silvertown and 
Charlesworth 2001).  There appears to be a trade-off between clonal growth and 
sexual reproduction, with decreased sexual reproduction associated with increased 
clonal growth as has clearly demonstrated in the wetland genus Mimulus 
(Scrophulariaceae) (Sutherland and Vickery 1988). Clonal growth is delayed until 
after flowering in Heiracium (Asteraceae) (Bishop et al. 1978) but the reverse is true 

 
11
in some bamboo species (Poaceae) (Silvertown and Charlesworth 2001). The trade-off 
between sexual reproduction and clonal growth in M. ericifolia is not at all clear.   
 
The particular way that a plant produces new lateral growths (ramets) can determine 
the distribution and intermingling of separate plants (genets) (Harper 1978). Plants 
that produce short and frequently branched connections between ramets generally 
spread along a front or phalanx (Silverton and Charlesworth 2001).  Conversely, 
plants with long-spacers and little branching, progress in guerrilla mode, infiltrating 
individuals of the same or other species (Lovett Doust 1981).  The phalanx mode of 
growth tends to occur in low-nutrient, high-light habitats (van Groenendael et al. 
1997).  The guerrilla mode of growth is more closely allied with soils where nutrients 
or moisture are not evenly distributed. It is not understood if the growth form of M. 
ericifolia is guerrilla or phalanx.   
 
Species utilising either the phalanx or guerrilla mode of growth may retain the 
connections between the ramets.  These physical attachments allow all the stems in a 
plant to function as one, allowing transport of nutrients, oxygen and water between 
spatially separate and potentially disparate but physiologically integrated ramets 
(Marshall 1990).  The physical attachments between stems may be of particular 
importance in M. ericifolia. If, as is thought, individual plants with multiple 
connections occupy large parts of an environmental gradient, e.g. soil moisture, these 
established plants would not be adversely affected should other parts of the plant be 
inundated. Conversely, clonality may allow plants to expand into areas normally too 
dry to support M. ericifolia, with the dry area stems being supported by those in 
moister habitats. Ramets of Fragaria chiloensis (Rosaceae) growing in well lit, dry, 

 
12
nutrient-poor habitats are known to share resources with connected ramets in shaded, 
well-watered, nutrient-rich habitats to the benefit of both (Alpert and Mooney 1986).  
 
The factors affecting senescence and death in M. ericifolia are not known. 
Theoretically, unless the habitat conditions change dramatically, clonal plants are 
potentially immortal. There are some studies of the longevity of individual clonal 
species. While the longest-lived clone of a woody plant so far identified is Lomatia 
tasmanica  (Proteaceae), in western Tasmania, with an age of approximately 43,600 
years old (Lynch et al. 1998) there are many others that are very old. A clonal hybrid 
Eucalypt, also in Tasmania, has conservatively been estimated to be 900 years old 
(Tyson  et al. 1998). Individual Creosote Bush (Larrea tridentata) plants in the 
Mojave Desert have been estimated to be 6,000-11,000 years old (Vasek 1980). 
Slightly older is the Box Huckleberry (Gaylussacia brachycera) in Pennsylvania at 
approximately 12,000 years old (Wherry 1972). Plants of M. ericifolia while 
exhibiting a similar growth habit to these last examples are unlikely to be as old as 
these previous examples as the Gippsland Lakes environment, as presently 
configured, is less than 6,000 years old (Bird 1965).  
 
1.1.4 Genetic diversity 
 
Long-term management and conservation of M. ericifolia populations, including 
determining planting densities for restoration plantings, is dependant on the 
identification of the number of individuals and genetic diversity within naturally 
occurring populations. Degree of genetic diversity can vary widely between and 
within species (Hamerick and Godt 1990). While genetic diversity is widely held to 

 
13
be desirable, species that primarily reproduce vegetatively are commonly found to 
have low genetic diversity (Simonich and Morgan 1994; Holsinger, 2000; Rivera-
Ocasio  et al. 2002; Nuortila et al. 2002).  Low genetic diversity in plants is not, 
however, directly related to reproductive success. This is especially the case in clonal 
plants (Eckert 2001) with many of our most common weeds being clonal. Salvinia 
molesta (Salvineaceae), a sterile hybrid and one of the world’s most abundant wetland 
weeds, relies exclusively on vegetative reproduction (Loyal and Grewal 1966).  
 
It may not be always be readily apparent when the population of a long-lived clonal 
species has fallen below a critical threshold for sexual reproduction (Fehrig 2001). 
This is especially the case with species with long generation times, in which the 
critical extinction event may not become evident for hundreds of years (Armbruster et 
al. 1999).  For some out-crossing clonal species, populations, which in fact are 
individuals, may give a false sense of security to conservation managers. This senario 
was the case for Box Huckleberry (Gaylussacia brachycera) prior to specific 
population studies (Wherry 1972) that determined the populations to be clones. If 
pollination requirements are not met, the plant becomes functionally asexual and is at 
risk of extinction.   
 
When trying to identify clones in the field, the inherent variability of the foliage and 
other morphological characteristics within and between clones often provides little 
guide to determining the extent of any given clone, but this is not always the case.  
Genetic testing and analysis allow positive identification of individual clones at a 
level of discrimination that is not possible with traditional morphological approaches 
(Tyson  et al. 1998). Genetic analysis also gives an indication of the size of the 

 
14
individual plant from which the level and type of recruitment over time can be 
determined as well as the rate of mortality.  Knowing the number of individuals in a 
population confers an ability to determine genetic diversity and conservation of 
genetic diversity (Aitken et al. 1998).  
 
No genetic studies have been carried out to date on M. ericifolia or indeed other 
Melaleuca species to determine natural population densities.  Genetic testing has not 
been carried out on what have been assumed to be individual plants that cover large 
tracts of land. Conservation of the species in the long term is dependent on the 
identification of the number of potentially sexually reproducing plants in a population 
and across the species’ distribution.  Although it is not envisioned that the extremes 
found in some studies (one plant per 16 ha for Gaylussacia brachycera (Wherry 1972) 
or one plant per 1.2 sq. km for Lomatia tasmanica (Lynch et al. 1998) will be found 
in M. ericifolia, at present there is no indication of the number of individual clones in 
a population, their size or longevity.  
 
Genetic testing can indicate the degree of clonal intermingling (the degree of overlap 
between adjacent plants). Studies in woody clonal species worldwide indicate that 
degree of clonal intermingling varies widely among species from complete separation 
of individuals to total mixing of ramets (Zhang et al. 2002; Van Kluenen et al. 2000) 
with phalanx species tending not to intermingle. Lack of clonal intermingling, should 
this prove true in M. ericifolia, would suggest alteration to present planting densities 
and configuration of plantings. Specifically, if individual M. ericifolia plants planted 
at close spacings do not overlap, the ecological fitness conferred by the clonal growth 
form will be negated.  

 
15
 
Molecular markers have been used as the most reliable tool to determine the number 
of individuals in populations of clonal species. Random amplified polymorphic DNA 
(RAPD) is a polymerase chain reaction (PCR)-based marker method that increases the 
number of markers without limit (Torimaru et al. 2003) and has been used to 
determine clonal diversity in a large number clonal species in Australia and overseas 
(Kreher et al. 2000; Widen et al. 1994; Williams et al. 1990). While RAPD markers 
have proved useful, recent work at the Royal Botanic Gardens Melbourne by 
Elizabeth James (RBG Melbourne pers comm.) indicate that Inter Simple Sequence 
Repeat (ISSR) allows for greater numbers of markers within an individual sample, at 
much reduced cost (Godwin et al. 1997).   
 
1.1.5 Sexual reproduction 
 
Seed production and gemination has been little studied in M. ericifolia. The main 
study of M. ericifolia was by Ladiges et al. (1981). They found that germination of 
Melaleuca seed was inhibited by submergence. Melaleuca ericifolia also failed to 
germinate at salinity levels above 14 g/L
-1
 although the range of salinities tested in 
this study was limited. Interestingly, germinated seed was able to survive in water for 
several weeks by floating on the surface. Ladiges et al. (1981) used a standard 
germination temperature known to effect germination in a wide variety of plants.  
Salter (2001) investigated the synergistic effects of salinity and water regime on 
seedling survival, but not germination, as part of an honours project. 
 

 
16
In a study of regeneration of a swamp in which M. ericifolia occurred, germination of 
seed and survival of seedlings was rare and limited to sites with specific conditions, 
namely weed free and constantly moist but not inundated (de Jong 2000). de Jong’s 
(2000) study does not record the period of emergence for M. ericifolia but does 
indicate that seed was planted in mid-summer. The likelihood of Melaleuca being 
reliant on higher temperatures for germination of seed is likely, based on the tropical 
derivation of the genus. No studies have been carried out to determine the tolerances 
and ideal temperature and light conditions for germination. None of the above 
germination studies investigated the potential synergistic effects of combining 
temperature, light and salinity as would be found under field conditions.  
 
Reproduction from seed in a long-lived clonal species may be of little importance in 
the short – medium-term, or possibly even to the long-term survival of the species.  
This is because only sufficient numbers of recruits are needed to replace plants that 
senesce and die, or to colonise new habitat (Rea and Ganf 1994).  Numerous 
examples exist of widespread and abundant, long-lived clonal, species with little or no 
record of seedling recruitment (Peirce 1998; Nuortila et al. 2002).  For example, some 
of the world’s most problematic weeds are not known to reproduce sexually, 
including Salvinia (Salvinia molesta) and Water Hyacinth (Eichhornia crassipes
(Room and Julien 1995; Wright and Purcell, 1995), the latter only reproducing 
sexually in it’s native habitat (Barrett 1980).  
 
The age at which plants reach their reproductive maturity is closely correlated to 
plant/adult longevity and availability of resources (Takada and Caswell 1997; Geber 
1990).  Delay of reproductive maturity can have a competitive advantage in nutrient 

 
17
restricted sites by increasing the amount of nutrients and energy available for seed 
production (de Jong et al. 1987). Under horticultural conditions there appears to be 
significant differences in the reproductive maturity in the sympatric species M. 
ericifolia and Rough-barked Honey-myrtle (M. parvistaminea) although this has not 
been proven in the field.  Longevity of both species is not known but there would 
appear to be potential differences in longevity based on growth form. M. ericifolia has 
the ability to spread laterally by means of vegetative growths from the roots, whereas 
Rough-barked Honey-myrtle lacks this ability.  
 
1.1.6 Rehabilitation approaches 
 
Approaches to the rehabilitation of wetlands has become increasingly polarised with 
various authors arguing for intervention or non-intervention (van der Valk 1998; 
Mitsch 1998). de Jong (2000) attempted to strike a mid-point between these two 
competing and incompatible theories by suggesting that some intervention (planting) 
may be required in wetlands where clearing and grazing have been the main form of 
degradation.  
 
Despite altered hydrology being cited as the most common form of disturbance in 
wetlands (Streever 1997), there has been little investigation into altering or restoring 
hydrological processes in coastal wetlands (de Jong 2000). Synergistic effects among 
altered hydrology, clearing, grazing and salinity are likely to have a significant impact 
on plant growth (Kozlowski 1997). Recent work initiated in Victoria, of which this 
project is a part, is investigating the management of high-value wetlands subjected to 
multiple environmental threats (Boon et al. 2005).  

 
18
1.2 Aims of this project 
 
This project forms part of a larger overall grant-funded project investigating the 
management and rehabilitation of brackish wetland facing multiple threats based at 
Dowd Morass on  the Gippsland Lakes at Sale, Victoria. Other related PhD projects 
based at both Victoria University and Monash University are specifically 
investigating the effects of water regime on ecological health, the effects of water 
regime and salinity on keystone species and invertebrate/plant interaction in relation 
to management. A fuller documentation of Dowd Morass and the overall project can 
be found in two handbooks prepared by the research team (Boon et al. 2005; Boon et 
al. 2007) 
 
The aims of this project were to:  
 
•  Determine the  number, distribution and intermingling  of clones in a 
naturally occurring population of M. ericifolia. Genetic testing will be carried 
out using Inter Simple Sequence Repeat (ISSR) will be used. Individual clones 
will be determined using a hierarchical analysis function in Microsoft Excel 
2000 (Microsoft Corporation, Troy, New York).  
 
•  Determine the rate of colonisation of M. ericifolia over a 46-year time frame 
from historical aerial photography. Rate of colonisation will be calculated by 
averaging growth rates of a number of clones of M. ericifolia determined 
through genetic testing and assisted by aerial photograph interpretation and 

 
19
visual assessment on the ground. Existing aerial photography dating back 46 
years will be used to map extension of lateral growth of selected clones.  
 
•  Carry out a  comparative study of the viability of the clonal and non-
clonal species M. ericifolia and M. parvistaminea and between populations of 
M. ericifolia across a majority of its range. Comparative analysis will be used 
to determine the trade-off between allocation of resources to sexual 
reproduction versus lateral vegetative growth.   
 
•  Determine the  ideal conditions and tolerance levels  under which 
germination of M. ericifolia can be achieved and the individual and potential 
synergistic effects of light, temperature and salinity (factors) on key 
germination indicators (percentage germination, percentage recovery and 
germination after inundation with salt water).  Standard graduated germination 
tests will be carried out in the laboratory using growth cabinets. Data will be 
analysed utilising a general linear model three-way ANOVA with fully 
orthogonal design using version 11 of SPSS. Key germination indicator 
recorded will be; total percentage germination.  
 
•  Determine the  sensitivity and tolerance levels of single-celled structures 
(hypocotyl hairs) to salinity, temperature and light. These structures have been 
shown to be critical to establishment of a range of wetland species (Baranov 
1957; Polya 1961; Matsuo and Shibyama 2002).  
 

 
20
•  Determination of safe site for recruitment of M. ericifolia. A range of 
methods will be used including historical aerial photography, historical 
climate data and on ground survey and assessment. Data collected will be 
compared to the germination tolerances and parameters identified in previous 
chapters.  
 
•  Formulation of recommendations for landscape-scale rehabilitation of 
brackish wetlands utilising M. ericifolia will be formulated using the findings 
of this and other studies.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
21
Chapter 2 
The study site
 
 
2.1 Introduction 
 
Fieldwork was carried out at Dowd Morass on the south-western shores of Lake 
Wellington near Sale, Victoria (38
o
07’S 147
o
10’E) (Figure 2.1). The study site is a > 
1,500 ha wetland on public land and is presently managed by Parks Victoria. Dowd 
Morass makes up part of the overall Gippsland Lakes Ramsar site and is listed on the 
register of the National Estate (DSE 1999). The water levels at Dowd Morass are 
managed and have been kept artificially high for at least the last 20 years, with one 
purposeful drawdown event (Schulz pers. comm.).  Levee banks within Dowd Morass 
have recently been restored to allow two distinct hydrological regimes to be 
maintained.   
 
 
 

 
22
 
 
 
Figure 2.1 Map of the Gippsland Lakes, Victoria. Lake Wellington is the large lake at 
the western edge of the lakes complex with Dowd Morass (red arrow) located on the 
southwest edge of Lake Wellington (copyright Google 2008, MapData Sciences Pty. 
Ltd. PSMA).  

 
23
2.2 History of Dowd Morass 
 
Alienation of the land at Dowd Morass, primarily for the purposes of grazing, started 
in approximately 1888 and continued until 1942 (State Rivers and Water Supply 
Commission 1972). In 1968 large sections of the easternmost section of Dowd Morass 
were converted to the Dowd Morass Wildfowl Reserve leaving most of the western 



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