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
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
Table of Contents
1.1 General ecological background to the project
2.0 The study site
2.2.2 Salinity regimes over past
∼ three decades
5.2.3 Interactive effects of salinity, light and
5.2.4 Effects of preliminary exposure to salt on germination
5.2.5 Effects of seed burial and substrate type on germination
5.3.2 Interactive effects of salinity, light and
5.3.3Effects of preliminary exposure to salt on germination
5.3.4 Effects of seed burial and substrate type
5.4.1 Poor seed viability and its causes
5.4.2 Effects of chronic and acute exposure to salt
5.4.3 Effects of environmental variables on germination
5.4.4 Effects of seed burial and substrate type
5.4.5 Implications for rehabilitation of coastal wetlands
6.0 Hypocotyl hairs and their importance for recruitment success in seedlings of Melaleuca ericifolia Sm. (Swamp Paperbark). 124
6.2.2 Life history of M. ericifolia 131
6.2.4 Effect of surface sterilisation on hypocotyl hair
6.2.5 Effect of water availability on hypocotyl hair development
6.2.7 Effect of salinity, light and temperature on hypocotyl
characteristics of hypocotyl hairs
6.3.3 Hypocotyl hairs and seedling development
6.3.4 Effect of water availability on hypocotyl hair development
6.3.4 Effect of salinity, light and temperature on hypocotyl
hair, root hair and secondary root development
6.4.1 Functions of hypocotyl hairs in M. ericifolia 149
6.4.2 Effects of environmental variables on hypocotyl hair
6.4.3 Implications for seedling establishment and plant
7.0 Historical recruitment events of Melaleuca ericifolia at Dowd Morass 155 Abstract 155
7.3.1 Recruitment events determined using aerial photographs
8.0 Safe sites for recruitment of M. ericifolia in Dowd Morass 175
8.2.1 Recruitment sites in Dowd Morass
determined in field inspections
9.4 Safe sites for germination in M. ericifolia 204
9.4.2 Spatial requirements: the importance of hummocks
9.5 Implications of plant and germination characteristics for
1.1 Distribution of Melaleuca forests and woodlands in Australia.
2.1 Map of the Gippsland Lakes, Victoria.
2.2 Dowd Morass, showing the location of internal levees.
2.3 Recent (since 1991) patterns in water levels in various sections
of Dowd Morass.
2.4 Recent (since 1991) salinity patterns in various sections of Dowd Morass.
2.5 Rookery in Area B of Dowd Morass in mid 2006.
2.6 Algal bloom in Area B (the rookery) at Dowd Morass.
2.7 Location of the four sites used for a complete sulfidic analysis of
2.8 Stands of Swamp Paperbark, M. ericifolia.
2.9 Dense swards of Common Reed, Phragmites australis.
2.10 Aerial photograph of a section of Dowd Morass, showing areas of
Common Reed (DR) and Swamp Paperbark
3.1 Exposed root system of a mature patch of M. ericifolia.
3.2 Individual patch of M. ericifolia at Wilson’s Promontory National Park,
3.3 Location of sampled patches of M. ericifolia at Dowd Morass.
M. ericifolia patch A1 showing sample points.
M. ericifolia patch A2 showing sample points.
M. ericifolia patches showing
3.4 Exposed edge of a patch of M. ericifolia showing the depth of the
extensive network of roots, Narawntapu National Park, Tasmania.
3.5 Two large patches of M. ericifolia showing individual genets (1-5)
3.6 ISSR DNA profiles for all samples using primer 814.
3.7 Visual differentiation of phenotypes.
3.8 Historical aerial photographs of a section of Dowd Morass.
3.9 Mean expansion rates of individual M. ericifolia clones at Dowd Morass.
3.10 Mean expansion rates of all clones of M. ericifolia.
4.1 Distribution of M. ericifolia in
4.2 Distribution of M. parvistaminea in
4.3 Linear regression of seed weight versus germination rate for
4.4 Germination rate for various population sized of M. ericifolia in
4.5 Comparison of germination rates and seed weights of various
populations of M. parvistaminea and M. ericifolia.
5.1 Effects of temperature, salinity and light regime on the germination
of M.ericifolia seeds.
5.2 Effects of prior exposure to saline conditions for up to 16 days, followed
by exposure to freshwater conditions, on the germination of
6.1 Percentage germination and presence of hypocotyl hairs 22 days after
soaking with sodium hypochlorite (30 sec to 30 min soaking) and
6.2 Microscopy images of seedling without and with hypocotyl hairs.
6.3 Development of hypocotyl hairs on seedlings grown on substrates
made up with various concentrations
6.4 Percentage of seedlings exhibiting positive geotropism when grown
on substrates made up with four different concentrations of agar.
6.5 Percentage of seedlings showing hypocotyl hair development
6.6 Hypocotyl hair and root development in M. ericifolia in
response to various salinity concentrations over 14 days.
7.1 Photos of a single section of Dowd Morass at six time periods from 1957
7.2 Dendrogram from the hierarchical
7.3 Rainfall data from the 5 outlier cases from the hierarchical cluster
7.4 Mean monthly temperature levels from East Sale weather station,
Sale, Victoria from July 1943 to June 2005.
7.9 Mean monthly salinity levels of surface waters in Lake Wellington,
Sale, Victoria from July 1968 to June 1975.
7.1 Sample sites for identification of possible recent recruitment of
M. ericifolia in
8.2 View of reed community at the western end of Dowd Morass.
8.3 close up of juvenile M. ericifolia recruit on a hummock.
8.4 Moisture content of substrata.
2.1 Summary of water quality data for Dowd Morass.
2.2 Water-column nutrient data for four areas at Dowd Morass.
2.3 Carbon, nitrogen and phosphorus content of sediments in four areas at
2.4 Soil moisture, electrical conductivity and in situ soil salinity for sediments
in three zones of Dowd Morass from 2003 to 2006.
2.5 Tritatable peroxide activity (TPA) results for 12 sediment samples from
2.6 Concentrations of heavy metals in two areas of Dowd Morass.
3.1 Source and Characteristics of aerial photographs used in this study.
3.2 Probability of observed phenotypes occurring based on allele frequencies.
3.3 Size of 18 individual clones of M. ericifolia.
4.1 Populations and location of seed collection sites for M. ericifolia across
4.2 Populations and locations of seed collection sites for M. parvistaminea
4.3 Classification of population size of M. ericifolia across
4.4 Population size, seed weight and viability of various populations of
M. ericifolia in Victoria and Tasmania,
4.5 Population size, seed weight and viability of various populations of
M. parvistaminea in South Gippsland, Victoria,
5.1Results of three-way ANOVA of primary and interactive effects of
salinity, light and temperature on the germination of M. ericifolia seeds.
7.1 Specific rainfall events identified from years identified as potential
recruitment periods for M. ericifolia at Dowd Morass.
8.1 Contingency table of potential recruitment sites for M. ericifolia.
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
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.
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.
The Department of Primary Industry provided access to aerial photography and
negotiated the potentially difficult area of copyright with ease and speed, thank you
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.
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
C) and low salinity levels (< 2 gL
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.
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
. 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
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
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
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
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
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
• the relevance of present planting techniques to a clonal species such as M. ericifolia.
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
(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
Swamp Paperbark (Melaleuca ericifolia), the species under investigation, is 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
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).
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
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
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
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,
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).
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
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
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 Gaylussaciabrachycera (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.
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
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.
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
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
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).
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 thenumber, distribution and interminglingof 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 therate 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
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 acomparative study of the viability of the clonal and non- clonal speciesM. 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 theideal conditions and tolerance levelsunder 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 thesensitivity 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).
• 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
• Formulation of recommendations for landscape-scale rehabilitation of
brackish wetlands utilising M. ericifolia will be formulated using the findings
of this and other studies.
Chapter 2 The study site
Fieldwork was carried out at Dowd Morass on the south-western shores of Lake
Wellington near Sale, Victoria (38
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
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.
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