ORIGINAL PAPER

Rehabilitation of Swamp Paperbark (Melaleuca ericifolia)wetlands in south-eastern Australia: effects of hydrology,microtopography, plant age and planting techniqueon the success of community-based revegetation trials

Elisa J. Raulings Æ Paul I. Boon Æ Paul C. Bailey Æ Michael C. Roache ÆKay Morris Æ Randall Robinson

Received: 8 December 2005 / Accepted: 24 October 2006 / Published online: 13 February 2007� Springer Science+Business Media B.V. 2007

Abstract Wetlands dominated by Swamp Paper-

barks (Melaleuca spp., Myrtaceae) are common in

coastal regions across Australia. Many of these

wetlands have been filled in for coastal develop-

ment or otherwise degraded as a consequence of

altered water regimes and increased salinity.

Substantial resources, often involving community

groups, are now being allocated to revegetating

the remaining wetland sites, yet only rarely is the

effectiveness of the rehabilitation strategies or

on-ground procedures robustly assessed. As part

of a larger project investigating the condition and

rehabilitation of brackish-water wetlands of the

Gippsland Lakes, we overlaid a scientifically

informed experimental design on a set of

community-based planting trials to test the effects

of water depth, microtopography, plant age and

planting method on the survival and growth of

seedlings of Melaleuca ericifolia Sm. in Dowd

Morass, a degraded, Ramsar-listed wetland

in south-eastern Australia. Although previous

laboratory and greenhouse studies have shown

M. ericifolia seedlings to be salt tolerant, the

strongly interactive effects of waterlogging and

salinity resulted in high seedling mortality

(>90%) in the field-based revegetation trials.

Seedlings survived best if planted on naturally

raised hummocks vegetated with Paspalum disti-

chum L. (Gramineae), but their height was

reduced compared with seedlings planted in

shallowly flooded environments. Age of plants

and depth of water were important factors in the

survival and growth of M. ericifolia seedlings,

whereas planting method seemed to have little

effect on survival. Improved testing of revegeta-

tion methods and reporting of success or other-

wise of revegetation trials will improve the

effectiveness and accountability of projects aim-

ing to rehabilitate degraded coastal wetlands.

Keywords Gippsland Lakes � Hummock �Microtopography � Water regime

Introduction

Hydrology is the most powerful element control-

ling the structure and function of wetland ecosys-

tems. Bedford (1996) identified three core

hydrological attributes affecting wetlands: the

source of the water, the quality of the water, and

the spatial and temporal characteristics of a

E. J. Raulings (&) � P. C. Bailey � M. C. Roache �K. MorrisSchool of Biological Sciences and Australian Centrefor Biodiversity: Analysis, Policy and Management,Monash University, Clayton 3800, Australiae-mail: elisa.raulings@sci.monash.edu.au

P. I. Boon � R. RobinsonInstitute for Sustainability and Innovation, VictoriaUniversity, St. Albans 8001, Australia

123

Wetlands Ecol Manage (2007) 15:175–188

DOI 10.1007/s11273-006-9022-6

wetland’s wetting and drying cycle. The hydrological

attributes of wetlands across the world has been

altered, often with devastating impacts on wetland

distribution and integrity. In Australia for exam-

ple, altered water regimes affect or potentially

threaten 27% of the country’s highest-value wet-

lands, that is those described as Wetlands of

National and International Significance (Davis

et al. 2001). Not only have patterns of wetting

and drying been modified globally, but water

quality also is often very poor in the remaining

wetlands, commonly as a result of changed inter-

actions between wetland bathymetry, surface-

water flows and ground-water inputs (Middleton

1999). As an example, many Australian wetlands

are currently subject to secondary salinisation due

to the rise of saline water tables and increasing

river-water salinity (Hart et al. 2003).

Dowd Morass State Game Reserve is a large,

brackish-water wetland in the Gippsland Lakes

Ramsar site (Victoria, south-eastern Australia)

that exemplifies these issues of wetland degrada-

tion. In order to provide a water regime condu-

cive to waterfowl hunting and to limit seawater

intrusions from the neighboring Lake Wellington,

the wetland has been more-or-less permanently

inundated for the past three decades. Despite the

maintenance of high water levels, salinities in

Dowd Morass range from <0.2 to over 19 g l–1

(5–25 dS m–1; Sinclair Knight Merz 2001), due

mostly to the continuing inputs of saline water

from Lake Wellington. These changes to hydro-

logical attributes have had marked effects on the

wetland vegetation. The dominant woody species

in Dowd Morass is Melaleuca ericifolia Sm.

(Swamp Paperbark). Melaleuca ericifolia is a

small clonal tree in the Family Myrtaceae that

grows in coastal (freshwater and estuarine)

swamps across southern and eastern Australia,

from southern Tasmania through to northern

New South Wales. Constant flooding, combined

with high salinity, has resulted in death of adult

plants and very poor recruitment of juveniles into

the population at Dowd Morass.

Since the distribution and abundance of

M. ericifolia has decreased markedly with the

clearing and draining of wetlands along the entire

coast of Australia (Bowkett and Kirkpatrick

2003), a priority of natural-resource management

agencies and non-government organisations

throughout Australia is the rehabilitation of

the wetlands that contain, or did contain, M.

ericifolia and other Melaleuca species (de Jong

1997; Turner and Lewis 1997; de Jong 2000).

Substantial resources are now being allocated

to rehabilitating degraded coastal wetlands in

south-eastern Australia. The rehabilitation strat-

egy is based largely on revegetation efforts,

usually commissioned by management agencies

and then devolved to contractors or community

groups, who in turn frequently transfer revegeta-

tion methods to wetlands that have been devel-

oped in terrestrial or riparian environments. With

few exceptions, the effectiveness of wetland

revegetation efforts have not been experimentally

tested and there is little accountability of the

success of the projects that have been undertaken

(de Jong 2000; Close and Davidson 2002).

In this paper, we report on a 2-year study in

which we collaborated with community groups

working in Dowd Morass by providing an exper-

imental design to a set of revegetation trials that

tested the effectiveness of a range of techniques

commonly used in wetland rehabilitation in

south-eastern Australia. Specifically, we tested

the effectiveness of planting at different water

depths, with different planting methods, using

seedlings of different age classes, and planting

according to wetland microtopography. The

results of the study will be useful not only in

identifying the optimal methods for revegetating

degraded coastal wetlands with M. ericifolia, but

also in more general terms in reporting on

the effectiveness of projects aiming at wetland

rehabilitation.

Methods

Species description

Ten species of Melaleuca dominate coastal and

inland wetlands throughout Australia (Specht,

1990). The Swamp Paperbark, M. ericifolia, forms

a vegetation type commonly known as Swamp

Scrub: Melaleuca-dominated Swamp Scrub

extends throughout southern and eastern Australia

176 Wetlands Ecol Manage (2007) 15:175–188

123

and is especially extensive in the coastal districts of

Gippsland, Victoria (Bird 1962; Ladd et al. 1976).

Melaleuca ericifolia is a shrub or small tree,

reaching a maximum height of 8 m. It grows

mostly at low altitude in poorly drained soils,

swamps and stream flats (Bird 1962; Gibson et al.

1987; Costermans 1998). Although M. ericifolia is

typically a wetland or wetland-margin dominant

species (Bird 1961, 1962) it can grow also in well-

drained soil (Bowkett and Kirkpatrick 2003).

While many Melaleuca species are reliant on seed

to produce new individual plants, M. ericifolia is

unusual in that it is extensively clonal. Recruit-

ment from seed is comparatively rare and the

seed bank in sediments seems quite depauperate;

seed is stored in the canopy and released follow-

ing desiccation or fire (Gibson et al. 1987).

Although adult trees produce great numbers of

seeds, seed viability at Dowd Morass is typically

low. Moreover, the germination of M. ericifolia

seeds is delayed by submergence in water

(Ladiges et al. 1981), and seeds that do germinate

often float on the water surface and are unlikely

to take root under flooded conditions. Seedlings

do persist, however, on small, sometimes vegetated

mounds (‘hummocks’) of other clonal species,

such as Paspalum distichum L., Juncus ingens

N.A. Wakefield, and Phragmites australis (Cav.)

Steud across Dowd Morass.

Study site

Dowd Morass is a large (1,500 ha), deep (40–

60 cm), brackish-water wetland on the south-

western shore of Lake Wellington in the Gippsland

Lakes, Victoria, south-eastern Australia (Fig. 1).

The Gippsland Lakes are connected to the

Southern Ocean via an artificial opening cut to

the sea in 1889 at Lakes Entrance to improve

navigation access. Under the wetland inventory

system used in Victoria, Dowd Morass is classified

as a Deep Permanent Freshwater Marsh, despite

the salinity regime noted in the ‘‘Introduction’’

section.

The Morass has a catchment area of about

65 km2 and receives fresh water as overbank

flows from the Latrobe River on its northern

boundary, nutrient-enriched overland flow from

surrounding agricultural land, and brackish water

from Lake Wellington. The electrical conductivity

Fig. 1 Dowd MorassState Game Reserve,located between theLatrobe River to thenorth and LakeWellington to the east,in the Gippsland LakesRamsar site, south-eastern Australia

Wetlands Ecol Manage (2007) 15:175–188 177

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of surface water in the wetland has fluctuated

over the past decade from about 5 - 25 dS m–1

(Sinclair Knight Merz 2001). It is thought that

Dowd Morass would have dried every 5 years or

so prior to European settlement; as noted in the

Introduction, the wetland has been almost

permanently inundated since 1975.

Revegetation trials

Melaleuca ericifolia tubestock was planted at two

sites in Dowd Morass (Fig. 1). These two sites

were chosen on the basis of internal homogeneity,

ease of access, presence of a suitable range of

water depths and hummocks, and the presence of

juvenile M. ericifolia in the surrounding areas.

Seed for the tubestock was collected from

M. ericifolia stands at Dowd Morass to ensure

local provenance, and germinated in composted

pine in a growing medium. Tubestock were

established from seed by a commercial nursery

(Gippsland Indigenous Plants Pty. Ltd., Valencia

Creek) and grown in this medium in 5-cm

diameter forestry tubes. Previous revegetation

projects using similar tubestock have over 90%

survival in terrestrial sites (John Topp, Gippsland

Indigenous Plants Pty. Ltd., personal communi-

cation). To assist in acclimatisation, tubestock

were placed in the Morass for 2–3 days before

each revegetation trial commenced.

The revegetation trials were undertaken in

collaboration with members of three community

groups interested in the ecology and manage-

ment of the Lake Wellington wetlands: Field and

Game Victoria (Sale and District), the Field

Naturalists Club of Victoria (Sale branch), and

Waterwatch Victoria. A small number of volun-

teers from other groups, for example, local

schools, also attended. Up to 60 volunteers

attended each planting session. Volunteers were

trained in planting techniques before each trial

to minimise differences in planting experience

among participants. Three experimental vegeta-

tion trials were undertaken. Of necessity, each

experimental trial developed iteratively on the

basis of knowledge generated in prior trials and

on the number of community volunteers avail-

able. Due to these factors, methods varied

slightly from trial to trial.

Experiment 1: effect of water depth and age class

Experiment 1 used a split-plot design to test the

effects of water depth and plant age on the

success of seedling establishment. This experi-

ment was undertaken at Site 1 in March 2004

(Fig. 1). Seed of M. ericifolia would naturally

germinate and grow during spring and summer,

so seedlings growing naturally in the Morass

would be 4 to 6-months-old by March. Four-

month-old and 6-month-old seedlings were

therefore selected to replicate the natural age

classes of seedlings in the wetland. The seed-

lings varied not only in age but also in height:

4-month-old seedlings were typically 16 cm high

whereas 6-month-old seedlings were typically

54 cm high.

Four replicate plots (each 18 m · 10 m) were

placed parallel to the water line at three water

depths at Site 1: (i) ‘exposed’ (saturated sediment;

mean surface water depth = 0 cm); (ii) ‘water-

logged’ (mean water depth = 1 cm); and (iii)

‘flooded’ (mean water depth = 9 cm). Three

water depths were chosen because community-

based replanting activities may have little control

over the depth of water in a wetland targeted for

revegetation (de Jong 2000). Within each plot,

4-month-old plants (n = 20) and 6-month-old

plants (n = 25) were planted 2 m apart using a

mattock to create a hole in the sediment into

which the tubestock was inserted. After planting,

volunteers measured the height of the tallest

green foliage (‘plant height’) and water depth for

each plant. Plant survival, plant height, and water

depth were recorded monthly for the following

8 months. A datalogger, located approximately

200 m from Site 1, collected data hourly for

electrical conductivity and water depth.

On the basis of the site’s long term meteoro-

logical records, it was anticipated that the water

level at Site 1 would initially fall, and gradually

increase with the onset of winter rains. However,

a storm in late April 2004 increased the water

depth at Site 1 by more than 30 cm (Fig. 2). Due

to ongoing wet weather, water levels continued to

increase until July 2004 and fell slowly thereafter.

Due to the unexpected flood event, the planned

water depth treatments became obscured within

1 month of planting. After the flood event, the

178 Wetlands Ecol Manage (2007) 15:175–188

123

response of plants largely reflected the duration

and extent of submergence as determined by their

height and planting position.

Experiment 2: effect of water depth and planting

method

To further explore the effect of water depth and

planting method (Hamilton versus mattock) on

plant survival, a follow-up experiment was

undertaken at Site 2 in November 2004

(Fig. 1). Site 2 was flooded at the time of

planting, but the water level was expected to

drop with a planned management-assisted draw-

down and natural evaporation over the summer

period. By planting in November, we antici-

pated that sufficient time would elapse for the

plants to grow before re-flooding would occur

later the following year. Hamilton planters

extract a core of soil in the same cylindrical

shape as forestry tubestock and are a standard

tool for planting terrestrial vegetation in

Australia. However, anecdotal evidence suggests

that in clay soils, such as are common in

wetlands, Hamilton planters will smear the

walls of the newly created hole, and this may

prohibit lateral root expansion and result in a

constricted root mass. Mattocks, which were

used to dig a coarse hole in the soil, are also

commonly used in revegetation and do not

create smoothed wall holes. However, mattocks

are typically regarded as more difficult, danger-

ous and time consuming to use, and this has led

to the widespread use of Hamilton planters in

terrestrial revegetation activities.

Four replicate plots (each 20 m · 8 m) were

placed parallel to the water line at two water

depths at Site 2: (i) ‘shallow’ flooding (mean

surface water depth = 9 ± 1 cm); and (ii) ‘deep’

flooding (mean water depth = 22 ± 1 cm). Each

replicate plot was divided into two sections in a

split-plot design. To test for the effectiveness of

different planting methods, volunteers planted

6-month-old plants 2 m apart in one section of

each plot using mattocks (n = 20) and in another

section of each plot using Hamilton planters

(n = 20). As in Experiment 1, plant height and

water depth were recorded for each plant imme-

diately after planting. Plant height and plant

survival were measured at regular intervals for

the following 5 months.

Experiment 3: effect of planting on vegetated

hummocks

Since we had observed that M. ericifolia seedlings

grew well on small raised hummocks in Dowd

Morass, we tested the effect of planting into

vegetated hummocks on plant survival and

growth at Site 2 during the November 2004

experiment. Fifteen M. ericifolia tubestock seed-

lings were planted in separate Paspalum disti-

chum hummocks using mattocks, and 15

tubestock seedlings were planted adjacent to each

hummock in the surrounding water (‘hollows’;

mean water depth = 11 ± 1 cm). Plant height

Month

Feb 04 Mar 04 Apr 04 May 04 Jun 04 Jul 04 Aug 04 Sep 04 Oct 04 Nov 04 Dec 04

Dep

th (

m A

HD

)

-0.4

-0.2

0.0

0.2

0.4

0.6

Ele

ctric

al C

ondu

ctiv

ity (

dS m

-1)

DepthEC (Water)

5

10

15

20

25

30Fig. 2 Surface waterdepth (metres aboveAustralian HeightDatum) and electricalconductivity (dS m–1) forExperiment 1 at Site 1from February toDecember 2004, asdetermined bydataloggers placed nearthe site

Wetlands Ecol Manage (2007) 15:175–188 179

123

and water depth were measured for each plant at

the time of planting and at regular intervals for

the following 5 months.

Soil chemistry

A single soil core was taken from each plot at the

two sites and separated into two depths: 0–10 cm

and 10–20 cm. At Site 1 cores were taken only at

the time of planting in March 2004. At Site 2,

cores were taken at the time of planting (Novem-

ber 2004) and again at the end of the experiment

when the site had dried (April 2005). Soil cores

were weighed before and after drying at 105�C to

determine soil moisture content. Soil electrical

conductivity (EC) and pH of 1:5 soil:water

extracts were measured using the procedures of

Rayment and Higginson (1992). Electrical

conductivity and pH were measured using a

calibrated TPSTM WP-81 probe and meter

(Springwood, Queensland, Australia). The in situ

soil salinity was calculated using the soil moisture

content and the EC of the 1:5 soil extracts.

Statistical analyses

Data were analysed using SYSTATTM version 11,

and screened for missing values, outliers and

normality, then transformed where required prior

to analysis. Experiments 1 and 2 were unreplicat-

ed, split-plot designs, so analysis followed the

procedures outlined by Underwood (1997) and

Quinn and Keough (2002). Water depth (Exper-

iments 1 and 2), age class (Experiment 1), and

planting method (Experiment 2) were treated as

fixed factors and plot location a random factor.

Age class (Experiment 1) and planting method

(Experiment 2) were treated as within-plot fac-

tors. Soil chemistry data were analysed by treat-

ing soil depth as a fixed within-plots factor.

Variables measured over time were analysed with

time as a fixed within-plot factor.

Logistic regression was used to determine

which factors contributed most to plant survival.

Logistic regression predicts the likelihood of

plants surviving in a particular treatment relative

to the likelihood that plants will die. McFadden’s

q, which is conceptually similar to the r2 value in

linear regression, measures the strength of the

association between the outcome (survival or

mortality) and the predictors (e.g. age class).

Values in the 0.2–0.4 range are considered to be

highly satisfactory (Tabachnick and Fidell 2001).

The odds ratio measures the increase (or

decrease, if the ratio is < 1) in the probability of

a plant surviving when the value of the predictor

unit (e.g. water depth) increases by one step

(Tabachnick and Fidell 2001). It is calculated in

relation to a reference group; the reference group

for this model is 6-month-old plants in the

exposed treatment (Experiment 1) and plants in

shallow water (Experiment 2). A chi-square

analysis, which compares the constant-only model

with the full model, was used to determine

whether the predictor variables reliably predicted

plant survival. A useful guide to logistic regres-

sion can be found at http://www.statpages.org/

logistic.htm.

Results

Experiment 1: effect of water depth and age

class

Sediment and water characteristics

At the time of planting a piezometer located at

the perimeter of the wetland indicated that the

groundwater was likely to be <50 cm below the

sediment surface in the wetland. The conductivity

of the groundwater and surface water was

11 dS m–1 and 25 dS m–1, respectively. At the

start of the experiment, the mean water level in

the exposed, waterlogged and flooded treatments

were 0, 1, and 9 cm, respectively (Table 1).

Depending on wind strength and direction, the

water surface could fluctuate by about 10 cm. The

storm of late April 2004 increased the water

depth by more than 30 cm at Site 1 and lowered

the salinity of the surface water to <10 dS m–1

(Fig. 2). Water levels continued to rise until July

2004, then fell steadily thereafter.

The pH of the soil at Site 1 ranged from 3.7 to

5.6, indicating mildly to strongly acidic soils. Soil

cores 0–10 cm deep (mean pH 4.6) were slightly

more alkaline than soil from the 10–20 cm depth

(mean pH 4.2: F1,18 = 7.757, P = 0.012; Table 2).

180 Wetlands Ecol Manage (2007) 15:175–188

123

There was no significant difference in soil pH

across the three water depth treatments

(P = 0.118). There were, however, significant

differences in soil moisture across water depth

treatments (F2, 18 = 9.059, P = 0.002) and soil core

depths (F1, 18 = 17.388, P = 0.001); the interaction

term was not significant. Soil moisture increased

with increasing water depth at Site 1 and, as

expected, was significantly higher in flooded plots

than in exposed plots (Tukey HSD, P = 0.014).

Soil from the upper 0–10 cm layer had signifi-

cantly less soil moisture than the deeper 10–20 cm

layer (Table 2).

Soil salinity, adjusted for in situ soil moisture,

ranged from ~ 16–36 dS m–1 at Site 1 (Table 2).

There was a significant effect of both water depth

treatment (F2, 18 = 4.631, P = 0.024) and soil

core depth (F1, 18 = 15.091, P = 0.001) on soil

conductivity, but there was no interactive effect.

Soil electrical conductivity was significantly greater

in exposed and waterlogged sites than flooded

sites, and soil cores 0–10 cm deep were signifi-

cantly more saline than cores 10–20 cm deep.

Note that the electrical conductivity of surface

water in the wetland has fluctuated over the past

decade from 5 to 25 dS m–1 (Sinclair Knight Merz

Table 1 Percentage survival, plant height and water depthfor Experiment 1 over a 9-month period for 4-month-oldand 6-month-old seedlings planted at three water depth

treatments at Site 1 in Dowd Morass. All the 4-month-oldplants died in May 2004

Date Age class (months) Water depth treatment Water depth (cm) % Survival Plant height (cm)

March 2004 4 Exposed 0 100 ± 0.0 15 ± 3Waterlogged 1 ± 1 100 ± 0.0 14 ± 4Flooded 9 ± 1 100 ± 0.0 18 ± 7

6 Exposed 0 ± 0 100 ± 0.0 58 ± 31Waterlogged 2 ± 1 100 ± 0.0 53 ± 19Flooded 9 ± 0 100 ± 0.0 50 ± 20

April 2004 4 Exposed 1 ± 1 29 ± 19 17 ± 21Waterlogged 3 ± 0 25 ± 7 13 ± 5Flooded 11 ± 0 26 ± 9 16 ± 6

6 Exposed 2 ± 1 76 ± 9 58 ± 27Waterlogged 3 ± 1 52 ± 10 50 ± 6Flooded 11 ± 1 59 ± 10 47 ± 15

May 2004 4 Exposed Not recorded 0 –Waterlogged Not recorded 0 –Flooded Not recorded 0 –

6 Exposed 36 ± 1 54 ± 5 58 ± 27Waterlogged 40 ± 1 37 ± 13 52 ± 31Flooded 47 ± 1 33 ± 10 50 ± 12

June 2004 6 Exposed 43 ± 1 42 ± 4 56 ± 18Waterlogged 48 ± 2 34 ± 12 49 ± 25Flooded 52 ± 0 29 ± 9 50 ± 8

July 2004 6 Exposed 54 ± 1 42 ± 9 56 ± 27Waterlogged 61 ± 2 8 ± 2 56 ± 19Flooded 64 ± 2 18 ± 6 53 ± 54

August 2004 6 Exposed 47 ± 1 43 ± 5 51 ± 12Waterlogged 53 ± 2 25 ± 10 52 ± 25Flooded 59 24 57

September 2004 6 Exposed 40 ± 1 42 ± 1 43 ± 12Waterlogged 46 ± 1 32 ± 13 46 ± 15Flooded 51 ± 0 29 ± 10 48 ± 19

November 2004 6 Exposed 38 ± 1 3 ± 2 –Waterlogged 35 ± 1 8 ± 2 –Flooded 44 ± 0 2 ± 1 –

Data represents mean ± standard error (n = 20 for 4-month-old plants; n = 25 for 6-month-old plants)

Wetlands Ecol Manage (2007) 15:175–188 181

123

2001), indicating that the soil salinities in soil pore

water were likely to be considerably higher than

were surface-water salinities.

Plant responses

Due to the unexpected flood in late April 2004, the

effects of the planned water depth treatments

could be evaluated using only data collected in

early April 2004. After this time plant responses

also reflected the duration and extent of submer-

gence. In April, 1 month after planting and prior to

the flood event, there was very high mortality of

plants (Table 1). Both the age of plants and water

depth were significant factors in seedling survival,

but there was no interaction. As indicated by the

odds ratio (Table 3), seedlings were three times

more likely to survive in the exposed treatment

than in the waterlogged treatment, although the

strength of this effect is somewhat equivocal given

the variance associated with the estimate (Wald

statistic = 3.5, P < 0.001; Table 3). Survival was

greater in older plants, and only 27% of the

4-month-old plants survived the first month

whereas 65% of the 6-month-old plants survived

for this time (Table 1). Statistical analysis demon-

strated that 4-month-old plants were significantly

more likely to die than survive (Wald statistic =

-5.7, P < 0.001; Table 3). The chi-square test for

the difference between the constant-only model

and the model specified was significant (P < 0.001),

although McFadden’s q value of 0.1 was not

completely satisfactory. Much of the unexplained

variation may be accounted for by differences in

survival across plots.

The height of many plants decreased over the

first month as a result of die-back of the apical

meristem (Table 1). Water depth was a significant

factor in determining changes in plant height

(F2,238 = 4.346, P = 0.048); plants in the exposed

treatment were significantly taller than those in

the flooded treatment (Tukey’s HSD, P = 0.039).

In contrast, age class was not a significant factor

in predicting plant height; this may be related to

the high mortality of 4-month-old plants and the

loss of statistical power. There was, however, a

Table 2 Summary of soil chemistry results for 0–10 and 10–20 cm soil depths for Experiment 1 and Experiment 2

Date Treatment Sedimentdepth (cm)

Soil pH(1:5) Soil moisture (ml g DW–1) In situ soil EC(dS m–1)

Experiment 1 March 2004 Exposed 0–10 4.2 ± 0.1 1.3 ± 0.1 35.7 ± 2.310–20 4.2 ± 0.2 1.5 ± 0.1 17.1 ± 0.9

Waterlogged 0–10 4.8 ± 0.3 1.4 ± 0.1 34.5 ± 8.710–20 4.2 ± 0.2 2.0 ± 0.2 18.8 ± 0.2

Flooded 0–10 4.8 ± 0.1 1.7 ± 0.2 17.3 ± 0.410–20 4.3 ± 0.2 2.5 ± 0.3 16.3 ± 0.7

Experiment 2 Nov 2004 Shallow 0–10 3.6 ± 0.1 1.3 ± 0.1 13.4 ± 1.210–20 3.6 ± 0.1 0.7 ± 0.1 15.8 ± 0.7

Deep 0–10 3.5 ± 0.1 1.4 ± 0.1 13.1 ± 0.610–20 3.4 ± 0.1 1.0 ± 0.2 16.0 ± 0.8

April 2005 Shallow 0–10 3.5 ± 0.1 1.0 ± 0.0 59.9 ± 3.910–20 3.5 ± 0.1 0.6 ± 0.1 27.9 ± 1.8

Deep 0–10 3.4 ± 0.1 1.3 ± 0.1 51.2 ± 4.010–20 3.3 ± 0.0 0.9 ± 0.1 26.1 ± 1.8

Values are given for the pH of 1:5 soil:water extracts, soil moisture content, and in situ soil electrical conductivity for eachtreatment. Data represent mean ± standard error (Experiment 1, n = 4; Experiment 2, n = 4)

Table 3 Logistic regression model for Experiment 1 ofwater depth, age class and their interactive effects versussurvival of plants 1 month after planting. The referencegroup is 6-month-old plants in the exposed water depthtreatment

Variable Oddsratios

95%Boundsof oddsratios

Waldstatistic(t-ratio)

P

Waterlogged 2.9 5.1–1.5 3.5 0.000Flooded 1.2 1.9–0.7 0.8 0.433Age 4-month 0.3 0.4–0.2 –5.7 0.000Four-month

waterlogged plants0.4 1.0–0.2 –1.9 0.051

Four-month floodedplants

1.0 1.0–1.0 – –

182 Wetlands Ecol Manage (2007) 15:175–188

123

significant interactive effect of water depth with

age class (F2,238 = 7.88, P < 0.001); the height of

4-month-old plants in April is less in the water-

logged treatment than either the exposed or

flooded treatment, but for 6-month-old seedlings

the height is lowest in both the waterlogged and

flooded treatments (Table 1). As before, among-

plot effects were a significant factor in determin-

ing plant height.

As a result of the flood in April, by May 2004

all the 4-month-old seedlings were deeply sub-

merged (shoot tips >20 cm below the water

surface) and had died (Table 1). Although the

height of some 6-month-old plants exceeded the

water depth, the plant tips did not emerge from

the water but instead lay flat on the surface. The

extent and duration of submergence was consid-

erably less for these taller, older plants than for

the younger tubestock and this was correlated

with their improved survival: more than 20% of

6-month-old plants survived 3–4 months of com-

plete submergence, and survival was highest

(40%) in exposed plants. Nevertheless, prolonged

inundation of 6-month-old plants caused the

growing tip to die, emergent leaves to be shed,

and the bark of the main stem to become thick

and spongy where submerged.

In August and September 2004, when water

levels started to drop again, survival of 6-month-

old plants appeared to increase in the water-

logged and flooded treatments (Table 1), possibly

as new shoots were produced on plants that had

previously been scored as ‘dead’ or because the

green shoots were easier to see when they were

not immersed in turbid water. The increase in

survival, however, proved to be transient and

more plants died within 1 month as water levels

fell further. Of the total number of seedlings

planted originally (540), <10% survived over the

8 months of observation.

Experiment 2: effect of water depth

and planting method

Sediment and water characteristics

Water levels fell over the experimental period

and, by January 2005, the surface water had

evaporated from the shallow plots to leave the

sediments fully exposed (Table 4). Water in the

deep plots at this time was 3–5 cm deep. By April

2005, all the shallow and the deep flooded sites

were dry. Apart from occasional rainfall, Site 2

remained dry for the remainder of the observa-

tion period.

The pH of soil at Site 2 ranged from 3.3 to

3.8, again indicating mildly to strongly acidic

conditions (Table 2). Shallow-flooded soils had

significantly higher pH than deep-flooded soils

(F1,12 = 12.002, P = 0.005), but there was no

significant change in soil pH over the duration

of the experiment. Soil from 0–10 cm depth had

significantly higher soil moisture than soil

10–20 cm deep (F1, 12 = 62.049, P < 0.001),

and soil cores taken from deep flooded sites had

significantly greater soil moisture than cores

in shallow flooded sites (F1, 12 = 21.694,

P = 0.001; Table 2).

When seedlings were planted in November 2004,

soil salinities were ~ 13 dS m–1 in the 0–10 cm

profile and ~ 16 dS m–1 in the 10–20 cm profile

(Table 2). There were no significant differences in

soil salinity across soil depths or water depth

treatments at this time. As the wetland dried out

however, the electrical conductivity of soil from the

0–10 cm depth increased to ~ 60 ± 4 dS m–1 in the

shallow flooded site and 51 ± 4 dS m–1 in the deeply

flooded site. These soil salinities are very much

higher than the range of water-column salinities

observed in the wetland. Salinities in the 10–20 cm

deep profile were around half the values observed

for the upper soil layers. By the end of April 2005,

salt encrusted the soil surface in both shallow and

deep flooded sites.

Plant responses

The logit regression model for seedling survival

2 months after planting at Site 2 was significant

(P < 0.001), and increasing water depth clearly

affected the likelihood of seedling survival. Two

months after planting, only 9 ± 3% of plants in

the shallow water treatment had survived

(Table 4). Deeply flooded plants were even more

likely to die (Wald statistic = –11.4, P < 0.001),

and only one plant had survived after 2 months

under these conditions. However, the low McF-

adden’s q2 value (0.01) for the model suggests

Wetlands Ecol Manage (2007) 15:175–188 183

123

there is considerable unexplained variation.

There was great variation in percentage survival

between plots in the shallow-flooded treatment,

indicating local plot factors were very important

in controlling plant survival. There was, however,

no significant change in percentage survival of

plants between January 2005 and April 2005.

Planting method did not significantly affect the

likelihood of survival within this time frame.

At the time of planting, the mean ± SE plant

height was ~ 47 ± 1 cm and there were no significant

differences in plant height across water depth

treatments or planting methods. Plants in the

shallow treatment increased in height, on average,

by 14 cm over the 5 month period to ~ 60 cm.

Surviving plants in the shallow treatment devel-

oped robust stems, with bushy branches arising

from the top half to one third of the plant. Planting

method had no significant effect (P > 0.05) on plant

height. The height of the single remaining plant in

the deep treatment was 52 cm.

Experiment 3: effect of planting on vegetated

hummocks

The average water depth in the flooded treatment

at the time of planting was 11 ± 1 cm and the

vegetated (Paspalum distichum) hummocks were

typically raised 20–25 cm above the water level

(Table 5). By January 2005, the sediment around

the hummocks was exposed and, apart from

occasional rainfall, the site remained dry for the

remainder of the experiment.

Two months after planting, 14 of the 15 plants

(93%) on vegetated hummocks had survived

(Table 5). In comparison, only 1 of the 15 plants

in the flooded treatment had survived. Plant

height (mean ± SE) on vegetated hummocks

increased by 5 ± 5 cm over the 5 month period

of observation, whereas the single remaining

plant in the flooded treatment had increased in

height by 18 cm over this time (Table 5). In

contrast to the morphology of shallowly flooded

plants in Experiment 2, the lateral branches of

seedlings on hummocks were distributed evenly

along the entire stem.

Discussion

Dowd Morass, in common with many other

coastal wetlands in south-eastern Australia, has

Table 4 Percentage survival, plant height and water depth for Experiment 2 over a 5-month period for 6-month-oldseedlings of M. ericifolia planted in two water depth treatments at Site 2 using either a mattock or Hamilton planter

Date Water depth treatment Planting method Water depth (cm) % Survival Plant height (cm)

November 2004 Shallow Mattock 9 ± 1 100 47± 2Hamilton 100 45± 2

Deep Mattock 22 ± 1 100 48 ± 2Hamilton 100 46 ± 2

January 2005 Shallow Mattock Dry 10 ± 4 47 ± 2Hamilton Dry 9 ± 4 51 ± 2

Deep Mattock No data <1 48Hamilton No data 0 –

April 2005 Shallow Mattock Dry 5 ± 3 61± 2Hamilton Dry 12 ± 4 61 ± 3

Deep Mattock Dry <1 52Hamilton Dry 0 –

Data represents mean ± standard error (n = 20)

Table 5 Percentage survival, plant height and water depthof plants planted directly into vegetated hummocks and inflooded hollows immediately adjacent to hummocks(Experiment 3)

Date Plantinglocation

%Survival

Height(cm)

Waterdepth(cm)

November2004

Hummock 100 40 ± 3 0Hollow 100 43 ± 3 11 ± 1

January 2005 Hummock 93 43 ± 3 0Hollow 6 50 0

April 2005 Hummock 93 49 ± 3 0Hollow 6 63 0

184 Wetlands Ecol Manage (2007) 15:175–188

123

been degraded by near-permanent flooding, low

soil pH and highly saline soil and surface water (de

Jong 1997; Turner and Lewis 1997; de Jong 2000;

Davis et al. 2001). The very poor survival of

tubestock seedlings observed in our study is

undoubtedly related to this highly stressful

combination of adverse environmental factors,

and demonstrates the difficulties associated with

rehabilitating degraded brackish-water wetlands.

The study clearly demonstrated that age class,

water depth and topography were critical factors

in the survival and growth of M. ericifolia seed-

lings. Due to the low survival, it was more difficult

to assess the importance of planting method, but

preliminary results suggest little difference between

Hamilton planters and the use of a mattock.

Our experience at Dowd Morass shows how

water regime and water quality interact to control

seedling establishment and thus affect the likely

success of revegetation trials. Location from the

waterline, up a strong water depth gradient,

strongly influenced soil salinities throughout the

surface (0–20 cm) soil profile in Dowd Morass. In

sediments that had dried out, the in situ soil

salinities increased dramatically, due to both the

concentration and accumulation of salts. The soil

salinity increased fourfold in the surface (0–10 cm)

layers and doubled in the deeper (10–20 cm)

layers. Moreover, the salinity of the soil pore

water (up to 60 dS m–1) almost always exceeded

the salinity of surface water in the wetland

(10–30 dS m–1). In locations where the sediments

had been exposed and then re-flooded, the soil

salinities may greatly exceed the salinity of the

overlying water because of the accumulation in

surface profiles of salts from deeper in the soil

profile. In contrast, where the sediments rarely

become exposed, the soil salinities may better

reflect those of the surface water or ground water.

Measurement of the water column salinity when

assessing environmental conditions is therefore

not a good indicator of salinities that rooted plants

are likely to experience in revegetation trials and

rehabilitation strategies.

Effect of seedling age

The survival of M. ericifolia seedlings at Dowd

Morass depended strongly on the age of the

tubestock plants. The mortality of 4-month-old

plants 1 month after planting was at least 20%

greater than that of 6-month-old seedlings at

the same time. Four-month-old plants had a

small root system that did not bind soil, and it

was difficult to plant these young seedlings in

the wetland without damaging their roots. In

contrast, 6-month-old plants had a larger root

system and planting was comparatively easy

across all water depth treatments. Damage to

the roots of younger seedlings may also have

increased salt uptake by the plants: the smaller

root system of 4-month-old plants may have

restricted them to the more saline surface layers

of the soil existing in the exposed and water-

logged sites, whereas the better developed roots

of 6-month-old plants may have been able to

penetrate to less saline zones deeper in the soil

profile.

Effect of water depth and soil salinity

Seedlings and young plants of many Melaleuca

species, including M. ericifolia, are known to be

highly tolerant of waterlogging (Ladiges et al.

1981; de Jong 2000; Salter et al. 2006), and are

capable of active root growth in waterlogged soils

through the production of aerenchyma in the

roots (Ladiges et al. 1981). It is noteworthy,

however, that the survival of 6-month-old seed-

lings of M. ericifolia in the exposed (i.e., dry to

semi-damp) plots was 15–25% higher than for

seedlings planted in the waterlogged or fully

flooded plots 1 month after planting. In a reveg-

etation experiment in New South Wales, M. erici-

folia had high survivorship under extremes of

inundation and drought (de Jong 2000), but the

soil was markedly less saline than in our trials at

Dowd Morass.

The depth to which plants are flooded imme-

diately after planting may be an important factor

in the survival of M. ericifolia seedlings during

revegetation efforts. Once submerged, all the

4-month-old seedlings had died within 1 month;

in contrast, some 6-month-old plants survived up

to 8 months fully submerged, and survival was

highest in exposed plots. Similarly, Denton and

Ganf (1994) reported that 4-month seedlings of

M. halmaturorum did not survive complete

Wetlands Ecol Manage (2007) 15:175–188 185

123

inundation over a 6-week period in a wetland in

South Australia. In a laboratory experiment, 1-

year-old M. halmaturorum plants covered by

water to 50% of their height had > 86% survi-

vorship after 14 weeks, whereas plants com-

pletely submerged had only 29% survival

(Denton and Ganf 1994). In Experiment 2,

seedlings of M. ericifolia covered by 20% of their

height (i.e., in the shallow flooded treatment) had

9% survival after 2 months, whereas plants cov-

ered by 44% (i.e., the deep flooded treatment)

had only one individual remaining by the time

observations had ceased.

There is likely to be a strong interaction in

field-based revegetation trials between age of

plant and depth of water on the survival of

seedling tubestock. Clearly, the taller, older

seedlings should be better able to withstand

inundation since they can maintain a greater

proportion of their foliage above the water

surface. This prediction was vindicated by the

results of Experiment 1; where on average

only 18% of the shoot of the 6-month-old

plants was submerged, compared with ~ 50%

of the shoot in 4-month-old seedlings. This

difference was reflected in the markedly better

survival of the older tubestock under flooded

conditions.

Seedlings of M. ericifolia are reportedly

tolerant also of high salinities (van der Moezel

et al. 1991; Salter et al. 2006). In a mesocosm

experiment, 90% of M. ericifolia seedlings

survived 10 weeks in exposed sediments where

soil salinities exceeded 66 dS m–1; however,

when these sediments were waterlogged or

flooded, there was 100% mortality within

9 weeks (Salter et al. 2006). Similar results were

observed in Experiment 2, since seedlings in the

shallow flooded treatment had high mortality in

the first month when the sediments were

flooded but, once the sediments became

exposed, the surviving plants persisted in soil

salinities ~ 60 dS m–1 for at least 5 months.

Nevertheless, the interaction of high soil salin-

ities with water depth is likely to have contrib-

uted to the very high mortality of seedlings at

Dowd Morass. The extremely low pH of the

soil at the two revegetation sites probably also

contributed substantially to the poor revegeta-

tion success.

Importance of hummocks

In contrast to the high mortality of seedlings

planted directly in water, planting tubestock into

raised hummocks vegetated with a dense growth

of Paspalum distichum increased markedly the

survival of M. ericifolia tubestock at Dowd

Morass. This finding is consistent with our field

observations that M. ericifolia seedlings and juve-

niles predominantly occur on hummocks that are

raised, even slightly, out of the surrounding water,

and can be explained in terms of hummocks

offering a refuge from the stressful combination of

waterlogging, salinity and soil acidity occurring in

the surrounding sediments.

Vegetated hummocks are composed predomi-

nantly of decomposing organic matter with large air

spaces, and may enhance the survival of M. ericifolia

by elevating the shoots out of the water column and

allowing improved root aeration. Vegetated hum-

mocks may also be less affected by salinity than

lower lying, waterlogged areas; the vegetation and

organic matter may facilitate the collection of

rainfall, favouring percolation and leaching of salts

from the root zone of seedlings.

There may however be an adverse effect of

hummocks on plant growth, since young plants on

hummocks may become water stressed during

periods of low rainfall if roots do not rapidly

locate deeper water sources (Rothwell et al.

1993). Although plants on vegetated hummocks

had the best survivorship, growth of M. ericifolia

was almost three times better in shallow flooded

sites that dried out over time compared with that

of plants in vegetated hummocks.

Implications for revegetation trials

at the landscape scale

Despite the reported tolerance of M. ericifolia

seedlings to inundation and salinity, our research

demonstrated that, in wetlands that experience

high salinities, planting tubestock directly into

waterlogged soils, irrespective of water depth, is

likely to be almost completely unsuccessful as a

186 Wetlands Ecol Manage (2007) 15:175–188

123

revegetation strategy. This result is most likely a

consequence of the interactive, and detrimental,

effects of waterlogging with soil salinity and/or

low pH on seedling survival. The combined

impacts of waterlogging and salinity, however,

may be minimized by selecting elevated planting

spots, after consideration of microrelief, soil

characteristics, species, water depth and local

climate (Roy et al. 1999). In a site such as Dowd

Morass, it is preferable to use the natural topog-

raphy of the wetland for revegetation, using

raised sites such as existing vegetated hummocks,

Phragmites beds, and localised mounds formed

through tree fall.

Where advantage cannot be taken of the

natural microtopography, areas may have to be

artificially raised to improve the chances of

seedling survival. Planting onto hummocks is

similar to a site preparation technique known as

mounding, which has been used since the 18th

century for reestablishing tree species on wet sites

(Londo and Mroz 2001). This technique has been

successfully applied in some Australian systems

and has been recommended for revegetation

because of its good soil moisture retention and

high plant survival (Close and Davidson 2002).

Unless intrinsic edaphic (e.g., salinity, pH) and

hydrological (e.g., water quality and water regime)

factors are fully understood, community-based

revegetation trials in coastal Melaleuca wetlands

are likely to be unsuccessful. The effectiveness of

community-based revegetation efforts needs to be

rigorously and quantitatively assessed, so that the

process is more accountable and transparent. The

mere act of planting large number of seedlings is

insufficient as a rehabilitation strategy if the young

plants do not mature into a self-sustaining popu-

lation. This is the result we observed in our

collaboration with community groups, as <10%

(and in some trials <1%) of tubestock seedlings

survived over the period of observation.

Acknowledgements We thank Parks Victoria forallowing us to conduct the experiments at Dowd Morassand for their support of the project. The Rangers, AndrewSchulz, Chris Holmes and Peter Kambouris, are thankedespecially. We are very grateful to John Topp of GippslandIndigenous Plants for growing the seedlings, and to theGippsland community for their assistance with planting,particularly Gary Howard and members of Field and

Game Australia (Sale and District), Field Naturalists andWaterwatch. We thank also Ni Luh Watiniasih, JacquiSalter and Matthew Hatton for their assistance in the field.This research was funded under Land and Water GrantsUTV2 and MU041, with additional support from WestGippsland Catchment Management Authority,Department of Sustainability and Environment,Department of Primary Industries, Parks Victoria andthe Gippsland Coastal Board.

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