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


part of the wetland in private ownership. Between 1959 and 1975 attempts to



Yüklə 5,47 Mb.
Pdf görüntüsü
səhifə2/13
tarix30.08.2017
ölçüsü5,47 Mb.
1   2   3   4   5   6   7   8   9   ...   13
part of the wetland in private ownership. Between 1959 and 1975 attempts to 
purchase the land in the western sections of the wetland were unsuccessful.  
  
In 1973, while the western sections were still in private ownership, further alienation 
of the wetland occurred when a series of levee banks approximately 0.9-1.9 m 
Australian Height Datum (AHD) were constructed (Figure 2.2).  These levees almost 
completely separated the eastern and western sections of the wetland (Figure 2.2). The 
levees were constructed “with a view to drainage and development for agricultural 
purposes”
 
(SRWSC 1972), to prevent overbank flows from the Latrobe River and to 
prohibit brackish water from Lake Wellington entering the western side of the morass 
(Keith Heywood, pers. comm.).  Two artificial drains were constructed in the early 
1970s to establish a hydraulic connection between Dowd Morass and the Latrobe 
River.   
 
In 1975 the State Government of Victoria purchased the western part of the Dowd 
Morass wetland and created a State Game Reserve incorporating all of Dowd Morass. 
Breaches were created in the levees to improve water circulation within the morass 
and to restore a more natural hydrology and water regime.  In 1987, the managing 
agency (Parks Victoria) installed gated culverts on the larger of the two drains (Drain 

 
24
1, Figure 2.2) so that water levels could be artificially managed (Sinclair
 
Knight Merz 
2003). 
 
The recent history of Dowd Morass and the wetlands of the Gippsland Lakes are most 
strongly influenced by a range of human-induced changes. At the time of settlement, 
Dowd Morass was a primarily freshwater wetland, filling via floodwaters from the 
Latrobe River and periodically with water from the variably saline Lake Wellington. 
Water levels within Dowd Morass would have naturally fluctuated with seasonal 
variations to rainfall and evaporation. The natural wetting and drying cycles prior to 
European settlement are estimated to have happened on a five-year cycle with 
complete drying out (drawdown) about every five years (Parks Victoria 1997). 
 
Five major human-induced changes have significantly altered the spatial and temporal 
water regime and water quality of the Gippsland Lakes and the surrounding wetlands.  
 
1. The formerly forested catchment of the Latrobe River has undergone major 
land-use change from the mid 19
th
 century. Primary amongst these changes is 
the conversion of large tracts of forest to agricultural land with subsequent 
alterations to water tables, nutrients and sediment inputs to the river (Gutteridge 
Haskins and Davey 1991).  
 
2. There have been major impoundments of waters of the Latrobe River, 
particularly Lake Glenmaggie (1926) and the Thomson Dam (1983). Both of 
these dams have reduced variability of flow within the river and reduced 
frequency of smaller flood events (Grayson 2003).  

 
25
 
3. The creation of a permanent connection between the ocean and the Gippsland 
Lakes at Lakes Entrance altered the salinity regime of the lakes system and 
lowered water levels in the lakes by approximately 60 cm. The permanent 
opening of the Gippsland lakes to the ocean has particularly impacted on Lake 
Wellington and the adjacent wetlands Dowd Morass and Heart Morass, which 
were primarily freshwater wetlands prior to European settlement (Gippsland 
Lakes Task Force 2004). 
 
4. The construction of the internal levee banks and drains significantly altered the 
hydrological regime of Dowd Morass. The drains allowed flooding or draining 
of the wetlands from the Latrobe River (Figure 2.2). Several of the 
compartments created by the levees have water levels maintained at artificially 
high levels and have been prevented from experiencing natural drawdown. The 
lack of internal connectivity created by the levees has maintained distinct water 
and salinity regimes for each compartment (Boon et al. 2007).  
 
5. The water regime at Dowd Morass has been actively managed since 1975 when 
the wetland was declared a State Game Reserve. Flooding of Dowd Morass was 
commenced in 1975 to prevent saline intrusion from Lake Wellington and to 
provide suitable habitat for waterfowl (Schulz pers. comm.). Since that time 
water levels have been maintained at an artificially high level except when there 
was a trial drawdown during the summer of 1997-98. This drawdown was 
prompted by evident deterioration in the condition of M. ericifolia adults and 
lack of recruitment of young seedlings (Schulz pers comm.).  

 
26
 
 
 
Figure 2.2 Dowd Morass, showing the location on internal levees and the resultant 
division of the wetland into five discrete zones. Taken from Boon et al. (2007).  
 
2.2.1 Water levels over past ~ three decades 
 
As noted earlier, a series of levee banks approximately 0.9-1.9 m AHD were 
constructed in Dowd Morass in 1973.  These levees almost completely separated the 
eastern and western sections of the wetland and radically altered the natural water 
regime of the wetland.  Analysis of aerial photographs by Boon et al. (2007) showed 
that surface water covered only 12 % (182 ha) of the wetland in 1964.  Water covered 
7 % (121 ha) of the wetland when the levees were constructed in 1973.   

 
27
 
The breaches in the levee walls created in 1975, while having some effect on restoring 
water regime, were not successful in restoring pre-levee water regimes. By 1982 the 
extent of open water at Dowd Morass increased to 31 % of the total area (515 ha) this 
being a conservative estimate due to the difficulty of detecting the presence of surface 
water beneath the canopy of Swamp Paperbark.   
 
Various episodic spot measurements of water levels in Dowd Morass are available 
from 1992 to 2003 but as they have not been calibrated, should be interpreted with 
caution (Figure 2.3).  These data do, however, support the notion that Dowd Morass 
has been flooded permanently since at least 1992, with the exception of the drawdown 
in 1998.  These data also demonstrate that water levels in Areas A – E of the Morass 
have fluctuated between 0.2 and 0.6 m over this period.  Moreover, water levels in 
Areas A – E rose and fell in concert, suggesting these areas are now relatively well 
connected hydrologically.   
 
Staff from Parks Victoria were concerned, in the mid 1990s, that near-permanent 
inundation was having adverse impacts on Swamp Paperbarks in Dowd Morass.  A 
drawdown of water levels was initiated in March 1997 by draining water through the 
gated culverts to the Latrobe River.  Water levels were completely drawn down 
during the summer of 1998 and the wetland was dry for 173 days.  This drying time 
was not considered by Parks Victoria staff as sufficient to achieve the management 
goals of restoring the Swamp Paperbark community.  
 

 
28
In March 1998, the managing agency opened the gated culverts joining Dowd Morass 
with the Latrobe River in order to allow water to flow into the wetland.  The Latrobe 
River was low at that time and there was only a small flow into the Morass.  During a 
major flood of Lake Wellington in mid-1998, brackish water from Lake Wellington 
backed up the Latrobe River and entered Dowd Morass via the Dardenelles and via 
overbank flow along the Latrobe River.  The effect on wetland salinity of this saline 
intrusion can be seen in Figure 2.5.  Since reflooding in 1998, water levels in Dowd 
Morass have been maintained between 0.3 and 0.8 m, deeper even than pre - 
drawdown levels (typically 0.2-0.6 m).  
 
 
 
 
 
 
 
 
 
 
 
Figure 2.3 Recent (since 1991) patterns in water levels in various sections of Dowd 
Morass. (Taken from Boon et .al .2007) 
 
 
 
 
 

 
29
2.2.2 Salinity regimes over past ~ three decades 
 
Spot measurements of electrical conductivity suggest that the salinity of water in 
Dowd Morass fluctuated between <1,000 and over 20,000 μS cm
-1
 between 1992 and 
2003 (Figure 2.4).   The effects of the saline intrusion from Lake Wellington are 
evident in Figure 2.5, with salinities reaching 20,000 μS cm
-1
in late 1998 and early 
1999. 
 
After the short-lived drying event and saline intrusion in 1998, the average salinity of 
surface water in Dowd Morass has increased and become more variable.  Prior to 
1998 surface water salinities were generally below ~ 8,000 μS cm
-1
 excluding one 
sampling period in 1995.  Differences across sites within the wetland also have 
become evident, with Area E > Area D > Area C > Area B > Area A (Figure 2.4).  
This pattern may reflect the influence of saline intrusions from Lake Wellington 
extending into Areas E, D and C but exerting little effect in Areas A and B.   
 
 
 
 
 
 
 
 
 
 
 
 
 

 
30
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2.4 Recent (since 1991) salinity patterns in various sections of Dowd Morass
 
(Taken from Boon et al. 2007) 
 
 
2.3 Water quality in Dowd Morass 
 
The report by Sinclair Knight Merz
 
(2001) contained a full analysis of all water-
quality monitoring data for Dowd Morass from 1991 to 2001. Table 2.1 shows a 
summary of these data.   
 
 
 
 
 
 
Year
19
91 
 
19
92  
199
3  
199
4  
199
5  
199
6  
199

 
19
98  
19
99  
200
0  
200
1  
200
2  
200

 
200

 
20
05  
Electrical Condu
ct
ivity
 (dS m-
1
)
0
5
10
15
20
25
Area A
Area B
Area C
Area D
Area E

 
31
Table 2.1 Summary of water-quality data for Dowd Morass, pooled over all sites, 
from 1991 to 2001.  These data were obtained from the Environment Protection 
Agency (EPA), Parks Victoria and WaterWatch, and analysed by Sinclair Knight 
Merz (2001).
 
 
 
Variable Mean 
+ standard 
error (n) 
Maximum Minimum 
Water temperature 
19 + 1 (219) 
35 

pH 6.6 
+ 0.1 (214) 
8.9 
2.8 
Dissolved oxygen (mg L
-1
) 8.5 
+ 0.3 (25) 
10.5 
5.3 
Salinity (mS cm
-1
)* 4.02 
+ 0.33 (223) 
19.45 
Not given 
Turbidity (NTU) 
91 + 10 (127) 
580 
< 1 
Total phosphorus (mg L
-1

0.23 + 0.02 (138) 
1.55 
0.02 
Total Kjeldahl nitrogen (mg L
-1
) 1.58 
+ 0.2 (9) 
2.40 
0.73 
Ammonium (mg L
-1
) 0.04 
+ 0.02 (7) 
0.10 
< 0.01 
Nitrate plus nitrite (mg L
-1
) 0.09 
+ 0.04 (16) 
0.67 
< 0.01 
* seawater = ~ 50 mS cm
-1
   
 
 
The skew and substantial range in most of the water-quality variables is most notable.  
For example, the mean salinity was just over 4.0 mS cm
-1
 but the median was only 
2.12 mS cm
-1 
and the maximum-recorded value was nearly 20 mS cm
-1
.  Similarly, 
water-column pH varied between 2.8 and 8.9, turbidity from < 1 to nearly 600 NTU, 
and total phosphorus from near the limit of detection to 0.23 mg P L
-1
.  The pH of the 
water column periodically dropped to less than 3 pH units, possibly due to the 
underlying acid sulfate soils. 
 
2.3.1 Project data (Boon et al. 2007) 
 
Measurements of a number of important water-quality variables were taken as part of 
the overall project carried out by the wetland ecology groups of Monash and Victoria 
Universities (Boon et al. 2007). Concentrations of total nitrogen and total phosphorus 

 
32
in the water column of Dowd Morass varied widely from area to area (Table 2.2).  
The highest nutrient concentrations were detected in Area B, the site of the ibis 
rookery.  The two species of ibises that nest at Dowd Morass are the Straw-necked 
Ibis (Threskiornis spinicollis) and the Australian White Ibis (Threskiornis molucca); 
Figure 2.5 shows the rookery in mid 2006 and Figure 2.6 shows the poor water 
quality, indicated by the algal bloom, in this region of the wetland. 
 
Table 2.2 Water-column nutrient data for four areas at Dowd Morass.  Means + 
standard errors are shown, n=5 (Taken from Boon et al. 2007) 
 
 
Date of sampling and wetland area 
Total nitrogen 
(mg N L
-1

Total 
phosphorus 
(mg P L
-1
) 
June 2003 
 
 
A 0.59 
 
+ 0.06 
0.03  + 0.005 
B 2.82 
 
+ 0.20 
0.39  + 0.05 
C 0.52 
 
+ 0.06 
0.02  + 0.0004 
D 1.62 
 
+ 0.26 
0.04  + 0.011 
November 2003 
 
 
A 3.32 
 
+ 0.40 
0.23  + 0.06 
B 4.30 
 
+ 0.25 
0.41  + 0.08 
C 3.62 
 
+ 0.19 
0.22  + 0.022 
D 2.67 
 
+ 0.10 
0.07  + 0.007 
 
 

 
33
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2.5 Rookery in Area B of Dowd Morass in mid 2006. Photo courtesy of 
Professor Paul Boon, Victoria University. 

 
34
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2.6 Algal bloom in Area B (the rookery) at Dowd Morass. The plant growing 
on the Swamp Paperbark hummock is Chenopodium glaucum. Photo courtesy of 
Matthew Hatton, Victoria University.  
 
 
2.4 Sediment quality in Dowd Morass 
 
2.4.1 Carbon, nitrogen and phosphorus contents  
 
Sediments in Dowd Morass have about 10-15 % w/w carbon and 0.7-1.2 % w/w 
nitrogen (Table 2.3).  Phosphorus concentrations are also high, typically over 0.5 mg 
g DW
-1
 (= 0.05 % w/w) (Boon et al. 2007).  
 
 
 
 

 
35
Table 2.3 Carbon, nitrogen and phosphorus content of sediments in four areas at 
Dowd Morass (Boon et al. 2007). 
 
Wetland 
area 
 Nutrient 
content 
(mg g DW
-1

 C:N:P 
ratio 
(by mass) 
 Carbon 
Nitrogen 
Phosphorus 
 
A 128  7.0  0.20 
640:35:1 
B 151  6.9  0.87 
173:8:1 
C 94  7.0  0.58 
162:12:1 
D 153  12.3  0.61 
250:20:1 
 
 
2.4.2 Soil salinity 
 
Sediments in Dowd Morass are often extremely salty.  Table 2.4 shows the soil 
moisture, soil electrical conductivity and in situ soil salinity for sediments in Areas B 
and D, as well as along the shoreline of the wetland, from 2003 to 2006.  By way of 
comparison, seawater has an electrical conductivity of about 50 mS cm
-1
; thus the 
value 30.8 + 1.7 mS cm
-1
 recorded for Area D in 2006 represents an in situ soil 
salinity of well over one-half seawater. 
 
 
 
 
 
 
 
 

 
36
Table 2.4 Soil moisture, electrical conductivity and in situ soil salinity for sediments 
in three zones of Dowd Morass from 2003 to 2006. Means + standard errors are 
shown, n=5. 
 
Sediment 
variable 
Depth 
(cm) 
Wetland 
area 
 Date  
 
 
 
 
2003 2004 2005 2006 
Soil moisture 
(mL g DW
-1

0-10 B 
2.3 
+ 0.2 
2.5 + 0.1 
2.4 + 0.2 
3.6 + 1.0 
  

2.2 
+ 0.5 
2.1 + 0.1 
3.0 + 0.3 
2.2 + 0.4 
  
Shoreline 
2.5 
2.2 
+ 0.1 
2.4 + 0.5 
2.6 
 10-20 

2.1 
+ 0.1 
2.2 + 0.1 
2.1 + 0.1 
2.2 + 0.1 
  

2.2 
+ 0.2 
2.1 + 0.1 
2.1 + 0.1 
2.2 + 0.1 
  
Shoreline 
2.2 
2.0 + 0.1
 
2.0 + 0.2
 
2.3
 
Soil EC 
(mS cm
-1

0-10 B 
3.8 
+ 0.4
 
6.6 + 1.2
 
12.4 + 0.8
 
11.1 + 2.1
 
  

3.6 
+ 0.9
 
6.2 + 0.5
 
13.2 + 1.4
 
13.4 + 2.5
 
  
Shoreline 
4.2
 
5.7 + 0.5
 
10.2 + 2.0
 
9.8
 
 10-20 

3.0 
+ 0.3
 
5.9 + 0.5
 
7.5 + 0.7
 
8.6 + 1.5
 
  

3.8 
+ 0.6
 
8.4 + 1.0
 
9.7 + 1.0
 
12.6 + 0.7
 
  
Shoreline 
2.9 
5.1 + 0.6
 
6.3 + 0.5
 
9.6
 
In situ soil 
salinity 
(mS cm
-1
)* 
0-10 B 
8.2 
+ 0.7
 
13.1 + 0.9
 
24.2 + 2.1
 
17.1 + 3.6
 
  

8.3 
+ 1.1
 
16.7 + 1.6
 
22.2 + 1.0
 
30.8 + 1.7
 
  
Shoreline 
8.3
 
13.0 + 1.1
 
21.4 + 0.8
 
18.9
 
 10-20 

7.1 
+ 0.6
 
12.4 + 0.9
 
17.1 + 1.4
 
19.7 + 2.5
 
  

8.3 
+ 0.8
 
20.6 + 1.7
 
23.3 + 1.7
 
29.0 + 1.6
 
  
Shoreline 
6.5 
12.6 
+ 1.2 15.4 + 0.6 
20.7 
* seawater = ~ 50 mS cm
-1
   
 
 
2.4.3 Soil pH and the presence of acid-sulfate soils 
 
Acid-sulfate soils are soils that produce sulfuric acid (H
2
SO
4
) when exposed to the air 
(National Working Party on Acid Sulfate Soils 2000).  In Australia, potential and/or 
actual acid sulfate soils are found along almost the entire coastline with the main 
exception being the steep limestone cliffs of the Great Australian Bight (National 
Working Party on Acid Sulfate Soils 2000).  Acid-sulfate soils are especially common 
along the eastern seaboard and there are many examples where their disturbance has 
created severe environmental problems: Trinity Bay East near Cairns (Qld) and 

 
37
Tuckean Swamp near Ballina (NSW) are the most well known examples (Hagley 
1996; Powell and Martens 2005).    
 
The sulfuric acid produced when acid-sulfate soils are activated moves through the 
soil, stripping iron, aluminium and manganese, as well as dissolving, in the worst 
cases, heavy metals such as cadmium.  This noxious mixture makes the soil highly 
toxic and, combined with the very low pH (< 3), renders the growth of most plants 
impossible (Fitzpatrick et al. 2000).  Acid-sulfate soils generally do not present a 
serious management problem as long as they are kept waterlogged.  They become 
problematic when wetlands surface soils dry out and oxidise.   
 
If potential or actual acid-sulfate soils are present, it may be unacceptable to instigate 
a strong wetting and drying cycle in hydrologically-altered wetlands because of the 
risk of severe damage to downstream estuarine ecosystems should the wetland drain 
even partially and the sediments start to oxidise.  Johnston et al. (2003), for example, 
reported extensive fish kills in the Clarence River estuary of northern NSW were 
caused by an oxygen-depletion event which was, in turn, caused by anoxic and iron-
rich surface waters draining from two acid-sulfate soil backswamps.   
 
Re-establishing more natural wetting and drying regimes is planned for a number of 
wetlands in the Gippsland Lakes, especially those in the Lake Wellington wetlands 
complex (e.g., Dowd Morass, The Heart Morass).  The existence of actual or potential 
acid-sulfate soils in these areas may present the single most important factor limiting 
the degree to which these wetlands can be episodically dried out and reflooded.  
Revegetation attempts are also likely to be compromised by the presence of acid-

 
38
sulfate soils.  It is possible also that acid release, perhaps combined with acute oxygen 
depletion, could account for some of the fish kills experienced in the Gippsland Lakes 
(John Ginivan, DSE, pers. comm.).   
 
Investigations by Boon et al. (2007) did show that actual and potential acid-sulfate 
soils occur in the Lake Wellington wetlands and probably also in wetlands and other 
coastal areas across the entire Gippsland Lakes region (Table 2.5, Figure 2.7).  In 
recognition of the likelihood of acid-sulfate soils being distributed widely around the 
Gippsland Lakes area and having the potential for major environmental impacts, 
Dowd Morass has been selected as a routine monitoring site as part of the CSIRO’s 
national acid-sulfate soils monitoring framework.  
 
Table 2.5 Titratable peroxide activity (TPA) results for 12 sediment samples from 
Dowd Morass (Taken from Boon et al. 2007). 
 
Wetland area 
Location 
TPA (mol H
+
 tonne sediment
-1

A1 
515684 / 5777786 195 
A3 
515254 / 5777448 73 
A5 
515822 / 5777514 25 
B2 
515408 / 5776653 55 
B3 
515363 / 5776889 53 
B5 
515533 /5776796 67 
C1 
516067 / 5777645 22 
C2 
516262 / 5777905 21 
C4 
516713 / 5778441 16 
D2 
516610 / 5777309 29 
D3 
516391 / 5777334 31 
D5 
516122 / 5776983 26 
 

 
39
 
Figure 2.7 Location of the four sites used for a complete sulfidic analysis of Dowd 
Morass sediments
 
(Crawford 2006
). 
 
2.4.4 Heavy metals 
 
A limited range of analyses for heavy metals in the sediments of Dowd Morass are 
available from samples taken by Boon et al. (2007) (Table 2.6). 
 
This limited amount of sampling suggests that sediments in Dowd Morass are not 
heavily contaminated with heavy metals. Only nickel concentrations exceed the 
International Standards on Quality Control (ISQC) or low trigger values proposed in 
the most recent
 
Australian and New Zealand Environment Conservation Council 
(ANZECC) guidelines (ANZECC-ARMCANZ 2000).  Moreover the guidelines 
suggest that trigger values should be relaxed when sediment organic carbon content is 
Lake Wellington 
Dowd Morass 

 
40
markedly higher than 1 %:  as the sediments have 10-15 % w/w carbon contents, even 
the values for nickel are not likely to be problematic.  
 
Table 2.6 Concentrations of heavy metals in two areas of Dowd Morass.  Samples 
were taken in late 2004 (Boon et al. 2007). 
 
Heavy metal 
Concentration in sediments (mg kg DW
-1
)  Relevant 
ANZECC 
trigger value
17 
 
Area B 
Area D 
 
Cadmium 
< 0.2 
< 0.2 
1.5 
Zinc 44 
50 
200 
Copper 16 
21 
65 
Lead 30 
39 
50 
Chromium 34 48 
80 
Barium 320 
610 
NA 
Nickel 28 
34 
21 
Antimony 
< 1 
< 1 

Arsenic 10 
16 
20 
Boron 75 
150 
NA 
Mercury 
< 0.1 
< 0.1 
0.15 
Selenium 2 


NA 
 
 
Ten of the 17 samples taken at Dowd Morass had a mercury concentration above the 
limit of detection (0.05 mg kg DW
-1
) (Boon et al. 2007).  These data would suggest 
very slight contamination of the wetland’s sediments with mercury, possibly as a 
consequence of gold mining in the catchment or from agricultural land uses. 
 
 
2.5 Vegetation of Dowd Morass 
 
There are four main vegetation communities found at Dowd Morass 
•  Low closed-scrub to woodlands of Melaleuca ericifolia (Swamp Paperbark); 
•  Swards of Phragmites australis (Common Reed); 

 
41
•  Submerged beds of Vallisneria americana (Eelgrass); and  
•  Small areas of mud flats containing salt-tolerant plants such as; Disphyma 
clavellatum  (Rounded Noon-flower), Distichlis distichophylla (Salt-marsh 
Grass),  Hemichroa pentandra (Trailing Hemichroa) and Sarcocornia 
quinqueflora (Beaded Glasswort).  
 
Historically, the area now occupied by Dowd Morass would have been part of a large 
estuary. Over time, through closure of the estuary, sedimentation and change in 
hydrological process, successional change in vegetation from open-water 
communities to woody vegetation has taken place (Bird 1961; Bird 1965). This is 
evidenced in recent times at Dowd Morass by the change from Reed communities to 
Closed-scrub composed of M. ericifolia in the period from 1957 until present.  
 
In a comprehensive study of successional change to vegetation in the Gippsland Lakes 
system, Bird (1962) predicts directional change from open-water through to woody 
vegetation and on to saltmarsh vegetation as salinity levels of the Gippsland Lakes 
increases. The management implications of this are that each of the prior seral stages 
of vegetation will be replaced as conditions change over time creating a highly mobile 
set of vegetation communities of temporary duration. Bird (1962) predicts that the 
long-term prospects for M. ericifolia in the Gippsland Lakes system are limited with 
eventual extinction of the species and replacement with a Saltmarsh community.    
 
Three of the four major vegetation communities are shown in Figures 2.8 - 2.10.  
 

 
42
 
Figure 2.8 Stands of Swamp Paperbark, Melaleuca ericifolia. Area B, Dowd Morass, 
Sale, Victoria. Photo courtesy of Professor Paul Boon, Victoria University. 
 
 
Figure 2.9 Dense swards of Common Reed, Phragmites australis, in the background 
with submerged beds of Eelgrass, Vallisneria americana, in the forground. Area D, 
Dowd Morass, Sale, Victoria. Photo courtesy Kay Morris, Monash University.   

 
43
 
 
Figure 2.10 Aerial photograph of a section of Dowd Morass, showing areas of 
Common Reed (CR) and Swamp Paperbark (SP). Individual clumps of Swamp 
Paperbark are clearly visible (an example is marked with the red arrow). Photo 
courtesy of Parks Victoria.  
 
SP
CR

 
44
Chapter 3 
Clonality in Melaleuca: a study of population structure and 
dynamics using molecular analyses and historical aerial 
photographs  
 
Abstract 
 
Determining the extent of clonality in M. ericifolia is critical to the understanding of 
structure and dynamics of populations of this species. Inter Simple Sequence Repeats 
(ISSR) were used to determine genet size and degree of intermingling, while historical 
aerial photographs are used to determine lateral expansion rates and longevity.  Individual 
‘dome-shaped patches’ of M. ericifolia were determined to be individual genets with the 
ISSR approach, and there was no evidence of intermingling of the 10 genets sampled. 
Genet size after 46 years ranged from 1,174-3,274 m
2
, additional plants not included in 
the genetic testing were speculated to be between 80-100 years old and were considerably 
larger in size. The implications of these findings, most notably lack of intermingling and 
growth rates, are discussed in relation to survival of genets in a wetland with variable 
water regime and configuration of plantings to maximise success and minimise costs.   
 
 
 
 
 
 

 
45
3.1 Introduction 
 
The identification of individual genets of clonal plants is critical to the understanding of 
population structure and dynamics, particularly for determining genet size, competitive 
relationships and genetic diversity within populations of clonal plants (Kennington and 
James 1997; Kreher et al. 2000). The extent and the type of clonality exhibited by the 
plant (e.g. phalanx vs. guerrilla) have major implications for survival, reproduction and 
competitive ability. Extensively clonal species are generally assumed to have lowered 
sexual reproduction due to increased energetic and nutrient costs of seed production 
(Sutherland and Vickery 1988; Lovett Doust 1989; Reekie 1999; Eckert 2001). 
Alternatively, clonal plants may have increased competitive ability in environments 
where sexual reproduction is limited due in part to resource sharing between ramets (Rea 
and Ganf 1994; Barsoum 2002; Peltzer 2002). Clonality is a major characteristic of 
wetland plants in Australia, with well over two-thirds being classified as clonal (van 
Groenendael et al. 1997; Hatton 2005). 
 
The development of the clonal growth form has arisen several times in the genus 
Melaleuca (Craven and Lepschi 1999) and more widely in the family Myrtaceae (Lacey 
1983; Kennington and James 1997; Tyson et al. 1998). Within the genus Melaleuca, 
regeneration strategies range from seed-only regenerators (e.gM. parvistaminea), those 
that resprout only from the main trunk (e.g.  M. uncinata, M. quinquenervia) through to 
extensively clonal species that resprout from stems and roots (e.g. M. ericifolia,  M. 
halmaturorum (Jeanes 1996; Craven and Lepschi 1999; Holliday 2004). Although there 
is occasional mention of the regenerative ability of various Melaleuca species in the 

 
46
literature, there is no comprehensive investigation of clonal regeneration capacity for any 
of the species.  
 
Clonality is often regarded as an adaptation to spatial and temporal heterogeneity of 
environmental conditions (Kleign and van Groenendael, 1999). Some of the conditions 
that lead to environmental heterogeneity (patchiness) in the situations in which M. 
ericifolia grows are fire, salinity, water level (drought and flooding), soil pH, and impacts 
from breeding colonies of of birds. In evolutionary terms, the clonal growth-form is very 
ancient and occurs in a wide range of plants (Mogie and Hutchings 1990) and 
environments (Klimes et al. 1997), but is particularly well developed in habitats that are 
particularly hostile to sexual recruitment (Rea and Ganf, 1994; Barsoum, 2002). Spatial 
and temporal availability of germination conditions or seedling recruitment sites may be 
the evolutionary driver favouring clonality. Additionally, artificially prolonged flooding 
has been shown to shift vegetation composition to one based primarily on clonal species 
(Ernst and Brooks 2003). 
 
The ability of the clonal growth form to effectively capture resources without having to 
proceed through sexual reproduction in potentially inhospitable sites confers a degree of 
competitive advantage in spatially and temporally heterogeneous environments 
(Silvertown and Charlesworth 2001).  The shift to clonal growth and corresponding 
reduction in sexual reproduction has been linked with increasing heterogeneity of the 
environment and decreases in available safe sites for germination; this being clearly 
demonstrated in the wetland genus Mimulus (Sutherland and Vickery 1988). Sexual 
recruitment in M. ericifolia is rarely recorded and presumed to be episodic in nature and 
limited to specific conditions (de Jong 2000). The impact of clonality coupled with 

 
47
reduced sexual reproduction may have long-term impacts on genetic structure of 
populations, genetic diversity within populations and evolutionary capability (Ellstrand 
and Roose 1987; Widen et al.1994).  
 
The production of lateral growths (ramets) generally follows two main configurations that 
can dictate the distribution and intermingling of separate plants (genets). Phalanx species 
produce short and frequently branched connections between ramets spreading along a 
front that excludes other genets (Harper 1977; Silverton and Charlesworth 2001).  
Guerrilla species produce long-spacers with little branching allowing plants to infiltrate 
neighbouring individuals of the same or other species (Harper 1977; Lovett Doust 1981).  
Ecologically, the two growth forms tend to occur separately although it is not uncommon 
for both forms to occur in the same wetland or for individual species to exhibit both 
forms at various stages of their life. The phalanx mode of growth tends to occur in low-
nutrient, high-light habitats (van Groenendael et al. 1997) with a low degree of spatial 
and temporal heterogeneity of environmental conditions (Kleijn and Van Groenendael,
 
1999).  The guerrilla mode of growth is more closely allied with soils in which nutrients 
and moisture are not evenly distributed. Anecdotal evidence suggests that M. ericifolia is 
a phalanx species but it is not known with certainty which mode of growth M. ericifolia 
exhibits.  
 
While the clonal growth form is widely recognised and studied in herbaceous plants, 
there are far fewer ecological studies of the clonal growth form in woody plants. Notable 
exceptions include Populus tremuloides and Larrea tridentata in western USA, Quercus 
species in Florida, Gaylussacia brachycera in eastern USA, Lomatia tasmanica in 
Australia (Lynch et al. 1998) and Hedysarum laeve in China (Wherry 1972; Vasek 1980; 

 
48
Abrahamson and Layne 2002; Peltzer, 2002; Zhang et al. 2002;). Expansion rates and site 
capture by these species is highly variable ranging from several centimetres per year for 
Larrea tridentata (Vasek 1980) to several metres per year for Populus tremuloides 
(Krasny and Johnson1992).   
 
The aims of this component of the study were to determine the extent of clonality in M. 
ericifolia and the degree on intermingling of genets. The use of a time series of aerial 
photographs of high resolution was seen as a way of tracking the growth of individual 
genets over a 46-year time frame. The use of molecular analysis to identify these 
individual genets would allow accurate tracking and to assess degree of intermingling. 
Inter simple sequence repeats (ISSRs) are components of a marker system that accesses 
variation in the numerous microsatellite regions dispersed throughout the plant genome 
and is suitable for species where little information is available on the genome 
(Zietkiewicz et al. 1994).  Primers target di- and tri-nucleotide repeat motifs, which are 
characteristic of microsatellites in the nuclear genome.  Generally one to three ISSR 
primers are sufficient for identifying individuals (Wolfe and Liston  1998; Esselman 
1999). The coupling of molecular analysis with aerial photography was seen to provide a 
degree of accuracy not available if only one of these methods was used.  
 
There is anecdotal evidence that M. ericifolia is extensively clonal and that it is a phalanx 
species (pers. obs.). The characteristically dome-shaped configuration of populations is 
typical of the phalanx manner of growth. Extensive ramet production from the roots and 
the formation of a front of ramets lends further evidence to the above observations 
(Figure 3.1, Figure 3.2). If this is the case, what are now thought to be populations will in 
fact prove to be individual genets. Competitive exclusion, a characteristic of the phalanx 

 
49
growth form, would imply the lack of intermingling of genets. Some of these 
‘populations’ of M. ericifolia are extensive, covering hundreds of m
2
. The implications of 
extensive clonality and large size of genets would mean that few plants would occupy 
large area, reducing potential genetic heterogeneity of true populations. For conservation 
managers, genetically homogeneous populations that are in fact individual genets would 
imply that present conservation measures are preserving very little genetic diversity. 
Similarly, genetically homogeneous populations would have implications in regard to the 
collection of seed for restoration projects; genets would have to be identified to ensure all 
seed was not collected from one plant. Further, present planting methods involving large 
numbers of genetically distinct plants at close spacings may reduce the competitive 
advantages conferred by the clonal growth form. Genetic homogeneity will be evident not 
only in molecular analyses but in the evaluation of individual patches seen in the 
historical series of aerial photographs.   
 
 
 
 
 
 
 
 
 
 
 
 

 
50
3.2 Methods 
 
The ability of M. ericifolia to form adventitious shoots was confirmed by physically 
examining exposing roots connecting ramets in individual patches of M. ericifolia and 
tracing these roots back to mature stems. (Figure 3.1). The clonal characteristic is 
common between all populations, a Tasmanian example has been used in Figure 3 as it 
was clearer than examples from Dowd Morass where herbaceous plants obscured ramets 
and connections.  The characteristic dome shape of the patches provided anecdotal 
evidence of the vegetative derivation of individual patches (Figure 3.2).  
 
 
 Figure  3.1 Exposed root system of a mature patch of M. ericifolia exhibiting strong 
production of vegetative growth (ramets) from exposed roots, Narawntapu National Park, 
Tasmania.  
50 cm

 
51
 
Figure 3.2 Individual patch of M. ericifolia at Wilson’s Promontory National Park, 
Victoria, exhibiting the characteristic dome shape, with tallest stems in the centre of the 
patch (approximately 8m high) grading down in height to the leading edge (paler green 
outer ring - approximately 1 m high). Surrounding plants are Common Reed (Phragmites 
australis). Total patch width approximately 50 m. Photo courtesy of Ms. Deborah 
Reynolds, Victoria University.  
 
 
 
 
10m

 
52
3.2.1 Sample collection and molecular analysis 
 
To determine if these individual patches were derived from one or several genets, 
sampling was carried out on a grid pattern on two large patches at Dowd Morass (45 m x 
120m and 30m x 68m) containing what appeared to be, from the circular patterning 
within the patches, three genets and two genets (Figure 3.3). The grid was arranged to 
ensure that samples were taken in the centre and edges of the patches and on either side 
of what appeared to be joins between the putative genets (Figure 3.3 a-b). A grid pattern 
was chosen in preference to random sampling as a grid more clearly determined the 
distribution of individual genets within a patch and clearly elucidates whether the plant is 
of guerrilla or phalanx growth habit (Chen et al. 2002).  An additional five individual 
ring-shaped patches of plants were sampled to determine if these were individual genets 
as there was anecdotal evidence of sexual reproduction (true seedling having alternate 
leaves, ramets opposite leaves) within the senescent interiors of these large patches of M. 
ericifolia (Figure 3.3 c).   
 
Approximately 200 g of actively growing stem tips were collected for each sample from 
individual aerial branches, half of which was placed in sealed plastic bags kept on ice and 
transported to an -80

C freezer. The other half was sealed in plastic containers and 
desiccated with silica gel, also kept on ice and transported to a 4
0
C refrigerator until 
processed.  Frozen material was collected and saved to ensure availability of material 
should the preferred desiccated material prove unsuitable.  

 
53
 
 
Figure 3.3 Location of sampled patches of M. ericifolia at Dowd Morass, Sale, Victoria. 
A = patches sampled for determination of genetic diversity of patches and intermingling 
of genets (close-up Figures 3.3a and 3.3b). B = Doughnut shaped patches sampled to 
determine if regeneration within the patch represents vegetative or sexual regeneration 
(close-up Figures 3.3c).  
A1
A2
B

 
54
 
 
 
Figure 3.3a Melaleuca ericifolia patch A1 showing sample points 
 
 
 
 
 
 
 

 
55
 
 
 
Figure 3.3b Melaleuca ericifolia patch A2 showing sample points 
 
 
 
 
 
 

 
56
 
 
 
Figure 3.3c Doughnut-shaped Melaleuca ericifolia patches (B) showing sample points. 
Lighter coloured edges represent actively expanding ‘front’, darker centres represent 
senescent older stems and area of regenerating young growths.  
 
 
 
 
 
 
 
 
 

 
57
DNA isolation 
 
DNA was isolated from leaf material dried in silica gel using QIAGEN Dneasy plant 
DNA extraction minikits (QIAGEN Pty. Ltd. Doncaster, Victoria. Aust.).  Samples (20 
mg) of dry tissue were ground with a small amount of acid-washed sand and DNA 
isolated according to the manufacturer’s instructions. 
 
Primer screening 
 
Primers considered promising for 
Melaleuca were screened and those that gave clear 
bands that were reproducible and could be scored readily were used to amplify DNA 
from all samples. In all, five primers were used: DatA, 888, BDBLz, HB15, and 814.   
 
DNA amplification 
 
DNA was amplified in 20 
μl reactions containing 10 μl QIAGEN HotStart Master Mix (8 
μl H
2
O, 1 
μl 10 μM primer, 1 μl DNA (20 mg).  Polymerase chain reactions (PCR) were 
performed in an Eppendorf MasterCycler® gradient thermal cycler using the following 
profile: 95
0
C for 15 min (1 cycle); 94
0
C for 45 s, 72
0
C for 1 min (35 cycles); final 
extension step of 72
0
C for 10 min with an indefinite soak at 4
0
C. 
 
PCR products were visualised on 2.0% agarose gels stained with ethidium bromide and 
photographed under UV light.  Gels were photographed with a Kodak EDAS 290 digital 
camera and Kodak 1D software. Each sample was scored manually using digital images 
and assigned a multilocus phenotype allowing comparison of all samples. When using 

 
58
dominant markers such as ISSRs, the term phenotype is generally used rather than 
genotype (the underlying genetic basis). This is because a plant that, for example, is 
homozygous for the dominant allele (AA) cannot be distinguished from a plant that is 
heterozygous (Aa) but a homozygote recessive is distinguishable (aa).   
 
PCR products were scored as present (1) or absent (0) for each individual which was then 
assigned a multilocus phenotype based on the combined PCR product patterns of all ISSR 
primers. The probablility of identical patterns having arisen independently via sexual 
reproduction was then calculated following the method described by Parks and Werth 
(1993). Due to slight amplification problems (not all fluoresced evenly) all primers were 
run twice. Poorly amplified samples were excluded from the scoring.  
 
Data analysis 
 
In clonal species such as 
M. ericifolia, the analysis of genetic diversity data can be 
misleading due to the individual genet being sampled multiple times although each 
sample is treated as if it were an separate individual. Determining a statistical basis for 
distinguishing if individual samples are derived from asexual reproduction from a single 
zygote or if the same phenotype was produced independently via sexual reproduction is 
difficult, particularly if individuals of the same phenotype are clustered (Parks and Werth 
1993; Widen et al. 1994).  
 
To overcome this difficulty, the approach used was to calculate the probability, P, (Eq. 
1), once a particular phenotype was found, of obtaining that same phenotype, assuming 

 
59
sexual reproduction, in (n-1) subsequently sampled individuals (Parks and Werth 1993; 
Sydes and Peakall 1998).  
 
P = (P
gen
)
n –1
 
Where n is the total number of individuals with the same multilocus phenotype and P
gen
 = 
probability of obtaining the observed multilocus phenotype via sexual reproduction. If P 
is small, it can be concluded that the most likely explanation for the observed cluster of 
individuals of the same phenotype is common derivation through asexual reproduction.  
 
For dominant markers such as ISSRs where only two phenotypes are possible (presence 
or absence of a particular fragment), P
gen
, represented as 
P
dgen
 (Sydes and Peakall 1998), 
is calculated using Eq. (2).  
 
P
dgen
 =IIx

Where x
i
 is the frequency of whichever phenotype (band presence or absence) was 
observed at locus i in the individual being considered. This approach has been used by a 
number of authors to analyse data from suspected clonal species (Parks and werth 1993; 
Widen et al. 1994; Sydes and Peakall 1998).  
 
As  M. ericifolia has been recorded as having multiple ramets arising from large inter-
connected roots (Figure 3.1), analysis of ISSR data was carried out according to the 
above equation to give the probability of phenotypes having arisen independently more 
than once. A complete set of the data and calculations is provided in Appendix 1.  
 
 

 
60
3.2.2 Analysis of aerial photographs 
 
The molecular analysis allowed for the determination and mapping of individual genets 
using aerial photographs. Aerial photographs of Dowd Morass, taken in 2003 at a scale of 
1:6,000, were obtained from Parks Victoria. These images were scanned at a resolution of 
1,200 dpi using a Powerlook 2100XL flatbed A3 scanner (Umax Technologies Inc., 
Dallas, USA). Each image was rectified using the Leica Photogrammetry Suite (LPS) 
component of Erdas Imagine
TM
 v. 8.7 software (Leica Geosystems, Heerbrugg, 
Switzerland). Erdas Imagine
TM
 uses a digital elevation model (DEM), ground control 
points (GCPs), and camera calibration data to remove geometric distortions existing in 
the original images. Since the vertical topographic variation within the sampled section of 
the wetland is less than one metre, the DEM used in the rectification process was 
assumed to be flat. The processing of the images was carried out by Michael Roache as 


Yüklə 5,47 Mb.

Dostları ilə paylaş:
1   2   3   4   5   6   7   8   9   ...   13




Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©azkurs.org 2020
rəhbərliyinə müraciət

    Ana səhifə