associations between the plant communities of floodplain wetlands, water regime and wetland type

ASSOCIATIONS BETWEEN THE PLANT COMMUNITIES OF FLOODPLAINWETLANDS, WATER REGIME AND WETLAND TYPE

ROSE BARRETT,a DARYL L. NIELSENb,c* and ROGER CROOMEa

a Department of Environmental Management and Ecology, La Trobe University, PO Box 821, Wodonga, Victoria 3689, Australiab Murray-Darling Freshwater Research Centre (CSIRO), PO Box 991, Wodonga, Victoria, 3689, Australia

c CSIRO Land and Water, PO Box 991, Wodonga, Victoria, 3689, Australia

ABSTRACT

Understanding how floodplain wetland vegetation is influenced by water regimes can inform the management of regulated riversystems by targeting appropriate environmental water allocations. In this study, we examined plant community structure in 21floodplain wetlands adjacent to theMurray River between Hume Reservoir and Tocumwal, south-eastern Australia. Correlationsbetween the water regime of the previous 25 years, and wetland type were investigated. We found the structure of plantcommunities, as assessed by the richness and percentage cover of plants, to be related to water regime, with clear differencesbetween the communities of wetlands with historical ‘Wet’, ‘Dry’ and ‘Intermediate’ water regimes. Plant community structurewas also related to wetland type, with differences being found between the communities of floodplain depressions, flood-runnersand cut-off meanders. Managers of riverine/floodplain ecosystems need to consider both wetland type and water regime whenplanning strategies for the restoration or conservation of floodplain wetland vegetation in regulated river systems. Copyright#2009 John Wiley & Sons, Ltd.

key words: aquatic vegetation; floodplain wetlands; water regimes; wetland morphology

Received 18 June 2009; Accepted 23 June 2009

INTRODUCTION

Floodplains are vitally important to the healthy functioning of rivers and streams. Regulation of river flow has

significantly altered the ecology of floodplain river ecosystems (Ward et al., 1999). In many parts of the world,

species-rich floodplain-river environments have become isolated, endangered fragments in the riverine landscape

because of the alteration of the fluvial processes that formed them (Ward et al., 1999; Buijse et al., 2002).

Floodplain wetlands contribute much to the ecology of lowland river systems, and their functioning is largely

driven by hydrological connections between the river channel and adjacent floodplain (Ward et al., 1999). In

particular, the water regimes of floodplain wetlands have a direct effect on the germination and establishment of

plants, and influence their competitive interactions (Riis and Hawes, 2002). Factors such as the frequency, season,

duration and depth of flooding, period between floods and variability of flooding contribute to the variation

observed in floodplain wetland plant communities (Froend et al., 1993; Nielsen and Chick, 1997; Blanch et al.,

1999, 2000; Brock and Casanova, 2000; van Coller et al., 2000; Robertson et al., 2001).

Maximum levels of biodiversity are predicted to occur in wetlands with intermediate levels of connectivity

(Ward et al., 1999). Infrequent flooding may reduce the exchange of energy, matter and organisms between

floodplains and the main river channel, leading to habitat fragmentation and reduced habitat heterogeneity (Ward

et al., 1999). These changes often result in reduced diversity and abundance of wetland plants (Casanova and

Brock, 2000). Likewise, excessive hydrological connectivity may also reduce habitat heterogeneity resulting in

reduced biodiversity (Nielsen and Chick, 1997; Bornette et al., 1998;Ward et al., 1999; Casanova and Brock, 2000)

with the development of semi-permanent wetlands supporting dense stands of near mono-specific emergent

vegetation such as Phragmites australis and Juncus ingens (Brock, 1994).

RIVER RESEARCH AND APPLICATIONS

River Res. Applic. 26: 866–876 (2010)

Published online 10 August 2009 in Wiley Online Library(wileyonlinelibrary.com) DOI: 10.1002/rra.1299

*Correspondence to: Dr. Daryl L. Nielsen, PO Box 991 Wodonga, Victoria 3689, Australia. E-mail: [email protected]

Copyright # 2009 John Wiley & Sons, Ltd.

Numerous studies refer to interactions between hydrology and geomorphology in the development of floodplain

wetland vegetation communities (Froend et al., 1993; Janauer, 1997; Ot’ahel’ova et al., 2007; Bornette et al., 1998,

2008; van Coller et al., 2000). The frequency at which a wetland is inundated and the intensity of inundation are

primary drivers of aquatic vegetation communities (Amoros et al., 2000). Frequent high velocity flows into wetlands

cause sediment scour that impedes the establishment of aquatic vegetation by breaking and uprooting plants but they

can promote high bio-diversity by hindering competitive exclusion (Bornette et al., 2001, 2008). Low velocity flows on

the other hand, often deposit finer sediments impeding seed development through deep burial (Bornette et al., 2008).

The local topography of floodplain wetlands interacts with water regimes to determine how wetlands receive

water during floods.Wetland morphology may modify certain aspects of water regime, such as the velocity of water

flowing into a wetland and the depth of the resulting flood. The velocity of water flowing into a wetland depends

largely on the slope and sinuosity of the wetland e.g. straight channels may experience higher water velocities than

more sinuous ones (Amoros and Bornette, 2002).

The majority of research investigating relationships between vegetation communities, hydrology and wetland

type has been undertaken in European river systems which are less variable in terms of their hydrology (e.g.

Ot’ahel’ova et al., 2007; Bornette et al., 2008) compared to the majority of Australian rivers (Puckridge et al.,

1998). There is currently limited research that deals specifically with the aquatic vegetation community structure of

floodplain wetlands along the Murray River, Australia, and the relationship of aquatic vegetation community

structure to hydrology and wetland type, although several studies have examined the effect of water regime on

communities or specific species (e.g. River red gums) (Bren, 1988; Nielsen and Chick, 1994; Siebentritt et al.,

2004; Alexander et al., 2008).

In this paper we examine 21 wetlands along a particular river zone of the Murray River in southeastern Australia

with the aim to explore that relationship between wetland type, water regime and vegetation communities. We test

the hypotheses that vegetation communities differ in wetlands experiencing different water regimes, and also

between wetlands of different physical type.

METHODS

Site selection and wetland type

The aquatic macrophyte communities in 21 wetlands on the Murray River floodplain between the Hume

Reservoir and Tocumwal, in south eastern Australia were examined (Table I). All wetlands experience similar

climatic conditions with rainfall varying from 410mm in the west to 710mm in the east. Prior to regulation of

flows the natural flooding regime for wetlands in this region would have been winter/spring inundation once every

5–10 years. River regulation, levee bank construction and draining have greatly reduced the flooding frequency of

these wetlands. Wetlands were selected to reflect a range of water regimes from almost permanently flooded to

almost permanently dry. The 21 wetlands were broadly classified into 3 wetland ‘types’ based on morphology and

origin as described by Pressey (1986):

� Floodplain depressions—9 wetlands resembling ‘lakes’ (if inundated) rather than channels.

� Cut-off meanders—8 lentic channel wetlands originating from changes in the course of the river over time.

Variously identified as cut-off meanders, ox-bow lakes, billabongs, or cut-off channels, these resemble the main

river channel in width and sinuosity and tend to have broad profiles and gentle slopes.

� Flood-runners—4 lentic channel flood-runners carrying water away from the main channel during high flows,

differing from cut-off meanders in origin and profile by being narrower and well incised with steeper margins;

never historically part of the main river channel, but usually closely associated with the present-day main channel.

Wetland water regime classification

For most Australian wetlands there are no long term records of water regime, and information on what plant

species are present is sparse (Australian Nature Conservation Agency, 1996; Brock et al., 2005). For this study two

components of the hydrological cycle were used to classify the water regime of each wetland.

(1) Commence-to-flow (CTF) threshold data for each wetland were obtained from the Murray Wetlands Working

Group in New SouthWales. These thresholds are an estimate of the river height at which a wetland will begin to

Copyright # 2009 John Wiley & Sons, Ltd. River Res. Applic. 26: 866–876 (2010)

DOI: 10.1002/rra

WETLAND VEGETATION AND WATER REGIME 867

Table

I.Locationanddetails

ofthe21wetlandsselected

bywater

regim

eandtype

Pressey

No.�

Wetland

Code

Latitude/Longitude

Type

Statusat

sampling

Category

01/0347

Haw

ksview

347

H347

368050 S

,1478020 E

Floodplain

depression

Dry

Dry

01/0185

Wetland185

W185

368010 S

,1468180 E

Floodplain

depression

Dry

Dry

02/0140

Wetland140

W140

358580 S

,1458530 E

Cut-offmeander

Single

pool

Dry

02/0009

Wetland9

W9

358500 S

,1458330 E

Cut-offmeander

Single

pool

Dry

02/0155

Duck

Hole

DH

358580 S

,1458460 E

Floodplain

depression

Dry

Dry

02/0147

Wetland147

W147

358580 S

,1458520 E

Cut-offmeander

Dry

Dry

01/0290

StantonsBend

SB

368030 S

,1468210 E

Floodplain

depression

Inundated

Interm

ediate

01/0340

Haw

donsLagoonWest

HLW

368050 S

,1478010 E

Cut-offmeander

Inundated

Interm

ediate

02/0179

LittleReedy

LR

358580 S

,1458550 E

Floodplain

depression

Dry

Interm

ediate

02/0234

Wetland234

W234

368010 S

,1458580 E

Floodplain

depression

Dry

Interm

ediate

02/0162

Wetland162

W162

358560 S

,1458420 E

Flood-runner

Isolatedpools

Interm

ediate

02/0115

HorseshoeLagoon

HL

358560 S

,1458410 E

Cut-offmeander

Inundated

Interm

ediate

01/0377

Norm

ansLagoon

NL

368060 S

,1468560 E

Cut-offmeander

Isolatedpools

Interm

ediate

02/0108

Wetland108

W108

358530 S

,1458360 E

Flood-runner

Isolatedpools

Interm

ediate

01/0094

StLeonardsLagoon

SLL

358580 S

,1468260 E

Cut-offmeander

Inundated

Wet

01/0279

Forest

Swam

pFS

368030 S

,1468220 E

Floodplain

depression

Single

pool

Wet

01/0276

LakeMoodem

ere

LM

368030 S

,1468230 E

Floodplain

depression

Inundated

Wet

01/0093

StLeonardsFlood-runner

SLF

358590 S

,1468260 E

Flood-runner

Isolatedpools

Wet

01/0301

LumbysBendLagoon

LB

368030 S

,1468170 E

Floodplain

depression

Inundated

Wet

01/0111

Wetland111

W111

358590 S

,1468250 E

Cut-offmeander

Isolatedpools

Wet

01/0260

RichardsonsBend

RB

368030 S

,1468440 E

Flood-runner

Inundated

Permanent

� Intheinventory

ofMurray

Riverwetlandsprepared

fortheRiverMurray

CommissionbyPressey

(1986),each

wetlandwas

allocatedauniqueidentifyingnumber,herereferred

toas

thePressey

No.Theprefixofthenumber

indicates

inwhichsectionoftheriver

thewetlandislocated;thesuffixisthenumber

ofthewetlandwithin

thesection.


DOI: 10.1002/rra

868 R. BARRETT, D. L. NIELSEN AND R. CROOME

receive water. Individual commence-to-flow thresholds will depend on the wetland’s elevation on the

floodplain, its distance from the river and the nature of its connection channels.

(2) Flow data for the Murray River were supplied by the Murray Darling Basin Commission. Daily data from 1980

to 2005 for gauges between Lake Hume and Tocumwal were supplied as gauge heights (in metres) and flow in

ML/day. The gauges relevant to this study were located immediately downstream of Hume Dam (Heywoods),

at Doctors Point (Albury), at Corowa, below Yarrawonga Weir (D/S Yarrawonga) and at Tocumwal.

Historical daily river heights and the commence-to-flow threshold of each wetland were used to determine when

it received water over the period 1980–2005. The flooding history of each wetland (1980–2005) was then

determined using the total number of days thewetland was connected to the river, the number of flooding events, the

average duration of floods and the average number of years between floods (Table II). It was beyond the scope of

this study to measure drying phases, or the magnitude or season of flows into the wetlands.

From these data the flooding history of each wetland from 1980 to 2005 was determined using following criteria:

� the total number of days the wetland was connected to the river, where connections were continuous for more

than 7 days (see below)

� the number of flood events (i.e. the number of times the river exceeded the commence-to-flow threshold of the

wetland continuously for more than 7 days)

� the average duration of those flood events (in days)

� the duration range of those flood events (in days)

� the average number of years between those flood events.

Cluster analysis of the wetland flooding histories (see Table II), using Primer (version 5.2.9, Primer-E Ltd,

Plymouth, UK), was used to group similar wetlands. Similarities were calculated using normalized Euclidean

distance which gives equal weightage to all parameters (Clarke et al., 2006), an appropriate measure when

multivariate environmental (rather than species) data are being examined (Clarke and Gorley, 2001).

Table II. Wetland and water regime. Flooding summary for wetlands from 1980 to 2005 (for connections to the river longer than7 days)

Wetland Total numberof days

connectedto river

Numberof floods(> 7 days)

Average durationof floods (days)

Durationrange (days)Min Max

Average numberof years betweenfloods (> 7 days)

Hawksview 347 60 4 15 9 24 6.3Wetland 185 60 4 15 10 24 6.3Duck Hole 77 5 16 11 22 5.0Wetland 140 82 5 15 10 22 5.0Wetland 147 82 5 16 11 22 5.0Wetland 9 86 5 17 11 23 5.0Hawdons Lagoon West 431 17 25 8 84 1.5Little Reedy 521 20 26 8 77 1.3Stantons Bend 717 26 28 8 86 1.0Wetland 234 800 21 38 9 102 1.2Wetland 162 1248 33 38 8 138 0.8Normans Lagoon 1343 55 24 8 127 0.5Horseshoe Lagoon 1543 44 35 8 140 0.6Wetland 108 1951 56 35 8 150 0.4St Leonards Flood-runner 3787 79 48 8 208 0.3Lake Moodemere 3843 81 47 8 207 0.3Forest Swamp 4024 73 55 8 244 0.3St Leonards Lagoon 4749 72 66 8 281 0.3Lumby’s Bend Lagoon 5717 54 106 8 309 0.5Wetland 111 5979 54 111 8 311 0.5Richardsons Bend 9338 6 1556 94 6195 N/A


DOI: 10.1002/rra


Vegetation sampling

The perimeter of each wetland was ascertained by eye, utilizing change in slope (usually a clear break in slope

around the rim), topography (the appearance of a well defined basin) and vegetation (often a fringing line of trees or

shrubs). The location of the wetland edge, midway and centre ‘zones’ was based on their location in relation to the

perimeter and centre of each wetland. Because of the variability of wetlands, sites in each zone did not necessarily

have uniform water depth or topography and did not necessarily reflect plant habitat zones as described by Brock

(1994). The edge zone would generally be the first to dry and the last to wet, followed by the midway zone and then

the centre. The centre zone would usually be the deepest when flooded and the area of ponding if the wetland held

water for any length of time.

A single survey of each wetland was undertaken in autumn 2005. To sample each wetland in a consistent

and repeatable manner, transverse and longitudinal transect lines were used to establish 9 sampling sites per

wetland, resulting in 4 edge sites, 4 midway sites and a single centre site (Figure 2). Three replicate 1m2

quadrats were randomly surveyed at each site and estimates of the per cent cover of each plant taxon within each

quadrat were recorded as a measure of vegetation abundance and taxon richness using a modified Braun-Blanquet

assessment (Braun-Blanquet, 1932).

Plants were identified using Aston (1973), Sainty and Jacobs (1981, 2003), Lamp and Collet (1989) and

Romanowski (1998). Macro-algae (charophytes), mosses and liverworts and eucalypt seedlings were not identified

to species level. Terrestrial grasses were grouped together.

Plants were assigned to the broad functional groups of Brock and Casanova (1997), which categorized wetland

plants according to their responses to water regime using the criteria of germination, growth and reproductive

response. The broad functional plant groups used in this study were: Submerged–plants found in the wet region of

the ecotone that do not tolerate drying and need free water for growth and reproduction; Amphibious–plants found

throughout the wet/dry ecotone that tolerate both drying and flooding; Terrestrial: damp–plants that prefer damp

ground and do not tolerate flooding; Terrestrial: dry–plants found in the terrestrial (always dry) region of the

ecotone that prefer dry ground and do not tolerate flooding. A further group was designated as Floating–plants that

float on the surface of the water. Wetland plants were taken to be those that would not be found in terrestrial

environments and included Floating, Submerged, Amphibious, and Terrestrial: damp plants. Terrestrial: dry plants

were assigned to one of 3 groups: terrestrial grasses, Eucalypt seedlings or ‘‘all other Terrestrial: dry plants’’.

Data analysis

The percentage cover of each plant was averaged across all quadrats to give an estimate of percentage cover for

each plant taxon within each wetland. Multivariate analysis of vegetation data (percentage cover) was performed

using Primer (version 5.2.9, Primer-E Ltd, Plymouth, UK) to discern differences in plant communities that

correlated with water regime or wetland type.

Non-metric multidimensional scaling (nMDS) derived from a Bray-Curtis similarity matrix was used to display

patterns of community composition. Analysis of Similarity (ANOSIM) was used to determine if significant

differences existed between different communities. Where ANOSIM indicated significant differences between

communities were occurring Similarity Percentages (SIMPER) were used to explore which taxa were contributing

to the differences between wetland water regime and wetland type.

All analysis was undertaken on square root transformed data so that the influence of more abundant species on

the communities was downgraded. For the analysis of water regime the single ‘Permanent’ wetland was excluded

from the ANOSIM and SIMPER analysis.

RESULTS

Wetland classification

The cluster analysis (Figure 1) separated the wetlands into four categories (Table I):

� Dry: thesewetlands are characterized as being connected to the main river channel on average every 5 years, with

connection only persisting for a period of 15 days. As a result thesewetlands are dry for extended periods of time.


DOI: 10.1002/rra


� Wet: these wetlands are be characterized as being connected to the main river channel on average three times per

year, with each connection persisting for a period of 70 days. As a result water levels in these wetlands fluctuated

never to the extent of drying.

� Permanent: this wetland could be characterized as having permanent connection to the main river channel. This

wetland remained constantly full with stable water levels.

� Intermediate: these wetlands are characterized by being connected to the main river channel annually with

connection usually persisting for a period of 30 days. This annual connection regime will have created a more

variable water regime with water levels fluctuating annually.

Fifty plant taxa were identified from the 21 wetlands (Table III). These plants and their percentage cover within

each wetland were used to assess the differences that water regime and wetland type has on plant communities. It

should be noted that at the time of vegetation sampling some of the wetlands in the ‘Dry’ category contained some

water, as did some of the ‘Intermediate’ category, and all of the ‘Wet’ category contained some water potentially

creating some initial variability in plant communities between wetlands in each category.

Effect of water regime

Forty one plant taxa were recorded from ‘Intermediate’ wetlands, 36 from ‘Dry’ wetlands, 32 from ‘Wet’

wetlands and 14 from the one ‘Permanent’ wetland.

Non-metric Multi-Dimensional Scaling indicated clear differences between the plant communities of Wet, Dry

and Intermediate wetland groups (Figure 3A). These differences in plant community were confirmed by ANOSIM

(P< 0.001) for all water regime combinations (note: ANOSIM was not undertaken on combinations that included

Figure 1. Cluster analysis utilizing the calculated flooding history of each wetland for the period 1980–2005 (refer to Table I for key towetlands)

Figure 2. Generalized scheme for establishing sampling sites within wetlands. *¼ edge sites; &¼midway sites; ~¼ centre site


DOI: 10.1002/rra


the single ‘Permanent’ wetland). SIMPER analysis of the communities within each water regime type revealed that

within the group of ‘Dry’ wetlands 42% of the within taxa similarity was due to the high percentage cover of

terrestrial grasses, with three other taxa contributing substantially to the plant community (Table IV). Within the

‘Intermediate’ group of wetlands 35% of the within group similarity was due to terrestrial grasses, with seven other

taxa having substantial contributions to the community, while the ‘Wet’ group of wetlands was dominated by

Juncus ingens and Persicaria hydropiper. SIMPER analysis indicated there was only 5% similarity between the

plant communities in ‘Dry’ and ‘Wet’ wetlands, 11% similarity between ‘Dry’ and ‘Intermediate’ wetlands and 4%

similarity between ‘Wet’ and ‘Intermediate’ wetlands. Not unsurprisingly, the differences between water regime

types were driven by the plants contributing most to the within group similarities. For example, Juncus ingens was

the dominant plant in the ‘Wet’ wetlands and was rarely found in either the ‘Dry’ or ‘Intermediate’ wetlands.

Effect of wetland type

Forty four plant taxa were recorded from Cut-off meanders, 34 from Floodplain depressions and 28 from Flood-runners.

Non-metric Multi-Dimensional Scaling indicated differences in plant communities were occurring between

Floodplain depressions, Flood-runners and Cut-off meanders (Figure 3B). These differences in plant community

were confirmed by ANOSIM (P< 0.050) for all wetland type combinations SIMPER analysis of the data within each

wetland type revealed that within Floodplain depressions 66% of the within group similarity was due to the high

percentage cover of Juncus ingens and terrestrial grasses, with two other groups also contributing substantially to the

plant community (Table IV).Within theCut-off meander and Flood-runner groups a greater number of taxa contributed

substantially to the plant communities present (Table IV). SIMPER analysis indicated only a 9% similarity between the

plant communities of Floodplain depressions and Cut-off meanders and 3% between the plant communities of

Floodplain depressions and Flood-runners and 4% between Cut-off meanders and Flood-runners.

DISCUSSION

Effect of water regime

In this study, different plant communities were found in wetlands that had been exposed to different water

regimes. Wetlands categorized as being ‘Wet’ were those wetlands that had been previously been exposed to

Table III. Plant taxa collected across the 21 wetlands

SubmergedCharophyte sp. Vallisneria gigantea

AmphibiousCallitriche sp. Juncus cf. usitatus Persicaria cf. prostratumCentella sp. Juncus ingens Persicaria hydropiperCentripedia cf. cunninghamii Juncus sp. Persicaria lapathifiliumCentripedia cf. minima Limosella australis Phragmites australisCrassula cf. helmsii Liverwort Potamogeton sulcatusCyperus cf. difformis Ludwigia palustris Pseudoraphis spinescensCyperus cf. eragrostis Ludwigia peploides Ranunculus sp.Cyperus cf. exaltatus Lythrum hyssopifolia Sagittaria gramineaCyperus sp. Moss Typha spDamasonium minus Myriophyllum sp. Un. creeping groundcoverEclipta sp Paspalum paspalodes 3 unidentified dicotsElatine gratioloides Persicaria cf. decipiens 1 unidentified monocotFloating 3 unidentified unknownsAzolla sp. Lemna sp.

Terrestrial: dampAlternanthera cf. denticulata Aster subulatus Cardamine sp.Alternanthera sp. Brassica sp. Conyza bonariensis

Terrestrial: dryTerrestrial grasses Eucalypt spp. All other Terrestrial:dry


DOI: 10.1002/rra


extended periods of inundation, and these were dominated by a single species, Juncus ingens. Previous research has

indicated that prolonged inundation leads to low plant diversity (van der Valk et al., 1994; Nielsen and Chick,

1997). Juncus ingens is typically abundant on the edges of wetlands and is well suited to permanent inundation

(Pressey, 1990). Our findings are consistent with the proposal that permanent inundation may produce edge or

shallow water zones dominated by stands of one or two species and a loss of ephemeral and terrestrial taxa (Brock,

1994; Nielsen and Chick, 1997). The presence of standing water also affects the ability of some aquatic plants to

germinate (Fennessey et al., 1994; Brock and Casanova, 1997), leading to limited recruitment of new species in

those zones and a subsequent reduction in species richness (Brock and Casanova, 1997; Bornette et al., 1998). The

dominant plants that thrive in near-permanently inundated wetlands are often those that can spread vegetatively (in

this study, J. ingens). The wetlands in the ‘Dry’ group were also dominated by fewer plants with terrestrial grasses

being the most common. This finding is consistent with the proposal that as wetlands become more permanently

Figure 3. nMDS ordinations of plant communities for each wetland, grouped by (A) Water regime and (B) Wetland type. Stress¼ 0.16


DOI: 10.1002/rra


‘dry’ plant communities will become more dominated by terrestrial species (Brock and Casanova, 1997). In

comparison the ‘Intermediate’ group of wetlands had more variable water regimes (as defined by the commence to

flow data and historical Murray River flow data) than the other groups, and historically had annual cycles of

flooding, with short connection times that would have resulted in more variable and fluctuating water regimes, and

consequently more plants contributing to the community (Brock and Casanova, 1997; Bornette et al., 1998). This is

consistent with the intermediate disturbance hypothesis, which predicts a maximum diversity of species at

intermediate levels of disturbance, where more heterogeneous habitat patches exist supporting a wide range of

species (Connell, 1978). Although drying following flooding has been shown to enhance the germination of many

wetland plants (Brock and Casanova, 1997; Brock et al., 2000), wetlands experiencing either prolonged drying or

wetting will have wetland plant communities with reduced abundance and diversity (Bornette et al., 1998;

Casanova and Brock, 2000).

Table IV. Dominant plant groups (contributing 90%) within each wetland group and within each wetland type (SIMPERresults—square root transformed data)

Taxa Average %cover

%contribution

Cumulative %contribution

Water regime‘Dry’ (No. of taxa¼ 36) Terrestrial Grasses 3.07 41.77 41.77

All other ‘terrestrials-dry’ 3.56 32.03 73.8Persicaria cf. prostratum 1.67 12.17 85.97Juncus cf usitatus 0.87 3.56 89.53

‘Intermediate’ (No. of taxa¼ 41) Terrestrial Grasses 1.54 34.74 34.74All other ‘terrestrials-dry’ 1.47 21.6 56.34Pseudoraphis spinescens 0.63 9.49 65.83Juncus cf. usitatus 0.62 8.38 74.21Myriophyllum spp. 0.64 6.29 80.5Juncus ingens 0.62 4.91 85.41Alternanthera denticulata 0.41 3.6 89.01Ludwigia peploides 0.33 2.92 91.93

‘Wet’ (No. of taxa¼ 32) Juncus ingens 3.39 80.61 80.61Persicaria hydropiper 1.2 12.86 93.47

Wetland typeFloodplain depression (No. of taxa¼ 34) Terrestrial Grasses 2.49 33.36 33.36

Juncus ingens 2.51 33.17 66.53All other ‘terrestrials-dry’ 2.52 22.14 88.67Persicaria hydropiper 0.79 4.28 92.95

Cut-off meander (No. of taxa¼ 44) Persicaria cf. prostratum 1.17 18.95 18.95Terrestrial Grasses 1.02 18.89 37.84All other ‘terrestrials-dry’ 1.06 13.9 51.74Juncus ingens 0.85 10.02 61.77Juncus cf. usitatus 0.67 8.95 70.72Alternanthera denticulata 0.4 4.92 75.64Terrestrial weed sums 0.35 4.12 79.76Pseudoraphis spinescens 0.51 2.99 82.75Myriophyllum spp. 0.41 2.82 85.57Persicaria hydropiper 0.32 1.91 87.48Cyperus eragrostis 0.2 1.89 89.37

Flood-runner (No. of taxa¼ 28) Myriophyllum spp. 1.01 24.82 24.82Juncus cf. usitatus 0.6 19.91 44.73Pseudoraphis spinescens 0.5 16.55 61.28Terrestrial Grasses 0.41 10.24 71.52Cyperus eragrostis 0.35 6.88 78.4Potamogeton sulcatus 0.2 5.25 83.65Ludwigia palustris 0.41 3.53 87.18


DOI: 10.1002/rra


Effect of wetland type

Significantly different plant communities were present in the different types of wetlands. Wetland type could

primarily be defined by morphology and location in association with the main river channel. Their location on the

floodplain influences when wetlands receive water and also the depth, duration and frequency of flooding (Walker

and Thoms, 1993; Reinelt et al., 1998; Shaffer et al., 1999) both of which will influence wetland plant communities

(Brock and Casanova, 1997).

High velocity scouring floods that disturb wetland biota and scour wetland substrates (Reinelt et al., 1998) may

be typical of flood-runners and cut-off meanders. Floodplain depressions may rather be flooded during overbank

flows, and potentially experience higher water levels and a greater extent and duration of inundation (Shaffer et al.,

1999), allowing different plant communities to develop to those in wetlands experiencing shorter flood durations in

particular.

CONCLUSION

The results from our work indicate that plant communities within floodplain wetlands are influenced by both

wetland type and water regime, and that within a particular riverine landscape an array of wetland types influenced

by a variety of water regimes will maximize wetland plant diversity. Our study also indicates that if wetlands are

flooded or dry for too long plant communities will become dominated by fewer species potentially resulting in

reduced plant diversity within the landscape, and that managing river flows to maintain variable connectivity may

help to restore a diversity of vegetation in wetlands that, under current flow regimes, are experiencing a loss of

species due to either prolonged inundation or prolonged drying phases.

ACKNOWLEDGEMENTS

The authors thank the Department of Environmental Management and Ecology at La Trobe University and the

Murray Darling Freshwater Research Centre for their support, the New South Wales Murray Wetlands Working

Group for supplying wetland data and the Murray Darling Basin Commission for supplying data and information

regarding Murray River flows. Authors thank Kat Breaks, Carrie Frost and Rebecca Chettleburgh for assistance

with field work, and Roz Webb (Hawksview landholder) for her assistance and ongoing commitment to wetland

rehabilitation on farms.

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associations between the plant communities of floodplain wetlands, water regime and wetland type

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