the value of plant functional groups in demonstrating and communicating vegetation responses to...

The value of plant functional groups in demonstrating andcommunicating vegetation responses to environmental flows

C. J . CAMPBELL*, C. V. JOHNS* , † AND D. L. NIELSEN‡

*Murray–Darling Freshwater Research Centre and Latrobe University, Mildura, VIC, Australia†Centre for Mined Land Rehabilitation, The University of Queensland, Brisbane, QLD, Australia‡Murray–Darling Freshwater Research Centre and CSIRO Land and Water, La Trobe University, Wodonga, VIC, Australia

SUMMARY

1. This study compares the effectiveness of using plant species, genera, family or water plant func-

tional group (WPFG) classifications for demonstrating differences in vegetation communities associ-

ated with inundation history.

2. Vegetation surveys were undertaken annually for 5 years from 2007–2008 to 2011–2012 at 18 flood-

plain wetlands. These wetlands are from two geographically separate locations situated along the

lower Murray River. Wetlands have different inundation histories and have received varied amounts

of environmental water since 2004. All plant species recorded were classified into WPFGs. An inun-

dation classification was determined for each wetland at each survey time based on inundation his-

tory and inundation status at the time of survey (wet or dry).

3. This study found that plant species composition at individual wetlands is often unique with few

species recorded across multiple wetlands. The use of WPFGs reduced the variability of plant com-

munities between individual wetlands, between the two geographic locations and within inundation

classifications. By reducing the variability between samples, broad trends in vegetation responses to

different watering histories can be identified.

4. Individual wetlands can develop completely different suites of plant species in response to the

same watering regime, particularly when separated over large distances. This variability can reduce

the confidence managers have in predicting the plant communities likely to develop in response to

prescribed watering regimes. Adaptively applying knowledge gained from monitoring to different

wetlands or wetlands in different geographical regions is also difficult if responses are highly vari-

able.

5. This study demonstrates that by classifying wetland vegetation into WPFGs the variability

observed between samples can be reduced and the influence of floristic differences between individ-

ual wetlands and geographic locations can be negated or lessened. We discuss how the use of

WPFGs can assist scientists and managers in demonstrating, predicting and communicating trends in

vegetation community responses as a result of different watering regimes. The adoption and applica-

tion of a consistent approach to the classification of plant species into WPFGs has the potential to

enable responses and predictions to watering events to be made across broad spatial scales.

Keywords: monitoring, plant classification, River Murray, water regime, wetlands

Introduction

Water regime, and in particular the presence or absence

of water, is recognised as being one of the main drivers

of patterns in wetland plant species composition (Brock

& Casanova, 1997; Casanova & Brock, 2000; Brock, 2011;

Roberts & Marston, 2011). Demonstrating and predicting

wetland vegetation responses to different watering

regimes can be difficult in intermittent floodplain wet-

lands. Plant communities in these habitats can exhibit

Correspondence: Cherie Campbell, Murray-Darling Freshwater Research Centre, P.O. Box 3428, Mildura, VIC, 3502, Australia. E-mail:

[email protected]

858 © 2014 John Wiley & Sons Ltd

Freshwater Biology (2014) 59, 858–869 doi:10.1111/fwb.12309

extensive spatial and temporal variability in species

composition and abundance (Boulton & Brock, 1999;

Alexander, Nielsen & Nias, 2008; Barrett, Nielsen &

Croome, 2010). This inherent variability may reduce the

confidence water managers have in predicting the plant

communities likely to result from prescribed watering

regimes. Ideally, knowledge gained from monitoring

vegetation responses can be adaptively applied to differ-

ent wetlands or geographical regions. This study dem-

onstrates that by classifying wetland vegetation into

water plant functional groups (WPFGs) (sensu Casa-

nova, 2011), the variability observed between vegetation

communities can be reduced and the ability to detect

broad trends applicable across different geographic loca-

tions can thereby be increased.

Plant functional group classifications have been

designed and used for a variety of purposes (Van Der

Valk, 1981; Boutin & Keddy, 1993; Brock & Casanova,

1997; Willby, Abernethy & Demars, 2000). Selection of

the most appropriate functional group classification

depends on the purpose of the study. If the classification

is based on responses to a particular disturbance, such

as flooding, then the functional groups produced can be

useful in interpreting and predicting change in commu-

nity composition relating to that disturbance (Noble &

Gitay, 1996; Brock & Casanova, 1997). In the case of

assessing the potential benefits of environmental water-

ing to plant communities, the primary objectives are (i)

to demonstrate effect and (ii) to identify any overarching

response trends. The latter is vital for managers to be

able to learn from experience, increase ecological under-

standing and make use of adaptive management princi-

ples to improve future environmental outcomes. This is

particularly critical where water resources are highly

limited and financial and logistical constraints prohibit

the assessment of vegetation responses to numerous

potential watering regimes at every wetland. The over-

arching purpose of functional classification is to help

synthesise large, complex data sets and to identify gen-

eral trends, by simplifying inherent taxonomic diversity

while retaining information about the relevant processes

and interactions of interest (Noble & Gitay, 1996; Willby

et al., 2000).

Brock & Casanova (1997) used 6 years of germination

data to develop a functional group classification defined

by species responses to wetting and drying, recently

termed water plant functional groups (WPFGs) by Casa-

nova (2011). This classification clearly distinguished

groups of species capable of occurring in different

hydrological habitat niches, ranging from those species

with no tolerance of or dependence on flooding, through

to species that require standing water for all active

growth stages. A number of recent studies in Australia

have used Brock & Casanova’s (1997) WPFGs (Casanova

& Brock, 2000; Reid & Quinn, 2004; Raulings et al., 2010;

Casanova, 2011). The characterisation of wetland plant

communities based on species responses to wetting and

drying has great potential. It can help determine the

water regimes required to sustain these communities in

different parts of catchments and in different climatic

areas (Casanova, 2011).

In this study, we compare the use of plant species

with various levels of classification from genera and

family to WPFGs to assess community responses to

water regimes and to explore differences between two

wetland complexes associated with the River Murray.

Specifically, we aim to determine (i) whether by focus-

ing on either higher taxonomic levels or WPFGs, the

variability in plant community composition between

wetlands and geographic regions will be reduced com-

pared with that found in species-level data, and (ii)

whether trends in community composition based on

differences in watering history become more apparent as

a result. We anticipate that reduced variability through

the use of WPFGs will lead to improvements in the abil-

ity of scientists and water managers to demonstrate,

generalise and predict plant community responses to

alterative watering regimes.

Methods

Study area and hydrology

This study was undertaken at 18 wetlands from two dif-

ferent geographic locations comprising sections of the

River Murray floodplain, in the lower Murray–Darling

Basin, Australia (Fig. 1). Nine of the wetlands are from

Hattah Lakes (HL) floodplain wetland complex and

nine are from Lindsay, Mulcra and Wallpolla (LMW)

Islands floodplain wetland complexes. HL encompasses

c. 13 000 ha of lakes and floodplain. LMW covers an

area of 26 156 ha and is dissected into its component

sections by three anabranches of the River Murray

(MDBC, 2006). Both HL and LMW are characterised by

intermittent and perennial freshwater lakes, billabongs,

anabranches and creeklines. Typical vegetation commu-

nities include aquatic macrophytes and lake-bed herb-

lands, Eucalyptus camaldulensis Dehnh. (River Red Gum)

forests and woodlands, E. largiflorens F. Muell. (Black

Box) woodlands, and Muehlenbeckia florulenta Meisn.

(Lignum) shrublands. HL and LMW are situated within

a semi-arid climate zone, with mean annual rainfall of

© 2014 John Wiley & Sons Ltd, Freshwater Biology, 59, 858–869

The value of plant functional groups 859

https://www.researchgate.net/publication/264240348_Plant_life_at_the_edge_of_wetlands_ecological_responses_to_wetting_and_drying_patterns?el=1_x_8&enrichId=rgreq-87d6dd05-420e-4ded-9d2e-3e2bddc0bf61&enrichSource=Y292ZXJQYWdlOzI2MDMwNjM2NjtBUzoyMjA0NTI5MzgwOTY2NDFAMTQyOTU3MTQ4NDE2MA==

https://www.researchgate.net/publication/263490860_Using_water_plant_functional_groups_to_investigate_environmental_water_requirements?el=1_x_8&enrichId=rgreq-87d6dd05-420e-4ded-9d2e-3e2bddc0bf61&enrichSource=Y292ZXJQYWdlOzI2MDMwNjM2NjtBUzoyMjA0NTI5MzgwOTY2NDFAMTQyOTU3MTQ4NDE2MA==

https://www.researchgate.net/publication/227764637_A_functional_classification_for_predicting_the_dynamics_of_landscapes_J_Veg_Sci_7329-336?el=1_x_8&enrichId=rgreq-87d6dd05-420e-4ded-9d2e-3e2bddc0bf61&enrichSource=Y292ZXJQYWdlOzI2MDMwNjM2NjtBUzoyMjA0NTI5MzgwOTY2NDFAMTQyOTU3MTQ4NDE2MA==

311.7 mm and 284.5 mm, respectively, and mean annual

evaporation rates exceeding rainfall (BOM, 2013).

The hydrology of floodplain wetlands in these systems

is driven by overbank floods, typically resulting from

rainfall in distant upstream catchment areas. The avail-

ability of surface water and the frequency of small to

medium overbank flood events in the mid-lower reaches

of the River Murray has decreased substantially due to

the stabilising effects of a series of large weirs and water

storage dams (CSIRO, 2008). During the millennium

drought (2000–2010), overbank flooding did not occur.

To mitigate the impacts of the drought, intermittent

pumping of environmental water into selected flood-

plain wetlands was implemented as an emergency mea-

sure from 2004 at both HL and LMW to maintain

wetland and floodplain flora and fauna communities.

Fourteen of the 18 wetlands received environmental

flows between spring 2004 and December 2010, with

inundation frequency varying between wetlands. A nat-

ural flood event in 2010–2011 inundated all surveyed

wetlands.

Vegetation assessment

Vegetation community composition and species abun-

dance data were collected annually on five occasions,

between December and March from 2007–2008 to 2011–

2012, from the 18 wetlands (MDFRC, 2012a,b). In each

wetland, four permanent transects (three for two wet-

lands established as part of an earlier study) were estab-

lished extending from the lowest to highest elevation,

with fixed (15 9 1 m) quadrats established at regular

(30 or 50 cm) elevation intervals depending on the mor-

phology of individual wetlands. The number of eleva-

tions sampled along transects varies depending on the

depth and size of the wetland, with elevations ranging

from the base of the wetland to wetland edge (Fig. 2).

During each survey, all live plant species with their

bases located inside the quadrat were recorded and

given a frequency score out of 15, according to the num-

ber of one-square-metre cells per quadrat the species

occurred in. These methods follow those employed in

previous work conducted on the Chowilla floodplain

that adjoins LMW, with sampling intensity and quadrat

size based on species area curves (Nicol & Weedon,

2006). Plants were identified using keys and descriptions

in floras (Harden, 1992, 1993, 2000, 2002; Walsh & En-

twisle, 1994, 1996). Plant names follow Walsh & Stajsic

(2007).

Functional group classification

Each plant species recorded was classified into one of 10

water plant functional groups (WPFGs) based on those

developed by Brock & Casanova (1997) and Casanova

(2011). The WPFGs were as follows: (i) terrestrial plants

that typically do not tolerate flooding (Tdr); (ii) terres-

trial plants that grow in damp places (Tda); (iii) woody

amphibious plants that tolerate wetting and drying

(ATw); (iv) emergent amphibious plants that tolerate

wetting and drying (ATe); (v) low-growing amphibious

plants that tolerate wetting and drying (ATl); (vi)

amphibious plants that respond to flooding with differ-

ent growth forms (ARp); (vii) amphibious plants with

floating leaves when flooded (ARf); and (viii) submerged

plants (S). Additionally, where there was insufficient

Fig. 1 The location of the two study areas, Lindsay-Mulcra-Wallpo-

lla Islands and Hattah Lakes, Murray–Darling Basin, Australia. The

symbols (▲) indicate the location of wetlands.

Fig. 2 Schematic of the survey design used to assess understorey

vegetation at wetland sites.


860 C. J. Campbell et al.

information known about a plant to classify into a spe-

cific group they were classified as either (ix) amphibious

(A): species that require damp conditions for germina-

tion and tolerate or respond to fluctuations in wetting

and drying; or (x) terrestrial (T): species that do not tol-

erate wetting. Species that could not be identified were

excluded from classification. Where possible, species

were classified according to published literature (Brock

& Casanova, 1997; Casanova, 2011). Previously unas-

signed species were classified into WPFGs using infor-

mation from published floras (Sainty & Jacobs, 1981,

2003; Cunningham et al., 1992; Harden, 1992, 1993, 2000,

2002; Walsh & Entwisle, 1994, 1996), field observations

from 5 years of surveys and seed bank germination tri-

als conducted in damp and inundated conditions

(authors’ unpublished data). The plant species list, with

functional group allocations used in our data analysis, is

provided in Supporting Information (see Table S1).

Inundation classification

For each sampling event, wetlands were categorised

into one of three inundation classifications based on

differences in their inundation history and hydrological

phase (Table 1). These classifications were as follows:

(i) ‘long-dry’ (LD) – wetlands dry for at least 2 years

and with no more than one inundation event in the

preceding 7 years; (ii) ‘intermittent-dry’ (ID) – wetlands

that were dry when surveyed but had held water in

the previous 2 years; and (iii) ‘intermittent-inundated’

(II) – wetlands with at least one elevation of quadrats

inundated at the time of survey. This classification

included wetlands that were completely or partially

inundated.

Analysis

Multivariate analyses of patterns in (i) plant species, (ii)

genera, (iii) family and (iv) WPFG composition and abun-

dance were carried out in PRIMER (V6.1.10), with the

PERMANOVA+ add in (PRIMER-E, Plymouth, U.K.)

(Anderson, Gorley & Clarke, 2008). Average abundances

were calculated based on data pooled at the individual

wetland level, per survey (i.e. averaged across quadrats

from all transects and elevations, for each wetland, for

each survey, according to (i) plant species, (ii) genera, (iii)

family and (iv) WPFGs). Prior to analysis, data were

square-root-transformed and the Bray–Curtis resemblance

measure applied to generate a resemblance matrix for

each category.

Two-way permutational multivariate analysis of vari-

ance (PERMANOVA) (Anderson et al., 2008) was used

Table 1 Classification of wetlands at Hattah Lakes and Lindsay-Mulcra-Wallpolla Islands into one of three inundation categories for each of

the 5 years of surveys based on inundation status at the time of survey (summer) and recent water regimes

Location Wetland name

Survey years

2007–2008 2008–2009 2009–2010 2010–2011 2011–2012

HL Chalka Creek ID ID II II II

HL Lake Boich LD LD LD II II

HL Lake Brockie ID ID LD II II

HL Lake Bulla II ID ID II II

HL Lake Hattah II ID II II II

HL Lake Little Hattah ID ID II II II

HL Lake Mournpall II ID II II II

HL Lake Nip Nip LD LD LD II II

HL Lake Yerang ID ID II II II

LMW Bilgoes Billabong LD LD LD II ID

LMW Crankhandle ID II ID II ID

LMW Lilyponds ID II II II II

LMW Mulcra Horseshoe Lower ID II II II II

LMW Mulcra Horseshoe Upper ID ID ID II II

LMW Upper Lindsay

Wetland Complex

LD LD LD II II

LMW Upper Mullaroo

Wetland Complex

ID ID II II* ID

LMW Webster’s Lagoon ID ID II II* II

LMW Wetland 33 LD LD LD II* II

LD, long-dry; ID, intermittent-dry; II, intermittent-inundated.

*On-ground surveys of these three wetlands were not possible in 2010–2011 due to access restrictions at the peak of the flood: inundation

information is based on aerial surveys and photography.



to determine whether significant differences could be

detected between inundation classification and wetland

sites and between inundation classification and flood-

plain region, and to determine whether there were inter-

actions between these pairings of factors. Where

significant effects of main factors, or interactions

between terms were detected, pairwise PERMANOVA

analyses were undertaken to identify which combina-

tions of levels within factors differed significantly and/

or to identify the sources of the interactions. All factors

used in all PERMANOVA analyses were fixed. All PER-

MANOVA analyses were performed using 9999 permu-

tations of the data and type III (partial) sums of squares,

with permutation under a reduced model as recom-

mended by Anderson et al. (2008).

Non-metric multidimensional scaling (nMDS), derived

from the Bray–Curtis similarity matrices for plant spe-

cies and WPFGs, was used to display patterns of com-

munity composition between location and inundation

classification (Clarke & Warwick, 2001). The variability

of communities within each of the three inundation clas-

sifications was visually represented by graphing the

average Bray–Curtis similarity of the three levels within

the factor ‘inundation classification’ for (i) plant species,

(ii) genera, (iii) family and (iv) WPFGs.

Similarity Percentages (SIMPER) analysis was used to

determine (i) the similarity of communities within inun-

dation classifications, (ii) the number and type of spe-

cies, genera, family or WPFGs that contributed 90% to

the similarities and (iii) the number and type of species,

genera, family or WPFGs that individually contributed

≥10% similarity. This information was used to describe

which plant species or WPFGs characterised specific

inundation classifications and to help predict the vegeta-

tion community likely to respond to particular watering

regimes. The mean number of plant species in each

WPFG and the mean number of WPFG’s present in each

wetland and survey were calculated for each of the three

inundation classifications. One-way analysis of variance

was used to determine whether there were differences

in the mean number of WPFGs. Pairwise comparisons

were undertaken using the Holm–Sidak method (Sigma-

Plot, version 11; Systat Software, San Jose, CA).

Results

Variability between wetlands

A total of 270 plant species were identified across the

wetlands. Of these, approximately 30% were unique to

only one of the 18 wetlands surveyed, with only one

species (c. 0.4%) common to all 18 wetlands (Fig. 3a).

A similar pattern was observed for genera (Fig. 3b)

and to a lesser extent for family (Fig. 3c). In contrast,

the reverse pattern was observed when the plant com-

munity data were classified as WPFGs with approxi-

mately 30% of WPFGs common to all wetlands

(Fig. 3d). Two-way PERMANOVA comparing plant

community composition at wetlands of similar inunda-

tion status at the time of survey (i.e. inundation classi-

fication) confirmed that plant communities differed

significantly between wetlands based on (i) plant spe-

cies, (ii) genera and (iii) family (P < 0.001 for all three).

However, plant communities were not significantly dif-

ferent between wetlands (P = 0.205) when classified as

WPFGs (Table 2).

Location and inundation classification

nMDS of the plant community data at each location

based on plant species composition and abundance

(Fig. 4a) indicates that there were some differences

between the communities occurring in each geographic

region as well as between some of the different inunda-

tion classification groups. These differences were con-

firmed by two-way PERMANOVA (P < 0.001 for main

effects of location and inundation classification)

(Table 3), which also detected a significant interaction

between location and inundation classification

(P < 0.001, Table 3) based on plant species composition

and abundance. Similar PERMANOVA results were

observed based on genera and family classification

(Table 3). In contrast, the nMDS plot based on WPFG

data does not show such strong differences in commu-

nity composition between regions (Fig. 4b). This obser-

vation was supported by the results of the

PERMANOVA based on WPFG data; no interaction was

detected between location and inundation classification

and the communities present did not significantly differ

between the two locations (P = 0.050) based on WPFG

composition and abundance (Table 3). The results of

pairwise comparisons indicated significant differences

(P < 0.001) in community composition between all pairs

of inundation categories for (i) plant species, (ii) genera,

(iii) family and (iv) WPFGs. Vectors indicating trends in

the relative abundance of different WPFGs (Fig. 4b) indi-

cate that a number of intermittent-inundated wetlands

are separated based on the presence and abundance of

plant species in the amphibious-floating (ARf) WPFG.

While long-dry wetlands are predominantly clustered

based on the presence and abundance of plant species in

the terrestrial-dry (Tdr) WPFG.



Variability between inundation classifications

The similarity of vegetation communities within inunda-

tion classification groups was consistently higher with

the use of WPFGs compared with plant species, genera

or family (Fig. 5). Using data based on plant species,

abundance and composition SIMPER analysis indicates

that there were no plant species that could be used reli-

ably to describe or discriminate between the inundation

classifications (Table 4). For example, according to

SIMPER, the average similarity between plant communi-

ties within the intermittent-inundated classification was

only 9.89%. Thirty-three plant species were required to

explain 90% of the similarity and only one species con-

tributed 10% or more similarity between wetlands in

this group (Table 4). The similarities of plant communi-

ties within inundation classifications progressively

increased from plant species to genera, family and

WPFGs (Fig. 5, Table 4). Using WPFGs, the similarities

of plant communities within inundation classifications

were increased and the functional groupings of species

describing the similarities within inundation classifica-

tions and differences between inundation classifications

were also clearer. For example, the long-dry wetlands

were dominated by terrestrial plants and the intermit-

tent-inundated wetlands by floating (ARf) and flood

tolerant or damp-loving (Tda) species (Table 4). Sub-

merged (S) and amphibious responder (ARp) WPFGs

were not influential in describing the similarities within

inundation classifications (Table 4). Species in these

WPFGs were only recorded from intermittent-inundated

wetlands sporadically and typically at low abundances.

Differences in taxonomic diversity according to inundation

classification

Wetlands that were classified as long-dry had fewer

WPFGs present per wetland per survey (mean =

3.53 � 0.74) compared with wetlands classified as

intermittent-dry (mean = 4.85 � 0.99) and intermittent-

inundated (mean = 3.93 � 2.34). One-way ANOVA

returned a significant difference (P = 0.044) between

inundation classifications; however, pairwise compari-

sons showed no significant differences between classifi-

cation groups (unadjusted P > critical level). While

pairwise comparisons showed that the mean numbers

of WPFG present were not significantly different, the

composition of WPFGs differed between inundation

classifications (Table 4).

The average number of plant species present within

each WPFG per wetland per survey also differed

(a)

(b)

(c)

(d)

Fig. 3 Percentage occurrence (presence/absence) of (a) individual

plant species, (b) genera, (c) families and (d) water plant functional

groups (WPFGs) at one wetland (highly localised) through to all 18

wetlands (common), LMW and Hattah Lakes, 2008–2012 (n) (a) 270

plant species; (b) 134 genera; (c) 54 families; (d) 10 WPFGs.



between the inundation classifications (Fig. 6). Species in

the submerged (S) and amphibious-floating (ARf)

WPFGs were only present at wetlands classified as inter-

mittent-inundated. This inundation classification also

had the greatest mean number of species in the amphibi-

ous-plastic responder (ARp) WPFG. In contrast, wetlands

Table 2 Results of the main-effect PERMANOVA comparing vegetation composition and abundance between inundation classification and

wetland sites for (i) plant species, (ii) genera, (iii) family and (iv) water plant functional groups (WPFGs)

Source d.f. SS MS F P (perm) Unique perms

Plant species Inundation classification 2 24949 12474 5.247 <0.001 9921

Wetland site 17 80233 4720 1.985 <0.001 9756

Inundation classification x Wetland site* 19 48303 2542 1.069 0.268 9768

Residual 48 114120 2378

Genera Inundation classification 2 25459 12729 6.839 <0.001 9911

Wetland site 17 69646 4097 2.201 <0.001 9771

Inundation classification 9 Wetland site* 19 38014 2001 1.075 0.306 9812

Residual 48 89347 1861

Family Inundation classification 2 17760 8880 6.048 <0.001 9911

Wetland site 17 49563 2915 1.986 <0.001 9771


Residual 48 70475 1468

WPFG Inundation classification 2 10602 5301 6.226 <0.001 9947

Wetland site 17 17095 1006 1.181 0.205 9853


Residual 48 40870 851

*Term has one or more empty cells.

(a)

(b)

Fig. 4 Non-metric multidimensional scaling (nMDS) ordination comparing (a) plant species composition and (b) WPFG composition between

18 wetlands over five separate annual surveys. Symbols indicate inundation classification of the wetlands at the time of survey and distinguish

between the geographical location of the wetland sites (HTH = Hattah Lakes, LMW = Lindsay-Mulcra-Wallpolla Islands). Vectors (b) display

the direction and extent of influence of WPFGs on the separation of sample points. (Tdr = Terrestrial-dry, Tda = Terrestrial-damp, T = Terres-

trial, ATl = Amphibious tolerator (low-growing), ATe = Amphibious tolerator (emergent), ATw = Amphibious tolerator (woody),

ARp = Amphibious responder (plastic growth), ARf = Amphibious responder (floating leaves), A = Amphibious, S = Submerged).



classified as long-dry had the greatest mean number of

species present in the terrestrial-dry (Tdr) WPFG with

very few species recorded on average from any of the

amphibious WPFGs. Wetlands classified as intermittent-

dry had the greatest mean number of species recorded

from the terrestrial-damp (Tda) WPFG as well as from

two of the amphibious WPFGs (ATe and ATl). Regard-

less of inundation classification, the average number of

plant species was greatest in terrestrial WPFGs (Tdr and

Tda), with fewer species recorded on average in amphib-

ious and submerged WPFGs. The mean number of plant

species recorded in WPFGs per wetland was highly vari-

able (Fig. 6).

Discussion

In this study, we compared the use of WPFGs with three

levels of taxonomic data; (i) plant species, (ii) genera

and (iii) family, to assess vegetation responses to differ-

ent water regimes. We found that analysis of data using

WPFGs enabled trends, based on differences in watering

history, to be detected across wetlands from two

spatially distant floodplain regions. These consistent dif-

ferences were not detected in the species, genus or fam-

ily level analyses because of the higher inter-regional

variability found in these data sets. The use of WPFGs

reduced the ‘noise’ caused by the spatial variability in

floristic data found at these other taxonomic classifica-

tion levels. This enabled generalisations to be made

about the composition and relative abundances of

WPFGs within wetlands from different inundation

classifications. These generalisations are applicable to

wetlands across both survey regions.

Our detection of consistent differences in community

composition associated with inundation history provides

a useful basis for predicting the WPFGs likely to occur

at other sites under the three broad watering regimes

described. Our results also highlighted issues such as

the paucity of particular groups of species expected to

occur in inundated wetlands, such as submerged (S) and

Table 3 Results of the main-effect PERMANOVA comparing vegetation composition and abundance between geographic location and inun-

dation classification for (i) plant species, (ii) genera, (iii) family and (iv) water plant functional groups (WPFGs)

Source d.f. SS MS F P (perm)

Unique

perms

Plant species Location 1 18805 18805 6.996 <0.001 9895

Inundation classification 2 38342 19171 7.133 <0.001 9900

Location 9 Inundation classification 2 13158 6579 2.448 <0.001 9874

Residual 81 217710 2688

Genera Location 1 16412 16412 7.546 <0.001 9928


Location 9 Inundation classification 2 9986 4993 2.296 0.002 9900

Residual 81 176160 2174

Family Location 1 8259 8259 4.885 <0.001 9928



Residual 81 136930 1691

WPFG Location 1 2054 2054 2.553 0.050 9953



Residual 81 65171 805

Fig. 5 Average Bray–Curtis similarity of vegetation communities

within inundation categories according to (i) plant species, (ii)

genera, (iii) family and (iv) water plant functional groups (WPFG),

calculated from PERMANOVA pairwise comparisons of the three

levels within the factor ‘Inundation classification’.



amphibious responder (ARp) WPFGs. This highlights

the need to investigate why these particular groups of

species are not more common in the sampled plant com-

munities during inundation phases.

The results of our vegetation surveys were consistent

with those of others who have previously demon-

strated that plant species composition at individual

wetlands is often highly site-specific, with very few

species common across a large number of wetlands

(Brock et al., 2003; Alexander et al., 2008; Barrett et al.,

2010). We found that this was also true of genera, which

were often particular to wetlands, and to a lesser extent

families. While the floristic uniqueness of individual

wetlands is interesting from a biodiversity point of view,

the high degree of variability in species composition

between wetlands makes predictions or generalisations

about plant community responses under different water

management regimes difficult. By classifying individual

wetlands at each annual survey into one of three inunda-

tion categories, we were able to compare vegetation

communities within and between groups of wetlands dif-

fering in inundation history and hydrological phase.

While there were still significant differences in the plant

species assemblages recorded between inundation classi-

fications, the similarity of plant species communities

between individual wetlands within inundation classifi-

cations was relatively low. This supports previous find-

ings that, at the species level, plant community responses

to watering regimes often vary significantly between

individual wetlands (Alexander et al., 2008; Barrett et al.,

2010). By reducing the number of response variables

used in the current study (in this case from 270 species

to 10 WPFGs), the similarity of communities between

wetlands within each inundation classification greatly

increased and the significant differences between indi-

vidual wetlands were removed.

One of the benefits of being able to reduce the

variability between samples is in being better able to

Table 4 Similarity percentages (SIMPER) analysis of (i) plant species, (ii) genera, (iii) family and (iv) water plant functional group contribu-

tions to the similarity of vegetation communities within inundation categories

Inundation

classification

SIMPER

av. similarity

No. of species, genera, families or

WPFG required to explain ≥90%cumulative contribution

Plant species, genera, family or WPFG with ≥10%contribution

Plant

species

Long-dry 29.13 19 species 1 species (Enchylaena tomentosa var. tomentosa)

Intermittent-dry 23.46 30 species 2 species (Glycyrrhiza acanthocarpa, Centipeda minima

ssp. minima)

Intermittent-inundated 9.89 33 species 1 species (Sphaeromorphea australis)

Genera Long-dry 42.09 12 genera 2 genera (Enchylaena and Rhagodia)

Intermittent-dry 30.82 21 genera 2 genera (Glycyrrhiza and Enchylaena)

Intermittent-inundated 12.32 22 genera 2 genera (Eucalyptus and Sphaeromorphaea)

Family Long-dry 40.74 8 families 3 families (Chenopodiaceae, Fabaceae, Myrtaceae)

Intermittent-dry 37.73 12 families 3 families (Fabaceae, Euphoriaceae

and Molluginageae)

Intermittent-inundated 17.04 15 families 2 families (Lemnaceae and Myrtaceae)

WPFG Long-dry 71.38 3 FG (Tdr, Tda, ATw)* 3 FG (Tdr, Tda, ATw)†

Intermittent-dry 56.83 5 FG (ATl, Tda, ATw, Tdr, ATe)* 4 FG (ATl, Tda, Tdr, ATw)†

Intermittent-inundated 25.23 7 FG (ARf, ATl, ATw, Tda, ARp,

ATe, Tdr)*

4 FG (ATw, ARf, Tda, ATl)†

*Listed in order of average abundance from highest to lowest.†Listed in order of percentage contribution.

Fig. 6 Average number of plant species recorded in water plant

functional groups (WPFGs) per wetland per survey according to

the inundation classification of wetlands.



summarise and predict vegetation responses to different

watering regimes. Vectors indicating trends in the

relative abundance of different WPFGs can be displayed

on nMDS ordinations. These vectors help to illustrate

and communicate the basis of trends in vegetation com-

munity composition associated with differences in water

regime that lead to the separation of samples in ordina-

tion space. In contrast, displaying vectors for trends in

the abundance of different plant species is often prob-

lematic due to the large number of species required to

distinguish between samples. For example, in the

current study, it would have been impractical to display,

in two-dimensional space, the relationships in vegetation

composition between samples collected from 18

wetlands, in 5 years of sampling with 270 contributing

plant species. An additional benefit of reducing the

number of response variables (i.e. moving from plant

species to WPFGs) is that it reduces the amount of infor-

mation required to predict the way in which wetland

vegetation communities are likely to respond to flow

regimes. By focusing on WPFGs rather than (largely site-

specific) species assemblages, research can begin to focus

on assessing the types of water regimes that lead to the

establishment of target WPFGs.

SIMPER analysis assisted in identifying the plant spe-

cies, genera, family or WPFGs that typified the vegeta-

tion communities found in wetlands belonging to each

inundation classification. However, the variability in

species composition between wetlands meant that a rela-

tively large number of species were needed to explain

the similarity in communities within inundation classifi-

cations. The use of indicator species such as Eucalyptus

camaludenis and Azolla spp. has not been specifically

tested as part of this study. However, the lack of any

individual species that readily characterise particular

inundation classifications means that many indicator

species are unlikely to be useful for assessing vegetation

responses to different water regimes.

Many of the species required to explain the similarity

in communities within inundation classifications are also

unlikely to occur at the majority of wetlands, due to

their highly localised distributions. This issue is likely to

be further exacerbated where the range of biogeographi-

cal regions from which samples are collected increases.

While both the regions used in this study are semi-arid

and located in the lower Murray–Darling Basin, WPFGs

could be used to compare data collected across broader

geographic areas. While geographic variability is likely

to contribute to variation in plant species composition,

trends in WPFG composition should largely be deter-

mined by the inundation regime and hence are likely to

remain comparable to a much greater extent, despite

changes in biogeographical region.

Vegetation communities at intermittent-inundated

wetlands were consistently more variable than intermit-

tent-dry wetlands, with vegetation communities at long-

dry wetlands being the most similar to each other. This

was true for all levels of assessment from plant species,

to genera, family and WPFG. Intermittent-inundated

wetlands varied considerably in water depth, with

between one and all surveyed elevations inundated at

the time of survey. The extent to which an individual

wetland is inundated affected both the type and range

of habitat niches available. This greater variability in

hydrological conditions between sites is likely to have

contributed to the larger differences in species and

WPFG composition and abundance found between wet-

lands in the intermittent-inundated category.

We found that, while the average number of WPFGs

present at a wetland did not vary significantly according

to the different water regimes, the type of WPFGs present

did vary. Long-term drying led to a dominance of terres-

trial-dry plants, while wetlands with an intermittent

flooding regime (regardless of whether the wetland

currently held water or had dried in the last 2 years)

maintained communities with more species that are

amphibious and capable of tolerating wetting and drying.

Intermittent-inundated wetlands were the only sites

from which species in the submerged (S) and amphib-

ious-floating (ARf) WPFGs were recorded. From a

management perspective, intermittent wetting and drying

is desirable in promoting a diversity of aquatic and

amphibious plants across a broad range of WPFGs

(Nielsen et al., 2013). By providing watering regimes on a

system-wide scale that are appropriate for the germina-

tion, development, reproduction and dispersal of a range

of WPFGs, it is likely that a diverse range of plant species,

representative of these functional groups would be

provided for despite locational differences in floristic

composition. In addition, by assessing the average num-

ber of plant species recorded in WPFGs, thought could be

given to creating management ‘benchmarks’, or measures

of ecological response to water management, based not

only on the presence of particular WPFGs but also on the

number of species recorded within individual WPFGs.

However, the high level of variability observed in the

average number of plant species recorded in WPFGs can

mean relatively large data sets are required to create

benchmarks and that benchmarks need to be regularly

reviewed as additional information is collected.

In addition to the above benefits, WPFGs may have

a role to play in improving communication between



https://www.researchgate.net/publication/234119147_Empirical_evidence_linking_increased_hydrologic_stability_with_decreased_biotic_diversity_within_wetlands?el=1_x_8&enrichId=rgreq-87d6dd05-420e-4ded-9d2e-3e2bddc0bf61&enrichSource=Y292ZXJQYWdlOzI2MDMwNjM2NjtBUzoyMjA0NTI5MzgwOTY2NDFAMTQyOTU3MTQ4NDE2MA==

scientists and water managers. Classification of species

into WPFGs groups enables the responses of different

plant communities to varying watering regimes to be

explained in terms of water requirements without the

need for an intimate understanding of botany or familiar-

ity with scientific names. At a basic level, WPFGs can be

used to group and describe species as; (i) submerged

species that require the presence of water, (ii) amphibious

species that will tolerate and/or respond to changes in the

presence or absence of water and (iii) terrestrial species

that will not tolerate inundation but may colonise a

wetland during dry phases (see also Brock & Casanova,

1997; Casanova, 2011). Using these descriptive categories

to describe the observed or predicted responses of

wetland vegetation, communities to different water man-

agement regimes are more interpretable for non-botanical

audiences than lists of plant scientific names.

By highlighting the usefulness of WPFGs for demon-

strating and communicating vegetation responses to dif-

ferent watering regimes, we are in no way discounting

the value of or need for plant species-level information.

The collection of floristic information at the species level

is vital as the basis of WPFG classification. Casanova

(2011) identifies three caveats relating to the use of

WPFGs, with the first being appropriate taxonomic skills

to enable different species to be distinguished reliably.

Additionally, we recognise that reporting the occurrence

of rare species and accurately recording the distributions

of individual species observed are inherently important

aspects of biological data collection.

Our recognition of the benefits of using WPFGs for

vegetation monitoring and reporting came about through

difficulties in reporting on and clearly expressing the

responses of wetland vegetation communities to environ-

mental water application, or in commenting on the ‘con-

dition’ of wetland sites, based purely on species

composition and abundance. These difficulties were par-

ticularly apparent when trying to compare responses of

vegetation communities to environmental water applica-

tion between wetlands with different watering histories

and wetlands at different stages of the wet-dry cycle.

Further difficulties arose when attempting to explain

these responses to non-botanical audiences for whom the

use of scientific names was not always informative.

Using WPFGs allowed the detection of change to be

focused on a smaller number of variables (e.g. 10 func-

tional groups compared to 270 species in the current data

set), the responses of which are linked, through their def-

initions, to the underlying watering regime and not

dependent on location. This avoids to some extent the

confounding issue of ‘species localism’ or the uniqueness

of plant species composition often naturally observed

between wetlands and between biogeographical regions.

This paper has shown how the use of WPFGs com-

pared with the use of species, genera and family-level

data reduces the variability between wetland vegetation

samples, often negating the influence of floristic differ-

ences between individual wetlands and geographic loca-

tions. The adoption and application of a consistent

approach to the classification of plant species into

WPFGs could potentially allow reliable predictions to be

made about plant community responses to different

inundation regimes across broader spatial scales.

Acknowledgments

The authors acknowledge the input from numerous staff

at the Murray–Darling Freshwater Research Centre in

fieldwork, review and encouragement. Thanks to the

Mallee Catchment Management Authority for details

of environmental watering events and to the Murray–

Darling Basin Authority for access to hydrological

outputs from BIGMOD. Fieldwork undertaken for this

paper has been funded by The Living Murray program,

which is a joint initiative funded by the New South

Wales, Victorian, South Australian, Australian Capital

Territory and Commonwealth governments, coordinated

by the Murray–Darling Basin Authority.

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Supporting Information

Additional Supporting Information may be found in the

online version of this article:

Table S1. Plant species list and associated water plant

functional groups (WPFGs).

(Manuscript accepted 5 December 2013)



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