Wetlands,
Biodiversity and Salt
Riparian Vegetation
Introduction
The riparian zone can be broadly defined as
the land adjoining, directly influencing or
being influenced by a body of water (Boulton
& Brock 1999).
The vegetation of the riparian zone is an
important component of non-riverine wetlands
because it:
August 2006
Aim
The aim of this work was to investigate what
components of the riparian vegetation change
when conductivity increases.
With increasing salinity, we may expect that
within the riparian zone:
•
plant diversity decreases
• can be a defining feature of some wetlands
•
community composition changes
• provides habitat for fauna
The riparian vegetation of non-riverine
wetlands in the Wimmera and North Central
CMAs were assessed. A 10 x 10 m quadrat
was used, within which all species were
identified and cover abundance recorded.
Change in riparian vegetation due to
increasing conductivity was assessed by
comparing 36 fresh wetlands to 14 secondary
salinised wetlands.
• is vital for wetlands functions and
processes
• creates a ‘buffer zone’, that may protect
the wetland against adverse impacts
coming from the surrounding landscape.
Riparian vegetation is a wetland component
with very high diversity. There are many
vegetative lifeforms, including trees, tall
shrubs, low shrubs, herbs and monocots, such
as grasses, sedges, rushes and lilies.
Riparian vegetation can be naturally very
variable. The boundaries of the riparian zone
may be hard to define, with no clear change
in vegetation, since it is a transition zone or
continuum among the terrestrial, aquatic and
groundwater habitats.
Riparian habitats are threatened by increases
in salinity levels, caused by secondary
salinisation.
Findings
Species richness
The riparian vegetation of the secondary
salinised sites had:
•
•
less native herbs
less native shrubs
•
more exotic herbs
than that of fresh wetlands.
Species cover
The riparian vegetation of the secondary
salinised sites had:
•
lower cover of native species,
especially shrubs
•
higher cover of exotic species,
especially herbs and monocots
higher cover of annual species
•
than that of fresh wetland
Photo: Michele Kohout
A Victorian
Government
initiative
Community composition of native
species
The MDS plot shown on the right in Figure 1,
is an indication of how similar sites are to one
another. The closer the points, the more
similar the sites are floristically. The plot
shows that the fresh sites are naturally quite
variable in terms of the native riparian
vegetation. The secondary saline sites are less
variable but are not distinctly different to the
fresh sites, yet.
Stress: 0.15
Fresh
Secondary
salinised
Figure 1: MDS plot - based on cover abundance (%)
of native species species.
Photos: Michele Kohout
Future riparian vegetation change
Vegetation is dynamic, and change in the native vegetation community of the riparian zone of
secondary salinised wetlands is inevitable. The vegetation change might follow a number of different
pathways. It may:
•
over the long term, become more like naturally saline systems, or
•
remain the same, or
•
form a new ‘system’, or
•
become more like that of fresh wetlands, if salinity is reduced.
We are unsure of the factors that will facilitate the shift, and in which direction. It is likely that
riparian vegetation change will occur over a long time, rather than change rapidly.
Implications
The implications of secondary salinisation causing the riparian zone to become more weedy and the
loss of native biodiversity are great. The natural functioning of the wetland may be affected and the
habitat available for fauna may be reduced. In addition, the ability of the riparian zone to act as a
buffer may be compromised.
As land managers, it may be possible to influence the future pathways of the native vegetation
component of the riparian zone in secondary salinised wetlands. However, more knowledge is
needed to identify how we could shift the system, over what time frame, and to identify the most
desired pathway and result for the riparian vegetation.
Reference: Boulton, A. J. and M. A. Brock (1999). Australian freshwater ecology: processes and management. Glen Osmond, Gleneagles.
Published by the Victorian Government Department of Sustainability and Environment Melbourne, August 2006
© The State of Victoria Department of Sustainability and Environment 2006
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