Dragonfly Aquatics by wuzhengqin


									Nick Romanowski
Wetlands writer, researcher and photographer
ABN 44 729 917 607

80 Aroona Court, Forrest
Victoria, Australia, 3236
(03) 5236 6320

Comments on revegetation works along the lower Barham River
Tidal section near bridge
This area has been heavily grazed over a long period of time, so revegetation in many areas
has proceeded from scratch, introducing locally sourced trees and shrubs which have thrived
on the higher ground near the river. However, in the lower, increasingly salt-affected soils
closer to occasionally saline waters,
the diversity and vigour of the new
plantings decreases and another suite
of indigenous plants, as well as some
weeds, takes their place.

Successful revegetation in fenced area
at left, grazed areas at right.

This planting can therefore be used as a reasonably precise guide to the indigenous species
best suited to varying conditions in this general area, and to fine-tune further plantings. A
surveyor’s level could be used to map where these grow best fairly precisely, using the lower
fringe of the area where all new plantings have thrived as the benchmark below which these
more terrestrial species will not grow well.

                                               Below this point a different set of plants
                                               becomes dominant, and includes both
                                               indigenous and introduced plants, all of them
                                               fairly low-growing. These include significant
                                               mats of the edible sea celery (Apium
                                               prostratum at left) which can be used as a
                                               guide to soil salinity by taste alone, as the
                                               plants on the higher, less salt-affected ground
                                               are bland in flavour, while those on boggy
                                               ground close to the water are distinctly tangy.
Other mat-forming indigenous plants here include creeping brookweed (Samolus repens) and
on the lowest, wettest ground waterbuttons (Cotula coronopifolia); all three of these species
can readily be propagated from cuttings.

                             Apium prostratum

                                                Cotula coronopifolia

                                     Samolus repens

                                      There are also several introduced weeds which may be
                                      abundant in places, of which the most conspicuous is
                                      bushy starwort (Aster subulatus, at left), an annual
                                      daisy which spreads by wind-blown seed. Although a
                                      prolific seeder, the tiny seed cannot germinate under
                                      mats of indigenous plants, which could be established
                                      to out-compete it as it is the most visually jarring of the
                                      three weeds.
Also present is a form of fat hen
(Chenopodium album), a larger
seeded annual which could be
controlled by pulling out over
several years, with an emphasis on
preventing seed formation.

                                                 Buckshorn plantain (Plantago coronopus) is a
                                                 fairly deep-rooted perennial and would take
                                                 more effort to remove, but even the largest
                                                 patches of this weed are fairly localised and
                                                 are only likely to spread slowly.

In the shallower water, the indigenous
common reed (Phragmites australis) is
making a comeback now that grazing has
been stopped, and is moving back into
seasonally flooded soils at an estimated 2
metres per year. This tall grass may need to
be replanted along the barren shore of the
river facing the caravan park, but should only
be used in small quantities here, to tie in
visually with the far bank where it is the
dominant plant.

                                                     Instead, river clubrush (Schoenoplectus
                                                     tabernaemontani) which forms a large
                                                     stand near the bridge should be used more
                                                     extensively here, and this species can
                                                     easily be grown from seed sown on
                                                     waterlogged soil in spring.
Eroded streambanks further upstream
The deeply channelized section of section being revegetated further upstream is a more
difficult and longer-term project for restoration. The river here would have been shallower
and broader before European settlement, filled with snags in the form of fallen trees and
branches which slowed flow rates, and spilling out over the surrounding floodplain during
wet periods so erosion was minimised or at least spread out. Clearing of the banks and
removal of snags has created faster, eroding flows in the main channel, so that this has cut
deeply into the soils below.

Removal of willows has been completed
before replanting, and these relatively
brittle trees have probably contributed to
collapse of the banks as they tear out easily
during floods.

                                                    Continued planting of blackwoods and
                                                    eucalypts on the high ground is
                                                    recommended as this will ultimately
                                                    provide larger trees which will become
                                                    snags when they die, slowing flows and
                                                    allowing silt to build up to higher levels.
                                                    However, this is a process that will take
                                                    many decades. As the canopy matures, it
                                                    will also shade out many of the annual
                                                    weeds which presently dominate the
                                                    sloping banks. These include drain sedge
(Cyperus eragrostis, below left) and nasturtium (Tropaeolum majus, above left), both of
which are introduced, while the status of pale knotweed (Persicaria lapathifolia, below right)
is not certain although it is widely regarded as a native.
Although some indigenous plants may be
found growing in the streambed itself
(including a water milfoil, probably
Myriophyllum simulans), these are only likely
to increase in numbers as snags gradually
refill this section of stream, slowing water
flow and allowing a greater diversity of
aquatics to grow.

Summary of recommendations: the recent plantings along the two sections of the Barham
River discussed in this report provide useful information for future revegetation in the lower
reaches of this river, which has been radically affected by grazing, clearing of streambanks,
and extensive erosion in the faster-moving sections.

In areas closer to the sea, terrestrial plantings should be confined to higher ground which is
less likely to be affected by salinity and tidal events, and the present plantings here provide a
fairly precise benchmark which could be mapped with a surveyor’s level. Below this level the
emphasis should be on establishing a dense cover of indigenous species which will ultimately
compete with the annual weeds present, and if possible removal of buckshorn plantain to
minimise its spread.

                                                      The bare banks of this side of the river
                                                      should be replanted against erosion in
                                                      parts, including with some common reed
                                                      to tie in visually with the far bank
                                                      adjacent to the caravan park, where this
                                                      is the dominant plant. However, the bulk
                                                      of such plantings would ideally be of
                                                      river clubrush, a more valuable habitat
                                                      and nesting plant, and it is also desirable
                                                      to leave some of the more gently sloping
                                                      open areas unplanted, as these provide
                                                      valuable resting places for some
                                                      waterbirds such as cormorants (seen
                                                      here on the bar nearest the bridge).

Upstream, continued planting of the higher banks with trees which will become the source of
snags as they mature should remain a priority. Plantings on the steeply sloping banks are a
more difficult proposition as these may be eroded out during floods, and few indigenous
plants are adapted to these relatively unnatural conditions. With time, both of these problems
should be mitigated by the gradual build-up of snags, slowing flows and trapping silt so the
stream bed rises, while a more extensive overhanging tree canopy will encourage shade-
loving perennial plants over the annuals.

                                                             Nick Romanowski, 6.5.2011

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