Category Archives: Wetland

Plant communities of seasonal clay-based wetlands of south-west Australia: weeds, fire and regeneration

Kate Brown and Grazyna Paczkowska

Key words: regeneration, fire, seasonal wetlands

 While the majority of seasonal wetlands in south-west Australia are connected to regional ground water, some found on clay substrates rely solely on rainwater to fill. These seasonal clay-based wetlands fill with winter rains and are characterised by temporally overlapping suites of annual and perennial herbs that flower and set seed as the wetlands dry through spring. Over summer the clay substrates dry to impervious pans. The seasonal clay-based wetlands of south-west Australia comprise a flora of over 600 species, of which at least 50% are annual or perennial herbs, 16 occur only on the clay-pans and many are rare or restricted.

These ecological communities are amongst the most threatened in Western Australia and have recently been listed under the Commonwealth Environmental Protection and Biodiversity Conservation Act as critically endangered. Over 90% have been cleared for agriculture and urban development and weed invasion is a major threat to those that remain. South African geophytes are serious weeds within these communities and Watsonia (Watsonia meriana var. bulbillifera) in particular can form dense monocultures and displace the herbaceous understorey.

Watsonia invading  a seasonal clay-based wetland

Watsonia invading a seasonal clay-based wetland

Regeneration following weed control and fire.  We investigated the capacity of the plant community of such a wetland to regenerate following removal of Watsonia, and the role of fire in the restoration process.

 Our study site, Meelon Nature Reserve, is a remnant clay-based wetland on the eastern side of the Swan Coastal Plain 200 km south of Perth. A series of transects were established in August 2005 and regeneration of plant community following Watsonia control and then unplanned fire was monitored until September 2011 (Table 1).

 Table 1: Six years of monitoring regeneration of a seasonal wetland at Meelon Nature Reserve

August 2005 Thirty 1m x 1m  quadrats established along five 30m transects in the wetlands where Watsonia was estimated to average greater that 75% cover.
September 2005 Cover ( modified Braun Blaquet) recorded for all native and introduced taxa and then Watsonia treated with the herbicide 2-2DPA (10g/L) + the penentrant Pulse® (2.5 mL/L).
September 2006 Cover recorded for all native and introduced taxa and then Watsonia treatment reapplied.
February 2007 Unplanned wild fire burnt across the study site.
September 2007  each year until September 2011 Cover recorded for all native and introduced taxa and then any Watsonia treated.

Analysis of similarity (ANOSIM) was undertaken to determine if there was significant change in species cover and composition from before Watsonia control to six years following the initial treatment. A  SIMPER analysis was used to ascertain the contribution of each species to any changes between monitoring years (Clarke & Gorley 2006).

Results. In the first year of the control program, a 97% reduction in the cover of Watsonia was recorded, but was associated with no significant change in the diversity or abundance of native flora. In February 2007, 18 months after the initial control program, an unplanned summer wildfire burnt through the reserve. In September 2007 monitoring revealed a significant increase in cover and diversity of native species in the treatment areas. Some species such as the Dichopogon preissii had not been recorded before the fire, others, such as the native sedges, Cyathochaeta avenacea and Chorizandra enodis increased greatly in cover following the fire. At the same time there was no resprouting of Watsonia or recruitment from cormels or seed.

Six years after the initial treatment the native sedges and rushes continue to increase in cover, the dominant native shrub Viminaria juncea is increasing, Eucalyptus wandoo seedlings are recruiting into the site and native grasses and geophytes are increasing in cover. The indications are that plant communities of the seasonal clay-based wetlands of south-west Australia have the capacity to recover following major weed invasion and that fire can play a role in the restoration process.

Table 2. Species that contributed to 90% of the significant change in cover and composition of species between 2005 and 2011.

 

2005

2011

Species

Average abundance (% cover)

Average abundance (% cover)

Cyathochaeta avenacea

10.0

23.5

Chorizandra enodis

2.3

15.7

Viminaria juncea

2.1

15.4

Caesia micrantha

2.6

2.7

Briza sp. Meelon

3.1

2.0

Eucalyptus wandoo

0.0

3.0

Austrodanthonia acerosa

0.4

1.8

Hypoxis occidentalis

0.0

1.9

Lepidosperma sp. WT2Q5 Meelon

0.1

1.3

Meeboldina sp. MU3 Meelon 2011

0.2

1.4

Dichopogon preissii

0.0

1.3

Drosera rosulata

1.5

0.2

Contact: Kate Brown, Ecologist, Swan Region. Department of Environment and Conservation, PO Box, 1167 Bentley Delivery Centre, WA, 6983. Email: kate.brown@dec.wa.gov.au

Chorizandra enodis

Chorizandra enodis

Dichopogon preissii

Dichopogon preissii

Hypoxis occidentalis

Hypoxis occidentalis

Restoration after pipeline installation: Pimpama Northern Gold Coast, Queensland.

Key words: Assisted natural regeneration, topsoil transfer, Wallum Froglet, Regional Ecosystem 12.3.5, pipeline construction.

Mark Bibby

Revegetation works were carried out in 2009-10 to accompany a civil construction project in the northern Gold Coast, Queensland, where a pipeline was being laid through a natural area.

The Regional Ecosystems on site included palustrine wetland (12.3.5), which is habitat for threatened flora species including Phaius australis, P. bernaysii and Schoenus scabripes and the Wallum Froglet (Crinia tinnula).

The goals of the project were to: reinstate vegetation on site after the construction of the pipeline; minimise weed establishment and other maintenance issues; to ensure that no canopy species were replaced over pipes (to avoid root damage to the pipes); and to achieve an optimal  outcome for local biodiversity, including the Wallum Froglet.

Summary of works.  The native vegetation in the path of the pipeline was removed from wet areas with excavators and a crew of regenerators (Figs 1a and 1b). As much as possible of the macrophyte vegetation from the watercourse area was temporarily moved to ‘holding’ trenches, created to allow for a variety of soil moisture levels. (These were lined with plastic and then filled with water).

Some 600 specimens of other plants were removed to a nursery for later replanting. The top 200 mm of topsoil and site litter from the remainder of the site were stripped and stockpiled on site for later replacement.

Fig 1a: Macrophyte holding trenches before replanting.

Fig 1b: Macrophyte holding trenches providing temporary habitat during works.

Following civil works (conducted 8 months after the topsoil stripping) the stored topsoil and litter was replaced (at 30-50mm depth) and plants from the holding trenches replanted in their original positions. Spaces were left between the patches of litter to allow for regeneration from the replaced topsoil. Stumps were replaced on site as habitat.

The 600 nursery-spelled plants were reinstated on site and further planting of tubestock was undertaken, with grasses and sedges translocated from nearby at the site. Seed was collected nearby and spread on site when available. The site was regularly visited by skilled bush regeneration weed control staff members for 12 months.

Results. A high level success was achieved with the translocation of holding trench stock following inundation of the site during summer rains.  After replacement of the topsoil, vegetation and litter, the watercourse and surrounding fringes established well and natural regeneration from the replaced topsoil and germination from the seed dispersed by hand occurred. One year after the completion of works, the site was recovering well (Fig 2a-c) and recent inspections showed that vegetation cover and diversity in the watercourse area is consistent with the pre clearing condition. The terrestrial restoration area is showing good recovery with 15 species (that were not planted on site) observed regenerating. The native to weed ratio is 9:1. Conversely in the area of disturbance (adjacent the project site) without restoration the native to weed ratio is 1:9.

Fig 2a: The watercourse after removal of the vegetation.

Fig 2b: The watercourse upon reinstallation of topsoil and stockpiled plants

Fig 2c: The watercourse after the completion of the contract.

Lessons learned.  The joy of this project was being able to convince the the civil engineers if not also ecologists that a more natural regeneration-style approach could offer preferable outcomes to a standard civil landscaping approach.  Particularly interesting was the need to convince them not to be afraid of some short term ‘mess’ to ensure a good result for a natural area.

Contact: Mark Bibby, Gecko Regen, / 139 Duringan Street,Currumbin, Qld, Australia. Tel:  +61 (7) 5534 6395. Email: admin@geckoregen.org.au ; http://www.geckoregen.org.au/

Restoring the Winton Wetlands in north east Victoria

Key words: wetland restoration, ecosystem function, Mokoan, woodlands, hydrology

The 8,750 ha Winton Wetlands Reserve is located near Benalla within the Goulburn-Broken Catchment in north east Victoria. The restoration project is one of the outcomes of the former Victorian Government’s decision to decommission Lake Mokoan, previously Victoria’s fifth largest water storage, and to allocate resulting water savings for environmental flows to the Snowy and Murray rivers (Lake Mokoan previously lost over 50 GL annually in evaporation).

The decision to decommission Lake Mokoan was controversial and at the time there was considerable local and regional opposition to the project. Dramatic improvements in wetland condition since de-commissioning have now engendered considerable community support for the project.

Figure 1: Location of Winton Wetlands within the Goulburn-Broken Catchment in North East Victoria

Prior to the establishment of Lake Mokoan in 1971, the Winton Wetlands consisted of a series of more than 11 interconnected redgum and open cane grass wetlands covering more than 3000 ha, interspersed with areas of remnant box grassy woodland and surrounded by farmland with a long history of sheep and cattle grazing. From 1971, the wetlands and surrounding woodlands and farmland were regularly inundated to create a 375 GL water storage covering an area of more than 7000 ha.

The original wetland and surrounding woodland ecosystems and associated ecological drivers, (particularly the local hydrology) have been substantially modified as a result of regular inundation and a long history of agricultural use in the surrounding terrestrial areas.

The aim of the project is to restore the wetlands and surrounding terrestrial areas by encouraging the recovery of ecosystem function rather than necessarily attempting to return the site to exact pre-European condition. The project will be one of the largest wetland restoration projects undertaken in Australia.

With the decommissioning completed in mid 2010, the Winton Wetlands Reserve was established in August 2011 and so the restoration project is still in its early stages.

Progress to date:

  • Completion of a Future Land Use Strategy with considerable community input and consultation.
  • Installation of an extensive pipeline system to provide alternative source of local water supply.
  • Decommissioning of the water storage to reinstate more natural inflow and water levels regimes.
  • Establishment of a skills based community management committee to manage and restore the wetlands.
  • Government commitment of $20M to restore the wetlands and implement the Future Land Use Strategy.
  • Development and implementation of Fire Management and Pest Plan and Animal programs.
  • Completion of flora and fauna, pest plant and animal and cultural heritage surveys.
  • Scientific & Technical Advisory Group to guide development of Restoration and Monitoring Plan.

Results to date: The Wetlands dried out completely in late 2009 due to the severe 2005 – 2009 drought. Substantial rainfall from September 2010 has reinvigorated wetlands (see figures 1 and 2), with water levels from natural inflows at 145% (45 GL) in early December 2010 overflowing into the Broken River system. The wetlands have made a remarkable recovery greatly assisting to build local community support for the project.

Figure 2: Winton Wetlands during the 2006–09 drought

Figure 3: Winton Wetlands after rain (November 2010)

Lessons learnt & future directions:

  • Wetlands are remarkably resilient (as, unfortunately, are carp)
  • Community engagement, understanding, and support is essential for the success of the long term restoration project.
  • Focus on immediate land management issues has assisted greatly in the Winton Wetlands Committee gaining credibility as a land manager.
  • Rapid conversion of land with a long history of agricultural use and inundation to areas of high ecological value is not feasible, so a transitional approach to ecological restoration will be required.

Stakeholders: The $20m in initial funding has been provided by the Victorian Government with the project aiming to be financially self-sustaining within 10 years. The Winton Wetlands Committee of Management is committed to working with traditional owners, the local and regional community, and government agencies to restore the Winton Wetlands.

Contact: Tim Barlow, Restoration Ecologist, Email: Tim.Barlow@wintonwetlands.org; Website: http://wintonwetlands.org.au