Reconstructing Western Sydney Grassy Woodland Understorey at Hoxton Park, Sydney, NSW
By Christopher Brogan
What was this project and why were works carried out?
In May 2012 Earth Repair & Restoration Pty Ltd were commissioned by Endeavour Energy to restore a small highly disturbed bushland remnant at the West Liverpool Zone Substation at Hoxton Park. Restoration works included extensive revegetation with native grasses and were designed to offset 12 native trees removed to facilitate construction works at the substation.
What was the project objective?
The objective of these works was to protect and enhance the remaining bushland by carrying out ecologically sensitive weed control in combination with revegetation. This bushland remnant is approximately 3,000 square meters in extent.
What did the site look like before the project started?
While the native shrub and ground layer was generally absent native canopy trees were present particularly in one part of the site and included Eucalyptus crebra, E. moluccana and E. tereticornis. A small number of Melaleuca decora were also present grouped together adjacent to the entrance to the substation off Jedda Road.
The ground layer was dominated by the invasive perennial Eragrostis curvula (African love grass). Other ground layer weeds included Asparagus officinalis (Garden asparagus), Avena fatua (Wild oats), Bidens pilosa (Cobblers peg), Brassica juncea (Indian mustard), Bromus catharticus (Prairie grass), Bryophyllum delagoense (Mother of millions), Chloris gayana (Rhodes grass), Chloris virgata (Feathertop rhodes grass), Cynodon dactylon (Couch), Cyperus eragrostis (Umbrella sedge), Ehrharta erecta (Panic veldt grass), Lactuca saligna (Wild lettuce), Onopordum acanthium (Scotch thistle), Paspalum dilatatum (Paspalum), Pennisetum clandestinum (Kikuyu), Plantago lanceolata (Plantain), Senecio madagascariensis (Fireweed), Setaria gracilis (Slender pigeon grass), Sida rhombifolia (Paddy’s lucerne), Solanum nigrum (Blackberry nightshade), Solanum sysimbriifolium (Viscid nightshade) and Verbena bonariensis (Purple top). The naturalised vine Araujia sericifera (Moth vine) and shrub Lycium ferocissimum (African box thorn) were also present.
What was the definition of success?
The contract period was 24 months. Success was defined using the following performance criteria:
- The survival rate for planted tubestock was to be greater than 80%.
- The percentage cover of weed species was to be Very Low i.e. < 5%.
- The percentage cover of the native grass and herb layer was to be High i.e. 67% to 100%.
How was percentage cover measured?
Two 5X5 meter quadrats were installed and percentage cover was estimated quarterly using the following classes:
- Very Low: < 5% Cover.
- Low: 6 to 33% Cover.
- Medium: 34% to 66% Cover.
- High: 67% to 100% Cover.
Was there any site resilience?
While it initially appeared that the native grass and shrub layer had been completely replaced, closer inspection revealed that in areas where native trees had been retained a number of species of native grasses and herbs were still present at very low percentage cover. These native grasses and herbs included Arthropodium milleflorum, Austrodanthonia bipartita, Chloris truncata, C. ventricosa, Dianella revoluta, Dichondra repens, Einadia hastata, Lomandra filiformis and Plectranthus parviflorus.
What were the causes and extent of disturbance?
Disturbance was a result of historic clearing for agricultural activities in addition to more recent clearing for the installation of electrical infrastructure. A layer of coarse fill material and asphalt had been deposited over the topsoil in some areas probably for car parking and this had compounded the decline in biodiversity values. Soils were generally highly compacted with a low organic matter content.
What was the goal ecological community?
Remnant bushland at the site had been mapped and classified by the New South Wales Office of Environment and Heritage as Cumberland Plain Woodland listed as an Endangered Ecological Community under the NSW Threatened Species Conservation Act (1995), and also the Commonwealth Environment Protection and Biodiversity Conservation Act (1999). The project was designed to reconstruct a Western Sydney woodland understorey. The presence of electrical infrastructure dictated that only grasses, herbs and shrubs were planted.
What did we do?
Due to the residual presence of native grasses and herbs under the area of native canopy and the high percentage cover of weeds particularly African love grass over the rest of the works area the project site was divided into two management zones:
- Management Zone 1 ~ The area of native canopy where native grasses and herbs were still present.
- Management Zone 2 ~ The highly disturbed area covering most of the site where native grasses and herbs had been replaced by
Two different methodologies were employed in the two different management zones:
- Management Zone 1 ~ Bush Regeneration ~ The identification and protection of native species followed by ecologically sensitive weed control ~ no mulch or planting.
- Management Zone 2 ~ Revegetation ~ Weed control followed by the installation of mulch and native tubestock propagated from seed collected from Western Sydney bushland.
A seed collection program could not be carried out due to the short time frame specified by the client. Plants were sourced from Australian Ecoflora a Western Sydney based specialist provenance nursery.
The scope of works included the following components:
- Weed control including cut stump & poisoning of woody weeds and high volume herbicide spraying for invasive perennial grasses.
- Supply and installation of 260 cubic metres of recycled wood waste mulch to a depth of 100mm over 2,600 square metres.
- Revegetation with 9,100 tubestock planted at a density of 3 to 4 per square metre.
Tubestock were installed in October 2012 and watered through-out November using a tap located in the adjacent small goods factory.[unitegallery HoxtonParkWoodland catid=5] [unitegallery HoxtonParkWoodland catid=6]
What was achieved?
This site provides an example of best practice management of a small bushland remnant which had declining biodiversity values prior to the commencement of the project. Native grasses and herbs present have been protected and enhanced by the installation of over 9,000 provenanced tubestock. The site is fenced which will prevent damage due to dumping or vandalism.[unitegallery HoxtonParkWoodland catid=7] [unitegallery HoxtonParkWoodland catid=8]
What advice can I offer?
- Always check your project site to identify any cryptic native species which may be present and protect them during weed control works particularly when spraying herbicide.
- Use good quality provenanced tubestock and budget for a seed collection program if the project timetable allows.
- Never under estimate the need to water tubestock and allocate sufficient resources to watering.
In May 2012 Earth Repair & Restoration Pty Ltd were commissioned by Endeavour Energy to restore a small highly disturbed Cumberland Plain Woodland remnant at the West Liverpool Zone Substation at Hoxton Park. Restoration works were designed to offset the loss of 16 native trees removed to facilitate construction works at the substation.
The objective of these works was to protect and enhance Cumberland Plain Woodland at the site by carrying out ecologically sensitive weed control for African box thorn and African love grass in combination with revegetation.
Site disturbance had included clearing for past agricultural activities in addition to more recent disturbance associated with the installation of electrical infrastructure. A layer of coarse fill material and asphalt had been deposited over the topsoil in some areas probably for car parking and this had compounded the decline in biodiversity values. Soils were generally highly compacted with a low organic matter content.
While it initially appeared that the native grass and shrub layer was completely absent, closer inspection revealed that in areas where native trees had been retained a number of species of native grasses and forbs were still present at very low percentage cover. These included Arthropodium milleflorum, Austrodanthonia bipartita, Chloris truncata, C. ventricosa, Dianella revoluta, Dichondra repens, Einadia hastata, Lomandra filiformis and Plectranthus parviflorus.
The site was revegetated in October 2012 with 9,100 provenanced tubestock with an emphasis on native grasses particularly Themeda triandra (Kangaroo grass) and Microlaena stipoides (Weeping grass). By December 2013 many of these had produced substantial quantities of seed which was collected and broadcast throughout the site.
The mulch selected for the project was manufactured from re-cycled green waste and post-consumer wood waste sourced from a local supplier and therefore had a relatively low environmental impact. All tubestock were propagated from seed collected from Western Sydney bushland remnants. Despite a family of Ravens pulling up several hundred plants presumably foraging for food the survival rate of planted tubestock was in excess of 95%.