As one of Australia’s most iconic wildlife species, Koalas are in the headlines as they come under increasing pressure from habitat loss. The impact on Koalas from catastrophic bushfires during the 2019-2020 fire season was graphically illustrated in the media and raised community awareness of their plight. Other threats to Koala habitat include habitat clearing from agriculture, urban development and infrastructure.
The final 155km section of the Pacific Highway upgrade between Woolgoolga and Ballina (W2B) delivered by Transport for NSW (TfNSW), Pacific Complete and its design and construction partners demonstrates that significant areas of new Koala habitat can be created as part of a major transport infrastructure project.
The W2B upgrade is the final link in the 657 kilometre highway upgrade between Hexham and the Queensland border. It is the product of an integrated engineering, urban design and environmental process progressively landscaped during its built and opened late last year. Transport for NSW also recently won the 2021 AILA Award for Infrastructure for the whole Pacific Highway.
The road passes through a diverse range of habitats that include forest, coastal shrub land, agricultural grazing land, sugar cane fields and a series of major river corridors. A key aspect of the W2B upgrade has been minimising the direct impact to these key sensitive environment areas, and provision of biodiversity offsets for native vegetation clearing required to construct the highway upgrade. While a substantial portion of the W2B project involved upgrading sections of the existing highway alignment; there are a number of other sections that adopt new green-field alignments. One of these sections is near Wardell, north of the new bridge over the Richmond River, and contains regionally significant Koala habitat supporting a well-known Koala community. The connectivity between a number of these Koala habitat areas has historically been disrupted by extensive fields of sugar cane cultivation and areas cleared for grazing.
TfNSW, formerly Roads and Maritime Services (RMS), engaged Niche Environment and Heritage consultants in 2015 to prepare a Koala Revegetation Strategy Report for the W2B upgrade. The report, which was co-authored by Dr. Rod Kavanagh, noted that of the 621 hectares acquired by TfNSW for the W2B upgrade in near Wardell, the highway footprint would occupy approximately 100 hectares of that, 370 hectares would be retained native forest and 151 hectares was cleared agricultural land. The Strategy identified 130 hectares of the cleared agricultural land as suitable for revegetation on either side of the W2B upgrade to mitigate the potential impacts of the highway construction on a range of wildlife species, particularly Koalas. The implementation of the revegetation strategy also supported other project initiatives to enhance animal connectivity opportunities within the fragmented landscape. A series of wildlife underpasses, designed with advice from specialist ecologists, was constructed as part of the W2B upgrade to allow Koalas and other wildlife to move safely under the new highway between existing and future habitat areas. As a result, implementation of this strategy would contribute to the creation new Koala habitat for one of Australia’s most iconic wildlife species. The 130 hectares of koala revegetation will be protected in perpetuity through the creation Biodiversity Stewardship Agreements administered by the Biodiversity Conservation Trust and funded by TfNSW. This will provide for the ongoing funding and management of the koala revegetation areas to ensure the habitat values are managed into the future.
Key steps included strategy development, landscape design, contract documentation, and implementation. Transport for NSW engaged Corkery Consulting Pty Ltd Landscape Architects to assist with the preparation of landscape design documentation for implementation of the new Koala habitat planting. In support, Dr Kavanagh provided expert advice on revegetation issues including tree species selection, tree spacing, planting layout and bushfire management. Species selection focused on trees known to provide Koala habitat and suitability for the prevailing soil conditions, drainage and topography. The advice of Dr. Kavanagh was incorporated in the documentation for planting work prepared by Corkery Consulting.
The revegetation site contained highly variable growing conditions including extensive areas with low elevation that were cultivated for sugar cane with restricted drainage, high water table and residual chemicals and fertilizers associated with sugar cane cultivation. The growing conditions included relatively well-drained lower slopes of hills to the west of the highway corridor and stable sand dune areas to the east. The revegetation strategy identified and mapped areas suitable for planting, taking account of existing infrastructure, vegetation and growing conditions. A priority schedule for the tree planting program was developed based on a comprehensive site inspection to assess the growing conditions of the proposed planting areas.
To ensure the outcomes and objectives of the revegetation strategy were met, the contract documentation provided to suitable tenderers included detailed planting plans, plant schedules, quantities, specifications and an indicative planting program. Local plant nurseries were contacted to confirm plant availability and supply arrangements for the tree species identified as Koala habitat. The project specifications for the physical planting work also included requirements to ensure that appropriate soil testing was carried out by a registered laboratory, before planting commenced, to inform the soil amelioration actions that were required to be implemented by the planting contractor, GMC Environmental Consulting.
One of the objectives and challenges of the site was to transition the area from historical cane fields to new native forest. Physical site preparation work included weed control by slashing and herbicide spraying. Mechanical ripping along planting lines was carried out to open up the heavy sub-soil, particularly on the former sugar cane cultivation areas. Protection of the newly planted trees from grazing stock and kangaroos was provided by constructing perimeter stock-proof fencing.
Planting activities commenced before major highway construction work started, with about 113 hectares planted. This ensured the trees were well established before project completion. Initially the tree growth was constrained by strong competition from heavy weed and pasture grass cover. During the initial establishment period, control of grass and weed competition was achieved by regular mechanical slashing and herbicide spraying, which also assisted bushfire management. The tree growth rate has accelerated over the last few years as the tree canopies begin to shade out the competing weeds and pasture grasses. Plant survival across the project continues to be very good. Some minor replanting has been required due to natural causes such as fire and drought. Average tree heights within the planted areas are now approximately 5 metres with some exceeding 8 metres. The final 17 hectares of the total 130 hectares were planted in early 2021 following completion of highway construction activities.
The performance of the revegetation work is being monitored over an initial five year period. This includes Koala monitoring which is being done in conjunction with the wider koala population monitoring program for the W2B upgrade project. The primary purpose of the plantings is to improve habitat connectivity and provide new koala food trees on land that had previously been cleared. Through the efforts of the W2B project team, the koala revegetation plantings, in combination with the wildlife connectivity structures, are making a significant contribution to the long-term sustainability of the local Koala population.
Woolgoolga to Ballina Pacific Highway upgrade, Koala Habitat Establishment
Location: Wardell, North Coast NSW, Australia
Landscape Architect: Corkery Consulting
Collaborators: Transport for NSW
Dr Rod Kavanagh (Niche Environment and Heritage)
GMC Environmental Consulting
Client: Transport for NSW
Conceptual Image Credits: Transport for NSW
Photography: ©Simon Hughes; Noel Corkery
Text: Corkery Consulting