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Australasian Plant Conservation

Originally published in Australasian Plant Conservation 18(3) December 2009 - February 2010, p 5-6

Planning and implementing conservation networks in Sutherland Shire, New South Wales

Ian N. Drinnan
Sutherland Shire Council, Sutherland. Email: idrinnan@ssc.nsw.gov.au


Council and students undertake habitat restoration works as part of the Schools in Greenweb Program, Sutherland Shire. Photo: Geoff Doret.

Introduction

Sutherland Shire encompasses an area of 370 km2 on the southern outskirts of Sydney. The area contains significant areas of national parks and nature reserves, along with large remnants of urban bushland. The area is predominantly Hawkesbury sandstone, with minor overlying areas of sand and shale. The vegetation beyond the formal reserve system is found on both public and private lands, in remnants ranging in size from 0.1 ha to over 100 ha. These remnants experience varying degrees of isolation, ranging from reserves connected by corridors more than 100 m wide to small isolated reserves separated by several kilometres. Remnants also contain a variety of vegetation types from well represented gully forest occupying substantial areas, to endangered ecological communities and threatened species found in only small remnants. The challenge for Council has been to design a conservation network to assist in managing biodiversity in such a fragmented and diverse environment.

Researching design parameters

After searching the literature to find specific design parameters for conservation networks in urban areas and finding very little, I commenced a study to identify if fragmentation thresholds existed for biodiversity within our area (Drinnan, 2005). I selected several reserves of varying sizes and degrees of connectivity and isolation, and examined the biodiversity within them, specifically the species richness of plants, birds, frogs and fungi. The results from this study, along with the general principles identified in extensive literature searches, were used to develop a series of design guidelines for our conservation network.

Conservation network design guidelines

My research found a threshold in reserve size of approximately 3.5 ha, below which species richness declined rapidly. A further threshold of 50 ha was also noted, above which species composition changed with significantly more forest interior and rarer species present compared to generalist or urban tolerant species. Therefore remnants of these sizes and above were seen as keystones in our conservation network. Other fragmentation parameters such as corridor width and distance to reserves were found to have a linear relationship, with species richness decreasing with separation distance and richness increasing with increased corridor width, but no thresholds were identified. Accordingly within the network larger reserves were ideally connected by wider corridors (Table 1).

Table 1. Corridor width guidelines for remnants of different size.

Remnant size

Desirable minimum corridor width

100 ha

200 m

50–100 ha

80–100 m

5–50 ha

30–80 m

2–5 ha

15–30 m

2 ha

Continuous canopy

Conservation network—from theory to practice

Once the basic guidelines for the design of the network had been developed, the on-ground works commenced. The vegetation of the Shire was mapped, utilising existing databases, aerial photographs and field surveys as required. Identified remnants of vegetation then formed the building blocks of a Greenweb Conservation Network (Greenweb) for Sutherland Shire.

Within the Greenweb, remnants and sites were identified as follows.

  • Core areas—areas of high significance to the sustainability of the Greenweb as they contain key habitat areas, key linkages and threatened species or endangered ecological communities. These key habitats are of a size that maintains their viability and are generally larger than 3.5 hectares.
  • Support areas—areas that provide ancillary habitat or secondary linkages between habitats. They also contain lands that form a buffer between developments adjacent to key habitats and corridors.
  • Restoration areas—areas that provide opportunities for the establishment and revegetation of corridors between core areas.

Figure 1. A portion of the Sutherland Shire Greenweb Network.
Key: Dark = Core areas, Mid = Support areas, Light = Restoration areas.

Core areas comprise the key elements of the Greenweb. However these core areas are not sustainable in isolation and corridors are necessary to connect them. In some instances these corridors already existed and were identified as support areas. Where there was a need to create corridors these were identified as restoration areas (Figure 1).

In addition to a site’s ability to fulfil a particular conservation role, preference was also given to sites that may play a role in water quality improvement, particularly riparian areas, and sites which may facilitate pedestrian as well as fauna movement. This enabled Council to obtain multiple benefits from some areas within the Greenweb.

From development to implementation

Once developed, the Greenweb provided the basis for conservation action in three key areas: development controls; prioritising Council natural resource management actions; and opportunities to support biodiversity conservation on private property.

Greenweb development controls

Specific planning controls relating to areas identified within the Greenweb have been incorporated into the Sutherland Shire Development Control Plan 2006. The development controls aim to:

  • maintain habitats in a size and configuration that ensures their ongoing viability and sustainability
  • ensure connectivity between remnants is maintained with corridor widths commensurate to the size of habitats they connect
  • minimise off-site impacts to adjoining bushland from weed invasion, stormwater and pollutant runoff
  • landscape with appropriate indigenous species to maintain and enhance core habitats and vegetated linkages.

Greenweb and Council natural resource management

Sutherland Shire Council has a range of programs that support and enhance the natural environment of the local government area. These include tree issue programs, community bushcare, street tree planting, Council bush regenerators, noxious weed officers and pest species officers. While the operations of staff and operational work units are governed by annual work programs, they are often historically based or reactionary in nature. The Greenweb creates a new framework by which works can be prioritised and approached in a more strategic manner. This ensures that valuable Council and community resources are allocated to areas where they will have the greatest conservation benefit.

Greenweb community support program

While many of the key areas of the Greenweb are located on public lands, many other areas—in particular corridors and linkages—are located on private property. In recognition of the significant role these lands play in the overall conservation of biodiversity within Sutherland Shire, Council offers residents within these areas support and assistance in managing biodiversity assets on their land. Support under the program includes:

  • vouchers for trees and shrubs from the Council nursery
  • supply and collection of weed bags
  • advice on weed control, plant selection and habitat creation
  • additional greenwaste collection service
  • regular information, newsletters and fact sheets
  • small grants (up to $2000) to undertake habitat restoration works on their property.

The Greenweb program has proven very popular within the community with 12 schools and more than 350 residents currently participating in it.

Conclusion

The development of the Greenweb Conservation Network has been a key step in the effective identification and management of biodiversity within Sutherland Shire. The Network has enabled Council to strategically manage its natural resources and to prioritise traditional work programs to obtain maximum conservation benefits. In basing the development of the Network on sound scientific principles, Council is also in a strong position for its external operations, such as defending conservation based planning decisions in the New South Wales Land & Environment Court and attracting external grant funding.

Reference

Drinnan, I.N. (2005). The search for fragmentation thresholds in a Southern Sydney suburb. Biological Conservation 124: 339-49.

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