Australasian Plant Conservation

Originally published in Australasian Plant Conservation 18(1) June - August 2009, p 14-15

Protecting Swamp Sheoke: an endangered species of Victoria’s Wimmera Woodlands

Adam Blake
Trust for Nature—Wimmera, Longerenong, Vic. Email: adamb@tfn.org.au

Background

Trust for Nature (Victoria) has been active in recent years targeting vegetation types that traditional instruments of permanent protection (including the National Reserve System) have struggled to access, secure or significantly restore. Historically the factor determining what was or wasn’t preserved was the real and perceived value and suitability of the land for production, much as it is today.

This has resulted in a trend of choosing to protect or not to protect based largely on soil type. The pattern that has inevitably emerged is one where there is now an over-representation of certain EVC’s (Ecological Vegetation Classes) protected on public and private land. Historically, this has been at the expense of other EVC’s which have made way for agricultural production and other forms of development. This pattern of over- and under-representation of vegetation types is well illustrated in the Wimmera Region of western and north-western Victoria.

The Bio Conservation Status of these EVC’s now reflects this worrying historic pattern. Vegetation types traditionally protected voluntarily on a large scale on private land, have been those on poor, sandy or skeletal soils. Equally there has been less protection of Plains Woodlands, Plains Grassy Woodland, Shallow Sands Woodlands, Plains Savannah, Low Rises Woodland and other vegetation types that occur across the more arable parts of the region on deeper, more fertile soils.

To complete the pattern, these same vegetation types occur in only very small amounts in public reserves, having been overlooked for reservation originally in favour of mountainous, forested and less arable land. Required now is an accelerated effort to protect and restore the best of what remains of the woodlands on private land and the various endangered EVC’s they comprise. There is much less now to protect, what remains is largely fragmented and the threats upon these ecosystems is, without any long-term security, greater than ever.

Woodland with Swamp Sheoke representing a secondary tree layer below Grey Box (Eucalyptus microcarpa) trees. Photo: Adam Blake

Casuarina obesa

Casuarina obesa (Swamp Sheoke) has endangered species status in Victoria and is listed as threatened in the state under the Flora and Fauna Guarantee Act 1988 (Vic.). Only nine known populations of this species occur in Victoria, eight of them found in central parts of the Wimmera region, west of Horsham. It also occurs naturally in south-west Western Australia where it occupies a greater range, in places being common. There is also one known population in south-west New South Wales.

All of the nine extant Victorian populations occur on private land and none occurs in a conservation reserve—a situation typical of other species on the agricultural Wimmera plains. But there is another set of obstacles to confront if protection is to result in the short- and long-term conservation of this species. Research previously conducted indicates the extant, isolated populations in the Wimmera are unisexual. This presents a problem for a wind pollinated species, occurrences of which are separated by several kilometres. It is therefore clear that permanent protection and rehabilitation is only a first (but fundamental) step in conservation of the species. Because specimens from the Wimmera populations are known to show considerable variability, this makes protection even more urgent if we’re to discover more about this little known member of the Casuarinaceae family.

Recently in the Wimmera, using GIS technology and by engaging with the landholder, a large population covering about 30 ha and representing thousands of specimens was ‘re-discovered’, for years known only to family members and more recently Trust for Nature staff. It hasn’t yet been established whether or not it is one of the aforementioned eight Victorian recorded occurrences. If so, it is possibly the largest, and potentially the healthiest and least fragmented. It remains largely unmodified as previous care and threat abatement activities by the landholder had preserved habitat quality. Light grazing had kept the grassy ground cover open and diverse, hardly reducing total cover in the areas providing habitat.

Structurally Swamp Sheoke provides the middle layer of small trees in the vegetation, in some places densely beneath an open canopy of (in this case) Grey Box (Eucalyptus microcarpa) and Black Box (E. largiflorens) trees. It grows on heavy soils at a location slightly higher than, but fringing, a seasonally inundated area. Preliminary bird surveys have turned up a number of important temperate woodland birds indicating a level of ecological function. These include Jacky Winter, White-browed Babbler, Diamond Firetail, Southern Whiteface and Brown Treecreeper. Now protected on a 90 ha Trust for Nature Covenant, itself connecting a large core area of public land, this represents the first Swamp Sheoke population to be permanently protected on land title.

Protection with a Conservation Covenant

One of the stated objectives in the Action Statement for this species (Walker 2003) is to protect existing populations from threatening processes and encourage natural regeneration. Another long-term objective is to ensure that single sex sites contain at least 100 plants of the opposite sex by 2010. It is hoped that with the long-term security of a covenant in place, this can be achieved at this newly protected site (if this population proves to be unisexual). Fencing of the area is the first task to be undertaken. This will allow the immediate cessation of grazing for an extended period of time and the more controlled use of grazing in the covenant for conservation purposes over time.

Increasing Habitat Extent

In an effort to target areas where net gain opportunities of endangered vegetation types occur, Trust for Nature collaborated with Greening Australia. Those areas only lightly modified with grazing and with reasonable tree density are seen as areas that could cost-effectively be restored for conservation, particularly if they met other key conservation significance criteria. It is critical that opportunities to increase the total extent of some habitat are sought if more ecological balance is to complement and be integrated into protected areas.

Restoration of this Swamp Sheoke community will be achieved with approximately 10 ha of revegetation by Greening Australia in areas previously modified by grazing. Incentives are being provided by Trust for Nature to the landholder as part of a Victorian Government funded Department of Sustainability and Environment / Trust for Nature statewide project, ensuring the permanent protection and ongoing management of this and other significant habitat. These actions will help the Swamp Sheoke and also benefit a range of other significant species, for example the endangered Red-tailed Black-Cockatoo (also listed under the Flora and Fauna Guarantee Act 1988), which this covenant assists by its position, and by providing habitat and both of the cockatoo’s two critical food trees.

Conclusion

Trust for Nature plans to build upon these partnerships in order to protect more endangered habitat. Identifying and protecting the most valuable remaining vegetation in the endangered category is fundamental to a landscape scale vision such as Habitat 141¹, a project that plans to restore ecological function across a large area of temperate Australia from the ocean to the outback, south to north through western Victoria.

Reference

Walker, I. (2003). Action Statement No.133 Swamp Sheoke Casuarina obesa. Department of Sustainability and Environment, Melbourne.

¹ See also preceding article by Andrew Bradeyin this issue

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