Acacia peuce - Waddy Wood

Monday, Jan 23, 2012 at 23:34

Stephen L (Clare) SA

Nationally listed as vulnerable, and classified as endangered in the Northern Territory, Acacia peuce can only be found in a few remote desert locations in Australia, all on the margins of the Simpson Desert. In the Northern Territory, it grows about 60 kilometres northeast of Andado Station. In Queensland it can be found growing between 10 and 60 kilometres north of Birdsville and a further 400 kilometres north of Birdsville from Marion Downs Station through to Boulia.

With no one common name, it can be commonly known by any of the following Europeans names, Waddy Tree, Waddi Tree, Waddy Wood and the Birdsville Wattle, depending where the trees are found. Aboriginal tribes also knew it by various names such as Aratara by the Arunda tribe, Kurriyapiri and Red Ochre Father by the Pitta Pitta tribe, Kungariya by the now extinct Midhaga tribe and Arripar by the Lower Arrente group. European association with the Waddy Wood goes back to 1860, with Waddy Wood seeds found in the diary of William John Wills, of the famed and ill-fated Burke and Wills Expedition. Those seeds would have been collected in the Birdsville area.

Acacia peuce is a slender, erect tree and can grow up to 18 metres tall, with grey- brown bark. Acacia peuce is very she-oak like in appearance, with usually short horizontal branches, and pendulous branchlets and phyllodes. Yellow flowers, which can occur from October through to March, are solitary and often inconspicuous. The flowers are followed by large, flat papery pods from December through to June. Seedpods are around 20 centimetres long and 3 – 5 centimetres wide and contain large flat seeds. Germination and seedlings establishment in Acacia peuce are periodic phenomena that culminate over short periods within cycles of above average rainfall and are usually concentrated to within 30 metres of large mature trees.

Waddy Wood timber is very dense and durable with dark red heartwood. Acacia peuce have the ability to fix nitrogen, which improves soil quality for many other species of plants that grow around the trees. Though the Waddy Wood is a long-lived tree of over 500 years, the trees are extremely slow growing. The young seedlings have a very long juvenile period before they mature and produce their first flowers, which can take between 70 and 100 years. In this juvenile phase, the young trees are upright in form with dense prickly foliage.

The timber is so dense it has been known to have damaged axes and saws and when dry is almost impossible to drill. For this very reasons it was sought after for timber posts in the past. Aboriginals used the timber for clubs.

The dating of the Waddy Wood timber gave rise to the realisation that dead Waddy trees can remain intact, storing carbon and providing habitat for at least 200 years (and likely much longer) after the death of the tree. The role of arid woodlands in carbon storage in Australia is virtually unknown and efforts to better understand the implications for carbon accounting posed by the durability of Acacia peuce are in progress.

Biochemically Acacia peuce is related to Acacia crombiei and Acacia carneorum. While the characteristics of its flowers and fruit are very similar to those of Acacia crombiei, Acacia peuce differs in having narrowly linear, flat phyllodes. While Acacia carneorum has similar, albeit shorter phyllodes to those of Acacia peuce, it has very different pods and seeds.

Waddy Wood locally dominant on stony flats or gibber plains areas between longitudinal dunes or on alluvial flats between ephemeral watercourses. The southern populations occur on fixed shallow sand aprons over clay and gibber slopes associated with denuded mesas. In the Boulia area, Acacia peuce is associated with alluvium and ancient riverbeds of the Hamilton and Georgina Rivers, with an average annual rainfall of 150 millimetres.

Of the 3 distinct areas where Acacia peuce is found, the Northern Territory populations are by far the smallest, with only around 1000 mature trees. By contrast there are over 1½ million mature trees in the Birdsville area The Northern Territory trees are the only trees that are found mostly within a dedicated Reserve, the Mac Clarke Conservation Reserve, while the Queensland populations occur on private Pastoral Properties. The geographic range of Acacia peuce within the Mac Clarke Conservation Reserve is small at around 20 kilometres, but occupying about 10 km2. All stands of Acacia peuce in the Mac Clarke Conservation Reserve, covering an area of 3041 ha, and the adjoining Andado Pastoral Lease. In 1985 only 475 ha within the Mac Clarke Conservation Reserve had been fenced, protecting less than 50% of the Acacia peuce in the Northern Territory, with the remaining stands fenced by 2004.

The Northern Territory population of Acacia peuce has a long history of monitoring, with the first phase taking place in 1979. This monitoring had the aim of providing baseline data for the management and conservation of the species. The program was designed to examine seedling emergence and survival, seedlings height growth rates, adult growth rates and flowering and fruiting patterns. At that time, fourteen 25 x 25 metre regeneration plots were established to monitor the fate of seedlings that emerged. Every individual seedling that was less than 20 centimetres high within the plots was individually labelled and monitored at least annually through to 1996. Today there are 26 individual established monitoring plots, mostly all within the Mac Clarke Conservation Reserve.

In addition to the seedlings, 36 adult trees and 10 seedlings were simultaneously monitored for growth rates and fruiting and flowering in relation to climatic events. In 1980 the population size and age structure was audited using 14 circular 50-metre radius plots, before the program was disbanded. In 2001 the population was audited again using the same methods that were previously used. All seedlings that emerged from the high rainfall of 2000 – 2001 were tagged and monitored, but none survived beyond 2004. National Parks Ranger staff now undertakes routine visits of four to five times a year to the Mac Clarke Conservation Reserve.

During the monitoring of these trees, one particular stand of mature trees was affected by fire. With prolonged rainfall and the subsequent high grass growing around the trees provided fuel connectivity between the stand of Acacia peuce and adjacent flammable dune fields. The resulting wildfire caused by lightning strikes had catastrophic consequences with 200 trees killed and only 9 trees surviving. Regeneration was negligible.

Today he greatest threat to Acacia peuce is fire, cattle impact through grazing, trampling and rubbing and lightning strikes directly on the larger mature trees.

A special thanks goes to Val for checking the draft and making the appropriate changes where necessary.

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