Autumn 2002
BIODIVERSITY

 

by
Greening Australia's Re-vegetation Manager

Neville Bonney

With biological diversity becoming the accepted modus operandi within tree planting programs, we need to understand the importance of individual fauna.

 

During the past three seasons, Greening Australia SA (Inc.) has on the majority of sites looked at the importance of habitat creation when designing seed mixes for re-vegetation projects.

 

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Observation over many years shows that plant species are in decline in South Australia.    Once common species on the landscape, such as Eucalyptus fasciculosa "Pink Gum", Eucalyptus cosmophylla "Cup Gum", Eucalyptus ovata "White Gum", Acacia mearnsii "Black Wattle", Acacia dodonaefolia "Hop Wattle", Acacia spinescens, Eutaxia microphylla and Grevillea lavandulacea are a few that come to mind which are rapidly becoming vulnerable species. In the case of the Grevillea species, we find that their seeding progeny these days are mostly hybrids from grevilleas in cultivation.    Monitoring, careful management and re-establishment are required.    When plant varieties are in decline, a chain reaction often takes place where other members of the food chain are affected.

 

Greening Australia (SA) has been responsible for enrichment programs for three species of fauns, those being the "Lowan" or "Mallee Fowl", "Regent Parrot" and "Sugar Glider".

 

In the South East of South Australia, depletion of Acacia mearnsii " Black Wattle, has also caused the reduction in the population of the tiny Possum-like "Sugars Gliders", which in turn is causing the death of some large majestic "River Red Gums" (Eucalyptus camaldulensis).    Mr. Robert (Bob) Beck, a noted naturalist, owns a Red Gum property at Mingbool east of Mount Gambier and has been monitoring the "Sugar Glider" decline now for more than thirty years.    He is of the firm belief that loss of the "Black Wattle" habitat has attributed to this decline.

 

An interesting article by Andrew Smith from the Ecosystem Management Department at the University of New England, Armidale, states the following in a recent article in relation to "Sugar Gliders", wattles and eucalypt die back....

 

"Dieback and the Scarab Beetle"

 

The larvae of "Scarab Beetles" live in the soil and feed on grass roots and decaying organic material.    After emerging from the soil in the spring the adults of some species feed voraciously on Eucalyptus leaves.    Dieback is episodic.    Research has shown that key elements for maintaining forest health and dieback resistance in rural ecosystems, are "Sugar Gliders and wattles (Acacia species)".

 

"The "Sugar Glider" is one of the most beautiful and intelligent of Australia's many species of possums and gliders.    "Sugar Gliders" are common inhabitants of the eucalypt forests and woodlands"

 

Although common, the "Sugar Glider" is rarely encountered because of its nocturnal and secretive habits, except when brought in by the family cat or aroused from a tree hollow by firewood harvesters.

 

The "Sugar Glider" is the principal predator of large adult scarab beetles in the forest canopy, consuming up to fifteen large adult scarabs per hour at night when the beetles are active.    Birds such as "Frogmouth Owls", may also take some adult "Scarab Beetles", but most birds are too small.

 

In dieback affected forest the number of insects in the canopy may be ten times higher than in a healthy forest, due mainly to a seasonal increase in "Scarab" coming from nearby pastures.

 

Increasing the intensity of insectivorous birds in dieback-affected forest is a difficult or impossible task, because there is not enough food for them to survive the winter when insects are scarce.    But increasing the number of "Sugar Gliders" which feed on wattles gums and other plant exudates (such as nectar and sap) during winter, can be achieved as part of the normal process of forest restoration.

 

Research in rural forest remnants in Victoria has shown that the number of "Sugar Gliders" is determined by the number of plant exudates available during winter.    The most important exudates are the gums produced by certain species of wattles, particularly "Black Wattle", Acacia meansii and the sap of the "Apple Box Tree", Eucalyptus bridgesiana.    The density of "Sugar Gliders has been shown to range from one animal per hectare where wattles are absent to as many as twelve per hectare where wattles are abundant.

 

At densities of ten per hectare "Sugar Gliders" could eat around 18000 large "Scarab Beetles" per hectare during the dieback season.    This is not enough to consume all "Scarabs" during the peak of a dieback outbreak, but should be sufficient to help the trees survive outbreaks and retain sufficient foliage to recover during the intervening periods.

 

Not all acacias produce gums and not all gums are suitable for "Sugar Gliders".    Gums differ in their time of production, quantity of production, nutrient value, solubility and persistence.    "Blackwood", Acacia melanoxylon for instance is not a gum producing wattle.

 

Other actions which can be taken to improve the habitat for gliders are to leave........ Tree hollows; Ground cover; Flowering trees and shrubs; Wildlife corridors

 

"Sugar Gliders" have been known to disperse more than 1km along roadside corridors, and can survive at high densities in linear forest habitats of little more than a single tree in width.    They can also disperse short distances (hundreds of metres) across open pasture.    Most effort should go into protecting and restoring roadside, stock route, road reserve and other corridors which link existing forest remnants.

 

Several of Greening Australia's direct seeding demonstration sites in the South East of South Australia, have been addressing this situation by seeding Acacia meansii onto "River Red Gum" sites in an effort to rehabilitate or enrich "Sugar Glider" habitat.

 

Incidentally, the loss of under storey in the upper southeast, due to vegetation clearance in the 1950's, has caused the loss of habitat for insectivorous birds and resulted in the seasonal proliferation of Lerps, Psylids and scale insects, which defoliate the "Pink Gums" and with sustained infestation will kill the trees.    Some observers have blamed phosphate fertiliser applied to the pasture causing soft lush growth on the trees, which makes them a target for Psylid infestation.    Our own observations are that there are often solitary healthy trees in the midst of infected trees and that the fertiliser would seldom appear to be applied closely to them, even if applied by aerial methods.    So that connection seems remote.

 

Greening Australia's immediate response is to assure that all of our re-vegetation projects contain a substantial mix of species suited to the site.    We aim to see that seed is collected from local provenances or on highly disturbed sites, see that the seed is from areas similar to the target establishment site.    This has seen good results over the past three years. [Ed.]

 

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This article is reprinted from the November/December 1992 Issue of "TREESPEAK” published by Greening Australia (South Australia) Incorporated and is reproduced with kind permission of the author.

 

 
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