Scientist narrows his vision on forest ecology

Dr. David Lindenmayer has written many books and papers on forest ecology and spent years researching the Leadbeater’s Possum in the Central Highlands. He’s always been a fearless advocate for Leadbeater’s Possum against those who seek to log it out of existence. His books make his research accessible to the general public. However we are sorry to say that he has recently had a turn – in his stand on logging. We are disappointed to see someone of his calibre now involved in a blatantly unscientific process. We don’t want to brand him an eco-rat with the others, but we disagree with him, and here’s why.

Besides supporting the WWF ‘blueprint for Tasmania’ which is basically a non-scientific plan to preserve the logging industry, he has come to see logging in native forests as acceptable if tiny islands of forest are left in each clearfelled area. Although much of his past work has helped argue the case against this exact type of pointless management, he is now advocating it as solid science. Other academics are shocked by Lindenmayer’s new-found politics. ‘

‘Variable retention harvesting’

In July, Dr Lindenmayer took 25 or so environmentalists out into the forests of the Central Highlands to explain new research he’s conducting under the DSE umbrella. The research attempts to ensure that mixed age forests are somehow maintained despite being subject to industrial logging.

This method, called ‘variable retention harvesting’, retains small islands of forest within a clearfelled area. In the test sites either one 1.5 hectare area is retained within an average 30 hectare logging coupe or three half hectare areas. The idea is that enough trees within the retained clumps would grow to the 200-400+ year old trees that Leadbeater’s Possums would live in, while feeding in the surrounding wattle regrowth.

Costly and flammable

One test site has several sites of rainforest significance, large stands of mixed age forest and old growth. The coupe we looked at had three 1/2 ha clumps unlogged. Lindenmayer’s research team worked closely with department to ensure the islands survived the post-logging hot burn. This method took two days instead of a few hours and cost $5,000 extra. The Department said that in future this cost would be reduced as areas to be maintained within the coupe would be set between coupes rather than within them. Which looks like it will be business as usual in the end. The areas between coupes are often in gullies, and Dr Lindenmayer has previously warned that “vegetation strips retained along watercourses. . .
are usually not suitable for Leadbeater’s Possum”(p.110 All quotes in this article come from Wildlife + Woodchips: Leadbeater’s Possum – A test case for sustainable forestry, by D Lindenmayer, University of NSW Press, 1996.). As well, retained strips of vegetation between coupes are often incinerated in post-logging burns. The site we inspected survived the fire. However, despite the best efforts, a larger test site of 1.5 ha above Marysville was not so lucky.

Unsuitable for Leadbeater’s

David was concerned about the loss of hollow bearing trees and said this would be a means of ensuring older trees survived. 1.5ha in a 30 ha coupe is 5% of the original forest; this flies in the face of Dr Lindenmayer’s earlier opinion that:

    [e]ven if half a forest block is reserved, there may still be significant negative effects of [logging] on Leadbeater’s Possum, because those areas most suitable for animals are also the ones most likely to be logged. (p.110)

Dr Lindenmayer has in the past emphatically denied that clumps of habitat trees in a sea of regrowth are useful for Leadbeater’s, as the possums prefer habitat trees that are regularly distributed, not in a “clustered or clumped arrangement”. He said that:

    if hollow trees are retained on logged areas, they are often clumped together to better protect them during logging and regeneration burns. However, there are significantly reduced rates of occupancy of clumped hollow trees, possibly as a result of the possums’ territorial behaviour. As they defend their nest-trees and the surrounding forest against member of their own and other species, when hollow trees are clustered together, competition for hollows and aggressive behaviour between animals may substantially reduce the number of occupied trees.(pp. 105-106)

He goes on to say that many attempts to conserve nest sites in logged areas have failed due to logging fires, and he reminds us that the large dead trees favoured by Leadbeater’s Possum are particularly flammable, collapsing as soon as they are burned, and that increased wind and temperature fluctuations in logged areas may hasten the collapse of retained trees. (p.106)

Fragmenting populations

And as for those juicy wattle feeding grounds that grow around each retained area after clearfelling, his prior research shows that Leadbeater’s rely on large tree crickets and other insects that live in the bark strips which hang from the branches of montane ash trees as “a valuable source of protein”, and “it may be a long time before these flightless insects can re-colonise logged and regenerated sites”.

Not to mention the dangers of isolation of the possums by fragmentation of the forest, in which small colonies in retained clumps could become extinct (perhaps by predation by owls which would also favour those same retained clumps) and never get re-colonised, gradually leading to larger extinction patterns.(p.107) He states emphatically:

    if key habitat refuges are destroyed or become highly fragmented or isolated, survival would be impossible as there would be no further sources of animals to recolonise logged and regenerated areas.(p.100)

Dysfunctional eco-systems

The main focus of Lindenmayer’s research is protecting the Leadbeater’s possum, however when asked about the Yellow-bellied Glider he responded that this species required old growth and would not be directly helped by this method, nor would rainforest, or the myriad of other factors that determine a functioning ecological system.

David’s research appears to be a micro model and does not address the problem logging has on biodiversity across the landscape. Research shows that it could take 1,500 to 2,500 years for forests to regain their ecological integrity after clearfelling. Maintaining a few trees within a coupe will undoubtedly have a minimal effect.

Gord ‘elp other areas

David said this model was only appropriate in the Central Highlands and further research would be needed to determine its applicability to other areas. He believes that the present reserve system along with this method would be sufficient to protect the Leadbeater’s Possum.

He also said that the Central Highlands and Tasmania would be the last areas to end logging. If that’s the case, we need to bring about that end as quickly as possible.

Liz Ingham Environment East Gippsland / Megan Clinton – The Wilderness Society

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