Trees are great survivors; some can live for hundreds to thousands of years. Don looked at two magnificent old gums in his garden, which to the casual observer look half dead and ready for the chop. Both are centuries old and even though they have hollows and parts of them have died off, they are really healthy and could well live another few hundred years. The value of hollows in trees as nesting sites for a range of native animals, birds and reptiles is only now being fully realised.
In the past tree surgeons would have tried to ‘fix’ Don’s trees by filling the cavities. Worse still they may even have recommended complete removal of the trees. Those sort of practices originated in Europe and America where hollow trees can be a real problem. However, research has revealed that Australian trees, particularly eucalypts, have evolved a wonderfully cunning survival strategy based upon the formation of hollows and the complete decay of the centre of the tree.
Mature trees are composed of an inert core, the heartwood, surrounded by a ring of sapwood, which conducts water and minerals through the tree. This wood is incased in a protective layer of bark. Young trees are solid to the core but older trees can forfeit their heartwood without any harm occurring. The sapwood will continue to conduct food and water throughout the tree and the decaying centre of the tree has a myriad of functions.
As the years go by the fast growing trees use up all the nutrients in the surrounding soil. Without changes to the food demands of the tree and some method of increasing the availability of nutrients in the soil, the tree would probably decline and eventually die. Rather than this happening a fascinating succession of events occurs: Pathogens such as fungus gain entry to the centre of the tree. They pave the way for termite attack, and finally a bush fire may burn through leaving the tree completely hollow. As the heartwood rots away, it provides the tree with a much needed boost of fertiliser. At the same time, hollows form in the trunk and limbs of the tree. The process is helped along when animals and birds make their homes in the hollows. These creatures renovate cavities with their beaks, teeth or claws; meanwhile all their droppings fall to the ground and feed the tree. Trees can’t move around to find nutrients, but by providing nesting hollows for native wildlife the trees ensure that the nutrients come to them. Bats, possums, gliders, owls, parrots, snakes, frogs and skinks as well as a number of rare and endangered species are hollow dependent. A notable example is Leadbeater’s possum, the faunal emblem of Victoria, which lives in large old trees in the montane ash forests of Central Victoria. A small hollow suitable for a pigmy possum takes about 100 years to form, while hollows suitable for parrots and larger animals can take up to 400 years.
New research has indicated that the critically endangered Australian Gouldian Finch is dying out because of a shortage of nesting hollows in gum trees. It seems that land management practices of annual burning off of grasslands in Northern Australia has seriously depleted the number of gum trees that the gouldian finches nest in. To make matters worse, another finch, the Longtailed Grass Finch, is evicting the docile Gouldian Finch from whatever nesting-hollows that remain. It takes about 150 to 400 years for a seedling gum tree to grow up and form suitable hollows for finch nesting, so this problem will continue for hundreds of years to come. Since there are only about 3000 Gouldian finches left in the wild, extinction seems inevitable. However, Save The Gouldian Fund may just solve the problem. They are attaching artificial nesting hollows to dead or living trees in certain areas and this has led to a 100% increase of Gouldian Finch numbers in those areas. Please donate whatever you can afford to: Save the Gouldian Fund, PO Box 1457 Cooranbong NSW 2265.
No they won’t. As any engineer will tell you, a hollow pipe is almost as strong as a bar. Hollow trees are structurally very sound and they may even benefit from increased flexibility when they lose their centres.
Plant, retain and protect native species which develop hollows don’t block or fill hollows: they are vital for the survival of both gum trees and native wildlife
