Alarming news for large old trees in both Australia & worldwide. PhD researcher Darren Le Roux from the ARC Centre of Excellence for Environmental Decisions & the Australian National University has shown that “Australia could lose 87% of its hollow-bearing trees in the urban landscape over the next 300-years. Under the worst case scenario, we could lose all large hollow-bearing trees within the next 115-years.”
This is a massive problem because it is old trees that have natural hollows that provide homes for many native Australian birds & animals. Nearly 20% of Australian birds use hollows in some way. For 60% of these, hollows are essential. It can take a tree anything from 120-200 years to create a hollow suitable for wildlife.
About 350 Australian animals species use hollows for either roosting or nesting. This includes –
- Half of our small bats.
- Nearly 90% of our parrots.
- All of our gliders.
- All but one of our owls.
- All of our tree-creepers. http://bit.ly/14Gxolm
Of the 22 species of bats that have been recorded to utilise tree hollows in NSW, 10 of these are listed as threatened. (Gibbons & Lindenmayer 1997).
If native wildlife dependent on tree hollows cannot access these, then their numbers will decline & many will face extinction. Our environment will be worse off for this & may never recover.
A municipality may have a large urban forest, but if these trees mainly consist of small trees, then their benefit to wildlife is also small. Marrickville municipality has one of the smallest canopy covers in Australia & almost half of its street trees are 5.3 meters tall or less.
A large old tree has more peeling bark & dead branches, which offers habitat to a range of wildlife, including insects & microbats. Large trees also produce larger quantities of nectar-producing flowers & therefore better food support for wildlife.
Mr Le Roux adds more to the issue of protecting larger older trees.
“We also need to change public perceptions about big old trees. Signs displaying the biodiversity values of large old trees & other key resources in public spaces will go a long way to encourage tolerance, dispel misconceptions & create an awareness & appreciation of the importance of these habitat elements.
The traditional urban green space is dominated by overly manicured garden-style spaces that do not necessarily benefit wildlife. We should re-think this concept & get a bit messier in our parks by retaining some of the resources that are commonly frowned upon.”
His research found that “the only way to arrest the decline of large old trees requires a collective management strategy that ensures –
- trees remain standing for at least 40% longer than currently tolerated lifespans.
- the number of seedlings [new trees] established is increased by at least 60% [to provide a new batch of older larger trees for the future] &
- the formation of habitat structures provided by large old trees is accelerated by at least 30% (e.g. artificial structures) to compensate for short term deficits in habitat resources. Immediate implementation of these recommendations is needed to avert long term risk to urban biodiversity.”
Even then, he predicts it will take a period of 250-years before we see an increase of trees with natural hollows. See – http://bit.ly/1yiDeY8
Mr Le Roux did this research in Canberra, which has a much larger urban forest & also a much larger percentage of green space than Sydney’s inner west. However, many of his suggestions to prevent extinction of urban wildlife could be implemented locally with some modifications.
He suggests planting trees for longevity in derelict land, in wetlands & in some parks. We have these types of areas. Certainly the areas along the Cooks River, which is already labeled a ‘priority biodiversity area,’ could have more trees, especially in areas away from the shared path. Marrickville Golf Course has heaps of room for more trees & is a perfect place for veteran trees to be allowed to grow. There are already a number of beautiful examples within the grounds.
There is a large amount of land along the rail lines, which could become mini forests. Surely that has to be better than the current, quite large areas of weeds or grass. I am not suggesting planting directly beside the line where trees could fall on the track. Trees in appropriate locations along the rail line would not only help urban wildlife, but would also buffer noise, clean the air, improve views, create privacy & raise property values of housing that backs onto the rail line.
Large older trees can be retained safely by adding a garden bed, shrubs &/or fencing to separate people from the tree & keep them safe from any falling branches. Obviously this approach is better suited to trees in parks than the majority of street trees – at least in Marrickville municipality.
Apart from creating a safety zone around the tree using shrubs & other habitat supporting plants, Mr Le Roux suggests physically re-enforcing the structural integrity of large, old trees with cables or supporting frames. I’ve seen this approach used in busy parks across Port Macquarie, which has many veteran trees, including those with large visible hollows.
The management & preservation of older & veteran trees is yet another area where we need to take steps, not only to prevent extinction of much of our urban wildlife, but also to ensure that future generations are able to live in an urban environment that does have diversity of wildlife. The community also needs to change their perception of parks & make allowance for wilder sections, as well as preserving local areas of bushland.