The trees of Mahoney Reserve

I had been meaning to get down to Mahoney Reserve on the corner of Illawarra & Wharf Roads Marrickville South since I saw ghostly skeletons of Poplar trees in the distance a

Showing the dead Poplars & giving an idea of their height

couple of weeks ago.  Once we got down to have a look it became apparent that all the Poplars are dying. 6 Poplars are stone dead. I was told they died last year. They stand like mutilated sentinels, a ghostly grey.

This is an avenue of 21 Poplars planted around 40-years ago. As a guess, each tree would be about 22-26 metres tall. These are substantial trees in Marrickville LGA as there are not many of this height & size. They are also landmarks as they are visible from many areas on both sides of the river.

In my amateur assessment, the trees have been killed by boring insects as there is evidence of borer holes all through these trees.  Only the 3 Poplars situated along Illawarra Road appear to be savable.  They seem to be in reasonable condition with only small amounts of dieback. They too have evidence of boring insects, but like the Poplar further along the Cooks River, intervention by chopping back the offending branches may just be what will allow them to survive if the borers have not yet reached the trunk. (See – http://savingourtrees.wordpress.com/2010/12/22/can-this-poplar-be-saved/ )

TreeHelp.com http://www.treehelp.com/trees/trees-insects.asp says the following –  “Boring insects are often the most harmful to trees & if left untreated can cause death. Boring, or tunneling, insects cause damage by boring into the stem, roots, or twigs of a tree. Some lay eggs which then hatch & the larvae burrow more deeply into the wood blocking off the water-conducting tissues of the tree.  Boring insects generally feed on the vascular tissues of the tree. If the infestation is serious, the upper leaves are starved of nutrients & moisture & the tree can die. Signs of borer infestation include entry/exit holes in the bark, small mounds of sawdust at the base & sections of the crown wilting & dying. It is important to regularly monitor a tree’s trunk for signs of boring insects to enable early identification & quick treatment. The key is to prevent infestation by keeping the tree as healthy as possible. This includes proper pruning, watering, mulching & fertilization. Pruning should be done in late fall or winter to avoid attracting insects to open wounds. Dead or fallen wood should be removed immediately. Once borers are present, control becomes extremely difficult, but steps should be taken to prevent further damage & to stop the spread to surrounding trees.”

A double row of Casuarinas dividing Mahoney Reserve & Marrickville Golf Course. These trees don't reach half the height of the Poplars

From my reading I understand that all trees should be checked periodically for signs of disease. Borer infestations can be diagnosed before dieback starts by seeing holes on the trunk or branches. At this state, systemic, chemicals can be put into the ground around the tree (maybe a problem with the Cooks River metres away, though they say the chemicals are non-toxic). Chemicals are also injected into the tree to kill off all boring insects at whatever stage of development they are at.  There is also a technique of literally skewering the insect to death.  Then the tree is fertilized to help fend off the stress it has been under.  If the tree is severely infected, it needs to be destroyed on site to prevent taking the insects to another location. The trunk & roots need to be removed from the soil as well & the soil treated before any new trees can be planted.

One by one we looked at the trees along the Wharf Road side of Mahoney Reserve. It was difficult to find a tree that wasn’t showing borer holes & rot.  Many had ant infestations as well.

The trees of Mahoney Reserve are very sick. Dieback takes a while to manifest, sometimes up to 5 years. My limited knowledge tells me that planting new trees will just provide further resources for the boring insects that are in control of this area unless the infestation is removed.

The Poplars especially, with their 2-3 metre girth are substantial carbon sequesters.  To have lost 6 & have the rest at serious risk of being chopped down as well is devastating on a number of levels.  Big canopy trees is what the park needs to replace the trees that have died & any others that will be lost.

We saw boring damage on about 70 trees in the one park & there are probably more. Just leaving the problem play itself out is not a solution. This park needs a comprehensive management plan to ensure what trees can be saved are saved & a replacement program be implemented to plant trees that will produce substantive trunks & shade. Shaded avenues along the parks & the river walks will be more & more essential as the sun is getting hotter & hotter.

I put up a 2 minute YouTube of Mahoney Reserve showing the trees – http://www.youtube.com/watch?v=pGlpS_YcRLY&feature=BF&list=ULPOgkK3s0Qo0&index=6

The avenue of dead & dying Poplars are on the left to centre with Casuarinas on the right