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Possum induced tree decline is an ecological disaster - A controversial opinion

[Candobetter.net Editor 4 April 2018. Our attention has been drawn to the fact that the title of this article could make people think that candobetter.net is generally in agreement with Dr Yugovic on this matter. The fact is that we do not agree, but we have permitted him to put his argument here, in response to other articles that find that tree dieoff has many other causes. These articles can be found under the general topic of 'predator restauration>.]In response to Hans Brunner’s post, I note he does not actually quote me and if he reads my article ("Do ecosystems need top predators?" on the SPIFFA website and in the journal Indigenotes) carefully he will find there is no recommendation for more foxes, cats and dogs. The term ‘plague’ of possums is not mine and I use it in quotation marks in the article. It is a term I have heard locals use, and with some justification.

(Photos provided by Dr Jeff Yugovic)

Possum induced tree decline is very real and is a very serious threat to indigenous trees on the Mornington Peninsula, with thousands of trees dead or dying in many locations. Just drive down Old Mornington Road, Walkers Road or Kunyung Road in Mount Eliza or visit Mount Martha Park to see for yourself, but you need to be able to identify indigenous eucalypts as the many planted non-indigenous eucalypts are generally not eaten by possums. I also attach further photographic evidence.

The evidence of possum damage is all too abundant and there are several consultant reports on this issue (see my article for some references). Mornington Peninsula Shire has an unreleased tree pathology report on tree decline on the Mornington Peninsula which says in relation to Mount Martha Park:

Diagnosis: The sparse crowns of the trees in plots appear to be indicative of browsing damage. Eucalyptus pauciflora appeared to be the main species affected. The probable cause of browsing animals is supported by the banded trees in one area of the park, which show significant crown recovery following the installation of the bands (Figure 20A). Prognosis: Continued unsustainable browsing will result in further defoliation and dieback and eventual death of trees in the Park.


We need to recognise the problem of possum induced tree decline, and move on to analyse what is causing this imbalance and how it can be addressed, noting that the phenomenon was not reported by early Europeans when Victoria was in its original and natural condition and seems to have developed since European arrival.

Jeff Yugovic

Comments

The photo of the tree with the possum band on the branch which has recovered its foliage is fairly compelling , but doesn't totally convince me that possums damaged the other branch. I wonder why I am so hard to convince. I would want to see other proof that possums had consumed a large amount of the tree's foliage. That would show up in possum scats if it were so. Has anyone watched their browsing behaviour? i.e caught them in the act. I am skeptical because of my experience with a council which was hell bent on evicting possums from a park.When the reason for installing over 100 metal guards on palm trees- that possums spread fusarium palm wilt, was found not to be true and that neither did the trees in question have this disease, after all, another reason was 'found'. This was that the possums were eating the palm fronds. It seemed that the decision had been made to put the bands on the trees whether they were needed or not.

For convincing evidence of possum induced tree decline, you only have to see it: possums can be readily observed in affected trees eating leaves and causing the defoliation directly, and they leave characteristic tear marks and bite marks on the remaining leaves.

In addition, possum droppings are abundant on the ground, and are obvious on decks, on rooves, in gutters and on hard surfaces. Incidentally, hygienic rubber gloved protection must be used when cleaning these often wet and difficult to access places as Brushtail Possum carries the parasitic diseases leptospirosis, giardia, cryptosporidiosis and Q fever, all transmittable to humans. Despite the problems associated with possums I still like them.

The tree branch in the article photo could not be saved because its angle was too low (it was near horizontal) so that possums could walk over the guard and continue to access the branch and eat its leaves. I watched the branch slowly die and was not able to prevent its defoliation.

I have had to remove possum killed trees (for safety reasons) and so have many other residents in the local area. It can cost $1500 to remove a large dead tree, so a possum guard is a sensible investment that saves money and saves trees. I have been involved in the installation of many possum guards on the Mornington Peninsula over 20 years and they definitely save trees.

Fusarium palm wilt is a problem of palm trees, and, whether or not it is spread by possums, it is not related to possum induced tree decline in native vegetation.

Jeff Yugovic

The article claims that there are thousands of trees dead or dying in many locations in Mornington Peninsula because of overgrazing by possums. One must remember that these areas were once small fishing villages, with holiday houses and camping. The rate or urban sprawl has increased, with more people living there permanently. Traffic and disturbances have continued to increase. It means loss of trees, and habitats for native animals.

The loss of habitat would mean that predators would be fewer, and more dispersed. It's easy to look at the lack of leaves on bare branches and dead or dying trees, but the big picture must be considered. It seems that while many of our Australian native species have fragile existences and cannot cope with changes and loss of habitats, and climate change, etc, some have the audacity to survive urbanization - then they are called a "pests".