NORFOLK Island Pines along WA’s coast are facing a slow death; being killed by a friendly fungus that appears to have run amuck.
But is a fungus really to blame or is there an even bigger elephant in the room?
At the southern end of the Fremantle Traffic Bridge there is a sign board telling us “This is Fremantle”with an aerial photograph showing all our Norfolk pines as brown. Unfortunately this photograph may be predictive.
Norfolk Island pine (Araucaria heterophylla) and Cook Island pine (A. columnaris) are not Australian species. They are endemic to the two named Pacific islands. Cook pines differ from Norfolk pines by having a rougher darker bark, a darker green leaf mass and, surprisingly, they lean slightly towards the equator.
Both species have become very popular in WA’s sandy sea-side suburbs. In some places, like the middle of the Esplanade Reserve, they’re the only tree species present.
All along WAs coast from Esperance to Geraldton there are reports of Norfolk pines showing a range of symptoms from early decline to death.
Some of the Somerville Auditorium’s awesome Cathedral of Trees are in decline. Most of the Cook pines I have seen appear to be healthy. In some places diseased Norfolk and healthy Cook stand together.
Why are Norfolk pines that have been perfectly healthy for decades now showing decline leading to death? If only old pines were dying maybe the deaths could be blamed on old age. However young pines seem more susceptible than old pines. What has changed?
Local scientists Hossein Golzar and Treena Burgess have isolated the fungus Neofusicoccum parvum from Norfolk pines.
This fungus is usually benign and grows on Norfolk pines and on other plants such as eucalypts and avocados without causing a problems.
But as the fungus produces spores, it might be spread far and wide by wind or rain, insects or birds like Carnaby black cockatoos and also by pruning tools.
Drs Golzar and Burgess postulate that our shorter, warmer winters and longer, hotter summers are putting our Norfolk pines under stress and turned a once friendly fungus into a pathogen.
In a recent talk at UWA, Dr Felipe Albornoz reported he and his colleagues have found N. parvum on both healthy and diseased trees at the Somerville Auditorium.
They also found that soil around diseased trees was 2.5 times more compact than around healthy trees. Norfolk pines have a relatively shallow root system so soil compaction or a drop in the water table could cause stress.
I know of a Norfolk pine that received a heavy pruning in December 2019 with the removal close to the trunk of four full length branches. Over the 10 months since then, the branches above the removal sites have developed severe decline while the branches below are still relatively healthy.
This suggests, but doesn’t prove, the pruning equipment transferred the fungus to this tree. A more likely possibility is that pruning stressed the tree and made it susceptible to colonisation by the fungus.
There is evidence that individual trees might be stressed or damaged by wind or hail, by soil compaction or a falling water table, and by hard or careless pruning.
But I find it hard to believe that these things can account for decline of so many Norfolk pines stretching right around the coast.
I’m convinced that Golzar and Burgess are correct. Climate change is the real culprit rather than the fungus. The fungus is taking advantage of the stress caused by climate change.
I think it is probably a three-stage problem. Firstly, the pine and the fungus live together in harmony (it may be a very delicately balanced harmony too); secondly, climate change-related stress and in some cases, man-made stress causes the balance to be upset; and thirdly, the fungus becomes aggressive in the weakened pine which slowly succumbs to the now pathogenic fungus and dies.
Unfortunately we have to live with the new changed climate, at least for the foreseeable future. It is becoming clear that Norfolk Island pines are no longer suited to our new climate. The jury is out on Cook Island pines.
Thus it is time to stop planting Norfolk pines and start planting in our gardens and parks Australian species more suited to our hotter dryer climate.
Dr Mac Nish is a retired plant pathologist who lives in East Fremantle