By Daniel Fuller
If what some people say about eucalypts were true, they’d be sentient monsters intent on destroying human civilisation itself. Apparently, they are widow makers, their roots damage property, they poison the soil, they cause fires, and the list of offences goes on. Dr Dean Nicolle shares some truths.
I had the pleasure of interviewing legendary Australian botanist, arborist and ‘gum nut’, Dr Dean Nicolle, as part of the Plants Grow Here podcast series celebrating National Eucalypt Day in March. Dr Nicolle established and also manages the largest collection of eucalypts in the world at Currency Creek Arboretum.
The questions I asked him were based on an illuminating article he wrote for Remember The Wild called “Eucalypt Mythbusting: A Comprehensive Guide”.
One of the main myths associated with eucalypts is that they are what is termed “widow makers” which insinuates their limbs could drop and kill you at any moment. Certainly, some eucalypt species are known to drop heavy limbs, such as river redgums (Eucalyptus camaldulensis).
However, that’s not the case for most eucalypts, especially multi-stemmed mallees and smaller shrubs like the Silver Princess (Eucalyptus caesia) which won’t cause much damage, even if they do drop a limb. The truth is that large trees do drop limbs, and many eucalypts are large trees.
Invasive roots that can damage structures are also attributed to eucalypts but again, this problem isn’t unique to eucalypts. Large trees with shallow roots cause damage to structures, including (but not limited to) certain eucalypt species.
It’s believed eucalypts encourage pests, including borers, lerps, and termites. Every plant species is susceptible to their own unique suite of pests and diseases, and eucalypts are no different. The pests that attack eucalypts aren’t especially troublesome, even the wide range of termite species they can harbour.
When you see termites in your house, you should be concerned but they aren’t a problem when they’re in the tree unless the tree has a higher likelihood of branch failure. Termites don’t affect tree health, they only impact tree structure as they eat the deadwood within.
Eucalypts are blamed for their supposed allelopathy, meaning that they poison the soil. However, during our chat, Dean mentioned a study in California that seems to disprove this theory, featuring Tasmanian blue gums (Eucalyptus globulus).
This study was able to prove that diversity below the trees was unchanged when compared to the diversity below native oaks, indicating that the eucalypts did not change the soil conditions drastically compared with other trees. However, the diversity of plants was increased where no trees were present, indicating it is the root competitiveness and shading that can kill plants beneath eucalypts, not a chemical process.
As I mentioned in my article in April’s edition of Hort Journal Australia about my interview with Linda Baird, CEO of Eucalypt Australia in, Dean points out that fire may be beneficial to certain eucalypts, however, most eucalypts don’t thrive with fire.
It came as a surprise to me that Dean believes that fire and smoke do not help any eucalypt seed with germination. Smoke water is water infused with smoke and is used by some propagators in the belief that it can help initiate germination by simulating post-fire conditions. Contrary to what I’d previously heard, Dean’s research indicates it’s unlikely to increase eucalypt germination success rates.
If you’d like to hear Dean going into more detail about these myths and a couple of others, subscribe to the Plants Grow Here podcast on Apple Podcasts or Spotify and listen to episode 95, “Eucalypt Mythbusting”.