The Times Australia
The Times World News

.

Why sweet-toothed possums graze on stressed, sickly-looking trees

  • Written by Gregory Moore, Doctor of Botany, The University of Melbourne
Why sweet-toothed possums graze on stressed, sickly-looking trees

From time to time, I’m contacted by people who have a favourite garden tree that seems suddenly to be in serious decline and lacking healthy foliage. Often the decline has been occurring over many months, but when first noticed, the change seems to have been dramatic.

The symptoms described accord with grazing — where animals nibble at foliage until it’s quite degraded — so I ask if they have seen brushtail possums in the tree.

More often than not the answer is a firm, “No!”

However, just because you haven’t seen them, it doesn’t mean the possums aren’t there. One owner, who said they weren’t aware of any possums, checked at night with a torch; they counted 56 possums in a single, sick-looking river red gum.

It’s not uncommon for one tree within a group of the same species to be grazed while other trees are left alone.

In the early evening, a steady stream of possums can be seen coming from all directions and from nesting sites in other trees hundreds of metres away, all homing in on the one sickly specimen.

To the human eye, this seems very strange behaviour. Wouldn’t the possums be better off grazing on a healthy tree?

But possums are real tree experts and know exactly what they are doing.

A mother and baby possum in a tree.
Possums are real tree experts and know exactly what they are doing. Shutterstock

Read more: Curious Kids: if trees are cut down in the city, where will possums live?[1]

It’s all about the sugar content

The common brushtail possum, Trichosurus vulpecula, will eat both plants and small animals if given the chance, but plants form the bulk of their diet[2]. Eucalypt leaves are a favourite, but they’ll nibble the leaves of other plants in our gardens.

So what is going on when one tree is grazed in preference to others? One of the main drivers revolves around sugar.

A possum is in a gum tree. Eucalypt leaves are a favourite for possums. Shutterstock

When plants photosynthesise, one of the first products of the process is sugar. Sugars are carbohydrates made up of carbon, hydrogen and oxygen atoms and one of the most common is glucose (C₆H₁₂O₆), which is the common sugar used in coffee, tea and cooking.

Sugar may be copping a bit of stick at present for its role in human diets, but in terms of plant metabolism, glucose is a marvellous molecule.

It is made from simple and ready available ingredients. It is soluble in water and can be easily transported around inside the plant. And it stores significant energy.

This makes it a very accessible and desirable molecule within the plant, but too much glucose in solution can cause problems for the plant and attract grazers[3] keen on an easy sugar hit.

The plant has evolved an elegant solution to these problems. It simply takes two or more glucose molecules and bonds them together to make starch‚ which is not very soluble in water, contains lots of energy and so is an ideal storage form of carbohydrate.

The plant converts any excess glucose that it has into starch[4] for later use when things might be tougher.

What’s this got to do with possums, again?

When a plant is stressed, one of its first responses is to mobilise its resources. Among other things, it often converts its starch reserves back to sugar. As soon as this happens, the stressed plant becomes sweeter than its healthier neighbours — and brushtail possums know it.

Some stressed trees emit chemicals[5] that can be picked up by grazers. In other cases, the grazers may come upon a stressed tree by chance.

In either case, the grazer gets an increased sugar hit and so will return to the tree when the opportunity presents; other grazers may follow.

In the case of brushtail possums, a possum may return to the same tree night after night and, despite territorial disputes, may be joined by other possums in a feeding feast.

A possum is in a tree. Plants form the bulk of the possum diet. Shutterstock

A stressed tree is a grazer’s delight

Initially, the tree may have been stressed by drought, poor nutrition or waterlogged soils. The increased grazing then adds to the level of stress.

And when lots of leaves are removed, many trees such as eucalypts, elms, oaks and even deciduous conifers will respond by producing new leaves and shoots. These lovely new leaves and shoots are soft and loaded with sugars — a grazer’s delight.

With more stress, the tree converts more and more starch into sugar and produces yet more new leaves and shoots — so the grazers[6] get a sweet and nutritious reward for their efforts. They will keep returning to the same tree.

All of this extra grazing comes at a price to the tree, which is exhausting its starch reserves, but getting little or no reward from the sugar produced.

Eventually, the tree will succumb. It may die from starvation due to the loss of its reserves and the failure of new foliage to survive long enough to photosynthesise. Or it may die from another environmental stress or a pest or disease attack.

Grazing can be lethal to a tree, but you can see why the grazers keep coming back.

Stressed trees are an easy and rewarding energy source. Perhaps, like us, the possums become addicted to a high sugar diet and simply can’t resist returning to the tree — even if, in the end, the tree is grazed to death.

Read more: Hidden housemates: when possums go bump in the night[7]

References

  1. ^ Curious Kids: if trees are cut down in the city, where will possums live? (theconversation.com)
  2. ^ diet (environment.des.qld.gov.au)
  3. ^ attract grazers (www.mytutor.co.uk)
  4. ^ starch (sciencing.com)
  5. ^ chemicals (research.libraries.wsu.edu)
  6. ^ grazers (www.doc.govt.nz)
  7. ^ Hidden housemates: when possums go bump in the night (theconversation.com)

Read more https://theconversation.com/why-sweet-toothed-possums-graze-on-stressed-sickly-looking-trees-169241

Times Magazine

Building a Strong Online Presence with Katoomba Web Design

Katoomba web design is more than just creating a website that looks good—it’s about building an online presence that reflects your brand, engages your audience, and drives results. For local businesses in the Blue Mountains, a well-designed website a...

September Sunset Polo

International Polo Tour To Bridge Historic Sport, Life-Changing Philanthropy, and Breath-Taking Beauty On Saturday, September 6th, history will be made as the International Polo Tour (IPT), a sports leader headquartered here in South Florida...

5 Ways Microsoft Fabric Simplifies Your Data Analytics Workflow

In today's data-driven world, businesses are constantly seeking ways to streamline their data analytics processes. The sheer volume and complexity of data can be overwhelming, often leading to bottlenecks and inefficiencies. Enter the innovative da...

7 Questions to Ask Before You Sign IT Support Companies in Sydney

Choosing an IT partner can feel like buying an insurance policy you hope you never need. The right choice keeps your team productive, your data safe, and your budget predictable. The wrong choice shows up as slow tickets, surprise bills, and risky sh...

Choosing the Right Legal Aid Lawyer in Sutherland Shire: Key Considerations

Legal aid services play an essential role in ensuring access to justice for all. For people in the Sutherland Shire who may not have the financial means to pay for private legal assistance, legal aid ensures that everyone has access to representa...

Watercolor vs. Oil vs. Digital: Which Medium Fits Your Pet's Personality?

When it comes to immortalizing your pet’s unique personality in art, choosing the right medium is essential. Each artistic medium, whether watercolor, oil, or digital, has distinct qualities that can bring out the spirit of your furry friend in dif...

The Times Features

How much money do you need to be happy? Here’s what the research says

Over the next decade, Elon Musk could become the world’s first trillionaire[1]. The Tesla board recently proposed a US$1 trillion (A$1.5 trillion) compensation plan, if Musk ca...

NSW has a new fashion sector strategy – but a sustainable industry needs a federally legislated response

The New South Wales government recently announced the launch of the NSW Fashion Sector Strategy, 2025–28[1]. The strategy, developed in partnership with the Australian Fashion ...

From Garden to Gift: Why Roses Make the Perfect Present

Think back to the last time you gave or received flowers. Chances are, roses were part of the bunch, or maybe they were the whole bunch.   Roses tend to leave an impression. Even ...

Do I have insomnia? 5 reasons why you might not

Even a single night of sleep trouble can feel distressing and lonely. You toss and turn, stare at the ceiling, and wonder how you’ll cope tomorrow. No wonder many people star...

Wedding Photography Trends You Need to Know (Before You Regret Your Album)

Your wedding album should be a timeless keepsake, not something you cringe at years later. Trends may come and go, but choosing the right wedding photography approach ensures your ...

Can you say no to your doctor using an AI scribe?

Doctors’ offices were once private. But increasingly, artificial intelligence (AI) scribes (also known as digital scribes) are listening in. These tools can record and trans...