Trees are killing koalas


By Mike Holt

Every time we interfere with nature we create more problems than we solve.

And yet we never seem to learn from our mistakes.

With the terrible floods that have been afflicting Australia lately, many people have offered theories about what might really be causing such widespread flooding.




It is obvious that today’s land management policies have not been effective. Instead, they have created conditions ripe for flooding. There are a few factors at work here, but by far the most important one is the tree planting and preservation policy.

For the past century or so perceived wisdom has said that if you plant trees along the banks of rivers they will prevent erosion and silting. But as we have seen, this is not the case.

Ecologists have also been telling us for years to plant more trees to combat the greenhouse effect. That sounds very reasonable. After all, trees take in carbon dioxide and exhale oxygen. So, obviously the ‘experts’ reasoned the more trees we plant the better.

Trees also help generate rain. It has been accepted as gospel for years that the more trees we grow the more water we will have.

Successive governments since the early 20th Century have accepted these ideas because so many ‘experts’ have said this is so.

As a result we have seen a long term policy of planting thousands…millions of trees along our watercourses.

But the ‘experts’ have led us up the wrong path again today, just as they did when they told governments to import prickly pear and cane toads in the past.

By planting too many trees along our waterways we are actually creating the wrong environment for a healthy watercourse. And the more trees we plant the less sustenance is available for our native animals, like the koala and possum.

Sounds strange? Not when you understand what is really happening.

What causes flooding?

We all know that water needs to flow downhill. If it can’t find a channel to flow down it will break over the banks of the watercourse where it normally runs and flood the surrounding countryside.

Next time you watch a news helicopter on TV flying over a flooded water course, look carefully at the waterscape below. It is very easy to see where the watercourse usually runs because it will be lined with trees.

We have had a huge volume of rain falling lately, so if planting more trees was supposed to reduce flooding, why are we seeing such devastating floods instead?

Today, even if farmers need to clear the land to increase production they are not allowed to cut down trees on their own property without getting council permission first. Yet our farmers are the custodians and nurturers of the land we all rely on. They are our best judges of what is best for the land to keep it healthy – not politicians and tree-hugging greenies.

Any gardener will tell you that thinning out and pruning encourages better growth. All plants need plenty of sunlight and water to grow well. When plants or trees are crowded together they become stunted as they compete for access to sunlight and for moisture from the ground.

So what happens when we don’t thin out the river bank trees?

Trees need huge amounts of water. A large tree can transpire about 600 gallons of water a day up to its leaves. That is enough to supply at least four average households with ample water for all their needs for a day.

But the more trees there are the less water there is available for each one.

As trees suck up these large quantities of water they create a ‘vacuum’ between the trees and the watercourse. Debris such as leaves, sand, soil, and twigs get sucked down into the waterway, silting it up.

When the next rain comes along the buildup of water cannot find a deep channel to flow down. Where it meets a blockage it is forced to spread out, causing floods like the ones we are seeing now.

If we want to help the water flow and at the same time reduce flooding we must have a policy that allows our best land managers to do what needs to be done.

We need much more research into water and land management. Some of the best people to talk to are those who work on the land, not politicians, especially the Greenies. Our policymakers should be talking to the farmers and other people who depend on the land for their livelihood. They are the people with the most to lose if they can no longer farm their land effectively. And as they live on the land and are able to observe how nature behaves they can also see what the best way to manage their land is.

So, to manage our water resources properly all we have to do is allow them to make logical decisions about their land, and this includes allowing them to decide if or when they need to thin out the trees on their land.

Thinning trees will encourage grasses to grow. These grasses bind the earth and prevent debris from sliding down into the water. A watercourse with only a few trees along it will deepen with each flood as larger volumes of water flow down the channel. Any blockages, such as trees and rocks that might fall into the channel will be swept away. The more water flowing through the channel the deeper it will get and the healthier the water system becomes.

The flash flood in Toowoomba and the subsequent destruction further down in the Lockyer Valley and Brisbane occurred because the water was dammed up behind debris in the waterways – the result of poor riparian land management. Eventually, the water built up to such a huge volume that when it broke free of the blockages a swathe of destruction resulted that devastated thousands of lives and businesses.

These floods come in cycles. This is not the first time that the Lockyer Valley and Brisbane have been dangerously flooded. It will not be the last. But we can mitigate the effects of the next one by taking sensible steps. I have spoken to the people tasked with restoring the river to health and I was impressed with the work they are doing. They are clearing the trees away from the banks and allowing the natural native grasses to grow.

We have already seen that building a dam didn’t work. When the water levels reached high levels the flood gates were opened at Wivenhoe. But the people responsible for that decision have admitted that they didn’t know when they should have made that decision. In the event, the decision came too late to be any use. The runoff water rushed downstream from the dam and built up water levels in the Brisbane River just before the floodwaters arrived from further up in the mountains. The already bloated rivers could not cope. That water had to go somewhere. We all know now where it went.

Building levees is not the answer either. Imagine a condom filled with water squeezed between two rulers. The more you constrict that condom, the higher it rises. The same thing happens when we build levees. The water level rises above the ground level and when a levee bursts its banks it quickly rushes out to flood the surrounding countryside.

We obviously need to think this through carefully and come up with viable solutions that will help us mitigate the effects of heavy rains.

Before we examine solutions, let’s see why planting too many trees is also affecting our wildlife, even when there are no floods.

We are not the only ones

Koalas depend on eucalyptus trees for sustenance. Ecological advisors have been telling us for years that increasing the number of trees will provide more habitats for koalas.

Despite this, we are seeing a worrying decline in koala numbers.

Now, imagine you are a koala sitting up in one of those trees along a creek. Koalas depend on getting their moisture from the tree leaves they chew on. But as the water in our watercourses dries up the overcrowded trees cannot supply enough moisture in their leaves to sustain the koalas.

Eventually, the koalas are forced to come out of the trees and drink from whatever water is left in the silted up rivers, creeks and billabongs. This water is full of organisms and pollutants that cause Chlamydia, and Giardia Lamblia – a deadly form of dysentery – and other diseases. Our koalas have no immunity to them and so they sicken and die.

When the koalas were getting their moisture from the leaves they were chewing on up in the trees they thrived. The trees filtered out all the pollutants. But as we have encouraged more trees to grow and compete for diminishing water supplies we have actually been killing our koalas and other wildlife by forcing them down out of the trees to drink.


Before we take the advice of the Greenies and ‘armchair ecologists’ we must be sure that they have really done their homework. Making a statement that sounds logical is not enough today. In some cases we have seen politicians make statements that are definitely not logical. Despite this they expect us to swallow their advice anyway.

A good case in point was the recent claim by Senator Brown, former leader of The Greens party, who tried to blame the floods on the mining companies. And then he went on to justify this by saying that because the floods were the fault of the mining companies should pay for the cleanup.

This sort of wooly thinking does no one any good. If people like this who do not even understand the problem are in positions of power where they can influence decisions, it’s no wonder we have a problem!

Thousands of people, our livestock, and our native wildlife all badly affected by the floods are proof that we need resource managers who to understand how nature works. We don’t need airy-fairy theories from people with good intentions or crackpot ideologies. We need solid scientific inquiry, and solutions that will work.

Right now – today – we must ask our governments to re-think their policies towards land management and especially trees. The current policies are obviously not working. We need to re-think our approach towards nature and start working with her instead of trying to bulldoze her into submission. In the end, nature will do what she wants, despite our efforts.

We need a comprehensive, logical and effective land and water management policy. It’s time we allowed our farmers and others who work closely with the land to have the power to thin out trees under good management policies. Local councils should be tasked to ensure that tree management is carried out in harmony with the entire water system. And they should monitor watercourse depths and calculate how much water can safely flow down them. If they see a problem they should take logical steps to correct the problem without fighting nature.

We cannot allow a band-aid approach any more. Instead of wringing our hands after the damage has been done our governments must be proactive and ensure that everything is done to facilitate the safe flow of water.

With more effective management of our natural water resources we can substantially reduce the effects of flooding on our cities and towns. But we will never do it if our government doesn’t sit down and do an exhaustive study in conjunction with people close to the land, as well as hydrologists and other scientists who understand how nature works.

Until we do this, we will continue to suffer the floods that are still devastating large areas of Australia today.



Silted up waterhole
Silted up waterhole

A silted up waterhole bordered by thick stands of young trees has become an almost dry waterhole, just one week after the huge rains in April 2010.

Almost dry waterhole
Almost dry waterhole

Another view of the same stretch of creek. The tree canopy inhibits grass growth and allows twigs, leaves and sand to slide down into the waterway.


Recipe for disaster
Recipe for disaster

A creek bordered by thick stands of trees is silting up. As this happens the creek gets narrower, forcing the next flood water to overflow its banks.

Harry's Creek runs deep and free all year round
Harry’s Creek runs deep and free all year round

This part of the Mungallala creek runs about ten feet deep through Harry Chamber’s property. Notice that very few trees line its banks. The soil along the bank is bound by grass instead. Compare this to the almost dry waterholes that run in adjacent properties in the other pictures.

Acknowledgement by the author

I was fortunate to meet Harry Chambers of Glenelg, Mungallala recently. Harry is 77 years old. He has lived and worked in the Outback all his life. His keen interest in how nature works has forced him to the conclusions stated in the above article. Harry describes himself as “a bloke who thinks outside the box because he was never forced inside the box in his early years.

Harry has proved his ideas through practical application. The pictures above were taken of the Mungallala creek on properties either side of his. The last picture was taken on Harry’s property where we went fishing and caught dozens of silver perch, spangled perch, eel-tailed jewfish and golden perch fish. Even in the driest drought, Harry’s part of the creek remains full of water. When the heavy rains come, the water flows through easily, but then it is backed up because of the silting on the next property where they have not managed the creek banks as Harry has.

Harry and other farmers like him have plenty to teach us if only we will listen.