Tag Archives: Tree Planting

wild koala joey needs lots of trees planted

How many trees does a koala need?

It is well known that koalas need eucalyptus (gum) trees. But how many gum trees do koalas need to survive, breed and thrive?

The answer depends on the location, but in most locations, koalas need more trees than you think.

koalas need many trees to survive


In fertile, wet, coastal Queensland and New South Wales koalas might only need 400 trees each. In dry western Victoria koalas might need 20,000 trees each.

In the You Yangs, our research has found that wild koalas need 7,000 to 30,000 trees.

Whichever way you look at it, koalas need a lot more trees planted. They also need the trees to be in fertile soil with high moisture.  Read why koalas need trees in rivers and drainage lines here. 


How to estimate how many trees a koala needs.

Here’s a summary of the home range sizes and tree estimate* for wild koalas in the You Yangs in 2017:

*tree estimate is based on mature eucalyptus trees at a spacing of 5m x 5m (so one tree every 5 m). This gives 400 trees per hectare (ha). In fact there are more trees than that in most koala home ranges. Acacias, Cherry Ballarts, Melaleucas and other important koala roost trees are not counted.


Pat (older female 13 yo): 18.3 hectares      = minimum 7,320 trees

Ngardang (young female): 30.9ha               = min. 12,360 trees

Misty (mature female): 22.5ha                     = min. 9,000 trees


Winberry (older male): 46.8ha         = min. 18,720 trees

Clancy (mature male): 47.4ha           = min. 18,960 trees

Anzac (older male): 34.9ha                = min. 13,960 trees

Cruiz (older male): 66.9ha                 = min. 26,760 trees

Average koala home range size in You Yangs = 38.2ha

(to calculate an average, add all the home range sizes you have together, then divide by how many home ranges you have)

To find the average home range size of koalas (in hectares) in your area check this information:


1.2 hectare (females) & 1.7 ha (males)  on French Island, coastal east Vic
23.9 ha (females ) & 37.3 ha (males)     in You Yangs, inland west Vic


15 ha (females) & 34 ha (males)           at south-east Qld
8 ha  (females) & 16 ha (males)            at Brisbane, south-east Qld.
101 ha (females) & 135 ha (males)       at Blair Athol, central Qld


11ha (females) & 45 ha (males)           at Pilliga Forest, north-west NSW
10ha (females) & 23 ha (males)           at Coffs Harbour, coastal NSW
44ha (females) & 82 ha (males)           at Lismore, inland north-east NSW

This excellent article gives a table of the known koala home range size in different parts of Australia, and details the different methods used to calculate them:
Goldingay, Ross L, and Barbara Dobner. “Home Range Areas of Koalas In an Urban Area of North-east New South Wales.” Australian mammalogy, v. 36,.1 pp. 74-80 http://citeseerx.ist.psu.edu/viewdoc/download?doi=

If in doubt, use the closest location, or use our You Yangs figures for anywhere west of the Great Dividing Range, and halve it for wet areas in coastal Queensland and New South Wales.


How many koalas share a territory / home range?

Koalas do share some of their home space with other koalas. This is also dependent on location and soil fertility & moisture. In the You Yangs the degree of overlap is small.

In 2017 Koala Pat shared around 80% of her home range with male Anzac, and around 20% of her home range with female Misty. Misty shared about 20% of her home range with Pat & Anzac, and about 50% with male Cruiz.  This situation is typical in the You Yangs.

So home range overlap equals 2   (ie. 2 koalas are using the same area).

Finding the home range overlap in your area is even harder than estimating home range size. There is very little data.  It could be as high as 4 or 5 in some rich fertile areas, or as low as 1 in dry areas.

If in doubt, assume it is 2.

koala home range size and overlap map


How many koala trees need to be planted?

The simple answer is as many as possible! But it does help to have an idea of how many to aim for.

First consideration is that a koala cannot live alone. Viable populations number in the hundreds or thousands of animals. If you are planning for an entire koala population, you need to be planting hundreds of thousands of trees.

how many trees do koalas need planted

If you are designing for a development that is cutting down koala habitat trees you need to be retaining enough trees for the current koala population, or planting new trees for that entire population. Leaving 100 trees “for the koalas” is not enough for even one koala.

If you are planning to help out an existing koala population, then you should try to plant for at least 10 koalas.

To estimate how many koala trees need to be planted use this calculation:

(average koala home range size in ha) x 400* trees = A / (home range overlap) = number of trees per koala. 

*400 trees per hectare. It is possible that this figure could be higher or lower depending on the fertility of the area and the size of the trees.

Around the You Yangs our calculation looks like this:

38.2 x 400 = 15,280 / 2 = 7,640 trees needed per koala.

7,640 x 10 koalas = 76,400 trees to be helpful.

And to provide for the entire koala population of the You Yangs:

127 koalas x 7640 trees = 970,280 trees.

Please don’t be put off by these numbers – any tree is better than no tree. But aim high. This is urgent.

chart showing wild koala population decline over 11 years

Read more about the koala population decline in the You Yangs here.

Koala Clancy Foundation have very proudly planted nearly 8,000 trees in the last 3 years. It feels like a lot, but it is not nearly enough.  Please help, by sharing this post, by alerting landowners, by attending one of our Koala Conservation Days, by donating.

koala clancy foundation tree planting near You Yangs Victoria


Koala Clancy Foundation are running our second annual Koala Tree Planting Information Event on Thursday 28 November at 7.30pm at Balliang Hall, Balliang VIC. More information here:




Ellis W. A. H. , Melzer A. , Carrick F. N. Hasegawa M. (2002) Tree use, diet and home range of the koala (Phascolarctos cinereus) at Blair Athol, central Queensland. Wildlife Research 29, 303-311. http://www.publish.csiro.au/WR/WR00111

Moore Benjamin D. Foley William J. (2000) A review of feeding and diet selection in koalas (Phascolarctos cinereus). Australian Journal of Zoology 48, 317-333.

Koalas Need Farmers & planting in drainage lines: https://koalaclancy.wordpress.com/2018/09/14/koalas-need-farmers/

Koala Population Decline in the You Yangs: https://koalaclancy.wordpress.com/2018/11/04/koala-population-decline-in-the-you-yangs-victoria/

You Yangs koala adult male face

Koala population decline in the You Yangs, Victoria

Awful, but hopeful.

In preparation for our first Koalas & Tree Planting community event on November 15, 2018 I felt that a graph would best show the decline in koala population. Little did I know how powerful that would be.

chart showing wild koala population decline over 11 years

This is a terrible graph, charting the premature deaths of many koalas. But it is also a hopeful graph.

Hopeful? What??

Yes, because in the You Yangs we now know we have a problem. And once a problem is known, action can be taken to fix it.


The simple fact is that the same catastrophic declines are happening everywhere.  These findings are in line with WWF’s 2018 Living Planet Report, that shows a 60% decline in wild animal* populations worldwide.

But its hard to make decision-makers listen if you don’t have data.  Now we have data.  Now we are taking action.

At our Koalas & Tree Planting Event in Little River on November 15, 2018 we showed and explained these images, and others.  Learn how everyone can do something to save our koalas and turn this graph around.

See the presentation here.

An explanation of the graph

We started koala research in the You Yangs in January 2006 – ten years into the Millenium Drought: the worst drought in Australia’s history. The koalas had been suffering since 1996, and would not get any relief until 2010.

The first year of research gave us a foundation to work on, so by 2007 we had a clear picture of the population. We could already see that there were very few joeys being born.

As you can see, koala numbers fell significantly each year until 2010 when they plummeted. We lost one-third of our koalas over the summer of 2009-2010. Thankfully, the rain came in 2010 and gave us some relief.

chart showing wild koala population decline over 11 years

The next few years saw a return to near-normal rainfall conditions, and small increases to the koala population. But koalas living in poor habitat don’t breed that fast. Most of our females breed from age 2 to 8 years, and some only have a joey every second year. A few of our females don’t ever successfully breed at all.

Importantly, the trees have not recovered. The rains kept them alive, but weren’t enough to make them thrive again.

Here’s two pictures of the same River Red Gum tree, in 2008: 12 years into a drought (when you would think it would be at its worst); and in 2015: after 5 years of ‘normal’ rainfall.

And no, its not just that tree.  Take a walk in the You Yangs – the River Red Gums are in poor condition right across the park. See some other then and now pictures of the forest here. 

comparison of River Red Gum tree in You Yangs from 2008 to 2015

Koalas suffer from poor tree condition long before we can see the tree is in poor condition.

The koalas and the trees of the You Yangs haven’t had time to return to pre-drought levels of fitness. And now, in 2018, we’re in another drought.

We have to act decisively to save the koalas of the You Yangs. The current trajectory is a recipe for local extinction.


What can we do?

We can’t make it rain.

But we do have a plan. Plant koala trees downhill in the river valleys and drainage lines of the Western Plains. It was koala habitat in the past, and could be again. Beside the rivers the soil is wetter than in the You Yangs. The correct local indigenous trees will grow fast there.

Read how we plant koala trees in “Koalas Need Farmers”

In addition, on hot days, wind blowing across waterholes and dams is cooler than the surrounding air. Trees along rivers and around waterholes and dams are highly preferred by koalas on hot days.

We can stop the local extinction of koalas in the You Yangs region. Act now.

We are running another Koala Tree Planting Event on 28 November 2019 in Balliang. Please come along. https://koalaclancyfoundation.org.au/component/jevents/eventdetail/91/-/koalas-and-tree-planting-information-event-balliang

koala clancy foundation tree planting near You Yangs Victoria

How did we get this data?

A koala research project started by Janine Duffy grew into a comprehensive research project involving 20 people monitoring +/- 43 koalas 310+ days a year. Around 3600 koala observations are taken every year. Funding for the project comes from a social enterprise tourism operation: Echidna Walkabout Nature Tours.

Echidna Walkabout’s Wild Koala Research Project is the only research on koalas in the You Yangs, and one of very few projects monitoring a natural (non-abundant) population of koalas in Victoria.

Read about our 2017 summary of Wild Koala Research in the You Yangs here.


*vertebrate animals: mammals, reptiles, amphibians, fish and birds.