Planting trees for koalas sounds lovely and positive in every way. But does it really help? Is it the best solution to the threats koalas face? Does it distract from better solutions?
After looking at the evidence and the science, Koala Clancy Foundation have determined that targeted tree planting, in the right places, is the best solution for our region. But it may not be in other places. To help you find solutions that are the best, below we’ve detailed the science and observations that have informed our decision.
Evidence that koalas need help
First, it is important to determine whether the koalas in a region need help.
In the You Yangs, we discovered that the koala population was declining by directly observing the population over 13 years. We count koalas in a discrete area and use nose pattern identification  to ensure that we are not double-counting individuals, so we have very accurate population numbers.
Why are the koalas declining?
As the graph shows, the Millenium Drought coincided with the biggest drop in numbers, as did a further drought in 2017-2020. Droughts and heatwaves are known to cause koala deaths. 
But there were 6 years between droughts, and the koala population didn’t recover to pre-drought levels. It may be impossible for koala populations to recover when droughts become more frequent, which is one of the expected impacts of climate change.
The trees in the You Yangs are dying.
Not long ago, the forested hills of the You Yangs were an island hub for wildlife. Surrounded by farmland, the forest stood tall and green, sheltering a vibrant suite of Australian mammals, birds, and insects. Swamp Wallabies, Black-chinned Honeyeaters, Diamond Firetails, and Koalas were seen often.
Long-term locals tell us stories of growing up visiting the You Yangs, and how green it was.
To a new visitor, the You Yangs forest still looks lovely. But for wildlife, there is a dire situation unfolding.
Part of our koala research included taking photographs of trees. These photographs show clear evidence of failing tree health.
In 2014, Ngardang, one of our well-known koalas, was a joey. We spotted her in this tree with her mother Babarrang. At the time it was lush and covered in foliage. Now, ten years later, the tree is a skeleton of what it once was and is surrounded by the invasive boneseed.
Read our 2017 research report  to see the tree death that we’ve observed.
Can we save the trees in the You Yangs? Not easily and not quickly. Trees are enormous organisms, with huge root systems, and there are many hundreds of thousands of them in a forest like the You Yangs. We don’t know the exact reasons for the tree death and decline in the You Yangs, but it is likely linked to drought. Watering entire forests is not an option.
When trees die, koalas die.
Koalas are 100% reliant on eucalyptus and closely-related trees. They can’t eat anything else. So when koala habitat trees die, koalas die too, unless they can find new habitat trees. That doesn’t mean they can simply move to another forested area – other koalas already live there at maximum carrying capacity*. The koala habitat has to be new.
*note: there are some exceptions – if the koala population has been destroyed by fire, flood or shooting in the past and has failed to recolonise.
You Yangs Koalas need help. Based on these observations of koala decline and tree death, and on climate expectations, koalas in the You Yangs will be locally extinct if we don’t intervene.
The next question is whether it is important to save these koalas. Of course, the answer is yes. But why?
It is critical to save koalas
Koalas are an umbrella species: by protecting them, many other species benefit. In fact, a high profile scientific study in 2019  found that koalas are one of the most impactful umbrella species in Australia. In this particular study, the management of koala threats benefited an additional 10 threatened species. This means that improving the outlook for the You Yangs koala population can have a positive flow-on effect to many other species in the area, both flora and fauna.
For example, our Balliang Grey Box Woodland project  involved the transformation of a bare paddock into the largest, most southerly block of endangered Grey Box Eucalyptus microcarpa woodland in Australia.
We planted trees to support koalas, but we knew the same forest could also help Brush-tailed Phascogale, Grey-headed Flying-fox & Fat-tailed Dunnart; critically endangered Swift Parrot, endangered Speckled Warbler & Barking Owl, vulnerable Diamond Firetail, Brown Treecreeper and Jacky Winter; endangered Tussock Skink & Glossy Grass Skink; endangered Fiery Jewel Butterfly and vulnerable Golden Sun Moth.
An ecosystem is nature’s enormous 3D puzzle – every species has a place and connects to many other pieces around it. Removing one piece from this jigsaw doesn’t just leave an empty space, it creates weakness in the whole system. Already the You Yangs ecosystem puzzle is full of holes: once there were Emus, Spot-tailed and Eastern Quolls, Dingoes, Bush Stone-curlews, Australian Bustards and Grey-crowned Babblers living there. As each became extinct, other smaller species declined, making each gap bigger and the system weaker.
The You Yangs ecosystem can’t bear another extinction of a large umbrella species. Nor can we.
Already Australia has the world’s worst record for mammal extinctions . If we lose koalas, we don’t just lose a species, we lose a genus and a family: Koalas are the last living members of family Phascolarctidae and genus Phascolarctos.
So we’ve established that koalas need help, and it is important to save them. The next question is what is the best method?
Earlier we discussed the importance of creating new koala habitat as the existing You Yangs forest is dying and declining and we can’t easily reverse that. Planting new trees in a drought-affected forest won’t work either – that will put more pressure on the existing forest. We need to look at what type of habitat koalas need most, and find places that are suitable but currently lack koalas.
What habitat do koalas need most?
- Research has shown that koalas in dry areas need access to rivers and waterways. 
- Research has shown that koalas need trees on fertile soil 
- Research has shown that revegetation sites close to existing koala populations work most quickly 
- Research has shown that koalas will use planted trees as young as 4 years old 
Where is there suitable fertile land near rivers and waterways?
In our region, the most fertile soils are on privately owned agricultural land. It is good growing land for crops and livestock. Many of the larger properties also have a river, creek or drainage line.
But most of them don’t have any koalas, because they don’t have enough trees. They need their growing land, but they don’t use the 10 to 50m strip along their river. Unmanaged and unmanageable, it grows weeds like Serrated Tussock that invades their productive paddocks, and harbours foxes and rabbits.
Revegetation with native tree, shrub and groundcover species along the river can help suppress weeds and remove cover for pests. And it’s what koalas need most.
Koala Clancy Foundation are working with private landowners who want a future with koalas around them. We are restoring the habitat that was once present on the land that they farm, and we’ll do it on any suitable property in the Little, Moorabool, and Barwon River catchments. We predominantly plant along the waterways; rivers, wetlands, tributaries, drainage lines, and creeks, because these habitats have the highest chance of sustaining a koala population .
Choosing suitable sites close to koala populations.
We choose projects on private land that are close to known koala populations. Our You Yangs Little River Koala Link project  gave us the chance to plant the first direct habitat link from the You Yangs to the Little River.
In this project, we joined the You Yangs to the Little River at its closest point, so that koalas can start to colonise new, fertile and cool habitat along the Little River. Once koalas get to the river, they can feast on 8km of trees we’ve planted since 2017, and on some huge old trees that have been preserved over generations.
Near Inverleigh on the Native Hut Creek, we have planted 16,000+ trees on a private property Plains Grassy Woodland project  adjacent to the Inverleigh Nature Reserve, which is known to have a small and struggling koala population. Our own observations have found koala scratches on trees, but no koalas… yet.
Along the Moorabool River at Gheringhap, at our Moorabool Tributary project  we have planted 8983 trees, and another 3073 trees upstream at our Down Yonder project . Recently we saw a female koala there, after many days of searching. Further upstream, we planted 3618 trees with the support of IFAW at Moorabool Manna Gums for Koalas. Koalas have been sighted nearby, but not on the property for many years.
Ensuring that trees grow and live long.
Evidence has shown us that koalas will use planted trees just 2 years old. However the trees take longer to provide shelter and a permanent living site for a whole community of koalas. The trees we plant need to survive and thrive.
Our tree planting approach  is highly targeted to plant the right trees in the right places that will have the most rapid effect.
In fact, we plant 35 to 40 different plant species, for a number of reasons.
Our koala research since 1998 has helped us understand the ecosystems that koalas live in, the trees they eat, shelter in, use for drinking, for social interactions, and as refuges on hot days.
We plant species that meet koalas diverse dietary needs, act as nurse plants to help the ecosystem thrive, provide climate resilience in extreme weather conditions, encourage the presence of beneficial insects and native birds, and suppress weeds.
We only plant species in areas where they would naturally occur. This gives the project a higher chance of success and helps to restore the local ecosystem.
We revisit most of our planting projects every year, and we have evidence of survival rates of 85% (You Yangs North ) and 93% (Sharkey Ballliang) after two years.
How do we know this is going to work?
We don’t yet have the evidence that this approach will work for You Yangs koalas, but the early indicators are positive. Koala Clem (pictured below and in the header) spent a lot of time amongst new planted trees at Staughton Vale in the Brisbane Ranges. Just recently we have found koala Morrie in a planted River Red Gum at our Moorabool Manna Gums planting site (pictured above).
We are determined to monitor koala use/growth/change in future years, so we are installing audio recording devices at several of our tree planting projects, with the support of IFAW. To ensure this shows real evidence of change, the recording devices will go in before, or during the first year of planting, so that we can show the situation before koalas are attracted to the planting.
But there are other places in Australia where tree planting has worked, and some that have been thoroughly researched.
Evidence of koala population growth as a result of tree planting
In the late 2000s, Gunnedah, NSW saw an increase in their koala population . Trees planted by farmers (mostly River Red Gums, Eucalyptus camaldulensis) on private farmland in the 1990s, were being used by, and actively sought out by koalas. Koalas were seen travelling long distances between areas of habitat to access these trees, though they were only 10-20 years old.
As a result of this evidence, Gunnedah proclaimed itself the Koala Capital of the World and was seen as a case study for reversing koala declines. But sadly, due to climate change, the area has suffered from severe droughts and heatwaves in the last decade, which have led to severe declines. Koalas around Gunnedah were recorded with the highest body temperatures ever known. Disease has also played a part, ripping through the weakened koala population.
In another part of NSW, Bangalow Koalas have reported a growth in koala sightings since tree planting began. 
In Victoria, Greenfleet reports that koalas were sighted within 3 years of tree planting at a site in South Gippsland. 
Visit our page dedicated to scientific information about koalas to learn more: https://www.koalaclancyfoundation.org.au/learn-about-koalas/koala-scientific-information/
 Koala Clancy Foundation, n.d., Identifying Koalas, https://www.koalaclancyfoundation.org.au/learn-about-koalas/koala-id-presentation/
 Gordon, G., Brown, A.S. and Pulsford, T.J.A.J.E., 1988. A koala (Phascolarctos cinereus Goldfuss) population crash during drought and heatwave conditions in south‐western Queensland. Australian Journal of Ecology, 13(4), pp.451-461. https://doi.org/10.1111/j.1442-9993.1988.tb00993.x
 Janine Duffy, You Yangs Koala Research Report, 2017 https://echidnawalkabout.com.au/you-yangs-koala-research-report-2017/
 Ward, M., Rhodes, J.R., Watson, J.E., Lefevre, J., Atkinson, S. and Possingham, H.P., 2020. Use of surrogate species to cost‐effectively prioritize conservation actions. Conservation Biology, 34(3), pp.600-610. https://conbio.onlinelibrary.wiley.com/doi/full/10.1111/cobi.13430
 Koala Clancy Foundation, Project: Balliang Grey Box Woodland Restoration, 2022 https://www.koalaclancyfoundation.org.au/project-balliang-grey-box-woodland-restoration/
 Koala Clancy Foundation, Koalas Need Farmers, 2018 https://koalaclancy.wordpress.com/2018/09/14/koalas-need-farmers/
 S. Rhind et al., Do Koalas Phascolarctos cinereus use trees planted on farms? A case study from north-west New South Wales, Australia., 2014, https://www.publish.csiro.au/PC/PC140302
 Kavanagh, R.P. and Stanton, M.A., 2012. Koalas use young Eucalyptus plantations in an agricultural landscape on the Liverpool Plains, New South Wales. Ecological Management & Restoration, 13(3), pp.297-305. https://doi.org/10.1111/emr.12005
 Koala Clancy Foundation, Project: You Yangs Little River Koala Link, 2022, https://www.koalaclancyfoundation.org.au/project-you-yangs-little-river-koala-link/
 Koala Clancy Foundation, Project: Plains Grassy Woodlands for Koalas, 2023, https://www.koalaclancyfoundation.org.au/project-plains-grassy-woodlands-for-koalas/
 Koala Clancy Foundation, 2023, Ongoing Project: Moorabool Tributary at Gheringhap, https://www.koalaclancyfoundation.org.au/tree-planting-project-moorabool-tributary-gheringhap/
 Koala Clancy Foundation, n.d., Koala Tree Planting Projects, https://www.koalaclancyfoundation.org.au/koala-tree-planting-projects/
 Koala Clancy Foundation, 2022, What we plant for koalas and why, https://www.koalaclancyfoundation.org.au/what-we-plant-for-koalas-and-why/
 Koala Clancy Foundation, n.d., Ongoing Project: You Yangs North, https://www.koalaclancyfoundation.org.au/ongoing-project-you-yangs-north/
 Carla Avolio, Gunnedah may hold key to reversing koala decline, 2012, https://www.australiangeographic.com.au/topics/wildlife/2012/06/gunnedah-may-hold-key-to-reversing-koala-decline/
 WWF, How planting trees can save koalas, 2023 https://wwf.org.au/blogs/how-planting-trees-can-save-koalas/
 Greenfleet, Koala Conservation https://www.greenfleet.com.au/pages/koala-conservation-1