Blue Gum High Forest


The majestic Blue Gum High Forest of Hornsby Shire is critically endangered

Blue Gum tree hug


Does it grow in my suburb?

Blue Gum High Forest grows in 14 suburbs within Hornsby Shire, in and amongst the places where over 99,000 people live. If you live in or near these suburbs, then Blue Gum High Forest is your neighbour: Arcadia, Beecroft, Castle Hill, Cherrybrook, Dural, Galston, Glenhaven, Hornsby, Normanhurst, Pennant Hills, Thornleigh, Wahroonga, Westleigh, West Pennant Hills.

What does it look like?

Blue Gum High Forest is a type of bushland with very tall and straight trees. It gets its name from the dominant Sydney Blue Gum tree (Eucalyptus saligna), with its distinctive smooth, blue-grey trunk and a sock of rough bark at its base. In a healthy Blue Gum High Forest, you will see other plants of various shapes and sizes, including trees such as the Blackbutt (Eucalyptus pilularis).

Why does it only grow in a third of Hornsby Shire’s suburbs?

Blue Gum High Forest has specific soil and rainfall requirements which, when added together, limit where it can grow. Trees in a Blue Gum High Forest need rich, deep soils to support their straight and tall growth. Such soils form from weathered shale rock or have volcanic origins. The second essential ingredient is a rainfall total above 1100mm (on average) per year. Where Hornsby Shire’s suburbs have this soil and rainfall combination, and where it hasn’t been cleared, you will find Blue Gum High Forest.

Blue Gum High Forest is not simply a group of majestic trees. It is an ecological community, with a unique and diverse combination of many different plants and other living things. From below the ground to the tops of the tallest trees, everything living in or visiting an ecological community contributes to its health.

A healthy ecological community is vital for the survival of every living thing that depends on it. Ecological communities nourish our soils, shelter and sustain wildlife, protect our waterways and absorb carbon dioxide while emitting oxygen.

Ecological communities are created by nature over thousands of years, so once an ecological community is gone, it cannot be replaced.

You will not find Blue Gum High Forest anywhere else in the world except Sydney’s north shore and its northern and north-western suburbs.

When an outpost of the British Empire settled in Sydney some 240 years ago, Blue Gum High Forest quickly became highly regarded for its straight, tall trees and its rich, moist soils. Its trees were felled for their timbers, and the forest was progressively cleared for agriculture. With transport corridors concentrated on the ridge lines where it mainly grows, and with increasingly dense urban development, Blue Gum High Forest was almost squeezed out of existence. Today less than 5% of its area remains, and Blue Gum High Forest is facing an extremely high risk of extinction. In fact, less than 200 hectares of Blue Gum High Forest exists on the entire planet, and the scattered and narrow patches left are under immense pressure.

Blue Gum High Forest is listed by the NSW Government and the Australian Government as a critically endangered ecological community. Once it is gone, it cannot be replaced!

Hornsby Shire contains 74 hectares of Blue Gum High Forest. This is 40% of all the Blue Gum High Forest that exists in the entire world! This means Hornsby Shire and its people are key to its survival.

Of the 74 hectares, there is a very special type of Blue Gum High Forest you won’t find anywhere else except for the valley where Hornsby, Thornleigh and Westleigh meet. It is a 14-hectare, grand forest of outstanding beauty and majesty called Blue Gum Diatreme Forest. It gets this name from the volcanic diatreme or pipe of magma there, which rose to the surface when dinosaurs dominated the Earth. Its survival is overwhelmingly dependent on Hornsby Shire and its people.

The small amount of Blue Gum High Forest remaining is subject to pressures that threaten its health and survival. Sustainably looked after for tens of thousands of years by traditional custodians, everything changed for Blue Gum High Forest when Europeans arrived in Hornsby Shire. Beginning in the late 1700s, trees were felled for timber followed by wide-spread clearing of the forest for farming. With the construction of railway lines and road expansion, suburbs replaced the once-rural areas. As Sydney's population grew, land-use development continued a-pace and the forest was almost squeezed out of existence. You can find out more by reading Hornsby Thematic History.

In 2022, Blue Gum High Forest is still under threat from many factors. Left alone and without help, these negative impacts would accumulate, and Blue Gum High Forest could quickly decline and become extinct.


Exotic plants, including weeds and garden escapees, constantly enter bushland and can take over all layers of a forest. This is especially the case along bushland edges and waterways, and in small or narrow patches of bushland that are surrounded by development. Think again if you don’t believe there are plants that can overpower the mighty Sydney Blue Gum and other canopy trees. Groundcover weeds such as Wandering Trad (Tradescantia fluminensis) can completely block the light reaching the forest floor. No matter how robust the tree, their seeds and seedlings need space and light to germinate and grow. This can’t happen with a thick blanket of weeds covering the ground.


As deep soils are replaced by concrete and bitumen for roads and footpaths, and buildings and facilities for the Shire’s growing population, there is increasingly less space for rain to be slowly absorbed into the ground where it falls. Now when it rains, urban creeks become raging torrents fed by pipes and gutters channelling water that has fallen on these hard surfaces quickly into our natural waterways and bushland. Along the way, this stormwater will carry with it any seeds or plant parts swept up in its path, loose soils, and nutrients such as fertilisers. With creeks flowing higher and faster than is natural, stormwater can reach far into bushland, laying down nutrient-rich sediments. Many bushland weeds thrive in these conditions and their growth can out-compete the native bushland plants. With much bushland located downslope of developed areas, water shedding directly from neighbouring properties can also give weeds the upper hand on the edges of bushland. Council’s Catchment Remediation Program of the last few decades continues to reduce the magnitude of these impacts. Council’s Water Sensitive Hornsby Strategy assesses the Shire’s water sensitive performance and sets a Vision for 2040.


Dumping is where natural or manufactured materials are taken into the forest, or moved within the forest, and left there. Natural materials include soil, rock and garden or tree prunings. Manufactured materials found in bushland include concrete and other building materials, discarded items such as furniture, and waste. Building up land or dumping material on top of the forest’s natural ground surface can starve the soil of oxygen and light. Seeds can’t germinate beyond a certain depth, and roots and other living things below the ground need oxygen to survive. The patch of forest affected cannot regenerate and its health declines.


Clearing of Blue Gum High Forest is not just limited to the cutting down of trees but involves the removal or killing of any of the plants (including shrubs, grasses and groundcovers) which make up this unique ecological community. Unauthorised clearing is a threat to the survival of Blue Gum High Forest. It includes private properties encroaching onto public land to create extra space, cutting or poisoning of trees and plants to improve views or access to sunlight or to prevent leaves and branches dropping into properties, track building to access natural areas and concerns about bush fire. Depending on the extent, some of these activities can be authorised by governments, including local Councils and state and national governments. If not authorised, and because of the critically endangered status of Blue Gum High Forest, these clearing activities can be considered illegal.

Clearing of Blue Gum High Forest is exacerbated by the digging up of soil by hand tools or machines. Blue Gum High Forest contains many living things below the ground surface. Digging up soil damages the future of the forest (in the location it occurs) by removing roots and vital stores of seed and the underground stems, bulbs and tubers of various plants. Digging also damages the roots of trees and other plants that grow alongside the cleared area.

Depending on the extent, some clearing activities can be authorised by governments, including local Councils. The reason why approvals may be granted is to provide places for people to live, work and recreate, or to manage risks to life and property. Any approval process requires rigorous environmental assessments, and options must be considered that reduce or eliminate any impacts on the forest.


Phytophthora and Myrtle Rust are exotic pathogens that damage bushland ecology and cause the death of plants in certain susceptible areas. These diseases can be spread by people moving through bushland and unknowingly picking up pathogens on their shoes and clothes.

From the tops of the tallest trees right down to the forest floor, Blue Gum High Forest supports many different species of wildlife, including those that are now under threat. Hollows in the tall, old trees are nurseries where many birds raise their young. This includes owls such as the rare Powerful Owl, and parrots such as the rare Glossy Black Cockatoo. Native mammals also need these old trees for roosting and feeding, such as rare and tiny microbats who sleep in little tree hollows and small niches. A healthy forest is rich in food for wildlife such as the Common Ringtail Possum, who feeds on the nectar, fruit and leaves of many forest trees and shrubs.

What is Council doing in parks and reserves to protect Blue Gum High Forest?

Guided by Council’s Biodiversity Conservation Strategy, Council has specialised staff and contractors who work to protect and repair bushland in parks and reserves and in selected unmade road reserves. Bush regeneration contractors restore bushland at around 80 sites across the Shire, including 21 Blue Gum High Forest sites. Bushcare volunteers work at 65 sites across the Shire, guided by specialist site supervisors employed by Council. Twelve (12) of these Bushcare groups work at Blue Gum High Forest sites.

Entrusted with looking after a precious forest teetering on the edge of extinction, Council must carefully assess and plan any work and activities that could damage Blue Gum High Forest in parks and reserves. With the aim being the forest’s long-term survival, Council conducts and supports plant and animal surveys to measure the forest’s health and to keep an eye on its wildlife and other dependents. A sound understanding of each patch of Blue Gum High Forest and its place in the Shire’s wider bushland network is essential. From an environmental impact perspective, the location and design of any proposed tracks and trails, shared pathways, play spaces and stormwater drainage devices (to name just a few) can be guided by survey findings. Options can be considered, and decisions made to ensure protection of critically endangered forests into the future is given the highest priority.

Council warmly invites the community to visit the parks and reserves where Blue Gum High Forest grows. To experience its majesty and to appreciate and understand the ways of nature, a visit to the forest is a must. Critical to the survival of the forest are human interactions that support its health and ongoing sustainability. As for precious works of art like Leonardo da Vinci’s Mona Lisa or Michelangelo’s David, access to and through Blue Gum High Forest must be appropriate and carefully managed.

What can I do to help protect Blue Gum High Forest?
  • Spend some time in a Blue Gum High Forest:
    • Take a gentle stroll along the sealed path in Normanhurst’s Kenley Park
    • Admire the forest as you ramble along the management trail and bushwalking track of Hornsby Valley’s Ginger Meggs Loop Walk
    • Grab a coffee or pack a picnic and head to Beecroft’s Fearnley Park, West Pennant Hills’ New Farm Road Reserve or The Lakes of Cherrybrook where you will also find play spaces for the kids
    • Get out of the car and amble up the centre track in Observatory Park, Pennant Hills
    • Wander down and back up the bushwalking track through the spectacular Blue Gum Diatreme Forest in Dog Pound Creek Bushland Reserve, Westleigh
    • Extend your immersive experience of the forest by bushwalking the Blue Gum Walk in Hornsby Valley
    • Enjoy the respite of being in nature.
  • Take up the offer of free plants from Warada Ngurang Community Nursery, where volunteers and staff propagate the plants, both big and small, that grow in a Blue Gum High Forest. Pop them in your garden and you will be helping creatures such as moths, butterflies and native bees that feed on and help pollinate the forest’s plants. You will also be helping wildlife such as the rare Glossy Black Cockatoo, who depends on a handful of trees for its food, including the Forest Oak (Allocasuarina torulosa), a small tree that grows in Blue Gum High Forest.
  • Participate in a guided bushwalk or event. Council’s free Guided Bushwalks and Events Program caters for all, with walks for beginner bushwalkers and those with limited fitness, right through to challenging half-day bushwalks for those with experience and good fitness. Kids' bushwalks and nature events are also provided. Not to forget our furry four-legged friends, Council also runs guided bushwalks for well-socialised dogs and their human companions. Look out for walks that mention Blue Gum High Forest.
  • Come along to a community planting event. Bring along your friends and family and experience the satisfaction of doing your bit to help the forest. There will be two community planting events held in or near Blue Gum High Forest per year, so keep your eye out for them on Council’s Events webpage.
  • Remove weeds of bushland from your garden, as they can spread from near and far into Blue Gum High Forest. With most originating overseas, these weeds often have fewer natural predators here in Australia than do home-grown Blue Gum High Forest plants. This means they often out-compete native plants with their vigorous growth and can severely damage the forest’s health. Find out if you have any weeds of bushland growing in your garden, and if so, how to remove them.
  • Keep your pets under control and never let them wander into any bushland areas, including Wildlife Protection Areas and national parks. Bushland is the home of wildlife. While some native animals, such as the Brush-tailed Possum, are relatively common and are often seen and heard, others are shy and secretive and may be uncommon or rare. Frogs and toads, reptiles, birds and mammals can be irresistible to cats and dogs. This is a very good reason to always walk your dog on a lead in Council’s parks and reserves (except for off-leash dog parks) and why cats should be prevented from entering bushland.
  • Join a Bushcare group. Becoming a Bushcare volunteer is an enjoyable way to learn about Blue Gum High Forest with like-minded people. There are 12 Blue Gum High Forest Bushcare groups working once a month, each guided by a specialist site supervisor employed by Council. Volunteers learn about the forest and its wildlife simply by being there and lending a hand. They help the forest by removing weeds, protecting and creating habitat for wildlife, and planting where needed to supplement natural regeneration. There are groups who work in Blue Gum High Forest on a weekday and others that work on a Saturday or Sunday. Some groups work in the morning while others work in the afternoon, and there is sure to be a time and location to suit.
  • Expand your knowledge about Blue Gum High Forest and Sydney’s native biodiversity and how you can help to reduce threats. You can do this by visiting the links within these webpages.
  • Report to Council any activities you suspect might be damaging Blue Gum High Forest.
  • Have your say on plans and policies that may affect the management of Blue Gum High Forest, including plans of management, landscape concept plans, and masterplans for parks and reserves. Find out about Council’s current and upcoming infrastructure and works projects, including any located in or near Blue Gum High Forest.

What can you do?

  • Spend some time in a Blue Gum High Forest
  • Plant some of the forest’s native species
  • Participate in a guided bushwalk or event
  • Come along to a community planting event
  • Remove weeds of bushland from your garden
  • Keep your pets under control and never let them wander into bushland
  • Join a Bushcare group.