Anyone who has visited California has likely seen them: the eucalyptus trees that populate the landscape from Big Sur down to San Diego. While eucalyptus trees are a type of gum tree, not all gum trees are eucalyptus trees. While they are a beautiful and fragrant species of tree, the eucalyptus, also known as a blue gum tree, is an invasive species of tree and often has an adverse effect on its surrounding environment.
What Is a Gum Tree?
A gum tree is a species of tree that is part of the Myrtle family. There are 12 distinct species of gum trees, and each of them is called "gum tree" because of the thick sap that oozes out of the trunk when they sustain any sort of damage.
Gum trees are indigenous to Australia, and they exist in many places in the United States and elsewhere because the seeds were brought by immigrants in the middle part of the 19th century. Australians leaving Oceania in search of a better life in the New World were aware of the important value that lumber and wood had in general. From building to operating ovens to keeping trains running, wood was critical to all parts of survival. It was a century of wood power.
For these reasons, many Australians traveled to California with seeds of eucalyptus trees. By the same token, much of California was low, marshy and shrubby scrubland. Settlers who had come from the East were accustomed to the environments afforded by dense, heavily forested areas and wanted to create a similar feel in California. This is how the creation of forests in the area began, most notably the eucalyptus trees on the Berkeley campus that were designed as a windbreak for athletes.
What Are Some of the Different Species of Gum Trees?
There is the blue gum tree, which is most commonly referred to as a eucalyptus tree. These trees are the most commonly planted of all gum trees everywhere around the world. It is so popular in the Oceania region that the Eucalyptus is actually the state flower of Tasmania.
The lemon-scented gum tree is another variety. It's known for emitting a strong lemon scent which can be used successfully as an insect repellent. It is native to northeastern Australia. The manna gum tree is a species that is immediately identifiable by its bark, which comes off in strips. These trees can grow up to 100 feet tall and are one of the few species of gum trees that can actually tolerate cooler climates.
The rainbow gum tree is unique both for its appearance and its provenance. One of the few species that is indigenous to lands below the equator, the rainbow gum tree is native to the Philippines and to Papua New Guinea. The rainbow gum tree gets its name from its bark, which has colors that vary in shade from green to red.
What Are Some Popular Species of Gum Trees?
The red flowering gum tree is native to Australia and has an unusual red blossom with stamens but no petals. It's a very popular gum tree for use in landscaping and decorating since the boughs are fairly low to the ground and the red blossoms are such a striking color. This variety of eucalyptus is known as a bloodwood.
Most people have seen eucalyptus branches from the silver dollar gum tree for sale in flower shops and at farmers' markets. They are native to southeastern Australia, and their branches are exceptionally fragrant and refreshing. The tree grows very quickly and can survive in cooler areas as well.
The scribbly gum gets its name from the scribbly looking markings left on the exterior of its trunk by the scribbly gum moth larvae that burrow into the bark. The moth can infect and affect a number of other species of gum trees, although its effects are largely limited to the decoration on the outside of the trunk.
Why Are Eucalyptus Trees Among the Most Unpopular Gum Trees?
While some people love eucalyptus trees for their fragrant branches and their beautiful bark, many other people hate the blue gum tree. The blue gum tree is known as an invasive plant, particularly in California. It's invasive because it has escaped cultivation and has grown wild. This has allowed it to move in on the territory that other native plants typically enjoyed, and the blue gum's tall stature creates a situation where it actually shades out other plant species.
Additional problems with the eucalyptus or blue gum tree are that the boughs break easily and can be dangerous to people walking under them. They also grow too large for their lot many times and need to be trimmed, which is costly and a hassle. Finally, the oils in the blue gum are very pungent and are considered to be a fire hazard. This can be exceptionally difficult in places like southern California where they are at high risk for forest fires and uncontained burning that leads to wildfires.
Because blue gum eucalyptus tends to grow in clusters, the risk of fire is very high. If one tree catches fire, the fire quickly spreads and can be disastrous. For this reason, the spread of eucalyptus growth is problematic for dry regions like southern California. It is also a problem in parts of northern California where deadly and destructive wildfires are common.
What Is Unique About Eucalyptus Trees?
Beyond the use of their fragrant blossoms, the shade they provide and their natural beauty, gum trees have a number of other remarkable qualities that make them unique. For one thing, no flowers on a gum tree have petals. Where other flowers have petals, gum tree blossoms have thousands of different stamens, allowing the tree to self-pollinate when necessary, which is often because they have very few natural pollinators.
Gum trees in general and eucalyptus trees in particular have unusual, square-shaped stems and a unique growth pattern that makes them very visually appealing. Leaves grow in pairs of two and look almost designed for beautiful symmetry. This makes them very popular in floral arrangements and as part of a tablescape.
Eucalyptus grows uncommonly fast. Most varieties of eucalyptus reach full maturity only 10 years after planting, which is highly unusual for a hardwood tree. Eucalyptus wood is used widely in the flooring industry, and the rapid growth of the trees ensures that they are a sustainable choice both in terms of the value of the wood and the fact that using eucalyptus trees is less impactful on the environment.
What Else Are Eucalyptus Trees Used For?
Eucalyptus branches and leaves contain an oil known as cineole. Cineole is a clear, organic liquid compound with a strong fragrance that is what you smell when you smell something called "eucalyptus." This ingredient that is found in high volume in eucalyptus trees is what protects it from predators. Very few species can ingest cineole. It is toxic to humans in high doses. However, cineole does have anti-bacterial, disinfectant and other sterilization uses that make it a natural choice for healers.
In regions with a high risk of malaria, eucalyptus trees are often planted. Since malaria is transmitted by mosquitoes, generally speaking, a wet area would be deadly. Mosquitoes love standing water, so areas with high populations of mosquitoes put humans at terrible risk. Planting eucalyptus trees helps to ward off mosquitoes because of cineole, making it a valuable resource.
Ashley Friedman is a freelance writer with experience working in the home, design and interiors space.