Which trees are weeds?

How do I know if my tree is a weed?

As a homeowner or gardener, you may have come across the term “weed trees” before. But what exactly are they and why do they have such a bad reputation? In this article, we will explore the characteristics of weed trees, their impact on the environment, and how you can help control their spread.

What Makes a Tree a Weed?

At its core, a weed is any plant that grows where it’s not wanted or has negative environmental impacts. Weed trees are those that have the potential to spread rapidly, outcompete native species, and disrupt the balance of ecosystems. They may be introduced or native plants with invasive characteristics such as large volumes of seed, effective seed dispersal mechanisms, rapid growth, vegetative reproduction, disturbance invasion, or allelopathy.

Types of Weed Trees

Noxious weeds are the worst of the bunch. These plants are declared noxious because they cause environmental or economic harm and present a risk to human health. In Victoria, there are four categories of noxious weeds: state prohibited weeds, regionally prohibited weeds, regionally controlled weeds, and restricted weeds. Landowners and public authorities responsible for crown land management must take all reasonable steps to eradicate noxious weeds on their land.

Environmental weeds are plants that invade native ecosystems and have the potential to negatively affect the survival of native flora or fauna. They include species that have been introduced to Australia from other countries and native species that have spread beyond their previous range. Some common environmental weed species in Victoria are Box Elder, Cape Wattle, Cherry Plum, Cootamundra Wattle, Desert Ash, Mirror Bush, Monterey Pine, and Sweet Pittosporum.

Are There Any Benefits to Weed Trees?

In some cases, mature weed trees are allowed to remain in parklands because of the canopy benefits they provide. However, care must be taken to control seedlings and plant more appropriate species for the future. If you have a weed tree in your garden, you may wish to recognize the benefits of its canopy while ensuring that seedlings are controlled.

Permits and Identifying Weed Trees

Many weed species on Environmental Weed lists are exempt from a planning permit if you desire to remove them, but correct identification is vital. Be sure of the species before you take action with a chainsaw, as some species may look similar to others. Here is a useful weed identification tool: http://www.environment.gov.au/cgi-bin/biodiversity/invasive/weeds/weedidtool.pl

How to Help

You can help reduce the spread of weed trees in Victoria by choosing garden plants wisely and selecting local indigenous plants where possible. Remove identified weed species from your garden and replace them with local indigenous plants. Familiarize yourself with your fire risk and remove those woody weed species that increase the fuel load and fire intensity around your home. Deposit your garden waste in your green-lidded Council bin or at your local landfill. Join a local conservation group and volunteer to protect the natural areas nearby.

Facts About Weed Trees

The term “weed” is not limited to non-native plants.
Weeds can reduce biodiversity in native vegetation and negatively impact ecosystems.
Noxious weeds are plants that cause environmental or economic harm and present a risk to human health.
Environmental weeds are plants that invade native ecosystems and have the potential to negatively affect the survival of native flora or fauna.
Correct identification is vital before taking action with a chainsaw.
You can help reduce the spread of weed trees by choosing garden plants wisely, removing identified weed species, and joining a local conservation group.

Seven common trees considered weeds in Australia:

Willow (Salix spp.) Willows are deciduous trees that can grow up to 30 meters tall. They grow rapidly and produce large quantities of seed, which can be easily dispersed by water. Willows can quickly establish in wetland areas and outcompete native vegetation.
Box elder (Acer negundo) Box elders are fast-growing deciduous trees that can reach up to 25 meters in height. They produce large quantities of seed, which can be dispersed by wind and water. Box elders can establish in riparian areas, wetlands and disturbed sites and outcompete native vegetation.
Tree of Heaven (Ailanthus altissima) Tree of heaven is a deciduous tree that can grow up to 20 meters tall. It grows rapidly and produces a large quantity of seed, which can be dispersed by wind. Tree of heaven can grow in a variety of habitats and outcompete native vegetation.
Chinese tallow (Triadica sebifera) Chinese tallow is a deciduous tree that can grow up to 10 meters tall. It grows rapidly and produces a large quantity of seed, which can be easily dispersed by birds. Chinese tallow can establish in wetlands and outcompete native vegetation.
Pepper tree (Schinus molle) Pepper tree is a deciduous tree that can grow up to 10 meters tall. It produces a large quantity of seed, which can be dispersed by birds. Pepper tree can establish in a variety of habitats and outcompete native vegetation.
Sweet Pittosporum (Pittosporum undulatum) Sweet Pittosporum is an evergreen tree that can grow up to 15 meters tall. It produces a large quantity of seed, which can be dispersed by birds. Sweet Pittosporum can establish in a variety of habitats and outcompete native vegetation.
Radiata pine (Pinus radiata) Radiata pine is a coniferous tree that can grow up to 50 meters tall. It grows rapidly and produces a large quantity of seed, which can be dispersed by wind. Radiata pine can establish in a variety of habitats and outcompete native vegetation.

Links for Further Reading

From the Tree Spotlight collection

Read about some trees different trees here: