When you think of a weed, that stubborn plant in the vegetable patch that is impossible to remove comes to mind. We have become accustomed to seeing weeds as the ultimate plant pests, which exist only to cause gardeners and conservationists headaches. It can be tempting to think that native plants are better than weeds.

Is this distinction useful or accurate? This issue can be clarified by looking at the complexity of weeds.

Native fauna such as the variegated fair-wren rely on weeds for food and habitat. Kathryn Lambert, Author provided

What you need to know about weeds

A weed can be a plant which has invaded and survived in an ecosystem that it had never been before. It can either be native or exotic and moves into new habitats if it has an edge over the resident plants.

Weeds produce many seeds and can survive in a variety of environments, including cities, deserts, and farmland. They thrive in all kinds of climates and temperatures.

The Cootamundra Wattle ( Acacia baileyana) is a native weed in Australia that has spread outside of its range. This species is known for its prolific flowering and has been used in many gardens.

The seeds are also transported by birds and ants, who use them as food. These seeds are viable for many decades and can germinate rapidly after a fire. This species is able to take over certain habitats and gardens.

Cootamundra Wattle is considered an invasive weed in Victoria, where it competes with native species. Momentary glimpse/Flickr, CC BY-NC-ND

What are the environmental effects of weeds?

First, it is important to recognize that native species do not always have a positive impact on the local ecosystem. For example, the native Christmas beetle is suspected of killing broad-leaf Peppermint Gums ( Eucalyptus divings ) in Australia. The same is true for categorizing plants according to their age in an ecosystem. This does not give us a clear picture of the role they play.

The assumption that underlies conservation and restoration is still the non-native species provide little in terms of benefits to ecology. This is not always the case.

Devil’s claw ( Martinynia anninua ) was introduced to Australia in the 19th Century as a garden weed, just like many other weeds that are now here. The plant has been manually removed in Gregory National Park, Northern Territory, for the last 20 years.

There is no evidence that this species has negatively altered the ecosystem by increasing nitrogen levels or decreasing biodiversity. Native birds and insects collect nectar and pollen by the devil’s paw, and its removal may be harmful to native fauna.

Blackberry, another exotic weed introduced to Australia for its fruit, has now spread across more than 8,8 million hectares. It has reduced productivity in primary industries and restricted access to water and land as it forms thickets.

This species is not only beneficial for the production of fruit and honey but also for providing food for browsing animals, habitat, and food for certain native fauna species. These include bandicoots, blue wrens, and other species. Its removal, as with many other weeds, could be detrimental to native fauna.

Lantana: The Case of Lantana

My research focused on Lantana, a prominent weed ( Lantana Camara). The weed is loved for its pink, yellow, and red flowers, but it’s also criticized for its environmental impact.

Lantana, which began as a garden plant in a suburban backyard, has unfortunately spread to other areas by birds and small animals that feed on the seeds and fruit. This species changed the soil’s nutrient properties by increasing nitrogen. This can cause stress or even death to forest trees. Some have blamed the species for the deaths of thousands of eucalypts that have occurred in northern New South Wales.

The native bush rat was caught in Lantana. Kathryn Lambert, Author provided

Lantana has become so invasive it’s now illegal to grow or sell it at nurseries. Every plant can be a seed bank.

What if the removal of Lantana, despite its negative impact on the floral diversity of the area, actually harms the native fauna? The Avian Behavioural Ecology Lab at the University of New England has conducted research that suggests this could be true in the forested areas of NSW.

We noticed that the number of Antechinus, bush rats, and other species decreased when Lantana began to die in this area after an eradication program. This weed is a valuable habitat for small native mammals.

It seems as though some native species have started to adapt and even depend on weeds for food and habitat. What if we removed them completely from these areas, and even from our backyards, for the sake of conservation?