Plants don’t stay put. They grow, spread, and sometimes end up far from where they started. In the tropics, that movement is causing big changes. Plants from other parts of the world – called alien species – are taking root in places they’ve never belonged. Some are harmless, but others are taking over.
Across the tropical and subtropical regions of the planet – an area known as the greater tropics – roughly 10,000 alien plant species are now thriving. Many of these plants were brought in on purpose. People wanted them for farming, gardening, or medicine. But once they got loose, a few of them started spreading fast.
Not every alien plant causes problems. In fact, most don’t. But the ones that do are known as invasive species. And their impact goes beyond plants – they’re changing entire ecosystems, pushing out native species, and even making life harder for the people who live nearby.
The plant that pushed people out
One of the most invasive plants in the world is called Lantana camara. It’s originally from the tropical Americas and was brought to Europe in the late 1600s as a pretty garden plant. Later, the Portuguese carried it to their colonies, including India.
“In the last century, large areas in the Western Ghats of India became overrun by Lantana. This triggered the native forest-dependent Soliga people to abandon their traditional livelihood and migrate in search of alternatives,” said Ninad Avinash Mungi, a researcher from Aarhus University.
India isn’t alone. Lantana now covers 74 million acres there – an area larger than the state of Arizona. In Australia, it has taken over 9.9 million acres, and in Hawaii, about 395,000 acres. And it keeps spreading.
“Invasive plants like Lantana competitively suppress native food plants in forests and on savannas. Scarcity of food makes herbivores decline, which further affects the carnivores. We’ve seen examples of tigers preying on livestock when herbivores decline,” said Mungi.
Ecosystems lose their balance
This isn’t just a plant problem – it’s a people problem too. In poor areas where communities depend on forests and savannas for food, firewood, and medicine, invasive plants can cut off their access.
As ecosystems get weaker, animals get hungrier. And that means more conflict – between wildlife and people. But this didn’t start yesterday.
“The tropics have historically been changed by people for thousands of years,” said Mungi. “But the pace changed during the colonial era.”
“People brought species from colony to colony, spreading plants and animals all over the tropics. Global trade after World War 2 has even further accelerated the process. Today, species are being exchanged all the time.”
Invasive plants overwhelm weakened lands
Forests used to keep these invaders in check. But human activity has changed that. Researchers point out that human-caused deforestation, wildlife extirpation, pollution, and land-use transformations are important drivers of invasive plant spread.
“These changes weaken the natural control over alien plants, facilitating their spread. Thus, invasive plants are initially passengers of disturbances, but eventually become drivers of disturbances,” Mungi said.
And with climate change speeding up, things are getting worse. In the Amazon, rising temperatures, logging, and wildfires are killing off native trees and plants. Invasive grasses make fires worse. They dry out easily and act like kindling, fueling the flames and preventing native species from regrowing.
“Paradoxically, increasing levels of CO2 in the atmosphere supports woody plants in place of grasses across savannas in the greater tropics,” Mungi said. “Here, woody invasive plants are benefitting from CO2, fire suppression, and loss of large herbivores.”
Some invasive plants help, not harm
There’s another side to this story. Some alien plants aren’t entirely harmful. In fact, they may help, especially when native species are already struggling.
“While invasive species require focused management, more neutral alien species can sometimes play a positive ecological role, particularly when native species are stressed by a changing climate or have been removed by people,” said Jens-Christian Svenning, a researcher at Aarhus University.
New types of ecosystems are emerging. These “novel ecosystems” may actually be more stable in a world of rising temperatures, extreme weather, and pollution. Protecting and expanding biodiversity can help keep invaders in check.
Alien plants are often seen only as a threat, but the reality is more complex. Most alien plants are neutral, and some can even play positive roles – especially as climate change pushes ecosystems toward collapse.
“Understanding both the risks and the buffering potential is key for smart management,” Svenning said.
Fighting invaders is costly
Managing widespread invasive plants is costly, and complete eradication is often uncertain because the species can easily re-invade.
“Since invasive plants have spread across natural areas, they can’t simply be bulldozed, as that would cause several undesirable impacts on ecosystems,” said Mungi. “A sustainable alternative is urgently needed.”
Mungi and Svenning have proposed a solution called Nature-based Solutions for Biological Invasions. Instead of fighting nature, this approach works with it.
One idea? Reintroduce large animals – such as elephants and buffalo – into floodplains and savannas. They can naturally control invasive plants simply by grazing.
Adapting to invasive plants
In some places, invasive plants are already part of the landscape and have become quite useful.
“In many areas across the greater tropics, locals have begun using invasive plants such as Lantana to build crafts and furniture, Prosopis juliflora for biochar production, and water hyacinth for commercial products. They have adapted to a new reality,” said Mungi.
Both studies emphasize the importance of working in partnership with local communities when managing invasive plants.
“Local communities are often more aware of their ecosystems and of creative ways to manage them,” said Mungi.
Invasions reshape our world
The world is not what it used to be. And it won’t stay the same. Invasive species are part of this shift. They’re changing forests, savannas, and coastlines. And they’re changing how people live, work, and survive.
The question isn’t just how to get rid of them – it’s how to live with them, manage them, and make better choices about the future of nature.
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