Taiwan gets creative in battle against ‘green cancer’

Taiwan gets creative in battle against ‘green cancer’

2024-02-18

Taiwan is fighting an ecological menace known as the Mikania vine, or the bitter vine. Native to Central and South America, it’s a fast-growing plant that can overtake agricultural crops, killing them along the way. Today the weed has already spread extensively across the country. Tonight in our Sunday special report, we meet the people who are battling the vine, and see how they’re turning it from a threat to an economic opportunity.

The banana trees are covered in a mass of green, as if shrouded by a blanket. They’ve been invaded by a weed known as the bitter vine. Once the vine covers a crop, it can pose a deadly threat. That’s why it’s known as the “green cancer.”

Bitter vine is native to Central and South America, and it thrives under strong sun. It’s a rapidly growing plant that climbs toward light. If left unmanaged, it can kill the crops that it invades. But removing the vine is labor intensive, and volunteers are often needed to help.

Liu Jung-chuan
Volunteer
We’re out in the country. Here in the country, this problem is very common. People are older here, and farming for a living is hard on them. All the young people have gone away.

Chuang Hsin-hsien
Volunteer
Banana trees, orange trees, and other plants. For instance, lychee orchards have it too. Wherever this vine can climb and find water and nutrients, it will grow.

Bitter vine has pointed leaves and small white flowers that bloom in the summer. It can grow an astonishing 24 centimeters a day. Besides being known as “green cancer,” it’s also nicknamed the “forest killer” due to its harmful impact on reforestation. It causes tree death after invading, altering the ecology. When its shallow roots replace the deep roots of trees, it can make mountain slopes unstable.

Lin Hsiang-li
Forestry and Nature Conservation Agency official
It likes high humidity and high temperatures – it does well in warm areas. Taiwan just happens to check all the boxes. In our surveys of the plant’s distribution, we’ve seen it spread from altitudes below 1,500 meters to areas above 2,000 meters.

In its native Central and South America, the bitter vine is kept in check by local insects and pathogens. But it has no such enemies in Taiwan. Tasked with fighting the weed, the Forestry and Nature Conservation Agency has explored a variety of ways.

Lin Hsiang-li
Forestry and Nature Conservation Agency official
The main removal methods are mechanical, biological, and chemical. Chemical methods entail spraying herbicides, and we haven’t considered it. Biological methods deploy the natural enemies of the bitter vine. Initially our experts studied the rust fungi as an option, but they were concerned about the risks, that is, the unintended harm that the fungi might have on other species.

Over the years, the government has found it hard to keep the vine in check.

Today, Hsu Kuang-yuan and his team are on a mission to kill weeds, here at a plot of public land in Taoyuan City. They use their hands and small sickles, as manual removal is the most effective strategy against the bitter vine.

Hsu monitors the progress, reminding the team not to let broken stems fall to the ground.

Hsu Kuang-yuan
Weed removal provider
This is a root that’s been pulled up. Look at this node over here. Just like the cathedral bells plant, the bitter vine can resprout from a broken stem.

The bitter vine is tenacious, and can multiply through broken stems. Fighting the plant is a year-round job for the Taoyuan City government.

The plant also has highly efficient seed dispersal. After flowering season each summer, the dispersal is even more astonishing.

Lee Chao-ching
Volunteer
Like this flower here. It’s already flowered and fruited and seeds have already formed. If you touch it, the seeds will fly. See here, I’ll show you, here they go. The seeds are so tiny it’s hard to see where they’re going. So after the vine blooms, it’s best not to touch it.

The plant can produce up to 170,000 seeds per square meter of vine. With a gust of wind, the tiny seeds are spread far and wide.

For some 40 years now, officials have had limited success in eradicating the weed. One reason is its prolific reproduction. Another issue lies in land ownership. When private landowners don’t want to manage the weed, there’s nothing public authorities can do.

Liu Hsiu-ching
Taoyuan Department of Agriculture official
Currently, all the government can do is try to persuade them. If we receive a public complaint, we seek out the landowner through the government system. We do our best to notify the landowner about their rights and responsibilities. We might even go to the community-level authorities and seek intervention or mediation.

In addition, there are places simply too dense and dangerous for weed control workers to reach.

Liu Hsiu-ching
Taoyuan Department of Agriculture official
For instance, Longtan District has many hilly areas. We can only work in areas that our people can reach, places that aren’t dangerous. Some hillsides aren’t steep but are actually quite dangerous. We can only do our best.

The challenge is too great for one agency alone. Working with local governments, the Forestry and Nature Conservation Agency offers cash to the public for pulling up vines.

Lin Hsiang-li
Forestry and Nature Conservation Agency official
In the past few years we’ve had this initiative. We buy uprooted bitter vines year-round. The Forestry and Nature Conservation Agency offers NT$5 per kilogram of uprooted vine, and some local governments add on a bit more.

The uprooted vines must be handled with care, to ensure they don’t come back from the dead.

Hsu Kuang-yuan
Weed removal provider
You can bury them. Pack them up and find a suitable place and bury them. After a while, they will die. They don’t grow back. The other way is to take them to the incineration plant and burn them.

Every year, the Forestry and Nature Conservation Agency buys hundreds of tons of bitter vine. Burying the weeds requires lots of land, but incineration increases carbon emissions. Could there be a better solution?

Huang Ying-pin is a researcher at the Industrial Technology Research Institute’s Central Region Campus. He’s developed a novel way to use the bitter vine. He takes dried and chopped-up vine, placing the pieces into a carbonization furnace.

Huang Ying-pin
ITRI Central Region Campus researcher
In this space, we can put stainless steel containers like this, which we fill with vine pieces. Then we heat it to 600 to 700 degrees Celsius.

The vine is treated at high temperature for a week. The smoke and vapor are condensed into an amber-colored vinegar. The vine’s high nitrogen content gives the vinegar unique properties.

Huang Ying-pin
ITRI Central Region Campus researcher
Regular vinegar, whether it’s wood or bamboo vinegar, has a smell to it that repels mosquitoes such as the yellow fever mosquito or the southern house mosquito. But the unique thing about the bitter vine is that its nitrogen content produces a different odor, one that can effectively repel the biting midge.

After processing, bitter vine vinegar can be sprayed to curb biting midge populations. It can be made into agricultural pest control or a repellent. What’s left of the vine after treatment can also be used as biochar, an excellent soil conditioner.

Here at his factory in Changhua, Tai Mu-tsun is busy making incense. Tai is an expert in medicinal plants, and he works with ITRI to make his products. Bitter vine is used instead of the traditional Chinese mugwort, to make incense that repels the biting midge.

Tai Mu-tsun
Incense factory owner
It just so happened that we ran into Dr. Huang and his team again. They found bitter vine to be effective against the biting midge, and they wondered if we wanted to try it. So we added it in and discovered that it’s even more effective than Chinese mugwort.

With a turn of the machine, a coil of incense is formed. The product takes just a few seconds to make, but it belies years of research and development.

Huang Ying-pin
ITRI Central Region Campus researcher
For researchers like us, if we develop a product or a technology and are able to transfer it to manufacturers and see it hit the market, that’s immensely gratifying.

Tai Mu-tsun
Incense factory owner
Before you launch a product on the market, it has to go through years of testing. We had to ensure this product really can repel the biting midge and doesn’t harm humans before we released it.

Meanwhile, others are exploring applications for the vine beyond insect control.

Lin Hsiang-li
Forestry and Nature Conservation Agency official
In Nantou, they’ve used it to make indigo dye. They’ve also used it in soaps.

Huang Ying-pin
ITRI Central Region Campus researcher
We’ve also tried combining it with construction materials to create what we call permeable bricks, or combining it with red brick clay. Our tests showed good permeability, water retention, and soil preservation properties.

The bitter vine came from far away, arriving as seeds before growing into an ecological crisis. But the plant has also inspired creativity and perseverance in those who live with it. Even as complete eradication remains elusive, Taiwan is finding ways to turn its “green cancer” into gold.

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