Venturing out into the countryside of Hualien County, we see many green masses covering fences, roadsides, and trees. Specialist Lü Kunwang of the Hualien Branch of the Forestry and Nature Conservation Agency (FANCA) teaches us to identify mikania vine. It has heart-shaped leaves with serrated edges; radial leaf veins; long, slender, soft stems; and a light purple hue at the growing tip of the plant.

In an abandoned banana plantation, the trees are tightly entwined and a number of their leaves have broken in two because of the extra weight on their tips. This is a classic example of how mikania vine strangles other plants, and if nobody intervenes to remove it, then sooner or later the victim plant will wither and die.

Data indicates that mikania vine can grow by as much as 24 centimeters per day on average, and in its flowering season can produce 170,000 seeds per square meter. It’s no wonder that one of its English names is “mile-a-minute weed.”
 

Action to control mikania vine

How did mikania vine get to Taiwan? Some say that seeds were accidentally imported through the movement of people or goods, or by birds flying in from other places. Others say that it was introduced deliberately because its rapid growth makes it suitable for use as ground cover to stabilize soil on slopelands.

Though at first it appeared only in small numbers and in scattered locations, about the year 2000 people began to take notice of what had become an omnipresent weed. According to FANCA statistics, in 2002 the area affected by mikania vine reached 56,848 hectares, mostly at elevations below 1,000 meters above sea level.

To effectively prevent the spread of mikania vine, besides increasing its efforts to raise public awareness, FANCA adopted a policy of purchasing uprooted mikania plants at NT$5 per kilogram year round. In addition, the agency declared the second half of August and the first half of September, prior to the flowering season, to be Mikania Vine Control Month, and named the first Saturday in September as National Mikania Vine Control Day, asking the public to participate. After many years of effort, by the end of 2021 the area affected by mikania vine had fallen to 3,391 hectares nationwide.

Hualien County was once one of the most severely affected areas in Taiwan. In 2020, Hualien had 3,681 hectares affected by mikania vine; it appeared most frequently on abandoned farmland and in fruit orchards and betelnut plantations.

In order to accelerate mikania eradication, the Hualien County Government raised the stakes by offering NT$8 per kilo of uprooted mikania vine. Wang Yi-ching, deputy director of the Hualien Branch of FANCA, says that to take on this “green monster” directly, the Hualien Branch proactively established the “Hualien County operations platform for the eradication of invasive plants” in cooperation with other government agencies, neighborhoods, indigenous communities, private organizations, and schools.

At the same time, to more effectively monitor the presence of mikania vine, the Hualien Branch of FANCA and the Department of Forestry at National Pingtung University of Science and Technology are collaborating on a project to send out camera drones during flowering season to take photos of areas affected by mikania vine. These images are then overlaid on cadastral maps in order to accurately determine the locations and quantities of mikania vines. Through multifaceted approaches, the area of Hualien County with mikania vine today has been reduced to about 800 hectares.

Transformation of a waste product

Because mikania vine propagates so prolifically, a new plant may spring up wherever a stem node is left touching the soil. Hence special care is needed in its eradication. Lü Kunwang explains the standard operating procedure for removing mikania vine: Follow the stem of the plant to the roots and then dig it out with the roots still attached. You should remember not to pull too hard, to make sure that broken stems do not fall on the ground and regrow. During Mikania Vine Control Month, branches of FANCA bring uprooted plants to a central location for disposal, either by packing them in garbage bags and burying them, or by incineration. At other times, people can simply roll up the vines and hang them on trees, where they will wither and die.

During Mikania Vine Control Month in 2022, the Hualien Branch alone cleared away a full metric ton of the vine. Unfortunately, handling such an enormous amount of waste material requires a great deal of manpower and money and increases carbon emissions.

“This got us thinking about whether it might be possible to turn this waste into something useful,” says Chiu Huang-sheng, chief of the operations planning section at FANCA’s Hualien Branch. With this in mind, the Hua­lien Branch then asked Zantan Studio, located in Fenglin, which specializes in making bamboo charcoal, to adapt their method for producing bamboo vinegar and wood vinegar and try to develop mikania vine vinegar. This would make a Cinderella story out of this waste product.

What is wood vinegar? Huang Ying-pin, manager of the Biomass Materials Technology Department at the Central Region Campus of the Industrial Technology Research Institute (ITRI), leads a team that has done many years of research into such vinegars. Huang tosses some mikania vine gathered from the roadside into a simple pyrolysis kiln, and as the biomass is decomposed by the heat, smoke and vapor curls up into the air. Huang explains that this is the basic process for making wood vinegar (a.k.a. pyroligneous acid).

During pyrolysis (thermal decomposition) of organic material, smoke and vapor are given off. To make wood vinegar, the smoke and vapor are collected and condensed into liquid, which is stored for about six months, during which time the liquid settles into layers according to weight. The upper layer consists of an oily liquid, the bottom layer is tar oil, and the middle layer is the vinegar.

As the names “wood vinegar” or “bamboo vinegar” suggest, these liquids include acetic acid. They have the aroma of smoked plums or monk fruit, and because they are rich in organic chemical compounds like phenols and alcohols, they can act as antibacterials and odor removers. It was the Japanese who first began to pay attention to the uses of such vinegars, adding them to cleaning products to reduce pungent odors such as ammonia and sprinkling them on farmland to revitalize the soil.

In order to ensure the quality and safety of mikania vine vinegar, FANCA Hualien Branch sent samples to the certification companies SuperLab and SGS to verify that it contains no heavy metal residues. They also went a step further and mediated the founding of a line of cleaning products made with wood vinegar, produced by the brand Dawoko.

Dawoko, whose ideal is to implement the circular economy, emphasizes that their main raw material for making wood vinegar is waste wood from the pruning of longan trees. “This residual wood material and uprooted mikania vine both make excellent raw materials,” says Hung Wei-lin, production manager at Dawoko.

In complete agreement with the idea of circular use of forest resources, Dawoko gladly agreed to work with  FANCA Hualien Branch and further distilled their mikania vine vinegar before adding it to seven products including shampoo, hand lotion, and liquid mosquito repellent. In their first batch they produced 5,000 bottles of product, and consumers responded well, rapidly buying up the entire stock.
 

Natural nemesis of the biting midge

There are slight difference among wood vinegars based on the different raw materials used, but most are effective antibacterials or disinfectants. Mikania vine vinegar not only is 99.9% effective against the bacterium Staphylococcus aureus, but as Huang Ying-pin explains, because it contains nitrogen and has a relatively strong odor, it is exceptionally effective at repelling Forcipomyia taiwana, a small black biting midge.

In order to promote the removal of mikania vine, ITRI has been working on applications for and development of mikania vine products. Inspired by the process of making wood vinegars, Huang Ying-pin and his team have expanded the applications of mikania vine to incense-type products such as mosquito coils. He says: “Incense-type products are burned when they are used, so in principle the process is similar to vinegar extraction.”

Huang has persuaded many businesses of the merits of using mikania vine vinegar. Though it is not really suited to being an independent product in its own right, mikania vine is recognized as an excellent supporting player. When used in combination with mugwort, known as “the king of herbs,” “they complement each other and are more effective together” in uses from repelling mosquitoes and midges to purifying the air, affirms Chen Xiuzhi, a buyer at Artemisia Biotechnology Company.

The environmental problems caused by invasive species cannot be eradicated overnight, but through cross-disciplinary cooperation and innovative thinking, people can find ways to take the initiative in tackling them. In progressing from simple removal of mikania vine to proactively developing uses for it, the experience of combating this plant and putting it to good use can be seen as an important symbolic step on the path towards the circular economy.

For more pictures, please click 《Invasion of the Mikania Vine—Turning “Green Cancer” into “Green Gold”》