This post is written by Sara Hendery, Communications Coordinator for the Feed the Future Innovation Lab for Integrated Pest Management.

Using satellite images, researchers in Nepal and the U.S. have observed a nearly 800 percent increase in spread of a single invasive weed – thus impeding agricultural production and degrading natural habitats – over the last 30 years.

Invasive species are spreading at unprecedented rates around the world. Their impact on native species remains a major issue for global food security, especially in developing countries with limited access to productive technologies to combat them.

That’s why the Feed the Future Innovation Lab for Integrated Pest Management collaborates with Tribhuvan University in Nepal and the Biocomplexity Institute at the University of Virginia to map the spread of seven invasive weeds throughout the Chitwan-Annapurna Landscape (CHAL) in central Nepal, an area known for some of the richest biodiversity in the world.

The teams use remote sensing, or satellite images that help researchers “sense” aspects of Earth, to examine whether coverage of the invasive weeds has increased or decreased throughout CHAL from 1990 to 2018. While all but one of the weeds demonstrated major increases in spread over time, the invasive weed Mikania micrantha showed one of the highest rates, with a 756.8 percent increase since 1990.

“Remote sensing allows us to not just see where this weed has spread, but where it could invade next,” said Pramod Jha, a professor at Tribhuvan University and one of the leaders of the project. “Knowing this will help us possibly halt the weed’s introduction to new areas and develop strategies to manage it and others. The use of remote sensing to study invasive plants is a relatively new area of research. Especially for an invasive plant that has developed such widespread coverage, remote sensing can offer a more efficient method of mapping occurrence, distribution, and abundance, than ground-level surveys.”

Mikania is a vine weed native to Central and South America that has become highly invasive and destructive to South Asia. In Papua New Guinea, the weed has caused yield losses of more than 30 percent, while efforts to control its spread in Malaysia are reported to cost almost $10 million annually. The noxious weed easily overtakes natural vegetation, fruit orchards, pastureland, and biodiversity. It is also difficult to control, as it produces large amounts of seed that can be spread easily by wind, water, and people. It spreads so quickly, its nickname is “mile-a-minute weed.”

Nepal is no exception to Mikania’s reign. There, it predominately invades forest areas and grasslands, and is listed as one of the top six worst invasive species that poses risk to native ecosystems. Agricultural production in Nepal is often insufficient to meet demand, thus farmers are moving closer to forestland for cultivation. From forests, Mikania creeps into farmers’ fields, reducing yields and increasing weeding costs. The plant so heavily blankets the ground floor, it prevents seedlings of other species from emerging, decreasing species diversity.

The weed is especially well-established in the Chitwan National Park, a world heritage site and a popular ecotourism destination. The park is one of the last protected homes of the endangered Greater One-horned Rhinoceros; however, Mikania outcompetes native plant species eaten by the rhino, threatening it further. 

“Not only do invasive weeds lead to habitat loss of native plants that are useful to humans and animals,” said Srijana Paudel, a graduate student at Tribhuvan University who helped determine the spread of Mikania, “but they also cause long-term environmental degradation and economic loss.”

Muni Muniappan, Director of the Feed the Future Innovation Lab for Integrated Pest Management, which is housed at Virginia Tech, said that examining the spread of invasive species is an area of research becoming even more urgent due to factors such as climate change, and is especially critical for Nepal. Invasive species often respond more rapidly to change than native species, which is why native species can so easily be pushed out.

 “Within a short horizontal span, Nepal has a climatic range that reaches from the Florida Keys to the Arctic,” said Muniappan. “The country’s unique geographic and topographic variations contribute to its rich diversity of agricultural crops and plant species, which is massively linked to the livelihoods, food security, and economic well-being of most Nepalese people. Conserving and protecting these resources is necessary.”

Nepal is considered one of the most vulnerable countries to climate change in the world. As the country becomes more vulnerable, predicting threats with the use of satellite images and other modeling practices will be one of its strongest defense mechanisms and one of its pathways to protection.