Invasive alien plant species (IAPS or ‘invasives’) threaten Nepal in a multitude of ways. They undermine the ecological integrity of agricultural areas, forests, and grasslands. They put livelihoods at risk by reducing natural resources. And they degrade Nepal’s cultural and world heritage sites. Unfortunately, despite growing research and scientific engagement, few proactive management solutions to combat invasives have been implemented in Nepal. Research must now be translated into policy: feasible solutions incorporating both social and ecological knowledge must be forged to address this complex, costly problem.

Specialists define invasives as “alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” Not all alien plant species are invasive, however; in fact, only a few are. An invasive is a non-native plant that proliferates unaided by human interactions and causes environmental damage. Several factors contribute to a plant becoming invasive: environmental adaptability, the ability to spread rapidly, and a lack of native predators, parasites, and pathogens.

Globally, invasives are an expensive problem. The Unite States alone spends over $5 billion annually to control them. But invasives also cause damage that is more difficult to quantify, such as habitat loss and diminished aesthetic appeal.

Humans help invasive plants spread across the globe—sometimes deliberately and sometimes accidentally—by introducing crops, timber, and ornamental species to new environments. Increased global trade and travel speeds the spread of invasives, making it more difficult to suppress their entrance into new territories. 

Damaging effects

By displacing native plants, out-competing crop plants, or altering ecosystem properties, invasive species can devastate environments. Nepal has currently identified 25 invasive plants, a number likely to increase with more research in understudied hill areas.

Chitwan’s ‘lahare banmara’ shows how a rapidly invading vine, Mikania micrantha, puts Nepal’s biodiversity at risk. Mikania grows up to 7cm per day, crowding out native vegetation, blanketing the grasslands that one-horned rhinos depend upon, and reducing thatch grasses, a valuable resource for people in Chitwan National Park and the surrounding buffer zone community forests.

Two other notable invasives in southern Nepal, Chromolaena odorata and Lantana camara, (both also called ‘banmara,’) decrease forest plant diversity, living up to their name ‘forest killer.’ Lantana causes photosensitivity in dairy cows and obstructive jaundice, whereas Chromolaena is known for its toxicity to livestock.

Some invasives develop deep roots capable of destroying powerlines, breaking sewage pipes, and damaging homes, historic buildings, and structures. Invasive alien plants diminish the aesthetic quality of heritage sites and alter the structural integrity of ancient buildings.

Aquatic invasives can be equally devastating. In Pokhara, Eichhornia crassipes (water hyacinth) threatens recreational activities and the beauty of picturesque Phewa Lake.

In Nuwakot, Pistia stratiotes (water lettuce) invades rice fields, damaging crops and decreasing the livelihoods of farmers.

Learning from mistakes

Controlling invasives demands a comprehensive management plan. Unfortunately, most management programmes are short-sighted, single application approaches that fail to address the social and ecological complexities of the problem concerning invasives.

For instance, management efforts far too often focus on herbicides. Herbicides are frequently applied without personal protective equipment, thus harming human health. They can also leave residues in the soil that reduce the growth and abundance of vulnerable native plants. Another management strategy, biological control techniques—releasing ‘natural enemies’ from the invasive’s native territory—can yield unpredictable ecological effects, in some cases destroying native plant species.

In addition, control methods often fail when research neglects social perspectives. In some places, local communities come to rely on fast-growing invasive plants for livestock fodder, firewood and building materials. In such cases, IAPS eradication efforts might deny these communities of available resources.

Confronting invasives in Nepal will not be easy. But we can strengthen our capacity to respond. First, Nepal must recognise the threat of invasives and construct comprehensive management strategies to address them. An integrated management approach should consider local perspectives and the social effects of controlling plants. Second, prior to applying management decisions on a large-scale, we must assess their unintended ecological consequences—that is, the possible harm to desirable or native plants. Third, a successful management programme requires public outreach to help communities navigate the causes of invasive species and to learn best management practices. Finally, a national strategy must be developed to regulate the unintentional arrival of IAPS.

Local institutions play an important role towards raising awareness about invasive species. The Natural History Museum in collaboration with the International Centre for Integrated Mountain Development (ICIMOD) and a number of other organisations recently held the nation’s first Invasive Weed Awareness Day on September 17, 2017.

Nepal needs scientific evidence to support management actions to address the invasives already causing problems and to develop proactive measures to restrict further introductions. More than just an ecological problem, invasives require management approaches that consider their social, cultural, and political context.

Given the magnitude of the problem globally and the immediate danger to Nepal’s biodiversity and livelihoods, a comprehensive IAPS management programme should be developed with urgency.

Clark is a Fulbright researcher in Nepal; Shrestha is professor of weed science from California State University, Fresno