- Native plants are declining in Nepal’s capital Kathmandu, largely due to habitat loss and the spread of invasive species.
- Several invasive plants are dominating ecosystems by blocking sunlight, altering soil and displacing native vegetation.
- Non-native species were introduced historically (since the 1850s) and through globalization. Today, a large proportion of Kathmandu’s plants are exotic, with some becoming invasive and harmful.
- Weak regulation, poor monitoring and preference for ornamental or fast-growing exotic plants in urban planning have worsened the problem, highlighting the need for stronger policies, early control and better institutional coordination.
KATHMANDU — Until a few decades ago, botanist Bharat Babu Shrestha observed abundant growth of Indian pennywort (Centella asiatica) across large areas of Kathmandu. But the low-growing herb, distinguished by its kidney-shaped leaves and medicinal properties in the traditional Ayurveda, is now gradually vanishing from Nepal’s capital.
Its disappearance has been attributed to shrinking open spaces, and largely due to the spread of another plant species creeping across Kathmandu: Crofton weed (Ageratina adenophora), locally known as kaalo banmara. The various species within the family of banmara — meaning “forest destroyer” in Nepali — the dense shrub with multi-colored flowers, with roots in Central and South America, is displacing many native species.
“There has been no qualitative assessment in Kathmandu, but our observations show that our native vegetation has been dominated and displaced by many invasive species,” said Shrestha, a botany professor at Tribhuvan University, Nepal. “Our research in Nepal’s Parsa and Shuklaphanta national parks have concluded that invasive species have reduced almost half of the native species in those regions, indicating similar impacts in Kathmandu.”
In Kathmandu, Crofton weed; the common lantana (Lantana camara), locally called kaade banmara; Santa Maria feverfew (parthenium weed, Parthenium hysterophorus), known as pati jhaar in Nepali; and blue billy goat weed (Ageratum houstonianum), locally called neelo gandhe, are said to be the dominant invasive species, according to experts.
Shrestha said that species such as the common lantana or the polka dot plant (Hypoestes phyllostachya), which is native to Madagascar, have become popular ornamental plants in Kathmandu’s gardens. He warned that once they spread from small pots to larger plots and forests, they could wreak havoc, as their thick canopy blocks sunlight, suppressing and eventually killing nearby species. He added that lantana is increasingly being used as a hedge plant across Kathmandu’s streets.
“Invasive plants are initially established in urban areas before its spread,” Shrestha said. “If we are able to identify and control them early on, they won’t expand in agricultural and natural areas, and we can minimize their impacts.”
Growing concerns
The non-native plant species are said to have first been introduced in Kathmandu in the 1850s after Jung Bahadur Rana, then prime minister of Nepal, brought home several exotic species, including bottlebrushes (Callistemon sp.), camphor trees (Cinnamomum camphora), silk oak (or kangiyo phool, Grevillea robusta) and eucalyptus from Europe. With the rise of globalization in the 19th and 20th centuries, many species arrived unintentionally through trade and transportation, while others were deliberately introduced by travelers as ornamental plants for gardens.
Today, experts estimate that three out of four randomly selected trees inside Kathmandu’s ring road, circling around the cities of Kathmandu and Lalitpur, could be non-native species. A 2024 study showed that 48% of the 158 species observed in Kathmandu’s Sanobharyang region, in proximity to community forest and national park areas, were non-native while 6% were invasive alien plants.
Krishna Prasad Sharma, one of the study’s co-authors and an assistant professor at Tribhuvan University, said that not all non-native plants and trees are harmful. Introduced trees such as jacaranda (Jacaranda mimosifolia) and avocado (Persea americana) — the latter becoming immensely popular among Kathmandu residents lately — usually do not encroach on other species’ territories and remain confined to their planted areas.
“Invasive species, on the other hand, release allelochemicals as a weapon to inhibit the growth of other plants around them,” Sharma said. “It modifies the soil properties, impacting farmlands, and its toxicity could also seep into the water system and through the food chain, harming human health. But its impacts would only be known in the long run.”
Ronish Pandey, who submitted his master’s thesis to Central Department of Botany, Tribhuvan University, on Kathmandu’s plant species composition last year, said that more than half of the 437 species of plants he surveyed in the capital’s green spaces — including urban parks and urban forests — were exotic, or non-native. Some 21% of the naturalized exotic species were found to be invasive, according to him.
“Some places are focusing on non-native species because of the economic perspectives as well,” said Pandey, who now teaches at the Amrit Campus, a science college in Kathmandu. “In Kathmandu’s parks and community forests, they focus on non-native ornamental plants because they flower better than native ones, which visitors want for photo shoots and social media posts.”
But while areas inside urban green spaces are more well-managed, experts are worried about the existing and new alien species being recorded in Kathmandu’s open areas and ponds.
Shrestha said the siam weed (Chromolaena odorata), locally known as seto banmara, was recorded at three locations in Kathmandu just last year. A 2025 study revealed that siam weed has “increased the challenge to the seedling recruitment of threatened native trees” such as bael (Aegle marmelos) in Ramechhap district.
“It’s also a fire hazard and helps spread wildfires easily,” Shrestha said. “We didn’t control in other parts of the country when we could, so now it has come to Kathmandu already.”
Who is responsible?
In Kathmandu’s neighboring district of Kavrepalanchok, the yellow flowering Singapore daisy plant (Sphagneticola trilobata) that is native to Central America — identified as one of the 100 worst invasive plants by the IUCN, the global authority on nature conservation — was introduced for urban greening purposes more than two decades ago. Similarly, the giant sensitive plant (Mimosa diplotricha) was used for riverbank stabilization around that same time.
Years later, the Singapore daisy is now invading farmlands, while the giant sensitive plant — locally known as ulta kanda — has killed hundreds of livestock due to its toxic leaves.
Experts say many non-native invasive species — there are about 29 altogether in Nepal — remain poorly understood, including how they entered the country, despite the existence of plant inspection and quarantine regulations since 1972. The Plant Quarantine and Pesticide Management Centre was later established in 1993 under the Ministry of Agriculture and Livestock Development to regulate, among other things, the entry and spread of invasive species in the country.
However, the growing number of exotic and invasive species in Nepal, including in Kathmandu, suggests lax implementation of such regulations. Experts say authorities are increasingly opting for exotic, non-native trees — including poplar, eucalyptus and jacaranda — as they require minimum care and have high survival rates for street beautification projects.
Pandey’s research shows that the parks maintained by the Kathmandu Metropolitan City (KMC) office also favored exotic flowering plants, with more than 60% of species in Ratna Park, Bhugol Park and Shankha Park in the city identified as non-native.
“It’s because they mostly don’t know what species to select, and the decisions are based on contracts with the lowest bidder,” Pandey said. “They end up selecting the cheapest one, and most of the plants come from India.
Shrestha said that it is concerning that invasive plants are being introduced in parks and ponds managed by the city, raising questions about the management’s awareness. He pointed to the pond in Kathmandu’s UN Park, which is covered in water hyacinths (Eichhornia crassipes), warning that it not only harms the aquatic ecosystem and dries up the water body but also risks spreading into the nearby Bagmati River.
“They’re being openly sold in private nurseries, with little awareness or monitoring,” Shrestha said.
Experts say that the absence of a dedicated national authority to oversee the issue, along with weak coordination among various government institutions, has led to limited monitoring and management of non-native and invasive species. Currently, the Plant Quarantine and Pesticide Management Center and the Forest Research and Training Center are tasked with monitoring invasive species in the agriculture and forests, respectively, but responsibility for urban areas, like Kathmandu, remains unclear.
“This matter has not been clearly allocated or defined as the responsibility of one particular institution,” said Sunita Ulak, senior researcher and undersecretary at the Forest Research and Training Center, which is under the Ministry of Forests and Environment. “There aren’t clearly defined laws even to take actions against those selling or planting invasive species. We are planning to identify it as a serious issue and make relevant strategies.”
To address the concerns, the Forest Research and Training Center hosted the country’s first conference on alien species in December 2025, issuing an 18-point declaration. The declaration called for strengthening measures in identifying such species at entry points, improving documentation and monitoring, and streamlining relevant policies.
Shrestha called the move a positive step but stressed that the recommendations must be strictly enforced. He added that authorities should invest in risk assessments before the seeds or saplings even reach Nepal’s borders and ensure that the regulations extend beyond agricultural and forest areas to include urban areas as well.
“We need a common acceptance that the biodiversity of urban area is also important and have conservation value,” Shrestha said. “Urban areas are the hotspots for invasive species, and that should be a common understanding.”
Banner image: Flowers of the blue billy goat weed (Ageratum houstonianum), locally called neelo gandhe. Image by The Cosmonaut via Wikimedia Commons (CC BY-SA 2.5 CA).
Government inaction leaves Nepal without strategy to tackle invasive species
Citations:
Tamang, S., Khanal, S., Chaudhary, T., Poudel, J., Rawal, B., Paneru, C., … Shrestha, B. B. (2025). Invasive weeds reduce plant diversity and alter species composition in Rangelands of Tropical Protected Areas in Nepal. Environmental Management, 76(1). doi:10.1007/s00267-025-02315-x
Poudel, S., Pant, R. R., Chettri, M. K., & Thapa, L. B. (2025). Effects of shade and leachate from invasive Chromolaena odorata (Siam weed) on seedling growth and development of native tree species in Nepal. Tropical Life Sciences Research, 36(2), 297–316. doi:10.21315/tlsr2025.36.2.14
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