Controlling Invasive Alien Plants

Nepal is rich in biodiversity. Many species of animals and plants are found in the country. This is because of a variety of bio-climatic conditions the country boasts. However, as in other countries, Nepal is facing the problem of invasive alien plants. Since the beginning of the 20th century, invasive plants have posed a threat to native plants. Such plants have become a serious threat to economic, social and ecological sectors on a global scale. Human activities are largely to blame for this. Factors like international travel and trade have made humans dispersal agents. 

Invasive plants outcompete native plants and suppress them. Animals dependent on vegetation may face difficulty finding fodder because as compared to native plants such as grass, invasive plants are unpalatable. When native plants are supplanted by invasive plants, the food cycle of herbivorous animas such as deer gets affected. Herbivorous animals need enough grassland and bushes. And carnivorous animals such as lions, tigers and leopards find their food web disturbed. All this leads to the degradation of ecosystems. In the process, even native plants may be driven to extinction.

Loss of biodiversity

Invasive plants grow densely and spread quickly. They are counted among the top five contributors to the loss of biodiversity. Biodiversity loss has been observed from highlands to wetlands and oceans. Invasive plants have adverse effects on agriculture. On the one hand, they degrade the fertility of soils, while on the other they affect the growth of crops. The effects may last longer. Invasive plants weaken the buffering capacity of protected areas. Protected areas are required for the sustainablility of biodiversity. Invasive plants also lead to the loss of habitats of wild animals. This may have an adverse impact on the ecotourism business, drastically reducing the number of wildlife-loving tourists. 

Invasive plants may produce human health issues. Their pollens may cause allergy and other health conditions among the people and animals living in the vicinity. Invasive plants degrade forests and affect ecosystem services. The livelihoods of those living in the vicinity of forests may be affected as the forest resources they are dependent on may decrease. At least 183 vascular non-native species, including four pteridophytes and 179 flowering plants, are naturalised in Nepal. Out of these, there are 26 invasive angiosperms, including four among the world’s hundred worst invasive species. The invasive species have affected agricultural systems and natural environments, including protected areas and Ramsar sites. The impacts have been felt from temperate mountain zones to lowlands. 

In Nepal, invasive plants are found from mountains to the Terai. However, the effects of the plants are more acutely felt in the Terai than in the mountains. Studies show that vegetation is gradually shifting upwards owing to climate change. One of the prominent invasive plants is the banmara (Ageratina adenophora). Native to Mexico, the plant grows wildly in many parts of the world, including in Nepal. It spreads quickly, smothering native plants. During the count of one-horned rhinoceroses in Chitwan National Park in 2021, 35 per cent of the rhinoceroses’ habitat was found to be invaded by Mikania micrantha, sometimes called a mile-a-minute owing to its quick-spreading nature. The vine suppresses native plants that provide fodder for the rhinoceroses, forcing them to venture out of the national park, which may result in human-animal conflict.  

Community forests in Nepal are also in the grip of invasive plants such as Mikania macrantha, Lantana camara and Chromolaena odorata. These plants are counted among the world’s hundred worst invasive species. Community forestry is a success story in Nepal. The country has maintained a good image in community forestry practices. Invasive plants may play havoc with the community forests. So the government should take concrete measures to control invasive plants infesting the community forests before it is too late.   

The government has adopted programmes for controlling invasive plants. Cultural and physical control methods are common. In addition, a few biological control agents have also been adopted. The government has initiated programmes dedicated to controlling invasive plants, focusing on Chitwan and Shuklaphant national parks. The programmes are run with the help of the National Trust for Nature Conservation. The activities under the programmes include, inter alia, cutting Mikania macrantha plants manually and releasing beetles to destroy Parthenium hysterophorus. The programmes are concentrated in the Terai. Such programmes also need to be initiated in mountainous areas before the problem worsens. 

Impact assessment

At the policy level, the National Biodiversity Strategy and Action Plan, 2014 is in place. The policy prioritises inventory, impact assessment, identification of dispersal agents, public education and participation and biological control methods. Developing countries like Nepal lack adequate scientific knowledge for use in policy formulation and management decisions. This leads to weak policy and management responses, which makes it difficult to cope with increasing threats posed by invasive plants. In fact, coping with invasive plants is a challenge worldwide. Failure of global efforts in the past to slow down the rate of invasion is witness to this. 

However, studies of the impacts of a few invasions have been conducted in Nepal. The impacts range from habitat destruction to species displacement to adverse effects on agriculture. Although studies are being conducted on the distribution of invasive plants in the country, more studies need to be carried out in affected areas. Further, research on high-altitude protected lands needs to be accelerated. Such studies should encompass gaining comprehensive knowledge of invasive plants, their distribution, dispersal patterns and ecological impacts such plants produce and the like. Regular monitoring and surveys of invasive plants are imperative to generate data and knowledge. On the basis of such data and knowledge, management decisions can be properly made so that programmes can be launched throughout the country to control invasive plants from mountains to lowlands. 

(Maharjan has been regularly writing on contemporary issues for this daily since 2000.)