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Rangelands, which are found in diverse ecosystems, support both livelihoods and rich biodiversity, and are principally used for grazing by domestic or wild animals. In Bhutan, these include both forest and open ecosystems, from the subtropical grasslands in the southern foothills to temperate rangelands at middle elevations and high-elevation alpine meadows (Wangda, 2011), where they are grazed mostly by yak and cattle. However, they are coming under increasing threat due to the rapid spread of weeds and invasive species, which is also a pervasive issue globally.
The proliferation of weeds and invasive species is recognised as one of the main drivers of rangeland degradation in Bhutan, which is further exacerbated by climate change, and changes in management practices and government policies (Millar & Tenzing, 2021). These bring about huge changes in structure and ecological functioning that have far-reaching consequences, including displacement of native species, changes in cultural practices, and socio-economic losses. Changes include an increase in aboveground net primary productivity, which promotes competition for light and changes in the dynamics of interactions with grazers and pastoralists. Furthermore, it impacts the water and nutrient cycles within an ecosystem, as well as infiltration capacities and fire dynamics. Fire is particularly important to rangelands, where it is a fundamental ecological process of many ecosystems.
Given the ecological diversity within Bhutan, there are varying drivers that affect changes in these systems. For example, the alpine and temperate rangelands across Bhutan are undergoing serious changes brought about by the encroachment of shrubs such as Rhododendron and Juniper. Among the few studies carried out in Bhutan, Dorji et al (2024) showed that an increase in the species and dominance of shrub species in the summer rangelands of Dagala in western Bhutan reduced plant species richness by 50–90%. Overgrazing in Bhutanese rangelands is an ongoing issue (Chophyel, 2009) that causes the proliferation of weeds and other unpalatable species such as Potentilla peduncularis Rumex, Senecio spp.
In subtropical to temperate regions, the spread of invasive alien species is a major threat to biodiversity (NBSAP, 2014). Globally, invasive alien species are considered among the two greatest threats to biodiversity (Dueñas et al., 2018), and their impacts are likely to be even higher in developing countries like Bhutan. Some of the most problematic species there include Lantana camara, Chromolaena odorata, Ageratina adenophora, and Mikania micrantha. These species are believed to have been introduced to Bhutan accidentally as seed contaminants, or deliberately as fodder or ornamental plants, and their movement has been facilitated by trade across Bhutan’s porous border with India (Yangzom et al 2020). Some of these species display aggressive growth and allelopathic effects – whereby a plant releases toxins to suppress the growth of other plants – enabling them to out-compete native species and form dominant stands.
The relationship between the drivers and impacts of encroachment is complex and depends on context (Maestre et al., 2020). For example, the effects will depend on the species and their functional traits, management history, and ecological conditions. This complexity and the importance of rangelands underscores the urgent need for further studies from Bhutan to aid our understanding of their impacts on biodiversity and ecosystem services in the otherwise understudied Himalayan rangeland system and is crucial for the development of appropriate management strategies.
Author affiliations
Mr. Tshering Dorji, PhD Student
University of Edinburgh (School of GeoSciences) & Royal Botanic Garden Edinburgh
Tshering.Dorji@ed.ac.uk or tdorji@rbge.org.uk
Dr. Colin Pendry
Editor (Flora of Nepal), Royal Botanic Garden Edinburgh
cpendry@rbge.org.uk
References
Chophyel, P. (2009). Rangeland management in Bhutan: A consultancy report. Thimphu, Bhutan: Royal Government of Bhutan, Ministry of Agriculture.
Dorji, T. (2023). Graminoid richness and composition patterns along a shrub cover gradient in Dagala, Bhutan. MSc. Thesis, University of Edinburgh, United Kingdom.
Dueñas, M. A., Ruffhead, H. J., Wakefield, N. H., Roberts, P. D., Hemming, D. J., & Diaz-Soltero, H. (2018). The role played by invasive species in interactions with endangered and threatened species in the United States: a systematic review. Biodiversity and Conservation, 27, 3171-3183.
Maestre, F. T., Eldridge, D. J., & Soliveres, S. (2016). A multifaceted view on the impacts of shrub encroachment. Applied Vegetation Science, 19(3), 369-370.
Millar, J., & Tenzing, K. (2021). Transforming degraded rangelands and pastoralists' livelihoods in Eastern Bhutan. Mountain Research and Development, 41(4), D1-D7.
National Biodiversity Strategy Action Plan. (2014). National Biodiversity Strategy Action Plan. Thimphu, Bhutan. National Biodiversity Center, Ministry of Agriculture and Forests.
Wangda, P. (2017). Rangeland Areas of Bhutan. National Research Centre for Animal Nutrition Bumthang
Yangzom, R. et al. (2018). A Pictorial Guide to Major Invasive Plant Species of Bhutan. Thimphu, Bhutan.