The encroachment of woody plants in grassland ecosystems is emerging as a major issue across multiple biomes around the world. This is also true for the open ecosystems of Bhutan where in addition to harbouring rich biodiversity and supporting various ecosystem functioning, they serve as a critical lifeline for the many transhumant pastoralist communities who rely on them for food and livelihoods. One such community affected by woody encroachment are found in Dagala, a high-elevational mountain range in western Bhutan occurring at about 4000 meters above sea level.

Figure 1. A typical house (left) in Dagala where the herders stay in the summer months before migrating with their yaks (right) to lower elevations.


In 2022, a study was carried out to gain a deeper understanding of the ecology of the rangeland and quantify the ecological impacts of woody encroachment in Dagala. This was conducted under the aegis of a Darwin Initiative project1, led by the Royal Botanic Garden Edinburgh, in collaboration with relevant stakeholders in Bhutan (Department of Forests and Park Services and the National Biodiversity Center) as well as the local community members of Jom Daga NWFP Group2. The goal of the project was to enhance Bhutan’s in-country capacity and community resilience for grassland conservation.

Figure 2. Working closely with the local communities relying extensively on their local knowledge, which culminated in a capacity-building workshop and mutual sharing of expertise on rangeland ecology and management.


Over the summers of 2022 and 2023, a total of 42 sites were sampled across a gradient of woody encroachment in Dagala. The Global Grassy Group’s (GGG) sampling protocol was used to quantify taxonomic and functional composition. Samples of soils and aboveground biomass were collected from each site for analysis. The participation of local communities in this study was critical and provided valuable expertise on the management histories of each site and the palatability of different plant species.

Figure 3. Sampling across different encroachment gradients using the GGG sampling protocol.


The study found that encroachment in the area was mainly driven by different species of Rhododendrons including other woody species of Berberis and Juniper. Highly encroached sites showed significantly lower species richness across various functional groups of grasses, sedges, rushes and non-graminoid herbs both at the plot and site levels. Assessment of species composition patterns showed a complex relationship to woody encroachment with a general transition from a grazing-tolerant community in open areas to a more homogenised shade-tolerant and less diverse community in highly encroached sites.

Figure 4. Woody encroachment in subalpine pasture showing the spread of Rhododendron and Berberis.


As one of the first studies examining the impact of woody encroachment in Bhutan, this research brings to light the profound negative effects on plant diversity, highlighting the need for critical intervention, particularly in the wake of many rangelands reporting lower productivity in the country. With such phenomenon linked to changes in climatic patterns, policies and management practices, it can have a significant multifaceted impact on conservation, economic livelihoods, and traditional land use patterns. It reinforces the need for more such studies from various ecological contexts to develop a holistic and socio-ecologically appropriate evidence-based to help restore ecosystems and maintain sustainable livelihoods through multiple stakeholder engagement3.


Notes

  1. The two-year project (2022-2024) was implemented through the Capacity and Capability funding offered by the Darwin Initiative supported by UK DEFRA. The study on the woody encroachment would form the basis of Tshering’s MSc research at the University of Edinburgh which has now expanded into a PhD project supported by the E4 DTP studentship.
  2. Jom Daga Ngomen Tshogpa is a community-based natural resource management group formed in 2014 for the sustainable management and utilization of natural resources. With about 80 households in the group including both pastoralists and non-pastoralists, the group collects several medicinal and aromatic plants from Dagala providing them an alternate source of income while empowering them to participate in biodiversity conservation and decision-making.
  3. Stakeholder engagement was key to the success of this project. We remain completely indebted to all partners in Bhutan and the UK, with particular mention to the Darwin Initiative and the people of Dagala.