We were surrounded by a wealth of highly prized medicinal plants and herbs as we walked through Jigme Dorji National Park
Grazing of plants by domesticated livestock is an important ecosystem service of either private or public grazing lands. However, not all plants growing in these areas are palatable or desirable. Several plant species can: be undesirable to livestock, be poisonous, outcompete desirable plants, or cause other issues such as blocking of livestock access to desirable plants. In this respect, it is important to understand the difference between native plants, invasive plants, and weeds.
Native or indigenous plants are those that have been growing in a particular habitat for thousands of years, oftentimes even before the arrival of humans to that area. These species co-evolve with their beneficial organisms and predators and are well adapted to the local environmental, climatic, and soil conditions.
Invasive or non-native plants or alien plants are those that are not native to the area. They are often introduced purposely or accidentally by humans or birds or grazing animals from another area. These plants usually proliferate and outcompete the native plants and cause environmental or economic harm. Often, these are not palatable or desirable to grazing animals and hence are detrimental to grazing lands. These plants usually disrupt ecosystem services of the grazing area and are, therefore, categorised as invasive weeds.
A weed is a plant that grows in a place where it is not wanted and competes with plants desired by humans, or in the case of pastures, grazing areas, and rangelands, by livestock. Thus, the term ‘weed’ is a plant that is perceived to be undesirable in the system of immediate interest to humans, e.g. agriculture farm, home gardens, grazing areas etc. Weeds can be plants of native or alien origin. Based on this definition, a native plant can also become a weed if it proliferates and competes with desirable plants of human interest. There have been cases where a native plant has aggressively taken over a landscape and outcompeted other desirable plant species. Such examples can be observed in grazing pastures and rangelands, and we present one such example from Bhutan.
Usually, it is preferred that pastures and grazing lands have a dominance of plant species palatable to the livestock and a balanced presence of some desirable plant species that may not be palatable but provide ecosystem services such as prevention of soil erosion, shade to the livestock, or other soil and environmental balances. In an ideal world, a perfect balance in these plant species is desired. However, oftentimes, undesired plants of native or alien origin can make incursions into the grazing areas, outcompete the desirable species, cause imbalances in the plant communities, and disrupt ecosystem services of the area. These problems often go unnoticed and within a short time it becomes ‘too late’ to implement economically viable management options.
Two problematic natives
In this section, we present an experience of how two native plants have caused imbalances in the plant communities in grazing lands (approximately 3300 m amsl) of Bhutan and caused disruptions in ecosystem services and the seasonal migration and use of these pastures by transhumant yak herders. The two native plants are Rumex nepalensis (Photo 1) and Anisodus luridus (Photo 2).
Although these are native plants, they have made incursions in the grazing areas, outcompeted the desirable and palatable native plants, almost become the sole dominant species (Photo 3, 4), and disrupted the ecosystem services of the grazing areas. Although most plant species have some desirable properties in them, unfortunately, until we find reliable information on such, they become weeds in these grazing areas. As a result, these grazing areas are losing their utility and becoming huge patches with limited ecosystem services to human interest and to the wild ungulates that also use these areas. The damages to the interests of yak herders were numerous, ranging from economic to social interests.
The case for management intervention
The economic and ecosystem costs of these imbalances in plant species seem to be huge and the task at hand of restoring these grazing lands seems to be overwhelming. However, a start must be made in tackling this problem as it has begun to affect the livelihood of the yak herders. Since these are grazing lands, a simple weed management system designed for agricultural weeds does not look to be a solution as we are dealing with natural areas that provide ecosystem services and thus the solution also must be a natural management intervention with least disturbance to the ecosystem.
In conclusion, there is a great need to study the problem in greater depth and develop solutions before more grazing areas face this situation and lead to losses in biodiversity and the pastoral cultures dependent on their seasonal use. Granted that these are native plants but when such plants cause imbalances in ecosystems, management intervention is warranted before the problem goes out of control. Such interventions could be reseeding of native species, prescribed burning etc., but studies are needed before such strategies can be implemented.