Carbon dioxide (CO2) is one of many greenhouse gases that keep the atmosphere warm by trapping heat radiating from earth. At present, human activity adds about seven billion tonnes of carbon dioxide into the air every year. Through the process of photosynthesis, plants capture atmospheric carbon dioxide and store the carbon in their living tissues. Forests, as integral components of this process, have played a pivotal role as carbon sinks for an extended period. On a global scale, they absorb nearly one-fourth of the carbon dioxide emissions generated by human activities.
Carbon sequestration is the process of removing (or capturing) carbon dioxide (CO2) from the atmosphere and storing it in plant material or soil. While trees sequester most of the carbon in their woody biomass and leaves, grasslands store it underground in roots and soil, making them more adaptive to climate change. As the world is witnessing more and more calamities due to climate change, the potential of grassland in soil carbon sequestration is also gaining attention. It is interesting to note that grasslands can store approximately one third of the global terrestrial carbon stocks acting as an important carbon sink.
Grassland ecosystems occupy nearly 52.5 million km2 and account for 40.5% of the earth's land surface (excluding Greenland and Antarctica). They provide habitats for biodiversity and many cultural services. They are managed worldwide to support livestock production. Grasslands reportedly hold approximately 34% of the Earth's terrestrial carbon reserve, with roughly 90% of this carbon concealed beneath the ground as root biomass and soil organic carbon (SOC). This makes them indispensable in the context of carbon sequestration within soil. Estimates suggest that on a global scale, we could potentially sequester between 0.2 to 0.8 gigatons of CO2 annually in grassland soils by the year 2030. Additionally, grasslands possess a unique advantage over forests in that they exhibit greater resilience against threats such as fire, drought, and disease. Even in cases of grassland fires, the SOC remains well safeguarded as it is deeply buried within the soil.
Vulnerability to Human Disturbances
Grasslands are known for their high vulnerability to anthropogenic pressures like overgrazing and land-use conversion to agriculture. All over the world, grasslands have undergone severe decreases in biodiversity and ecosystem functions, leading to reductions in SOC storage. Climate change affects grassland SOC storage by modifying the processes of plant carbon inputs and microbial catabolism and anabolism. Human intervention appears to have driven grasslands to transition from carbon sinks to carbon emitters within the greenhouse gas equation. This shift can be attributed to the rising numbers of livestock and the rapid transformation of natural landscapes into pasturelands. The process of overgrazing typically results in diminished contributions of both above- and below-ground organic matter, ultimately leading to a decline in soil carbon reserves. This, in turn, exerts an impact on various soil properties, encompassing physical, chemical, and biological aspects.
Grasslands and Mountains
Mountain grasslands are globally important ecosystems. They are considered as heritage sites with “outstanding values” to ecological communities by adding a further “layer and support to the existing protection measures.” The mark grasslands of Kashmir, Bugyal of Uttarakhand, Khajjar of Himachal Pradesh, Dzukou Valley of Uttarakhand, Ukhrul of Manipur, Saramati of Nagaland, etc. are some examples of montane grasslands in India. They provide many of the important goods and services for human beings including food, timber, fresh water, protection from natural hazards, carbon storage, and many other functions including recreation and tourism. They also provide forage for grazing animals and habitat for varieties of wild animals. Furthermore, mountain grasslands are regions of high diversity and species-rich ecosystems that co-evolved with centuries of livestock grazing. Human societies since ancient times have depended on grasslands for ecosystem provisioning, regulating, cultural, and supportive services for their own security. However, mountain grasslands are increasingly under threat from human activities and impacts of climate change. Socio-economic changes of the past decades have caused a progressive abandonment of the traditional use for grazing of some areas, while grazing pressure at easily accessible grasslands have increased.
Enhancing carbon sequestration in grasslands can be achieved through a combination of practices, including strategic grazing management, the cultivation of beneficial forage species, judicious fertilizer application, and irrigation, as well as the restoration of degraded grasslands. Effective grazing management and the restoration of biodiversity offer cost-effective and high-yield pathways for implementing natural climate solutions in grasslands worldwide, leading to increased carbon capture and storage. Controlled grazing practices have the potential to boost carbon retention in grasslands, particularly when employing rotational grazing methods that stimulate the expansion of root systems.
The efficacy of this approach in bolstering soil carbon reserves is most pronounced when grazing management measures are in place to prevent both overgrazing and excessive soil compaction. These negative factors can otherwise undo the progress made in sequestering carbon in grassland soils by depleting vegetation and impeding robust vegetative growth. Infact, with good grazing management, perennial plants can live and reproduce for many years with an ongoing cycle of pruning, root-sloughing, and regeneration, contributing more and more carbon to the soil indefinitely. Also, by reducing the area of grasslands converted into cropland each year, the emissions associated with clearing and tilling the land can be reduced. Additionally, the implementation of agro forestry systems such as silvipasture can bolster carbon absorption by extending the growing season, broadening the range from which water and soil nutrients are sourced, and, in the case of nitrogen-fixing species, boosting soil fertility.
(Author is a PhD, Forestry from Forest Research Institute, Dehradun. Email: email@example.com)