Grasslands are pivotal to soil carbon sequestration and combating climate change

Global extant and status of grasslands

Grasslands including savannas comprise a large expanse, ca. 41% of the world’s land surface. Large areas of grasslands and savannas that are used as rangelands and support many livelihoods, are under mounting threat of conversion to agricultural lands. More recently, grasslands are also under threat of conversion by forest restoration C offset projects that misconstrued grasslands and savannas as degraded landscapes. Research has shown that grasslands and savannas have evolved with fire and herbivores and the relative ‘openness’ of these ecosystems is not at all a sign of ecosystem degradation.  A meta-analysis supported the maintenance of grassy biomes, where it was found that globally, land-use conversions reduced soil C stocks especially from native grassland to either farmland (by 59%) or plantation (by 10 %). Although grasslands and savannas sequester less C per unit area than forests, their wide coverage of the earth’s land surface make them equally important sinks of C. As such maintaining the ‘grassy’ state of these important ecosystems may better safeguard their biodiversity, C sequestration potential and ecosystem service provision.  

Grassland soil C sequestration

Grasslands sequester carbon mainly through the soil. They facilitate this by supporting dense plant root networks that can go into deeper soil depths and produce compounds that aid in binding C to soil. Soil C sequestration, therefore, plays a pivotal role in the C cycle, acting as a major sink for atmospheric CO₂, and thereby helping to mitigate the impacts of global warming. Through emerging technologies such as satellite-driven high-resolution mapping, more detailed and concise monitoring of soil C sequestration dynamics over time is now possible and available for global use. Such technologies help elucidate the nature and importance of grasslands and savannas to climate change mitigation through enabling the study of historical ecological trends.  

Ecosystem variation within tropical rangelands has distinctive impacts on soil C sequestration. Grassland and savanna ecosystems, with their amalgamation of trees and grasses, present both aboveground and belowground C sinks, offering vast potential for long-term C storage. Furthermore, the interplay between wildlife and these ecosystems adds another of layer complexity, for instance, herbivores' grazing patterns, such as those of mesoherbivores  and megaherbivores, influence plant growth and decomposition rates, subsequently affecting C sequestration in the soil.  

Landuse change as a major driver of soil C sequestration.

Soil C sequestration is affected by many drivers, chief among them being landuse change. A global meta-analysis study further emphasized the need to promote informed land management that seeks to effectively restore soil C. For example, changing landuse from farmland to other ecosystem types always led to soil C increase while the reverse always led to soil c decrease. The environmental benefits of soil C sequestration are thus multi-faceted. Beyond the reduction of atmospheric CO₂, soils rich in organic C manifest resilience against climatic extremities like droughts and excessive rainfall. Such resilience underscores the value of conserving C sequestered in soils in withstanding the unpredictable weather patterns engendered by climate change. Other concomitant benefits of soil C sequestration include improvement of biodiversity especially soil biodiversity that has strong knock-on effects on aboveground processes. With the current  global focus on developing a biodiversity metric and monitoring mechanism, enhancing soil C sequestration through informed landuse management can aid in meeting both local and global biodiversity conservation targets.

Conclusion

In summary, grasslands and savannas offer a pivotal case study for understanding soil C sequestration's nuances. It is evident from extant literature that a synergistic relationship exists between ecosystems, regional wildlife, and soil C dynamics. Moreover, there's a need for further research to fully understand these nuances in different types of grasslands and savannas and under various landuse management systems. As the world grapples with the multifaceted challenges of climate change, exploring and understanding these relationships is of paramount importance for informed land management and conservation strategies.

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