A Role for Drylands in a Carbon Neutral World?

Abstract

Drylands are a critical part of the earth system in terms of total area, socioeconomic and ecological importance. However, while drylands are known for their contribution to inter-annual atmospheric CO2 variability, they are sometimes overlooked in discussions of global carbon stocks. Here, in preparation for the November 2021 UN Climate Change Conference (COP26), we review dryland systems with emphasis on their role in current and future carbon storage, response to climate change and potential to contribute to a carbon neutral future. Current estimates of carbon in dryland soils and vegetation suggest they are significant at global scale, containing approximately 30% of global carbon in above and below-ground biomass, and surface-layer soil carbon (top 30 cm). As ecosystems that are limited by water, the drylands are vulnerable to climate change. Climate change impacts are, however, dependent on future trends in rainfall that include both drying and wetting trends at regional scales. Regional rainfall trends will initiate trends in dryland productivity, vegetation structure and soil carbon storage. However, while management of fire and herbivory can contribute to increased carbon sequestration, impacts are dependent on locally unique ecosystem responses and climate-soil-plant interactions. Similarly, while community based agroforestry initiatives have been successful in some areas, large-scale afforestation programs are logistically infeasible and sometimes ecologically inappropriate at larger scales. As climate changes, top-down prescriptive measures designed to increase carbon storage should be avoided in favour of locally-adapted approaches that balance carbon management priorities with local livelihoods, ecosystem function, biodiversity and cultural, social and economic priorities.

Primary production responses to extreme changes in North American Monsoon precipitation vary by elevation and plant functional composition through time

“…Changes in productivity across space and through time drive carbon storage, nutrient cycling and land–atmosphere interactions (IPCC, 2014). Shifts from carbon sinks to carbon sources in drylands are mainly driven by water availability (Scott et al, 2015), and because drylands cover nearly half of the global land area and store one‐third of the global carbon stock (Hanan et al, 2021), this variation can impact the global carbon cycle (Lal, 2004). Assessing differences in the sensitivity of production across highly responsive dryland ecosystems can inform their vulnerability to climate change and uncover the underlying mechanisms necessary to improve regional predictions of future ecosystem function.…”

Assessment of Land Degradation Factors

“…Drylands, home to 38% of the world's population (2.7 billion people), account for 44% of the world's cropland and 50% of its livestock [9], as well as about 30% of the global carbon [17]. Drylands are, therefore, central to sustaining the habitats, crops, and livestock that support most of the world's population [13].…”

Restoring Sahelian landscapes with people and plants: insights from large‐scale interventions

“…An estimated 29–45% of the world's cultivated plants and many livestock breeds originated in the drylands (Safriel et al 2005). Drylands are also thought to store between 30 and 45% of global terrestrial carbon in soils and vegetation (above‐ and belowground biomass, and surface‐layer soil carbon) (James et al 2013; Hanan et al 2021). Yet the transformation of land to intensive agricultural production, overgrazing, overharvesting of firewood, among other factors, has steadily contributed to a reduction of vegetation cover (FAO 2019).…”