Quantifying the recarbonization of post-agricultural landscapes

Abstract

Despite worldwide prevalence, post-agricultural landscapes remain one of the least constrained human-induced land carbon sinks. To appraise their role in rebuilding the planet’s natural carbon stocks through ecosystem restoration, we need to better understand their spatial and temporal legacies.

Fig. 1. Typical post-agricultural landscape (PAL) trajectory involving land clearing from the primary forest (natural control) for agricultural use (agricultural control) and ecological succession following agricultural cessation (shown here as early-, middle-, and late-stage PALs).

The rebuilding of ecosystem carbon stocks in PALs is represented by the increasingly darkening top soils and growing plant biomass. However, the ecological and structural legacies of land clearing, tilling, and other destructive practices have lasting impacts on above- and below-ground properties, preventing a rapid return to pre-disturbance states. Instead of sampling the same PAL over time (i.e., repeated measurements), a quicker and less expensive alternative is to compare samples from an active agricultural plot and one (i.e., with the paired-plot method) or more (i.e., with the chronosequence method) PALs that share the same environmental and management characteristics except for the time since agricultural cessation. When sampled simultaneously and analyzed sequentially, these plots can reveal the temporal dynamics of ecosystem carbon. Active agricultural plots represent the expected baseline of all the plots before agricultural cessation, while natural control plots can be used to represent pre-disturbance states and, therefore, idealized PAL end-states. Not only are the logistical barriers to paired-plots and chronosequences much lower than repeated measurements, and so they should be established widely to fill data gaps, but existing published data using these approaches are also a largely untapped resource for benchmarking successional carbon modeling.

Fig. 2. The suitability of an agricultural site will determine if and how it should be managed as a recarbonizing post-agricultural landscape (PAL).

New and existing PALs can have a high or low potential for soil and ecosystem carbon (C) sequestration and high or low feasibility when considering various competing needs (e.g., food production), trade-offs (e.g., wildfire risk), and conflicts (e.g., local land rights). Depending on the carbon data available, the definitions used, and the land use factors considered, possible land management trajectories include (1) implementing or (2) preventing new PALs and (3) protecting or (4) restoring or converting existing PALs into more appropriate land uses. Increased temporal data and improved spatial estimates of PALs will support decision-makers in navigating scenarios like these. This graphic was created with BioRender.com.