Mean annual ecosystem carbon fluxes in woody, grass and soil pools across intact tropical savannas and dry forests at 10 km resolution, 2000-2024

This dataset is a multi-band GeoTIFF providing mean annual area-density carbon fluxes (MgC ha-1 yr-1) across the intact tropical savanna and dry forest biome, mapped at 10 × 10 km resolution. It maps fluxes for the major ecosystem carbon pools: above-ground woody carbon (AWC), below-ground woody carbon (BWC), above- and below-ground grass carbon (AGC, BGC), and top soil organic carbon (SOC; 0-30 cm). For each pool, the raster includes a posterior mean and lower/upper 95% credible bounds (e.g., awc_flux_mean/lo/hi). A total woody carbon flux (TWC = AWC + BWC) mean is also provided (twc_flux_mean). Positive values indicate net carbon gain (sink) and negative values indicate net loss (source), expressed per hectare per year.

Fluxes are derived by upscaling plot-observed changes in AWC to the full area of intact tropical savannas and dry forests using a statistical model, then extending to other pools using pool-to-pool relationships. First, a generalised additive model (GAM) is developed between the relative rate of AWC change (lambda, % yr-1) from 424 permanent plots (2000-2024) spanning the dry tropics and a set of predictor variables. The predictors capture climate (mean annual precipitation and temperature and their recent trends), fire regime (burned years and its trend), soils (sand content and soil organic carbon density), and human pressure (travel time to nearest city). The lambda predictions are multiplied by a global above-ground woody carbon stock map (ESA CCI-Biomass) to predict mean annual AWC flux (MgC ha-1 yr-1). BWC flux is then estimated from below:above woody ratios or a published root:shoot function at each pixel. AGC and BGC fluxes were modeled using a relationship that links grass biomass to rainfall and woody stocks. SOC flux is inferred from a relationship between SOC spatial data (SoilGrids, 0-30 cm) and AWC (CCI-Biomass). Together these produce pool-specific flux means. Uncertainty is quantified by drawing from the posterior of the upscaling model and propagating the pool relationship methods. The lower (lo) and upper (hi) bands represent the 95% credible interval for each pool's flux.

The mapping domain is restricted to the intact tropical savannas and dry forests where environmental conditions are well represented by the field plot network (approximately 74% of the intact extent). Pixels outside this area, transformed land covers, non-woody vegetation, and evergreen closed-canopy rainforests are excluded. The fluxes represent mean annual changes over the study period since 2000. This work is part of the SECO project, resolving the current and future carbon dynamics of the dry tropics funded by NERC (NE/T01279X/1).