Integrated LiDAR-supported valuation of biomass and litter in forest ecosystems. A showcase in Spain.

Belowground components (biomass and soils) can stock as much carbon as the aboveground component of forest ecosystems. In this study, we present a fully-integrated assessment of the biomass budget and the three pools evaluated: aboveground (AGBD) and belowground biomass in root systems (BGBD) and litter (LD). We turned National Forest Inventory data, airborne Light Detection and Ranging (LiDAR) data actionable to map three biomass compartments at 25-m resolution over more than 2.7 million ha of Mediterranean forests in the South-West of Spain. We assessed distributions and balanced among the three modelled components for the entire region of Extremadura and specifically for five representative forest types. Our results showed belowground biomass and litter represent an important 61 % of the AGBD stock. Among forest types, AGBD stocks were the dominant pool in pine-dominated areas while its lowers contribution was found over sparse oak forests. The three biomass pools estimated at the same resolution were used to produce ratio-based indicators to highlight areas where the contribution of belowground biomass and litter can exceed AGBD and where carbon-sequestration and conservation practices should acknowledge belowground-oriented carbon management. The recognition and valuation of biomass and carbon stocks beyond the AGBD is a must step forward that the scientific community must support in order to properly assess living components of the ecosystem such as root systems sustaining AGBD stocks and to value carbon-oriented ecosystem services related to soil-water dynamics and soil biodiversity. This study aims at enforcing a change of paradigm in forest carbon accounting, advocating for a better recognition and broader integration of living biomass in land carbon mapping.