POTENTIALITE DE STOCKAGE DU CARBONE DANS LES ECOSYSTEMES HERBACES SOUMIS A DIFFERENTES FREQUENCES DES FEUX CAS D'IVOHIBORO (Commune Ivohibe)

In Madagascar, grassy ecosystems are recognized for their importance as grazing zones, for their floristic richness, and for being areas frequently affected by fire. The grassy ecosystems of Ivohiboro, which include the new protected area, are part of this context. However, their capacity for carbon storage remains insufficiently documented. This study evaluates the effect of fire frequency on carbon storage across different land use types within Ivohiboro. Five land use categories (forest, grassland, shrubland, Foxhole reforestation, and Eucalyptus reforestation) and five fire frequency levels (frequency 0: 0 fires in 7 years; frequency 1: 1–2 fires; frequency 2: 3–4 fires; frequency 3: 5–6 fires; frequency 4: 7 fires in 7 years) were considered. The analysis focused on total carbon stocks, taking into account the carbon stored in biomass (aboveground biomass, roots, deadwood, and litter) as well as in the soil. Floristic inventories from 89 plots were used to estimate biomass carbon stocks. For soil organic carbon, samples were taken at different depths and analyzed for bulk density, coarse fragment content, and organic carbon content. For total biomass carbon stock, compared to areas with fire frequency 0, significant reductions were observed under higher fire frequencies: 47.75% under frequency 2 in forests, 59.15% under frequency 3 in shrubland, and 89.92% under frequency 4 in grassland. Regarding soil carbon stock, fire frequency did not show significant reductions in either surface or deeper layers. However, organic carbon content showed significant decreases at frequencies 3 and 4 in the 0–10 cm to 20–30 cm soil layers. For total carbon stock, no significant effect of fire frequency was found across any landuse type. This study shows that high fire frequencies do not affect total carbon stock but reduce total biomass carbon and soil organic carbon content. If such burning rates persist, these reductions could significantly affect total carbon storage in the long term.