Fire enhances forest degradation within forest edge zones in Africa

African forests suffer from severe fragmentation that further causes forest degradation near forest edges. The impact of fires used for slash-and-burn on forest edge effects remains unclear. Here, using high-resolution satellite-based forest-cover and biomass datasets, we find that edge effects extend a median distance and an interquartile range of $$0.11_{ - 0.04}^{ + 0.06}\,{\mathrm{km}}$$ and $$0.15_{ - 0.05}^{ + 0.09}\,{\mathrm{km}}$$ into moist and dry forests, and biomass within the forest edge zones has a carbon deficit of 4.1 PgC. Fires occurred in 52% of the forest edges and increased the carbon deficit by $$5.5_{ - 2.9}^{ + 4.3}\,{\mathrm{MgC}}\,{\mathrm{ha}^{{-1}}}$$ , compared with non-fire edges, through both the direct impact of fires intruding into forests and the indirect impact of changes in the local atmospheric circulations increasing canopy dryness. If small-scale slash-and-burn practices continue, increased fragmentation during 2010–2100 will result in a carbon loss from edge effects of 0.54–4.6 PgC. Fragmentation-caused forest degradation could be avoided by implementing dedicated forest protection policies supported by satellite monitoring of forest edges. Fire exacerbates forest degradation in the forest edge zones in Africa, increasing the carbon deficit caused by forest fragmentation, according to analyses of high-resolution satellite data on forest cover and biomass.