The effect of fire regimes on above-ground biomass change in Baikiaea-dominated woodlands of the Chobe region, northern Botswana, 1991 – 2023

Abstract

Accurate assessment of fire-vegetation dynamics is crucial for accounting for changes in carbon fluxes. We use a fire frequency index (FFI) against data collected from Permanent Sample Plots (PSPs) in two Forest Reserves, in 1991 and 2023, to assess the effects of the recent fire history (1991-2023) on tree basal area (BA—as a reliable proxy for biomass) changes at PSPs in Chobe Botswana. We explore the efficacy of applying remotely sensed Vegetation Indices (VIs) to map predicted BA on the basis of 1991 assessment data. Our results show a significant increase in plot BA between 1991 (Mean = 3.73 m²/ha) and 2023 (Mean = 5.63 m²/ha) between 1991 and 2023. Fire frequency alone (dominated by severe fires), explained 27% of variation in ΔBA (p < 0.001); infrequently burnt plots accrued BA, frequently burnt plots lost BA. For mapping predicted BA at landscape scale, we found that 2023 plot BA was most strongly correlated with NDVI from a March 2023 image and plot Canopy Cover; no significant relationships were observed between assessed 1991 VIs and 1991 plot BA, probably as a result of the quality of the available Landsat archive imagery. Our results suggest management of fire alone is key to maintaining and enhancing woody biomass and achieving woodland degradation mitigation and climate initiatives in regional Baikiaea miombo woodlands. The influence of fire on change in woodland structure supports the development of incentivised savanna burning approaches, including carbon sequestration methodologies, for sustainable management of woodland savannas under semi-arid rainfall conditions (ca. 600 mm MAR) in northern Botswana and regionally.