From smallholder to commercial farming: the impact of termite mound levelling and spatial heterogeneity in mound morphology on soil organic carbon in Miombo woodlands, Central Africa

Abstract Context The recent expansion of commercial agriculture in the Miombo woodlands of central Africa has led to widespread levelling of termite mounds. These mounds contain significantly lower soil organic carbon (SOC) than surrounding soils, and their levelling could largely reduce SOC content in the plough layer, which remains understudied. Objectives We aim to investigate the effects of mound levelling on SOC of the plough layer in a 1.5 km 2 plot used for commercial farming and quantify the contribution of pre-existing termite mounds to SOC variation in the levelled cropland. Methods Before and after levelling, we conducted unmanned aerial vehicle (UAV) surveys with structure-from-motion (SfM) technique, and paired soil sampling (0−25 cm) in between-mound areas. Results Termite mounds were regularly distributed but morphologically heterogeneous in the plot, with volumes ranging from 7.2 m 3 to 820.9 m 3 . Large termite mounds clustered in areas with higher topographic wetness index (TWI). Three years after levelling, SOC content in the plough layer of the plot overall reduced by 26% but variability increased by 29%. In the levelled plot, mound morphology, soil texture, and TWI explained over 40% of SOC variation, with mound morphology (characterized by hypsometrical integral, HI) being most influential. Older, larger mounds (with lower HI) were associated with lower SOC after levelling. Conclusions The immediate and significant reduction of SOC content in the plough layer due to termite mound levelling in commercial farming may affect productivity. Further research is needed to assess its long-term agricultural and ecological impacts at larger scales.