Effect of charcoal production and woodland type on soil organic carbon and total nitrogen in drylands of southern Mozambique

Abstract

African woodland ecosystems function as important reservoirs for soil organic carbon (SOC) and total nitrogen (TN). However, these ecosystem functions are particularly sensitive to social-ecological factors, the impacts of which remain understudied. Here, we examine how SOC and TN and other soil properties vary across woodland types and how charcoal production, the main source of woodland disturbance in the study area, changes these factors in dry woodlands of southern Africa, focusing on three woodland ecosystems that represent the main types in southern Mozambique: Androstachys forest, Combretum woodland and Mopane woodlands. Drawing on data from soil surveys at 0–5 cm and 0–30 cm depth in different vegetation types as well as both distant from and proximate to sites of active charcoal production, we estimate that these woodlands in Mabalane District store on average 19 ± 10 (±SE) Mg ha⁻¹ of SOC, and 2.2 ± 0.9 Mg ha⁻¹ of TN at 0–30 cm, significantly lower than values reported for other woodlands in the region such as Miombo. Our analysis shows that the woodland types do not differ in terms of the amount of SOC and TN stored in soil, and that soil in the charcoal kilns had twice the amount of SOC (30.0 ± 1.8 Mg ha⁻¹) and TN (4.5 ± 0.5 Mg ha⁻¹) compared with non-charcoal soils. This study adds to our understanding of the impact of charcoal production on soil SOC and TN in dry woodlands of southern Africa, and demonstrates some localised impacts of charcoal production. We discuss the implications of our findings in the light of emerging carbon-based payments for ecosystem services programmes in the region.