Shifting soils: The characteristics and dynamics of termite soil sheeting in a savanna

Termites build two kinds of above-ground biogenic structures: mounds and sheeting. Sheeting is constructed to protect foraging termites against desiccation and predation while they consume the organic material that the sheeting covers. The movement of soils by termites profoundly affects soil turnover rates and modifies the patterns of water and chemical movement in soils. Despite this, the characteristics and dynamics of soil sheeting are not yet well understood. Within a broadleaf mesic (650 mm p.a.) South African savanna, we found that the fungus-growing genus Odontotermes dominated both horizontal and vertical sheeting production. In terms of quantity, there were approximately two tonnes of soil sheeting per hectare present across both the soil surface and the trees of the mesic savanna at each survey time. We found that horizontal sheeting is produced year-round while vertical sheeting is more frequent in dry seasons and in dry years. Termites are selective builders: the physical and chemical composition of horizontal and vertical sheeting differed from each other and from the matrix soils. Termites select medium-sized sand particles, silt and clay particles for the construction of horizontal sheeting and small sand particles for the construction of vertical sheeting. Horizontal sheetings was significantly enriched in nitrogen, sodium and phosphorus, while vertical sheetings was enriched in nitrogen. In savannas, primary production is strongly limited by nitrogen. These nutrient differences likely give rise to the creation of nutrient rich patches, on a finer scale than those created by termite mounds, with potentially important consequences for savanna spatial dynamics.