Spatial and temporal variation in the diversity, abundance, and energetic returns of underground storage organs on the coastal lowlands of the Cape Floristic Region, South Africa

Abstract

A rich, abundant, and nutritious flora with underground storage organs (USOs) is deemed an important energy source for Stone Age hunter-gatherers in the Cape Floristic Region (CFR) of South Africa. Research on USO richness, abundance, and energetic returns is largely confined to the south coast of the CFR. We extend this research to the west and southeast coasts by surveying 212 sites equally in the growing (spring) and dormant (autumn) seasons and across three biomes in all three regions. We quantify USO apparency (visibility above ground) to foragers based on phenological patterns of 131 edible USO species across CFR coastal lowlands. Apparency is seasonally constrained to cooler months in the strongly winter-rainfall west coast but less seasonal along the bimodal-rainfall south coast, and non-seasonal-rainfall east coast, providing longer periods for foraging. In all the surveyed regions, richness, abundance, and energetic returns of edible USOs peaked in winter/spring and were dominated by high-energy cormous species. On an annual basis, energetic returns were highest on the south coast, owing to USO apparency peaking in autumn, a feature absent at the other sites. In all regions, hotspots of USO energetic returns were rare, but most common on the south coast. Energetic returns were mostly higher in Strandveld than in Fynbos and Renosterveld. We discuss the implications of these findings for forager mobility in the three regions of the Cape coastal lowlands.