Hidden biodiversity: Dryland soil seed banks across ecological sites and states

Grassland degradation can hinder global dryland ecosystems with aboveground vegetation a key indicator of transitions from a healthy reference state to undesirable, or degraded states. The soil seed bank may either mirror, or diverge, from its associated aboveground vegetation. To better understand this relationship, we examined vegetation and seed banks across soil types (ecological sites) and vegetation/soil states (ecological states). To assess the soil seed bank, we sampled replicate soil seed bank collections across 67 individual ecological site and state combinations in the northern Chihuahuan Desert U.S.A. We found low species overlap between aboveground vegetation and the soil seed bank ranging from 0% to 30%. Sand dominated ecological sites contained the highest seed densities, yet densities and richness did not differ markedly across most vegetation states within an ecological site. The soil seed bank was dominated by perennial native grasses (>69%) with a low proportion (3%) of shrub seeds. Results indicate that irrespective of degradation levels, functional groups characteristic of historical native grasslands persist in the seed bank. Understanding soil seed bank biodiversity and how it relates to edaphic gradients and degrees of land degradation provides insight into the restoration potential of degraded arid ecosystems in a changing climate. • Seed banks should be included when assessing biodiversity in semi-arid systems. • Sand dominated soils had the highest seed bank densities across ecological sites. • Seed bank densities did not mimic ecological state degradation in ecological sites. • Native perennial grass seeds were dominant across ecological sites and states.