Divergent patterns of richness and density in the global soil seed bank

Soil seed banks are an important component of plant population and community dynamics, buffering temporal heterogeneity and allowing populations to recover following disturbance. At the same time, patterns in soil seed banks are likely to reflect scale-dependent patterns in above-ground vegetation, patterns that differ strongly across world regions. Here, we investigate components of diversity in the soil seed bank across global biomes and ecosystems. We find that patterns of species richness in the soil seed bank diverge from patterns of seed density, although our results indicate high levels of uncertainty, especially at smaller spatial scales. Importantly, we show that habitat degradation is consistently associated with lower richness, potentially limiting future ecosystem recovery. Among ecosystems, Mediterranean and tropical regions exhibit high species richness, but seed density m^-2 in the soil is highest in wetlands and arable systems. We identify lower seed densities in both high-diversity tropical biomes that are characterised by short-lived seeds, and low-diversity boreal and tundra biomes with more stable established vegetation. Our findings of divergences between species richness and seed density across global biomes, and how they are impacted by habitat degradation, give valuable insights to the understanding of plant biodiversity worldwide.