Soil seed bank dynamics under Leucosidea sericea encroachment in high-altitude grasslands: Implications for restoration at Vuvu in the Eastern Cape Province, South Africa

Abstract

Woody plant encroachment is widely associated with declines in grassland biodiversity and ecosystem functioning, yet its effects on below-ground regeneration processes remain poorly understood, particularly for native resprouting species. In South Africa’s montane grasslands, the native shrub Leucosidea sericea forms dense thickets that transform vegetation structure, but its influence on soil seed bank dynamics is unclear. Here, we assessed how encroachment and slope aspect (north- vs south-facing) influence seed bank density, species diversity, composition, and functional structure using a seedling emergence approach under controlled conditions. Soil samples were collected from 60 5 m × 5 m plots using three 0.25 m × 0.25 m quadrats per plot taken from two corners and the centre. Samples were collected from 0–5 cm depth from encroached and non-encroached sites of north- and south-facing slopes. A total of 4535 seedlings representing 83 species emerged from the soil seed bank. Contrary to expectations, L. sericea encroachment did not reduce seedling density, species richness, or Shannon diversity across sites. Instead, encroachment drove significant shifts in species composition and functional structure, with seed banks dominated by annual forbs and showing reduced representation of grasses. Notably, L. sericea was absent from the seed bank, indicating that its persistence is driven primarily by vegetative resprouting rather than seed-based recruitment. Slope aspect further modulated these patterns, with greater compositional turnover observed between encroached and non-encroached north-facing slopes. These findings demonstrate that woody encroachment by a native resprouting species can decouple seed bank size from functional composition, maintaining diversity while altering regeneration trajectories. This functional reorganisation has important implications for restoration, as intact seed banks may not translate into recovery of grass-dominated systems. Effective management should therefore prioritise restoring functional groups, particularly perennial grasses, rather than relying solely on passive regeneration.