Regeneration dynamics of Portulacaria afra in restored succulent thicket of South Africa

Abstract

Introduction Over-grazing by livestock has resulted in the widespread degradation of South Africa’s succulent thicket ecosystems. This is characterised by a significant reduction in the cover of the dominant succulent shrub, Portulacaria afra. Because this species is unable to regenerate naturally in degraded habitat, active reintroduction is required to restore ecosystem function. However, reintroduction success is relatively low, and the recruitment barriers for this species are poorly understood. Methods By conducting pairwise plot surveys in actively restored and adjacent degraded succulent thicket habitats, the extent of P. afra seedling abundance in these contrasting ecosystem conditions is quantified. Results Seedling abundance was significantly greater in restored ecosystems (W = 23, p = 0.03225). Additionally, seedlings found in restored habitats were strongly associated with open habitat, whereas seedlings in degraded ecosystems were more restricted to nurse sites (X2 = 122.84, df = 2, p-value < 2.2e–16). A weak (R2 = 0,237), but significant (p = 0, 0295) correlation between P. afra cover and seedling abundance was recorded. Conclusion Active restoration of succulent thicket habitat through P. afra reintroduction appears to overcome recruitment barriers. This may suggest that, despite the poor survival of introduced individuals, natural recruitment could contribute to the regeneration of restored succulent thicket ecosystems.

Restoring South African subtropical succulent thicket using Portulacaria afra: root growth of cuttings differs depending on the harvest site during a drought

“…Due to the intrinsic drought-hardy nature of P. afra ( Guralnick & Ting, 1987 ) and its ability to readily grow vegetatively from cuttings, the restoration of succulent thicket has focused predominantly on the active planting of unrooted P. afra cuttings (with limited guidance on selecting source material to optimize root development and establishment). Where successful, this practice has regenerated soil organic carbon ( Mills & Cowling, 2006 ), promoted the return of microbial communities ( Schagen et al, 2021 ), and facilitated the return of natural recruitment dynamics ( Galuszynski, 2023 ; van der Vyver et al, 2013 ). However, this restoration has failed to produce consistent results, with large-scale planting initiatives in the Great Fish River Nature Reserve and Addo Elephant National Park (representing ∼21.3 million planted P. afra cuttings) reporting a mean survival of 28% with high variation across sites ( Mills & Robson, 2017 ).…”