Lessons from patch dynamics for ecology and restoration: The succulent Karoo, Sandveld example

Abstract

A series of long-term field and glasshouse experiments were conducted in the semi-arid Sandveld Bioregion of southern Africa, across a wide range of post-mining site and soil conditions, on the two major plant groups, leaf-succulent shrubs (LSS, which establish in open micro-habitats) and non-succulent shrubs (NSS, which establish in sheltered micro-habitats). Seeding experiments applied a sequential ecological framework intended to reduce the impact of impeding natural ecological processes whilst incorporating processes that facilitate plant establishment. Experimental plots were scaled to naturally operating ecological dynamics at the patch scale, and various potentially facilitative types of shelter and soil amelioration, tested separately. Results are reported over three or six year periods and from four or seven field sites. Shelter generally had a greater effect on plant establishment than soil ameliorants, but this could be either positive or negative, and varied for the two plant groups: LSS establishment was inhibited or neutral under all forms of shelter, NSS were facilitated by types of artificial shelter that could be removed or biodegraded without impacting young plants. Both groups were strongly inhibited under transplanted nurse plants. Water absorbing gels improved LSS establishment but other soil ameliorants had no effect, while milled kelp or nutrients improved NSS establishment (measured as a biomass index or plant abundance, respectively). Finally, site had a greater effect than either shelter or soil ameliorants, and could not be related to any soil or other factors measured, supporting recent studies that explicitly quantify the substantial unknown effects of site and year. Specific recommendations are made for comprehensive, seed-based, nucleated restoration designs for the Sandveld and similar bioregions, while the over-arching results are of universal import to dryland restoration and ecology.