Soil seed banks of remnant and degraded Swartland Shale Renosterveld

Abstract

Questions: What are the characteristics of soil seed banks in highly endangered renosterveld vegetation and adjacent degraded sites? What is the contribution of the soil seed bank to restoring renosterveld vegetation after degradation through agriculture or afforestation? Location: Tygerberg Nature Reserve – one of the largest remaining fragments of Swartland Shale Renosterveld, Cape Floristic Region, South Africa. Methods: Assessment of vegetation, soil parameters and soil seed banks in three renosterveld sites, two adjacent abandoned fields, one pine plantation and one pine plantation clear-cut site. Smoke primer (i.e. fire surrogate) was applied to soil seed bank samples to evaluate fire as a possible management and restoration tool. Results: Abandoned agricultural fields adjacent to renosterveld remnants are characterized by alien grass cover, nutrient enrichment of the soil and depletion of the indigenous soil seed bank. In contrast, pine plantations show less alien species infestation, soil nutrient alteration and have a viable soil seed bank as well as re-development of indigenous renosterveld vegetation after clearance. Seedling recruitment was not significantly influenced by application of a smoke primer compared to the magnitude of fire response in fynbos. Conclusion: Abandoned agricultural fields (previously renosterveld) at Tygerberg have a very low restoration potential. In contrast, pine plantation sites should be given priority in restoration, because soil chemistry is less significantly altered and a viable indigenous soil seed bank is still present, which can be successfully activated through clearance management