Conservation ecology of Frithia humilis, an endangered succulent of sandstone outcrops in Mpumalanga, South Africa

MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Translocation involves the movement of organisms, by human intervention, from one area to other suitable (receptor) habitats. In a conservation context, translocation can be employed to support species preservation, population restoration and/or for ecological research. Despite decades of internationally published research, translocation remains a controversial endeavour. However, due to continual degradation and fragmentation of natural habitats in the face of human development, translocation is becoming a vital component of conservation efforts. Prior to the development of an Exxaro coal mine in Mpumalanga, a population of an endangered Highveld succulent species, Frithia humilis Burgoyne (Aizoaceae/Mesembryanthemaceae), was saved from extirpation by means of translocation. Three receptor habitats were identified within the distribution range of the species. The largest part of the donor population was transplanted to sandstone outcrops of the Ecca Group (Karoo Supergroup), resulting in four subpopulations residing on geological substrates typical of the species’ habitat. The remaining portion of the donor population was experimentally translocated to two habitats containing non-native geologies, namely sedimentary outcrops of the Wilge River Formation (Waterberg Group) and (igneous) felsite oucrops of the Rooiberg Group (Transvaal Supergroup). A control population was identified, occupying Ecca and Dwyka Group (Karoo Supergroup) sediments, as a measure to compare the response of translocated populations. A monitoring programme, utilising a plant age classification system, was initiated in February of 2010 to elucidate demographic trends and to gauge the response of translocated populations to novel environments. Plant survival, plant growth, flowering, fruiting (representing reproductive response) and seedling emergence were chosen as indicators to measure translocation success over the short term. Furthermore, quantitative and qualitative entomological investigations into the identity of possible F. humilis pollinators, as well as the presence of pollinator species at receptor habitats, were made. A repeatable methodology for post-translocation monitoring and scientifically sound baseline data for future comparative purposes were successfully established. Initial results showed that F. humilis subpopulations replanted on Ecca standstones had positive responses to translocation: Subpopulations survived and all but one increased in size. Individual plant growth increased, higher reproductive output was evident and seedling emergence was pervasive. Positive responses indicated that F. humilis populations translocated onto typical geologies had the potential to establish and persist over three years. Knowledge of this early success is of immense value to the conservation of the species, as a limited number of known natural populations remain. Coal mining, targeting coal seams underlying typical F. humilis habitats, is also likely to remain a threat. The viability of translocating F. humilis populations to non-typical geological substrates has shown limited efficacy. Poor survival along with inferior reproductive response confirmed Wilge River Formation outcrops as poor receptor sites for translocated F. humilis populations. Rooiberg felsite outcrops also proved to be dubious receptor sites, primarily since there was a downward trend in seedling emergence over time, suggesting inferior germination conditions. Nevertheless, translocation to non-native geological substrates did not have disastrous short-term consequences for these populations, since flowering, fruit production and seedling emergence continued, albeit at reduced (or continually declining) rates. Potential pollinator species of F. humilis were not revealed through quantitative surveys of insect diversity. Qualitative surveys proved more efficient and accurate at pinpointing insect pollinator species. This study provided the first evidence of Apidae, Megachilidae (Hymenoptera) and Bombyliidae (Diptera) insect species pollinating F. humilis. The generalist nature of the plant-pollinator relationship, as well as the presence of generalist pollinator species at some receptor habitats, probably contributed to the initial positive response of F. humilis flowering and fruiting after translocation. Results from this study, however promising, should be viewed as initial indications of translocation success. The literature review revealed a plethora of literature recommending post-translocation monitoring programmes for five years to several decades. This study confirmed that successful establishment of F. humilis can be determined after three years, but that long-term monitoring is required to evaluate persistence.

Masters