Ecology, population biology and conservation status of Euphorbia schoenlandii Pax, an endemic to the Succulent Karoo, South Africa

• Published in: South African journal of botany Vol. 170; pp. 48 - 60
• Main Authors: Jabar, L., Siebert, S.J., Pfab, M.F., Cilliers, D.P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2024
• Subjects: CITES; Euphorbiaceae; Nephopteryx divisella; Non-detriment findings; Species distribution modelling; Succulent Karoo; Threatened species; Succulent Karoo; Species distribution modelling; Threatened species; Nephopteryx divisella; Euphorbiaceae; CITES; Non-detriment findings
• ISSN: 0254-6299
• DOI: 10.1016/j.sajb.2024.05.013

•Euphorbia schoenlandii has been heavily impacted by habitat loss and degradation.•There is a high degree of isolation between the three remaining populations.•Plants are negatively affected by the stem-boring larvae of nephopteryx divisella.•Extant populations are stable and recruiting overall, especially at coastal sites. Many threatened plant species in South Africa occur outside of protected areas and these include numerous succulent species that are traded internationally. Despite the potential impact that this may have on rare and endemic succulent species, limited population data exist to inform the non-detriment findings required by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) to ensure that international trade is sustainable. A concerted effort is being made in South Africa to gather such data for threatened succulents in the Euphorbiaceae. As part of this effort, the study set out to locate the extant populations of Euphorbia schoenlandii, an endemic of the Succulent Karoo, and acquire a better understanding of the population biology and ecology of the species. We applied the point-centred quarter method to estimate population size and density at each locality. This first-ever comprehensive field survey allowed for the determination of the geographic distribution of the species, as well as the sizes and number of populations. Biotic and abiotic environmental variables were employed to generate a habitat profile and a species distribution model for conservation purposes. Population structure, regeneration potential, and stability of the three known populations were also assessed. According to this study, approximately 29 152 individuals remain in the wild. It was shown that the species is often associated with nurse plants. Various potential pollinators were identified, but of concern was the considerable infestation by an alien snout moth (Nephopteryx divisella), a known pest of euphorbias. The first adult size class contained the highest proportion of individuals, which is indicative of pulse recruitment. Seedling numbers were low, most likely because the surveys were conducted during a drought period. Overall, this study provides the first data on various aspects of the population structure and ecology of E. schoenlandii. It provides valuable information regarding current threats, and also highlights the vulnerability of the species to further habitat loss and degradation or future illegal or unregulated harvesting.