Drivers, predictors, and probabilities of plant extinctions in South Africa

Abstract

Understanding how and why plants are driven to extinction is important if future extinctions are to be prevented. Here we examined reasons for extinctions of plants using data from the South African Red List, which includes 33 Extinct taxa from 15 families and 24 genera including seven infraspecific taxa. We also compared Extinct taxa with those that are threatened and not-threatened, exploring predictors of extinction based on traits, distribution, and anthropogenic threats. Finally, we applied two structured approaches to estimate the probability of extinction—the first uses argument-maps based on threat information and the second is based on survey-effort. We found that most extinctions were recorded in the Cape Floristic Region and were of perennial shrubs. Most taxa recorded as Extinct were only known from one site and are assumed to have been range restricted. Range size was, therefore, unsurprisingly the strongest predictor of extinction. The next strongest predictor was habitat loss. Based on the argument-map approach only 36% of Extinct taxa met an assigned extinction threshold, with most taxa categorised as Critically Endangered Possibly Extinct (50%). Only two taxa had sufficient data to evaluate the survey-effort approach. We support the use of both the argument-map and the survey-effort approaches to evaluate evidence for extinction but caution against strictly applying these methods as the only assessment tools. These approaches provide an evidence-based, quantitative, and well-documented process to support Red List assessments. Furthermore, they highlight knowledge gaps, the value of surveys and the need to improve threat documentation and monitoring. Use of these approaches can improve understanding of species ecology, thereby providing an essential foundation for conservation efforts to prevent extinctions.