The genetic legacy of fragmentation and overexploitation in the threatened medicinal African pepper-bark tree, Warburgia salutaris

Abstract

The pepper-bark tree (Warburgia salutaris) is one of the most highly valued medicinal plant species worldwide. Native to southern Africa, this species has been extensively harvested for the bark, which is widely used in traditional health practices. Illegal harvesting coupled with habitat degradation has contributed to fragmentation of populations and a severe decline in its distribution. Even though the species is included in the IUCN Red List as Endangered, genetic data that would help conservation efforts and future re-introductions are absent. We therefore developed new molecular markers to understand patterns of genetic diversity, structure, and gene flow of W. salutaris in one of its most important areas of occurrence (Mozambique). In this study, we have shown that, despite fragmentation and overexploitation, this species maintains a relatively high level of genetic diversity supporting the existence of random mating. Two genetic groups were found corresponding to the northern and southern locations. Our study suggests that, if local extinctions occurred in Mozambique, the pepper-bark tree persisted in sufficient numbers to retain a large proportion of genetic diversity. Management plans should concentrate on maintaining this high level of genetic variability through both in and ex-situ conservation actions.

The Utilization of Selected Threatened or Protected Plant Species; A Case of Limpopo Province, South Africa

“…For instance, its use in the treatment of constipation after attending funerals as reported by THPs in the Waterberg district was also documented by Phanuel et al [34] in Kenya. Furthermore, its use to treat stomach ache/disorders is consistent with the findings of Senkoro et al [32] in Mozambique.…”

“…Its use to treat high blood is a first record for South Africa. The above-mentioned uses are, however, also common in other African countries such as Kenya [31], Zimbabwe [23] and Mozambique [32].…”

“…The effectiveness of some of these species against coughs is supported by [24,38] for A. amatymbica and [23,30] for W. salutaris. Amongst the species used to treat sore throats, only W. salutaris was previously mentioned for South Africa [36] and Mozambique [32], thus the documentation of A. amatymbica to treat sore throats is a first. Furthermore, amongst species used for TB, only S. aethiopicus [36] and W. salutaris [30] were mentioned in the literature.…”

An updated checklist of Mozambique’s vascular plants

“…According to Darbyshire et al (2019) the main threat factors for vascular plants in the country are habitat loss and degradation, driven by the recent population growth and the consequent increased pressure on natural ecosystems. The growing commercialisation and the over-exploitation of medicinal plants are also becoming an increasing threat ( Bandeira et al 1996 ; Senkoro et al 2020 ). For example, Warburgia salutaris (G.…”

“…Bertol.) Chiov., one of the most widely used medicinal plants in southern Africa, as a consequence of the increasing commercial demand in the last few years has been subjected to uncontrolled harvesting, resulting in a widespread tree mortality and even in the extinction of local populations in many areas, changing its conservation status to globally Endangered ( Senkoro et al 2020 ). Moreover, about 75.1% of Mozambique’s threatened taxa (Vulnerable, Endangered and Critically Endangered) are endemic to Mozambique (111 strict-endemic; 115 near-endemic) (Fig.…”