Distribution and conservation status of the Endangered pepperbark tree Warburgia salutaris (Canellaceae) in Swaziland

Abstract

The Endangered Warburgia salutaris (Bertol. f.) Chiov. (Canellaceae), a sought-after medicinal plant in southern Africa, is on the verge of extinction as a result of overexploitation for illegal trade. As part of formulating a conservation strategy for the species in Swaziland we sought to determine its distribution and population status and to revise its national conservation status. Field surveys were conducted in all physiographic regions of Swaziland. Eighteen locations of species presence were found, of which 14 were new records. Three were within protected areas, and seven were in areas worthy of protection. The largest subpopulations occurred in two of the latter areas, Ngudzeni and Sitsatsaweni (351 and 230 individuals, respectively), and one unprotected area, Bulunga (250 individuals). Warburgia salutaris has a severely fragmented distribution and an area of occupancy of 192 km2. Of 700 mature individuals 38% were ring-barked and 7% felled, and some subpopulations had ring-barked juveniles. This indicates a plausible decline in number of mature individuals. Most localities in unprotected areas are eroded and invaded by alien plants, indicating a decline in habitat quality. Our findings indicate that W. salutaris should be categorized as Endangered nationally based on criteria B2ab (iii,v). Although this status implies a lower level of threat than the previous national categorization as Critically Endangered, it does not imply an improved conservation effort in the country, but rather a more accurate assessment based on more data. We have clarified the conservation status of W. salutaris in Swaziland, discovered some previously undocumented subpopulations and identified potential conservation interventions. We recommend that this information be used in setting priorities to ensure conservation of the species.

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

“…However, subsequent studies confined the distribution of W. salutaris to only a sub-region of southern Africa, i.e. South Africa 21,49 , Eswatini (previously known as Swaziland) 24,50 , Zimbabwe 29,[51][52][53] , Malawi 54 and Mozambique 55 . This species is commonly used to treat several ailments such as common colds, throat and mouth sores, or coughs 47,48 .…”

“…However, with commercial demand increasing, W. salutaris groves were repeatedly raided by harvesters that often debarked the whole tree, especially mature plants 56 . Severe harvesting resulted in high tree mortality in many areas and in the extinction of many local populations 21,24,57 and consequently, W. salutaris is considered threatened throughout its range 50,58,59 , and listed as an Endangered Species in the IUCN Red List 57 . The most extreme case is that of Zimbabwe, where the species is listed as extinct in the wild 29,60 .…”

“…According to the Red List classification for Mozambique, this species is considered Vulnerable VU A2 cd 58 . Despite this critical situation, only a few studies on the populations dynamics of W. salutaris are available; of the 60 research and review papers available in the Web of Science on W. salutaris on 05 February 2020, only seven addressed this topic 21,24,48,[61][62][63] while the vast majority are focused on the medicinal applications of this species. Nevertheless, amplified fragment length polymorphisms (AFLPs) have been used to solve genetic relationships between W. ugandensis, W. salutaris and W. stuhlmanni showing a high degree of genetic variation among individuals within populations as well as between populations 62 .…”

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“…Chiov.) is more dramatic, as this medicinal plant has not only been classified as Endangered in Swaziland (Dludlu et al, 2017), but its population is steadily shrinking due to illegal trading and uncontrollable harvesting. Its increasing popularity as a traditional medicine contributed to its overexploitation, resulting in its classification as Extinct in the Wild in Zimbabwe (Botha et al, 2004; Dludlu et al, 2017).…”

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“…Its growth habitat is forests and kloofs. Dludlu et al (2017) reported eighteen localities where Warburgia salutaris is found in Eswatini, across a wide range of habitats, physiographic zones, geology, and vegetation type. The Warburgia salutaris plant (Figure 1) is listed as endangered in the International Union of Conservation of Nature (IUCN) red data list and as critically endangered in the Swaziland National Trust Commission (SNTC) (2016) list.…”