Dioscorea sylvatica Eckl.
|Forest Elephant's Foot (e)|
Status and Criteria
|V.L. Williams, D. Raimondo, N.R. Crouch, A.B. Cunningham, C.R. Scott-Shaw, M. Lötter & A.M. Ngwenya|
|There was a large population decline from 1955-1960 as a result of indiscriminate commercial harvesting for diosgenin, a substance that was used to manufacture cortisone and other steroid hormones. Exploitation of tubers for the local medicinal plant trade is ongoing, and is preventing recovery. The overall decline is estimated to be >30% over the past 90 years (generation length estimated to be 30 years).|
|Not endemic to South Africa|
|Eastern Cape, Free State, KwaZulu-Natal, Limpopo, Mpumalanga|
|Western Cape, Eastern Cape, KwaZulu-Natal, Free State, Gauteng, Mpumalanga, Limpopo Province, Swaziland, Zimbabwe and Zambia.|
Habitat and Ecology
|Malelane Mountain Bushveld, Soutpansberg Mountain Bushveld, Wakkerstroom Montane Grassland, Northern Drakensberg Highland Grassland, Northern Zululand Mistbelt Grassland, Lydenburg Montane Grassland, Ithala Quartzite Sourveld, Pretoriuskop Sour Bushveld, Northern Zululand Sourveld, Granite Lowveld, Northern Coastal Forest, Makhado Sweet Bushveld, Pondoland-Ugu Sandstone Coastal Sourveld, KwaZulu-Natal Coastal Belt Grassland, Maputaland Coastal Belt, Albany Dune Strandveld, Northern Escarpment Dolomite Grassland, Eastern Free State Sandy Grassland, Sundays Thicket, Humansdorp Shale Renosterveld, East Griqualand Grassland, Great Fish Thicket, Springbokvlakte Thornveld, Eastern Valley Bushveld, Mamabolo Mountain Bushveld, Ohrigstad Mountain Bushveld, Sekhukhune Plains Bushveld, Sekhukhune Mountain Bushveld, Southern Lebombo Bushveld, Western Maputaland Sandy Bushveld, Legogote Sour Bushveld, Thukela Thornveld, Ngongoni Veld, KwaZulu-Natal Sandstone Sourveld, Northern KwaZulu-Natal Moist Grassland|
|Wooded and relatively mesic places, such as the moister bushveld areas, coastal bush and wooded mountain kloofs.|
|During the first half of the 20th century, the commercial production of synthesized active ingredients of pharmaceutical products were not yet far advanced. It was often more economical to derive the necessary chemical constituents from natural products, including wild-harvested plants. It was discovered that Dioscorea sylvatica, and specifically D. sylvatica var. rehmannii, contains high concentrations of diosgenin, a substance that was used to manufacture cortisone and other steroid hormones. Between 1955 and 1959, 3466 tonnes of Dioscorea sylvatica was wild harvested from the former Transvaal province for the commercial production of cortisone. This translates into between 116 000 and 380 000 mature individuals, as whole plants are removed to process the fleshy tuber for diosgenin (Codd 1960). During 1958 alone, 1151 tonnes was harvested. However, during 1959, the amount of plants harvested fell drastically to only 465 tonnes. This was because D. sylvatica wild populations in areas designated for harvesting had become completely depleted, to such an extent that after 1959 wild harvesting were no longer commercially viable (Codd 1960). Attempts were made to grow D. sylvatica in large scale cultivation, however, it proved to be too slow growing, and the use of D. sylvatica in cortisone production was subsequently abandoned (Codd 1960, Rowley 1987). Codd estimated that an area that had been "worked-over" would take at least five years to recover, but the yield would be lower.
During the harvesting period (1955-1959), restrictions were in place to try and maintain the sustainability of the harvesting. Harvesting was only allowed on private land by means of a permitting system, and tubers had to be at least 30 cm in diameter. No harvesting was allowed on state-owned or conservation land (Codd 1960). However, how seriously these restrictions were observed, especially the minimum tuber size, is not certain.
The total long term effect of this rapid depletion of subpopulations in some areas, as well as what proportion of the total population was removed, is not known. At present, the species is wild harvested for the muthi trade at far lower levels - about 16.3 tonnes per year (approximately 326 50kg-size bags, equivalent to 500-2000 mature individuals) was estimated to be traded in KwaZulu-Natal (Cunningham 1988). Cunningham (1988) also classified the species as 'vulnerable and declining', i.e. a species that is vulnerable to over-exploitation, and the wild populations are subject to localised over-exploitation and appear to be declining outside conserved areas but are represented by populations in strict nature conservation areas. Williams et al. (2007) records D. sylvatica occurring in 60% of muthi shops in 1994 and estimated that 249 bags were sold annually. Additionally, the species was sold by 28% of the Faraday Street market traders in 2001 and the annual quantity purchased by the traders was estimated to be 514 bags. Dold and Cocks (2002) estimated the annual trade in D. sylvatica in the Eastern Cape to be >3 tonnes, and indicated that it was heavily traded, vulnerable and becoming scarce in South Africa. Scott-Shaw (1999) said that it was rare in KwaZulu-Natal and becoming very rare where exploitation was heaviest.
It has not been nominated through market surveys as among the species that are 'very popular' or 'becoming scarce' (Mander 1998), and observations in the field indicate that it is not extremely scarce, and in contrast to some of the other heavily exploited medicinal species, can still be found in areas relatively close to the markets (D. Styles, pers. comm., 2007). This possibly indicates that the population have made a good recovery since the 1955-1959 commercial harvesting period, and that the harvesting restrictions were effective in preventing the population from declining to such levels that recovery was impossible. However, the field observations of D. Styles were made in KwaZulu-Natal, while the commercial harvesting was mainly concentrated in Mpumalanga and Limpopo (Codd 1960). A comparative survey of subpopulations on privately owned vs. state owned land in these provinces could be useful in attempting to quantify what the long term effect of the harvesting on the population is.
During the Medicinal Plant Red List Workshop (14-15/01/2008, SANBI, Durban) (V.L. Williams, D. Raimondo, N.R. Crouch, A.B. Cunningham, R. Scott-Shaw, M. Lötter and M. Ngwenya), the following points were made: a) D. sylvatica is most commonly encountered in protected areas, especially well protected areas (N.R. Crouch); b) it must have been very common in the woodland and savanna of the Tugela River basin, but extreme pressure from pastoral grazing is changing the micro-habitat of the bush (C.R. Scott-Shaw); c) It is always present in the Eastern Cape markets and is very slow growing and rare in the wild. The subpopulations are also small and only seen now and then (A.P. Dold); d) Subpopulations tend to be smaller than in the past (except in the Drakensberg); in thornveld they are sparse and never abundant e.g. 2-3 plants together and then none after that; e) Ongoing pressure from the medicinal plant trade is keeping the population numbers at lower levels.|
Cunningham (1993) classified D. sylvatica as "vulnerable and declining" in a preliminary assessment of the threat status of a number of heavily exploited medicinal plants. According to Scott-Shaw (1999) D. sylvatica is becoming very rare in areas where it is heavily exploited. However, according to David Styles (pers. comm. 2007) although whole tubers of this species are frequently seen in the Durban muthi markets, it can still be found with relative ease in the wild, even in places relatively close to Durban such as the KwaZulu-Natal Midlands around Nottingham Road. Cunningham (1993) estimated that about 16.3 tons of D. sylvatica is traded in the Durban markets annually. This translates to between 500 and 2 000 plants per year, based on Codd's estimate that the average tuber weighs between 9 and 30 kg (Codd 1960). Although this species is highly sought after (Scott-Shaw 1999), Mander (1998), in a detailed study of the KwaZulu-Natal medicinal plant trade, do not include D. sylvatica among the most popular species or species nominated by traders as being in short supply. D. sylvatica has also not been reported to be heavily traded in the Witwatersrand area (Williams et al. 2000).
|There are taxonomic problems with the different varieties of D. sylvatica, and Wilkin (2001) even goes as far as to suggest that D. sylvatica and D. elephantipes may be the same species. D. sylvatica var. rehmannii was heavily exploited in the 1960s for the commercial production of cortisone (Codd 1960). However, the current threat to this species is mainly harvesting for the muthi trade, and muthi harvesters are not likely to distinguish between variants. Therefore all the variants were assessed together as a single taxon, as the current poor delimitations of even such basic information as the distribution ranges of the different variants are making separate assessments extremely difficult.|
|Williams, V.L., Raimondo, D., Crouch, N.R., Cunningham, A.B., Scott-Shaw, C.R., Lötter, M. & Ngwenya, A.M. 2008. Dioscorea sylvatica Eckl. National Assessment: Red List of South African Plants version 2017.1. Accessed on 2020/04/06|
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