Franschhoek Silkypuff

Taxonomy
Scientific Name
Diastella buekii (Gand.) Rourke
Higher Classification
Dicotyledons
Family
PROTEACEAE
Common Names
Franschhoek Silkypuff (e)
National Status
Status and Criteria
Critically Endangered A4a; B1ab(i,ii,iii,iv,v)
Assessment Date
2019/08/06
Assessor(s)
A.G. Rebelo, D. Raimondo, H. Mtshali & L. von Staden
Justification
Monitoring of the population of Diastella buekii recorded a population reduction of 65-86% in the past 39 years due to ongoing habitat loss and degradation. As threats to the last three to four severely fragmented remaining subpopulations are severe and ongoing, it is expected to continue to decline at a similar rate, leading to a population reduction exceeding 80% within three generations. The remaining population is small, and occurs within a small extent of occurrence (EOO) of 34 km².
Distribution
Endemism
South African endemic
Provincial distribution
Western Cape
Range
This species is endemic to the Berg River Valley between Franschhoek and Paarl in the Western Cape.
Habitat and Ecology
Major system
Terrestrial
Major habitats
Swartland Alluvium Fynbos
Description
It prefers moist places on alluvial sandy flats, 200-300m. This species forms low, mat-like shrubs in suitable habitat. Mature individuals are killed by fires, and only seeds survive. Seeds are released after ripening, and dispersed by ants to their underground nests, where they are protected from predation and fire. It is pollinated by insects.
Threats
This species has declined almost to extinction due to extensive historical habitat loss and fragmentation, mainly due to agricultural expansion - its habitat is well-suited to vineyard and fruit cultivation. It has also lost habitat to commercial timber plantations. This species is able to survive plantation forestry through persistence in soil-stored seed banks, from where it is able to regenerate once plantations are felled. However, if sites are repeatedly planted in short succession, the seed bank is depleted and subpopulations decline rapidly. Remaining habitat fragments where the last few populations persist are all in poor condition due to the impacts of inappropriate fire management, overgrazing, spreading of alien invasive plants, infrastructure development, sand and gravel mining, disruption of wetland water flows and water tables due to the effects of surrounding timber plantations, which are known to deplete underground water sources more rapidly than natural vegetation, as well as water abstraction through boreholes. One subpopulation was lost to the development of a housing estate and golf course, and two other subpopulations are under pressure to be developed for low cost housing and vineyards. During a severe drought in the Western Cape between 2017 and 2019, new boreholes were established in Wemmershoek Vlei, the habitat of one of the two largest remaining subpopulations. A State of Emergency was used to circumvent environmental impact assessment regulations, and an extremely fragile site that is home to numerous Critically Endangered plant species was further disturbed and degraded. There is ongoing pressure to extract groundwater from Wemmershoek Vlei as well as at La Motte, with potential severe consequences for this seep-dependent species.
Population

Historical records suggest that this species was once common between Paarl and Franschhoek. After extensive habitat loss and fragmentation, it was thought to be extinct in 1976 (Rourke 1976), as the last known record dated from 1934. It was subsequently rediscovered growing among pine plantations at La Motte near Franschhoek in September 1976, and further field surveys confirmed that five isolated subpopulations remained in 1980. These subpopulations were monitored by the Protea Atlas Project between 1993 and 2001, with some follow-up monitoring by volunteers of the Custodians of Rare and Endangered Wildflowers (CREW) Programme between 2010 and 2017. At the Wemmershoek Vlei National Heritage Site, the subpopulation has remained relatively stable. In 1991 there were 20 mature individuals and several juveniles. There was a fire in 1996, but it did not impact any of the mature individuals, nor did it stimulate any germination from soil-stored seeds. Monitoring observed no fire-related population fluctuations, even though it is expected from this species' ecology. Currently, there are about five small stands of 10 to 50 plants each, with the subpopulation therefore estimated to contain about 50-250 mature individuals. The La Motte subpopulation, which was found in 1976, consisted of 2000 plants in 1980. The site, which is utilized for growing pine trees, was planted in 1971-1972, and as the pines matured and the canopy closed, the subpopulation declined to about 250 plants by 1989 (Manders 1989). A five hectare patch has been set aside for the preservation of this subpopulation, but regeneration from soil-stored seed banks were poor, and by 2001 there were still only about 200 plants surviving. This subpopulation was last monitored in 2006, when 50 plants were recorded, but the site was not thoroughly surveyed, and it is possible that up to 200 plants are still persisting at this site. At Meerlust forest station, there were initially only about 50 plants recorded, but the subpopulation increased to 100 plants when pine plantations were cleared. The site has been poorly managed and has become increasingly degraded over the years due to alien plant invasions, overgrazing and too frequent fires, and in 2001 only two plants survived when the seep they were growing in dried up. In 2005, a pipeline installed through the site eliminated the remaining plants, and since then there has been almost no regeneration from the seed bank. This subpopulation was last recorded in 2011, when there were about five plants remaining. This subpopulation is likely to be entirely lost to a low cost housing development in the near future. The largest remaining subpopulation occurs at Kleinberg south of Victor Verster prison. The site has also been under plantations, and plants occur scattered in road verges and small open patches among the pine trees. The subpopulation has been relatively stable since monitoring began in the 1990s. Currently plantation forestry is being phased out, with the site earmarked for transfer to CapeNature to be managed as a nature reserve, and the subpopulation appears to be increasing, with most recent estimates (2015) indicating that there are between 250 and 500 plants. There has however also been proposals to put the site under vineyards, based on the argument that it is too degraded for conservation as a result of historical pine plantations. However, since this is the largest remaining subpopulation, every effort should be made to restore the natural vegetation at this site. Protea Atlas Project monitoring recorded ongoing decline in the subpopulation at Kliprug, due to alien plant invasion, gravel mining and bulldozing of fire breaks. There were 200 plants in 1994, but by 1998 there were only 20-40 plants. An Environmental Impact Assessment for a golf course development failed to mention the presence of this Critically Endangered species at the site, and subsequently, the entire subpopulation was lost to development. When monitoring began in the 1980s and 1990s the remaining population of this species consisted of an estimated 2500-2700 mature individuals. Currently, there are only about 350-950 plants remaining, indicating an observed population reduction of 65-86% within 39 years, which is less than two generations for this species. If the observed rate of population decline is to continue, which is likely due to severe, ongoing threats to this species, it is likely to decline by 75-100% within three generations (45-60 years). The population is considered severely fragmented, as all remaining subpopulations are small, and occur on isolated habitat remnants. Ant dispersers are unlikely to move seeds beyond individual habitat fragments.


Population trend
Decreasing
Assessment History
Taxon assessed
Status and Criteria
Citation/Red List version
Diastella buekii (Gand.) RourkeCR A2a; B1b(i,ii,iii,iv,v)c(iv)Raimondo et al. (2009)
Diastella buekii (Gand.) RourkeEndangered Hilton-Taylor (1996)
Diastella buekii (Gand.) RourkeEndangered Hall et al. (1980)
Bibliography

Goldblatt, P. and Manning, J.C. 2000. Cape Plants: A conspectus of the Cape Flora of South Africa. Strelitzia 9. National Botanical Institute, Cape Town.


Hall, A.V., De Winter, M., De Winter, B. and Van Oosterhout, S.A.M. 1980. Threatened plants of southern Africa. South African National Scienctific Programmes Report 45. CSIR, Pretoria.


Hilton-Taylor, C. 1996. Red data list of southern African plants. Strelitzia 4. South African National Botanical Institute, Pretoria.


Manders, P.T. 1989. Experimental management of a Pinus pinaster plantation for the conservation of Diastella buekii. South African Journal of Botany 55:314-320.


Raimondo, D., von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. and Manyama, P.A. 2009. Red List of South African Plants. Strelitzia 25. South African National Biodiversity Institute, Pretoria.


Rebelo, T. 2001. Sasol Proteas: A field guide to the proteas of southern Africa. (2nd ed.). Fernwood Press, Vlaeberg, Cape Town.


Rourke, J.P. 1976. A revision of Diastella (Proteaceae). Journal of South African Botany 42:185-210.


Citation
Rebelo, A.G., Raimondo, D., Mtshali, H. & von Staden, L. 2019. Diastella buekii (Gand.) Rourke. National Assessment: Red List of South African Plants version 2020.1. Accessed on 2021/12/02

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Distribution map

© C. Paterson-Jones


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