Conservation biology of the succulent shrub, Euphorbia barnardii, a serpentine endemic of the Northern Province, South Africa

Euphorbia barnardii, Dyer & Sloane is a relatively small, succulent shrub f ound in the Northern Province of South Africa. In 1994 it was listed as end angered by the Transvaal Threatened Plants Programme, because only three po pulations, totalling 1150 plants, were found. However, our study found five populations totalling 10 783 plants (9503 were reproductive). One populati on, found 50 km from the others, in the Bewaarkloof district, differs in te rms of habitat type and morphology and may therefore be a different taxon. The other populations occur in Sekhukhuneland, Soil analyses showed that E. barnardii is restricted to ultramafic (serpentine) substrates. A sample of 2015 plants was examined in 1995 for size, stage, new growth, dead branche s, reproduction (indices of vigour), damage and disease. Analysis of the re sults of 10 years' demographic monitoring (1985-1995) on two of the Sekhukh uneland populations showed that one population, which was vigorous in 1995, showed little change in population size and structure, while the other, wh ich had low vigour in 1995, showed a precipitous decline to local extinctio n in the monitoring plot. Aerial photographs taken in 1957 (1963 for Bewaar kloof) and 1986 showed large increases in human population density within 1 .5 km of the E. barnardii populations except at Bewaarkloof, where it decre ased. An increase in human habitation is associated with an increase in liv estock (mostly cattle and goats) which trample plants. Trampling damages th e terminal segments, which may lead to lowered reproductive output and incr ease susceptibility to opportunistic bacterial wilt pathogens. Bacterial wi lts were prevalent oil all populations but were particularly high at Bewaar kloof and on the population that showed a steep decline in numbers. Disease incidence was associated with the level of plant damage. The impact on pla nts further up the slopes and on the cost of hills (quite far from human se ttlements) was to a far lesser degree but further increases in human popula tion density could change this situation. While this study has shown that t he population size of E. barnardii is much greater than previously thought, the species is still threatened by several different processes and should be listed as 'Vulnerable (Ala + c, B1, B2b + e, C1, D2)' according to World Conservation Union categories.