Jj. Midgley et al., POPULATION ECOLOGY OF TREE SUCCULENTS (ALOE AND PACHYPODIUM) IN THE ARID WESTERN CAPE - DECLINE OF KEYSTONE SPECIES, Biodiversity and conservation, 6(6), 1997, pp. 869-876
Arborescent succulents are conspicuous elements of the arid flora of t
he far north-western Cape Province. In the Richtersveld and two adjace
nt more southerly areas (Springbok and Nieuwoudtville), we surveyed th
e population structure of the following three species, Pachypodium nam
aquanum (Apocynaceae), Aloe dichotoma and A. pillansii (a rare endemic
) (both Liliaceae). Only in the Richtersveld, did both Aloe species ha
ve a high proportion of dead individuals and all three species had few
seedlings there. Populations in adjacent areas had lower levels of mo
rtality and greater recruitment. Mortality appears to be due to damage
by baboons and porcupines. This apparent decline is potentially serio
us because all three species appear to be keystone species. They suppl
y perches to raptors, nesting sites for other birds, nectar for birds,
and food, habitat and moisture to other animals.