Ecology and Biology of Uapaca kirkiana, Strychnos cocculoides and Sclerocarya birrea in Southern Africa - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 326

Because of its large size, it produces a large area of improved microenvironment
within the subcanopy, which has been said to be a key resource area, being
characterized by higher moisture and nutrient levels than open environments
(Belsky et al. , 1989; Shackleton et al. , 2002). These conditions are conducive to
the development of different subcanopy woody plants, grasses and other macro-
and microorganisms. Removal of a large dominant species may result in the loss
of these subcanopy species. The dominance and large size of S. birrea also
make the crown of the tree an important habitat for small vertebrates and
invertebrates, as well as parasitic plants (Shackleton et al. , 2002). Several
loranthaceous parasites have been recorded on S. birrea, the most favoured
being Erianthemum dregei , the haustorium of which is sold as a ornamental
curio, and the wood rose, which are important for the livelihoods of rural curio
traders (Dzerefos, 1996; Hall et al. , 2002; Shackleton et al. , 2002).
Several vertebrate and invertebrate species make use of the fruits, the most
notable of these being elephants in southern Africa. Other animals reported
include rhinoceroses, warthogs, kudu, baboons, velvet monkeys, zebras,
porcupines and millipedes (Shackleton et al ., 2002). There is no work on what
proportion of the diet or nutrient intake S. birrea contributes to these animal
species. Foliage is browsed by elephants, kudu, giraffes, nyala and domestic cattle
(Palmer and Pitman, 1972), as well as by the larvae of at least eight species of
butterfly and moth (Pooley, 1993; Kroon, 1999), including larvae of the emperor
moth Pavonia pavonia (Saturnidae) (Sileshi et al ., Chapter 20, this volume), a
popular food in southern Africa. The prevalence of malaria may be associated
with this species as there have been reports that the water-filled holes in the
trunks of S. birrea are important breeding grounds for mosquitoes - more so than
any other tree species in Kruger National Park (Palmer and Pitman, 1972).
Fire, livestock, tree removal and soil disturbance affect the regeneration
and/or population character of S. birrea . Fires remain the most regular and
often destructive annual event over the greater part of the area of distribution
(Lamprey et al ., 1967; Coetzee et al ., 1979). Earlier observations in Zambia
and Madagascar have shown that well-established subsp. caffra is fire-tolerant;
this has been attributed to woody constituents that are highly fire-resistant, the
thick bark, and a strong capacity to replace branches burnt during severe fires
(Fanshawe, 1969; White, 1983; Hall et al ., 2002).
Biology
With no available information on species germination in the wild, there have
been references to intervals of 6-10 months between seed dispersal and
germination in the field, which allows a period of dormancy (Teichman, 1982;
Lewis, 1987). The growth rates in the field are variable depending on the
environment. In Malawi, mean heights of 1.9 and 3.9 m have been reported
after 27 months and 48 months, respectively (Hall et al ., 2002). Earlier
estimates by Poynton (1984) gave height increments of 0.6 m per year while
Shone (1979) and Nerd et al . (1990) report increments of 1 and 2 m of height
growth over the same period in South Africa and Israel, respectively. No
estimates for the longevity of S. birrea have been established but observations