Agriculture Reference
In-Depth Information
Ecosystem functions
The most notable important feature of
U. kirkiana
is its association with
ectomycorrhizas, some of which have a significant impact on the livelihoods of
communities living near the forest where this species grows. Ectomychorrizas
are conspicuous on roots at 5-10 cm depth and associations of endo-
ectomychorriza have also been reported on the species (Hogberg, 1982; Thoen
and Ba, 1989).
Amanita
,
Cantharellus
,
Lactarius
and
Russula
constitute the
most common genera of fungi which typically form ectomycorrhizas, especially
in the
Uapaca-Brachystegia
miombo woodlands (Hogberg and Piearce, 1986;
Ngulube
et al
., 1995). Ramachela (2006) recently studied the ecological
interactions involved in the establishment and growth of natural woodland of
U. kirkiana
in Zimbabwe. The study showed that soil pH and potassium had
significant effects on mycorrhizal diversity.
Several insects, some of which are serious pests, feed on
U. kirkiana
(Sileshi
et al
., Chapter 20, this volume). In winter, the tree is host to the edible
stinkbug
Encosternum delegorguei
(Hemiptera), which in Malawi and
Zimbabwe is sold for cash in the market and is an important source of protein
and money. Ngulube
et al
. (1995) have noted associations with vertebrates
arising from their role as seed dispersers as they feed on the fruits. The
interaction with the natural vertebrate fauna is due to browsing animals such as
elephants and eland and the feeding on the fruits by monkeys and baboons,
which probably also play a major role in dispersal. As a dominant or
codominant tree of the miombo vegetation in hilly sites, it is useful in
watershed management and the control of erosion. The tree also improves the
microclimate within the canopy because of its dense rounded crown.
Biology
Uapaca kirkiana
is dioecious and the unisexual inflorescences originate from
axillary positions among the leaves or more often below them on the second or
third season's wood of the branchlets. The spatial distributions of male and
female trees in natural populations are largely unreported. In some Zambian
populations, male and female reproductive individuals are randomly
distributed with a male:female ratio of 1:1, and a mean distance of 11.1 m
between the male and female individuals was recorded (Hans and Mwamba,
1982; Hans
et al.
, 1982). Similarly, a sex ratio of 1:1 in mature
U. kirkiana
trees
has been reported in Malawi (Ngulube, 2000). Pollination is presumed to be by
insects. The most common and diverse groups of insects include bees (Apidae),
flies (Syrphidae), beetles (Lagriidae, Chrysomelidae and Melolonthidae), ants
and wasps. Butterflies are less common but moths are potential pollinators.
Flowering coincides with the onset of the rainy season (October/ November),
and the period extends over the entire 5-6 months of the rainy season. Flowering
intensity is variable throughout the period, the greatest proportion of trees
flowering between January and March (Ngulube, 1996). Male trees flower earlier
than female individuals. Bud development takes about 16 days for male flowers
and twice as long for female flowers. During anthesis, female flowers remain
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