Environmental Engineering Reference
In-Depth Information
15
Effects of four indigenous trees
canopy covers on soil fertility
in a Ghanaian savanna
Charles Anane-Sakyi, Abubakari Sadik Abdulai, and Saa Dittoh
Introduction
The northern savanna zone covers approximately two-thirds of the total area of
Ghana (Map B). It is mostly affected by different seasons, especially the
harmattan
dry season. Its natural climax vegetation is characterized by a
ground flora of perennial grasses like
Panicum maximum
,
Pennisetum pur-
pureum
,
Andropogon gyanus
, and
P. pedicelatum
, with scattered, more or less
fire-resistant deciduous broad-leafed trees and shrubs of various sizes and den-
sities. In the extreme north-eastern area of the Sudan savanna, the common tree
species are
Vitellaria paradoxa
(sheanut tree),
Parkia biglobosa
(
dawadawa
tree),
Faidhebia albida
(
Acacia albida
),
Adansonia digitata
(baobab), and
Diospyrum mespiliformis
(ebony tree). They are grown in an orchard pattern
with food crops underneath even in densely cropped areas.
Owing to pressure on the land caused by high human population density, many
farmers remove the indigenous trees to increase cropping space without consider-
ing the effect of such a practice on the soil properties, especially soil fertility.
Moreover, various agroforestry systems are being promoted in the area with exotic
woody species without considering the effects on the indigenous trees. There
is abundant information on the influence of trees and shrubs on soil fertility in a
wide variety of ecosystems (Radwanski and Wicken, 1967; Gerakis and
Tsangarakis, 1970; Kellman, 1979; Hattan and Smart, 1984; Belsky et al., 1989;
Isichei and Muoihalu, 1992) which indicates that woody species increase the fertil-
ity of the soil under their canopies.
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