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The village of Kambi ya Simba is located in Karatu
District, Arusha Region, sandwiched between the Northern Highlands
Forest Reserve (to the north) and the Rift Valley escarpment (to the
south). The village occupies an area of approximately 40 sq-km
and a north-south distance of approximately 11 km. Along this
north-south axis, there is a 500 m change in elevation, which has a
strong effect on climate. The village
is divided into three geographically distinct regions - Northern,
Central and Southern - as shown below.
Kambi ya Simba is inhabited by the Cushitic-speaking
Iraqw. The Iraqw are the largest ethnic group in Karatu district and
their language is related to the Afro-Asiatic languages spoken in
northeast Africa (e.g., in Somalia and Ethiopia) rather than the Bantu
languages spoken in most of Sub-Saharan Africa (e.g., Swahili). They
are less commonly known as the Mbulu (which is somewhat pejorative)
and the name ‘Iraqw’ has several alternate spellings, such as Iraqu
and Erokh. Traditionally, Iraqw are agro-pastoralists, meaning that they keep
farms and herd livestock (i.e., cows, sheep and goats), though
nowadays, many rely solely on
subsistence agriculture.
The
main crops grown in the village are wheat, maize, and beans (red
beans, soybeans, etc.). The decision whether to grow wheat or maize
is largely economic: wheat is a cash crop, whereas maize is grown
mostly for subsistence. Climatic factors also play a role: a dryer,
hotter climate in the Central and Southern regions prevents wheat
cultivation in most areas. Fruits and vegetables are also cultivated
in and around settlements, but only in small (< 1 acre) plots. In
addition, barley, millet, and sunflowers are grown by some farmers,
but these are less common than fields of wheat and maize.
Nearly
all crops are rain-fed, however, a bimodal rainfall pattern provides
potential for two successive growing seasons. The main growing
season is from March to June-August with the other possible from
late November to February. Using both growing seasons has become
increasingly common, though it occurs at the direct expense of a
fallow period.
Since the mid-1970's, the population in the village
has quadrupled - from around 1500 to a present estimate of around
6000 - while crop yields have declined precipitously. In the case of
wheat, yields have plunged from 5.0 – 6.0 t/ha in the early-1970's
to 0.8 – 2.0 t/ha as of 2003-4.
These changes have been accommodated and induced, in
part, by extensive deforestation and a burgeoning livestock
population. Land shortage, a more recent phenomenon, effects
considerable grazing pressure and has compelled increasing numbers
of farmers to settle marginal lands.
Methods of soil conservation remain basic and,
ostensibly, have been only moderately effective in reducing soil
loss. These include use of vegetated contour ridges (i.e., bunds),
application of manure, and tethering of livestock to prevent
overgrazing; more effective means of intervention (e.g., terracing,
strip-cropping with frequent rotation, zero-tillage systems) are not
utilized.
Using an approach combining satellite and soils data
with social research, we have prioritized areas in the village of
greatest erosion risk (see publications
for method details and results) and are currently in the process of
implementing a broad range of programs to address the problem.
The above figure depicts estimated soil loss rates in
the village of Kambi ya Simba as of October 2002. The base image was
generated from ASTER satellite data, where the color 'red'
corresponds to infrared reflectance (e.g., the forest area just
above the village's northern border), 'green' corresponds to that
which is actually red on the ground, and 'blue' corresponds to that
which is actually green on the ground. Within the village perimeter,
however, colors correspond to estimated rates of soil loss (as shown
in the key). Data is missing from the gray areas (i.e., due to cloud
cover), and the village's soil types are outlined in black. For more
information, please visit our
publications section. |
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Soil loss research in Kambi ya Simba village
