Jozani biodiversity inventory report 2002 - Coastal Forests of Kenya ...

Quaternary rocks have a mixture of tropical laterites, limestone, fish bones, sharks teeth, garnets,
kyanites and tourmalines. Their maximum thickness ranges from 25-35m. The Quaternary rocks
range in colour from a complex of red, chocolate, brown to white cream and grey. The Miocene
rocks are mainly rhythmic fluviatile sediments of the dissected Rufiji River delta. These include
limestones, sandstones, marls, sandy clays and clayey sands in 5 meter bands. They also include
lenses of crystalline limestone and anhydrite frequently with local ferruginous and siliceous
cementing with a maximum thickness of 2560m. Modified Miocene rocks are hard, dense, pearly
white with crystalline limestone in strata and lenses. Other Miocene rocks are grey, white,
opaline, coarse or angular siliceous sands, lightly cemented. These can also be thick grey-green
and dense, roughly sorted chalky rocks.
2.6 Soils
Soils are closely related to the parent rocks and geomorphology. However, since the forest and
most of the surrounding areas are under coral rag, the soils are shallow and in many areas the rag
is emergent. In the Quaternary parent rock areas the laterites, alluvials and colluvials are
predominant with some areas covered with marine, fluviatite sands and sandstone. The Miocene
soils are comprised mainly of rythmic fluviatite and deltaic sediments and limestones. There are
also sands, sandstones with marls, sandy clays and clayey sands.
In forested areas the soils are mostly clay loam attaining black colouration due to humus. The
forest soils are mostly damp or water logged in areas with a high water table. Patches of sandy
soil appear in places like Pete where the soil is brown and in Unguja Ukuu where the sandy soils
are grey. In the mangroves there is fine mud clay, black in colour though the substrata could be
comprised of sand. The coastline in Chwaka is sandy but some areas are muddy, especially
where mangroves are present.
2.7 Climate
The climate of Jozani forest and Chwaka Bay like other East African coastal areas is determined
by geographical location and seasonal changes brought by the general circulation of air over the
Indian Ocean. The monsoons have the dominant influence on wind direction and strength,
temperature and rainfall. The northwest monsoon (Kaskazi) prevails from November to February
and is characterised by high air temperatures of greater than 30 0 C and weaker winds. The
southeast monsoon (Kusi) lasts from April to September and is marked by lower air temperatures,
approximately 25 0 C, with stronger winds. Inter monsoon periods are calm. Rainfall in the
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