Ecology and Development Series No. 10, 2003 - ZEF
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Ecology and Development Series No. 10, 2003 - ZEF

Ecology and Development Series No. 10, 2003 - ZEF Ecology and Development Series No. 10, 2003 - ZEF

zef.de
13.07.2015 Views

Description of the study area and sampling design3.1.2 Geology and soilsEthiopia is part of a large regional geological structure, the Horn of Africa. The underlyingbasement rock in this region consists of intensively folded and faulted Precambrian rocks,overlain by Mesozoic marine strata and Tertiary basalt traps (Westphal 1975). The Tertiaryvolcanic rocks include rhyolites, trachytes, tuffs, ignimbrites, agglomerates, and basalt.These rocks form the substrates of most of the Afromontane forests (Friis 1992).Generally, the soils of the area are red or brownish ferrisols derived from volcanicparent material. The prevalence of high rainfall has masked other soil forming-factors andhence, very similar soils have developed on a variety of parent materials. Other soil groupsin the area include nitosols, acrisols, vertisols, and cambisols (Tafesse 1996).3.1.3 Topography and drainage systemsThe forest area is characterized by a rolling topography, and is highly dissected by smallstreams and two major rivers, Geba and Dogi. The landform frequently changes from flatsurfaces on the top of plateaux to very steep slopes and valley bottoms within shortdistances. The altitudes in the study area range between ca. 1200 m at lower river valleys toca. 2000 m a.s.l. The study plots are located between 1250 and 1700 m.The Dogi River drains into the Geba, which flows southwest ending in the BaroRiver, one of the main tributaries to the Nile, and drains most areas of the forested areas inthe southwestern part of the country.3.1.4 ClimateGenerally, the forest area is hot and humid. The mean annual temperature is about 20 o C,ranging from a mean minimum of 12.7 o C to mean maximum of 26.1 o C. There is only aslight difference in temperature throughout the year, with the hottest months in February toApril (maximum 29 o C) and the coldest months during July to September (minimum 12 o C).The mean annual rainfall is 2100 mm year -1 , with high variation from year to year, rangingfrom about 1400 to 3000 mm year -1 . The rainfall pattern is uni-modal, with low rainfall inJanuary and February, gradually increasing to the peak period between May and October,and then decreasing in November and December (Figure 3.2).29

Description of the study area and sampling designMean minimum temperature Mean maximum temperature Mean3530Temperature ( O C)2520151050Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMonths400350300Rainfall (mm)250200150100500Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMonthsFigure 3.2. Annual rainfall and temperature distribution patterns (Source: EthiopianMeteorological Service).30

Description of the study area <strong>and</strong> sampling designMean minimum temperature Mean maximum temperature Mean3530Temperature ( O C)252015<strong>10</strong>50Jan Feb Mar Apr May Jun Jul Aug Sep Oct <strong>No</strong>v DecMonths400350300Rainfall (mm)250200150<strong>10</strong>0500Jan Feb Mar Apr May Jun Jul Aug Sep Oct <strong>No</strong>v DecMonthsFigure 3.2. Annual rainfall <strong>and</strong> temperature distribution patterns (Source: EthiopianMeteorological Service).30

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