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ACTA PHYTOGEOGRAPHICA SUECICA 79 Tamrat Bekele V ce�(f; tr21 �ll ([}) Iffi ceCC(fDn CLD�Y @ f[ re II1rnml�Iffilt AftIf([]) mm@ illl Q�rm ce if(())If�§�§ @ITil QIID� C(p;Iffi�Ir2lll JFll��esnrn (Q)[ §llncew�9 IE�llnnCIDJ1Dll21 OPULUS PRESS AB UPPSALA 1993 ISBN 91-72 10-079-6 (paperback) ISBN 91-7210-479- 1 (cloth) ISSN 0084-59 14 Editor: Erik Sjogren Editorial Board: A.W.H. Damman, Storrs, CT F.J.A. Daniels, Munster L. Ericson, Umea 0. Gj rerevoll, Trondheim D. Glenn-Lewin, Ames, lA 0. Hamann, Copenhagen H. Sjors, Uppsala H. Trass, Tartu Technical Editor: Marijke van der Maarel-Versluys © Tamrat Bekele 1993 Drawing on Title page: Impression of an African forest, by David Backeus (10 years old). Edidit: Svenska Vaxtgeografiska Sallskapet Villavagen 14, S-752 36 Uppsala DTP: OPULUS PRESS AB Printed in Sweden, 1993 by TK Uppsala AB, Uppsala Acta Phytogeogr. Suec. 79 Vegetation ecology of remnant Afromontane fo rests 3 Abstract. Tamrat Bekele. 1993. Vegetation ecology of remnant arbutifolia-Peucedanum winkleri type, Erica arborea-Myrica Afromontane fore ts on the Central Plateau of Shewa, Ethiopia. salicifolia type, Spiniluma oxyacantha-Scolopia theifolia type, -Acta Phytogeogr. Suec. 79, Uppsala. 61 pp. ISBN 91-72 10- Scolopia theifolia-Podocarpus gracilior type, Podocarpus 079-6. (9 1-7210-479- 1). gracilior-Olea europaea type, Podocarpus gracilior-Allophylus abyssinicus type, Juniperus procera-Sideroxylon gillettii type, The floristic composition and structure of the vegetation of Podocarpus gracilior-Maytenus arbutifolia type and Euphorbia Afromontane forest remnants on the Central Plateau of Shewa, obovalifolia-Podocarpus gracilior type. There is a strong con Ethiopia are described and related to environmental factors. The trast in species composition between the humid and dry forests: study was conducted in four forests: one humid forest, the Jibat the humid forest is characterized by a mixture of deciduous forest, and three dry forests, the Chilimo, Menagesha Suba and species while the dry forests are dominated mainly by the two Wof-Washa forests. 146 releves were analysed, 77 in Jibat, 30 in conifers Juniperus procera and Podocarpus gracilior. Chilimo, 20 in Menagesha Suba, and 19 in Wof-Washa. Analy is of community-environment relationship revealed The sample plots were u ually 30 m x 30 m for tree and strong correlations with altitude, soil chemical factors - espe hrubs, and 2 m x 2 m for herbaceous plants. For each species cially organic matter and total cations- and the physical factors the cover/abundance value was estimated. Height and diameter sand and clay content. It wa deduced from the structural com at breast height of all woody individuals taller than 2 m and parisons and vegetation history of the fo rests that Wof-Washa is thicker than 2 cm were measured. Profile diagrams were made an old forest while Jibat, Chilimo and Menage ha Suba are in selected transects in two of the forests, Menagesha and Wof forests in different stages of secondary development. Washa. Seven general patterns of species population structure were The fo llowing environmental variables were measured in recognized for the forests, and interpreted in terms of the dy each sample plot: altitude, slope, and exposure. Representative namics of the species: (1) good reproduction and continuous soil samples from each sample plot were analysed for chemical recruitment, (2) poor reproduction, but relatively many indi properties: pH, Electrical conductivity, Na, K, Ca, Mg, N, P, viduals in medium-size classes, (3) good reproduction but bad Cation exchange capacity, and Organic matter, and for physical recruitment, (4) good reproduction but irregular recruitment, (5) properties: Sand, Silt and Clay . good reproduction and continuous recruitment, but under-repre The releves were classified with the clustering and reloca sentation of medium-sized individuals, (6) poor reproduction tion program TABORD, and the two-way indicator species but relatively many individuals in higher size classes, and (7) no analysis program TWINSPAN. The resulting clusters were in reproduction, and only very large and old individuals present. terpreted as community types and given provisional names after Floristic comparisons with other montane forests showed u ually two dominant or characteristic pecies. Community that the Jibat forest is more related to the southwestern humid environment relationships were analysed with the ordination forests of Ethiopia, while the forests ofChilimo, Menagesha and program Canonical Correspondence Analy i (CANOCO pro Wof-Washa were related to each other, and other dry forests on gram) and the Discriminant Analysis program DISCRIM. the Southeastern Plateau of Ethiopia. Eighteen community types were described: Arundinaria alpina type, flex mitis-Rapanea simensis type, Syzygium guineense-Psychotria orophila type, Olea hochstetteri-Olinia aequipetala type, Croton macrostachyus-Ficus sur type, Olea Ta mrat Bekele, Department of Ecological Botany, Uppsala welwitschii-Carissa edulis type, Syzygium guineense- Vepris University, Villavdgen 14, S-752 36 Uppsala, Sweden. Perma dainelli type, Erica arborea type, Juniperus procera-Myrsine nent address: Department of Biology, Addis Abeba University, africana-Ehrharta erecta type, Juniperus procera-Maytenus P. O. Box 1176, Addis Abeba, Ethiopia. Fax+ 251 1 552112. Acta Phytogeogr. Suec. 79 Vegetation ecology of remnant Afromontane fo rests 5 Contents 1 Introduction 7 2 The Central Plateau 8 2.1 Physiography 8 2.2 Geology 8 2.2.1 Bedrock 8 2.2.2 Soils 8 2.3 Climate 10 2.3.1 Rainfall 10 2.3.2 Te mperature 10 2.3.3 Climatic classification 10 2.4 Vegetation 11 2.4.1 General vegetation survey 11 2.4.2 Forest vegetation of Ethiopia 11 2.4.3 Human impact 12 2.5 History of climate and vegetation 14 2.6 Phytogeographical description 15 2.6.1 Africa 15 2.6.2 The Afromontane Region 15 2.6.3 Ethiopia 16 3 Study area: location and description 17 3.1 Introduction: Dry and humid Afromontane forests 17 3.2 The Jibat forest 17 3.3 The Chilimo forest 17 3.4 The Menagesha Suba forest 19 3.5 The Wof-Washa forest 22 4 Floristic, environmental and statistical analysis 24 4.1 Sampling procedure 24 4.1.1 Vegetation analysis 24 4.1.2 Site description and soil analysis 24 4.2 Multivariate analysis 25 4.2.1 Classification 25 4.2.2 Ordination 26 Acta Phytogeogr. Suec. 79 6 Ta mrat Bekele 4.3 Results 26 4.3. 1 Classification: humid forest types 26 4.3.2 Classification: dry forest types 28 5 Analysis of the vegetation structure 36 5. 1 Introduction 36 5.2 Methods 37 5.3 Results 37 5.3.1 Tree density 37 5.3.2 Tree height and diameter 37 5.3.3 Basal area 38 5.3.4 Stratification 41 5.3.5 Species population structure 44 5.4 Discussion 47 6. Phytogeographical description 48 6. 1 Survey of tree and shrub species 48 6.2 Comparison between East-African montane forests 49 7 General Discussion 51 8 Acknowledgements 53 9 References 54 Appendix 1. 58 1 Introduction Ethiopia is a mountainous country with remarkable con quent volumes are in preparation. The second project, trasts: it comprises rugged mountains, flat-topped pla entitled 'Vegetation and land use study of the Central teaux, deep gorges and river valleys, and rolling plains. Plateau of Ethiopia' was launched in 1987. The first The altitudinal variation ranges from 110 m below sea vegetation studies have been devoted to grasslands and level at Kobar Sink (Dallol Depression) to 4620 m above shrublands (e.g. Zerihun & Backeus 1991). The present sea level at the highest peak of Mt. Ras Dejen. The study forms part of the latter project and has the fo llowing biological resources (flora, fauna and vegetation) of the specific objectives: country are still incompletely known. In other East-Afri 1. To study the floristic composition and structure of the can countries, notably Kenya, Tanzania and Uganda, the natural forests of the Central Plateau of Shewa, Ethiopia, overall composition and distribution of the vegetation and to classify the forest vegetation; have been better described, and Flora's are also available. 2. To investigate the ecological relationships of the forest Ethiopia has a long history and a rich cultural heritage, communities, with a special emphasis on the history of and it has been able to withstand foreign invasions which vegetation and climate, the present human impact, and the may be one of the explanations of our relatively poor general dynamical status of the forest types. knowledge of the country. In this study, the definition of forest given in two Given its unique physical setting and biogeographical important studies of East-African vegetation (Greenway position in Africa, a complete assessment of the vegeta 1973; White 1983a) has been adapted: "Forest is a con tion of Ethiopia contributes significantly to the general tinuous stand of woody individuals, at least 5 m in height, understanding of African flora and vegetation. The eco with crowns touching or intermingling". This is a prag logical crisis the country is facing - drought, deforesta matic definition, applicable to most of the vegetation of tion, soil erosion - has locally been catastrophic and the forests described here. Where the term woodland is detrimental to the biological richness of the country. used, it refers to open woody vegetation with open space Ethiopia is an agricultural country with about 85 % of the between crowns in the canopy. See further Eiten (1992), population earningit s living in direct interaction with the giving the same definitions, who discusses the variation biological and physical environment. A full understand and confusion regarding the names used for vegetation. ing of the present remains of natural and semi-natural This study deals with the four major remnant forests vegetation is required as a basis for the future design of a left on the Central Plateau of Ethiopia: Jibat forest, Chilimo sound resource exploitation programme on a sustainable forest, Menagesha Suba forest and Wof-Washa forest.