SINET : Ethiop. J. Sci ., 31(2):103–120, 2008 © Faculty of Science, Addis Ababa University, 2008 ISSN: 0379–2897 FLORISTIC COMPOSITION AND STRUCTURE OF THE DRY AFROMONTANE FOREST AT BALE MOUNTAINS NATIONAL PARK, ETHIOPIA Haile Yineger 1 , Ensermu Kelbessa 2 , Tamrat Bekele 2 and Ermias Lulekal 3 1 Department of Biology, Jimma University, PO Box 5195, Jimma, Ethiopia E-mail: [email protected] or [email protected] 2 National Herbarium, Department of Biology, Faculty of Science, Addis Ababa University PO Box 3434, Addis Ababa, Ethiopia 3 Department of Biology, Debre Berhan University, PO Box 445, Debre Berhan, Ethiopia ABSTRACT : The floristic composition and structure of the Dry Afromontane Forest at Bale Mountains National Park was studied from July 2003 to June 2004. A total of 90 plots were established at three sites (Adelle, Boditi and Gaysay) at an altitudinal range of 3010–3410 m. The cover abundance values, density, and diameter at breast height and list of species were recorded in each plot. About 230 species belonging to 157 genera and 58 families were identified and documented. Analysis of vegetation data revealed 5 homogenous clusters. The densities of trees in the diameter class >2 cm were 766 and 458 individuals ha -1in Adelle and Boditi forests, respectively. The basal areas were about 26 and 23 m 2ha -1 in Adelle and Boditi forests, respectively. About 43% of the basal area in Adelle and 57 in Boditi forests were contributed by Juniperus procera and Hagenia abyssinica , respectively. Both Adelle and Boditi forests were found at an earlier secondary stage of development and had, more or less, a similar trend of development. The population structures of tree species were assessed and these had clearly signalled the occurrence of excessive cutting of selected diameter classes of ecologically, economically and medically important tree species for various purposes, particularly for construction. Key words/phrases: Bale Mountains, floristic composition, plant community, vegetation structure INTRODUCTION are mainly the results of altitudinal variations, and these have supported so many other endemic flora The highland area of Ethiopia was once covered and fauna (Miehe and Miehe, 1994). Moreover, the with extensive forest resources ( EMA , 1988). park is a site for the origin of numerous water However, the country has lost these resources at an bodies that are incredibly vital for the livelihood of alarming rate due to various reasons. According to both the lowland and highland dwellers (Williams, EFAP (1994), the annual loss of forest resources of 2002). However, the BMNP and many other the country is estimated between 150,000 and protected areas in Ethiopia are not well managed 200,000 ha. and their resources are being exploited The most important reason behind the rapid unsustainably (Shibru Tedla, 1995). deforestation rate in the country is the ever- For effective management and conservation of increasing human population growth. This rapid this unique ecosystem of the country, there is an increase in human population is associated with a urgent need to develop a sound management plan, very high demand for agricultural and grazing and this, in turn, requires detailed baseline lands, forest resources for firewood, charcoal, information on the ecology of the area. Menassie timber, construction, and many other purposes. Gashaw and Masresha Fetene (1996) studied the Fire, inappropriate investment activities, and lack plant communities of the Afroalpine vegetation of of viable land use policy have also been key factors Sanetti plateau. Miehe and Miehe (1994) studied for the rapid decline of forests in the country (Friis, the Ericaceous forests of the Bale Mountains. The 1992; Taye Bekele et al ., 1999). National Herbarium (2004) carried out a general The Bale Mountains National Park ( BMNP ) is biodiversity assessment of the park and primarily established for the conservation of the surrounding areas. Nevertheless, the floristic critically endangered Ethiopian endemic mammal composition, plant community and structural species, the Ethiopian Wolf ( Canis simensis ) and analysis of the Dry Afromontane Forest in the Bale Mountain Nyala ( Tragelaphus buxtoni ). Nonethe- Mountains National Park have not previously been less, the park has extremely diverse habitats that investigated. Therefore, the present study was 104 Haile Yineger et al. conducted to determine the floristic composition, The study area has a bimodal rainfall identify plant communities and carryout structural distribution from March to October, with the analysis of the Dry Afromontane Forest in the highest rain falling in April and then from July to park, and this is believed to contribute a lot to the October (Fig. 2) ( NMSA , Personal communication). effort being made in the development of a sound The dry season extends from November to management plan for effective conservation of the February. The mean annual rainfall is 1218.64 mm. park resources. The mean annual minimum and maximum temperatures of the area are 2.36°C and 15.5°C, respectively. The lowest and highest values of MATERIALS AND METHODS mean monthly minimum temperature were recorded in December (–1°C) and August (6.1°C) Study area respectively. The corresponding values for the The study area is located in Oromia National mean monthly maximum temperature were Regional State, Bale Zone, between latitudes observed in October (14°C) and February (21.3°C), 07 005.98’–07 008.99’N and longitudes 039 043.43’– respectively. 039 045.39’E (Fig. 1). The altitudinal range of this The vegetation in the northern part of the Bale area lies between 3010–3410 m a.s.l. The lava Mountains forms the southern margin of the outpourings of the Miocene and Oligocene geolo- ‘widespread, largely undifferentiated Afromon- gical periods were responsible for the formation of tane forest area’ of central and north Ethiopia the Bale Mountains (Mohr, 1963). The rocks (Miehe and Miehe, 1994). Altitudinal and formed from these trapean lavas mainly consist of associated climatic variations along this site have trachytes, with some amounts of rhyolytes, tuffs, resulted in the formation of four distinct vegetation basalts, and associated agglomerates (Morton, zones each of which has its own unique flora and 1976). The trachytic and basaltic rocks weather fauna. These are the grasslands of Gaysay valley predominantly to the fairly fertile loam soils that and Dinsho, the Juniperus-Hagenia forests, the Erica are of reddish-brown to black in colour (Miehe and or heather belt, and the Afro-Alpine moorlands of Miehe, 1994). the plateau and the central peaks (Williams, 2002). 10° 40° 40° 40° 39°30' 39°45' 40°00' 40°15' E ri tr e a an d u S 10° Ethio pia 10° ia al om Keny a S Adaba 20° 20° 7°15' 7°15' Hako% Sinanana Dinsho $$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$ $ % $$$$$$ $$$$$$$$$$$$ $$$ Robe $$$$$$$$$$$$ $$$$$$ %Dinsho $ 10° 40° a k % l e N %Goba S %Adaba 7°00' Goba 7°00' Legend % Towns $ Sampling Poin ts Roads Rivers 6°45' 6°45' Woreda Bou ndary Bale Mountains National Park 39°30' 39°45' 40°00' 40°15' 30 0 30 Kilometers Fig. 1. Map showing the study area. SINET : Ethiop. J. Sci ., 31(2), 2008 105 Fig. 2. Climadiagram (after Walter, 1985) showing rainfall distribution and temperature variation from 1994–2002 at Dinsho (BMNP Headquarters). Data source: National Meteorological Service Agency. Site selection and plot establishment Gaysay grassland shows little altitudinal A reconnaissance survey was made from 30 July variation, and therefore, floristic data were to 2 August 2003 to obtain an impression on the collected from this site following Kumelachew general physiognomy of the vegetation and Yeshitela and Tamrat Bekele (2002) through identify sampling sites in the study area. The subjectively selected homogenous representative fieldwork was done between 3 August and 12 stands. In such a way, 22 nested plots (5 x 5 m for August 2003, September and November 2003, and shrubs and 2 x 2 m for herbs) were analysed from January and June 2004. Based on the this site. reconnaissance survey, three sites (Adelle and Altitude was measured for each sample plot Boditi forests, and Gaysay grassland) were chosen using ‘Pretel’ digital altimeter. GPS readings of within the park area some 5 to 7 km northeast of latitude and longitude coordinates were also the Bale Mountains National Park ( BMNP ) recorded for each plot. headquarters. These sites were chosen because they were relatively better protected and the extent Vegetation data collection of human disturbance was relatively less than in A complete list of herbs (plants whose stem does the other areas of the Dry Afromontane Forest in not produce woody, persistent tissue), shrubs the park. The Gaysay grassland is almost a flat area (woody plants having several stems at or near the that lies between Adelle and Boditi. The altitudinal base of the plant and less than 3 m tall), lianas ranges of Gaysay grassland, Boditi and Adelle are (woody plants which use trees and other means to 3010–3060 m, 3060–3410 m, and 3070–3350 m climb over the canopy) and trees (woody plants above sea level, respectively. having a dominant stem and more than 6 m tall) Five line transects were laid on each of the two were made in each plot. The occurrence of lichens, sites (Adelle and Boditi) beginning from the bryophytes and vascular epiphytes were also Ericaceous zone to the edge of the forests. The noted. The 1–9 modified Braun-Blanquet scale (van distance between transects was 500 m. A total of 32 der Maarel, 1979) was used to estimate the cover- (Adelle) and 36 (Boditi) nested plots (30 x 30 m for abundance values of tree and shrub species. trees, 5 x 5 m for shrubs and 2 x 2 m for herbs) The diameter at breast height ( DBH ), i.e., 1.3 m were established at every 35 m drop in altitude from ground was estimated for each tree and along these transects.