The Lowland Forest Ecosystem was first described by Chaffey (1979) as Lowland Forest that is comparable to the Moist Semi-deciduous Forest of Gana and Uganda and the Lowland Seasonal Rainforest of Malawi. He further stated that most of the species are classified as the Pan-Guineo-Congolian species. Friis (1992) described this vegetation as Dry Peripheral Semi-Deciduous Guino-Congolian Forest whereas Tesfaye Awas et al. (2001) described this ecosystem as Baphia abyssinica-Tapura fischeri Community in his study on vegetation of Gambella.
This ecosystem is characterized by unimodal rainfall brought by tropical monsoon blowing from south Atlantic and Indian Ocean. It is also characterized by heavy rainfall during the wet season (May-October) and very little precipitation during the dry season (November-April). This forest occurs on well-drained sandy soils, with altitudinal range of 450 to 800 m, mean annual maximum temperature of 35 to 38° C, mean annual minimum temperature of 18 to 20° C, mean annual temperature of 28 to 30° C and annual rainfall range of 1300-1800 mm (Friis, 1992, Demel Teketay, 1999).
The eastern part of the forest extends on the Precambrian basement, which is exposed at the edge of the plateau. Elsewhere the forest is situated on Pleistocene-Holocene deposits, which overlie the older rocks (Zerihun Wouldu, 1999).
The Lowland Forest Ecosystem is restricted to the lowlands of the eastern Gambella Region in Abobo and Gog Weredas. The forest is locally known as Abobo-Gog Forest.
7.3 Species Diversity
The lowland forest is characterized by the presence of certain tree species, which are widely distributed in tropical Africa. In Ethiopia the majority is confined to the lowland area and utmost extends as far as approximately 360E longitude and to an altitude of about 1,400 m (Chaffey, 1979).
According to the recent inventory that was carried out by the Forest Genetic Resources Conservation Project in 2001, Abobo-Gog Forest has more than 106 woody plant species including lianas (Anonymous, 2001). Out of these species, only 79 species that are represented in 20 families are identified so far. This figure is higher than the one reported by Friis (1992), which is 57 species.
The characteristic species of this forest are Baphia abyssinica and Tapura fischeri (Chaffey 1979, Friis, 1992, Tesfaye Awas et al., 2001). The common species in the upper canopy include Celtis gomphophylla, Celtis toka, Lecaniodiscus fraxinifolius, Zanha golungensis, Trichilia prieureana, Alistonia boonei, Antiaris toxicaria, Malacantha alnifolia, Zanthoxylum lepreurii, Diospyros abyssinica, Milicia excelsa, Baphia abyssinica, Vepris dainellii and Celtis zenkeri. The common species in the middle layer include Acalyphla neptunica, Erythroxylum fischeri, Tapura fischeri, Ziziphus pubescens and Xylpia parviflora (Chaffey 1979, Friis, 1992, Tesfaye Awas et al., 2001). The common species in the shrub layer include Whitfieldia elongata, Argomuellera macrophylla, Alchornea laxiflora, Mimulopsis solmsii, Oncoba spinosa, Oxyanthus speciosus, Rinorea ilicifolia (Friis, 1992)and Chazaliella abrupta (Tesfaye Awas et al., 1997b) Acalypha acrogyna (Tesfaye Awas et al., 2001). Lianas like Hippocratea africana and H. pallens are found in this ecosystem (Tesfaye Awas et al., 2001).
7.4 Uses and Values
Lowland Forest Ecosystem have both service and production roles as the other forests of Ethiopia. The Forest Genetic Resources Conservation Project carried out a Participatory Rural Appraisal (PRA) to study the relationship between the forest and the surrounding people.
The major uses of the forest identified by the farmers include house construction, agricultural implements, boat making, fuel wood and charcoal. In addition, villagers are producing furniture and timber and use the forest as a source of feed and food and as well as edible salt. Furthermore, water is obtained from some plant stem and enjoyed by the inhabitants. Few species also serve to prepare alcoholic drinks and oil is extracted from seeds of some species. The forest dwellers also utilize tree/shrub species for hanging beehives, medication, and soil and water conservation.
Shifting cultivation is a popular practice in the region (Anonymous, 2001), and it is carried out with three to five years cycle and the amount of land cleared ranges from 0.5 –3.2 ha/family. Pair- wise ranking exercise was conducted in Pwotelam Kebele to identify the most preferred vegetation cover to undertake shifting cultivation. The result revealed that Baphia abyssinica; species locally named Kobey and Ulam were accorded first to third rank in that order. These species are favored because farmers presume that the land under these species is fertile and maintain better production utmost for five years. Though the farmers benefit from this practice, it is severely affecting the forest cover. Moreover, it is a risky practice the farmers use fire to clear the vegetation and the fire may escape and burn the adjacent forest. Non-cultivated food plant species such as Albizia grandibracteata, Capparis erythrocarpus, Coffea arabica, Cordia africana, Lannea welwitschii, Lepidotrichilia volkensii, Morus mesozygia and Whitfieldia elongata are gathered from this ecosystem by the indigenous people (Tesfaye Awas et al., 1997a).
7.5 Threats and Rates of Change
The lowland forest area is sparsely populated by probably no more than a few thousand people. Because of the sparse population there is little use made of land in much of the lowland forest. River terraces and cleared areas within the forest are used for crops. The attempt to settle people from the north in the fringes of forest has not been successful (Zerihun Wouldu, 1999).
The sole farming system in Gambella Region is shifting cultivation. Hence, land clearing is the first and the most important activity, and commonly performed through slash and burn. Therefore, the fire set to establish agricultural land in Abobo-Gog forest has contributed a lot to the depletion of the forestland.
Development projects have caused pronounced forest destruction during their establishment. Hence, Alwero Irrigation Development Project, the main and the feeder roads that were constructed to connect Gambella with Abobo, and various settlements and state farms have also contributed to the shrinkage of the forest. Like wise road construction being carried out to link Abobo with Godere through Pwotelam is also blamed for excessive clearing of the natural forest.
In general, the inhabitants of the area utilize the wood and non-wood products throughout the year. Each family is involved in collection of wood for household consumption every day. Hence, the extractions of fuel wood have contributed a lot for the shrinkage of the forest.
7.6 Conservation Status
Even though Abobo-gog forest is recognized as priority forest for conservation, nothing was done so far to protect the forest from ruthless exploitation. The villagers and other users pose threats to the forest in general and to some species in particular. This is meant for subsistence and to generate additional income.