The study was conducted on the islands of Lake Ziway, south-central Ethiopia (Figure 1). The study area lies in the Lakes Region or Main Ethiopian Rift (MER) of the Ethiopian Rift Valley (ERV), specifically at the junction

of the East Shewa Zone and Arsi Zone, within Oromia National Regional State (ONRS). Lake Ziway is located at 7˚52' - 8˚8' N and 38˚40' - 38˚56' E close to Ziway town, which is located about 160 km south of Addis Ababa. It lies east of Ziway town, west of Assela town, north of Mount Aluto and south of Mount Bora. There are five main volcanic islands in Lake Ziway, namely Galilla, Debre Sina, Tullu Guddo (the largest), Funduro and Tsedacha. The former two are administered by the East Shewa Zone while the latter three are administered by the Arsi Zone. The altitude of the islands ranges from 1549 m asl at the lake banks to 2033 m asl at the Tullu Guddo summit (known locally as Woizero).

The islands and immediate areas to the eastern and northeastern sides of Lake Ziway are similar in geological structure. They consist of basaltic lavas and cinder cones as well as silicic flows and domes formed during the Quaternary age as a result of fissure eruptions [18] . The rocks of the areas to the west of Lake Ziway are composed of alluvial material and lacustrine sediments. The waterbed of Lake Ziway and the swampy areas around the lake are mainly composed of coarse pumice material [17] . Most parts of the islands are covered by volcanic rocks, mainly basalt and pumice. Soils of volcanic origin, particularly ash, are common on the slopes while soils of colluvial and lacustrine origin are common along lake banks. Generally, the soils are shallow and sandy, and are characterized by low organic matter. The colour of the soils is mostly grey, whitish or brown depending on location.

The Lake Ziway area is characterized by arid climate. It has a bimodal rainfall distribution with short-term, highly variable “small” rains from February to June and “big” rains from July to September. The dry season extends from October to January. Strong and persistent winds are characteristic feature of the Lake Ziway area. Data obtained from the National Meteorological Services Agency (NMSA) for the study area showed that the mean annual temperature is 20.5˚C and the mean annual rainfall is 702 mm.

Open Acacia woodland is characteristic of the Rift Valley area [19] . The vegetation of the Lakes Region of the ERV varies with the climate from open Acacia woodland in the plains of the rift floor to forest areas on the escarpments. Predominant vegetation types are Acacia woodland, bushland, shrubland and wooded grassland [19] [20] . Much of the shorelines of Lake Ziway are covered with a belt of lush marshy vegetation. The islands have vegetation consisting of different trees and shrubs interspersed with climbers and herbs. Lake Ziway harbours fish, hippopotamus and Nile monitor, and is a habitat for a variety of birds. The islands are habitats for monkeys, warthog, porcupine and various kinds of birds.

The inhabitants of the islands of Lake Ziway are the Zay people. They inhabited the islands sometime between the early 14th and the middle of the 17th centuries for different reasons [21] . They speak Zayigna, which belongs to one of the main language groups called Semitic. The Zay people are Christians strongly dedicated to

their religion. There is a church in each island. The land use systems on the islands are: cultivated land, forest land (which is also grazing land), settlement area, religious site, and fishing area or the lake. The Zay people used to inhabit all the five islands until very recently. At present, however, they live on three of the islands: Tullu Guddo, Funduro and Tsedacha. The other two islands, Galilla and Debre Sina, were abandoned mainly due to shortage of land and limited services. The economy of the Zay people is mainly based on traditional fishing and subsistence agriculture. Fishing has played a vital role not only in the subsistence economy but also in the development of the unique culture which has flourished on the islands [22] .

Participatory Rural Appraisal (PRA) was employed to generate socio-economic data following Martin [23] and Cunningham [24] . Data were collected by field observations, interviews and group discussion. Field observations were made on land use types, extent of soil erosion and vegetation degradation, human impacts on the vegetation resources, and indigenous resource management systems and practices.

Interviews were undertaken using semi-structured/open-ended questionnaires prepared in advance. From a total of 294 households (130 in Tullu Guddo, 20 in Funduro, 144 in Tsedacha), 60 households (20%) were randomly selected, and the household heads were interviewed. Six key informants, suggested by the local people and local representatives, were selected and interviewed informally so as to enrich the data. During the interviews with key informants, emphasis was given to issues related to the vegetation resources in order to get in- depth information about the past and present status, indigenous resource management systems and practices, utilization, and major threats. Three clergymen, suggested by the local people and local representatives, were selected and interviewed. Six relevant stakeholders, namely Woreda Rural Land and Natural Resources Administration Office, Woreda Agriculture Office, Woreda Administrative Office, Woreda Church Office, Ziway Fish Production and Marketing Enterprise and Ziway Fisheries Resources Research Centre, were selected from the East Shewa Zone in Ziway town, and interviewed.

A group consisting of elderly people, youth, women, clergymen and representatives of the local communities was formed. At the beginning of the discussion, the aim of the study was explained briefly to the participants so as to ensure openness in the discussion. During the discussion, emphasis was given to the strategies needed to conserve the vegetation resources and solve the existing socio-economic problems on the islands. The ideas and suggestions forwarded by the group participants were recorded.

Microsoft Excel software was used for analysis of the survey data, and the results of the analyses were presented using descriptive statistics.

The 60 households had a total of 418 members, of which 49.3% were males and 50.7% females (Table 1). The mean family size of the households was 7. About 75% of the households were male-headed while 25% female- headed. About 67% of the household members were in the age of £20 years, 31.1% from 21 - 60 years and 1.9% > 60 years (Table 1). There was high young generation, indicating that the population is growing. The human population growth has resulted in increased pressure on the natural resources in general and the vegetation resources in particular. About 37.3% of the household members were illiterate and 62.7% literate varying from primary to higher education (Table 2). Out of the total households, about 28.3% received health and family planning education.

The mean land size of the households was 0.79 ha. Out of the total households, about 33.3% had access to £ 0.5 ha, 53.3% from 0.5 - 1.0 ha, 11.7% from 1.0 - 1.5 ha and 1.7% > 1.5 ha. About 88.3% of the households had their own land, 23.3% rented land, 6.7% shared cropland, and 3.3% were landless (Table 2). Most of the land was used for crop cultivation, only a very small portion was used for fruit and vegetable production, and no land was allocated for woodlot. The shortage of land was a major problem, and led to infringing of farmlands into the natural vegetation.

The occupations of the households were diverse. The major activity was fishing (85%), followed by crop production (80%) and livestock production (75%) (Table 2). The households cultivated mainly cereal crops such as Eragrostis tef, Eleusine coracana and Zea mays, as well as Sorghum bicolor, Hordeum vulgare and Triticum spp. They also cultivated leguminous crops such as Phaseolus vulgaris; oil crops such as Linum usitatissimum; cash crops such as Gossypium spp., Catha edulis and Rhamnus prinoides; and fruit crops such as Citrus aurantifolia, Carica papaya and Psidium guajava. Crops were largely produced for consumption. Generally, homegardening was very limited. The households reared cattle (81.7%), goats (80.0%), sheep (33.3%), donkeys (16.7%) and poultry (86.7%). The mean number of livestock per household was 13, and for cattle, goats, sheep, donkeys and poultry were 3, 5, 2, 1 and 5, respectively. The households reared both indigenous and improved varieties of poultry (about 18.3% had improved varieties). The main reasons for rearing animals were for draught power, transport, production of milk and meat for consumption, income from sale of animals and their products, as well as hide and skin for bedding and mattress. The existence of diverse economic activities had relieved the pressure on the vegetation resources.

The mean annual income and expenditure of the households were ETB 1804.27 and 1742.02, respectively. The contribution to the annual income from fish sale alone was ETB 1365.60. Thus, the fishing industry was the main pillar of the economy as most of the income (75.7%) was derived from this sector. The other sources of income included sale of animals and their products, fruits, honey, handcrafts and local drinks, and casual work.

About 52% of the households planted trees and the rest 48% didn’t pant trees in the last five years preceding this study. Some exotic tree species (e.g. Eucalyptus camaldulensis, Jacaranda mimosifolia, Melia azedarach, Schinus molle, Spathodea campanulata subsp. nilotica) and indigenous tree species (e.g. Olea europaea subsp. cuspidata, Euphorbia tirucalli) were planted in homesteads, farm boundaries, roadsides and churchyards. The main reasons for planting trees were control of soil erosion, provision of wood and other products, and provision of shade and amenity. About 78.3% of the households were willing to plant trees in the future if seedlings are supplied to them. The reasons that prevented the households from planting trees were shortage of land (10%), have enough in the natural vegetation (6.7%), lack of seedling supply (11.7%), lack of awareness (5%) and other factors like steep and rocky land (6.7%). The percentages of the reasons that prevented the households from planting trees were relatively small. This showed that the households understood the importance of tree planting and affirmed their willingness to plant trees in the future.

However, tree planting in homesteads and other areas was very limited on the islands. Thus, there is a need to create awareness in the islanders on the importance of tree planting since it provides various products and thereby reduces the pressure on the natural vegetation. Measures have to be taken to promote planting of indigenous tree species, as well as appropriate exotic tree species. On the other hand, caution should be taken since the exotic species may become invasive and thereby affect the native flora.

The island communities were highly dependent on the vegetation resources for wood and other products. The natural vegetation was the major source of fuelwood, construction material, farm implements, edible fruits, medicines, fodder and bee forage.

According to the informants, the major woody species that provide fuelwood, construction material and farm implements were Cordia africana, Ehretia cymosa, Celtis africana, Acacia tortilis, A. etbaica, Euphorbia abyssinica, E. tirucalli, Aeschynomene elaphroxylon, Maytenus senegalensis, Ziziphus mucronata and Calpurnia aurea. The informants expressed that Olea europaea subsp. cuspidata and Juniperus procera were common on the slopes of Tullu Guddo until very recently. However, selective cutting for their valuable wood has now left the trees with only very few individuals. Aeschynomene elaphroxylon and Cyperus papyrus were economically important in making local boats, which are used as the main means of water transport. All households used fuelwood for cooking, but the fuelwood consumption varied among the households. The other sources of energy for cooking were dung (15%), crop residues (38.3%), charcoal (36.7%) and kerosene (21.7%). The sources of light for the households were oil lamps (98.3%) and “fanos” (30%). The percentage of using charcoal for cooking was relatively high, but the households expressed that the actual consumption was very low and its use was only occasional.

The local people were found to be familiar with different edible wild plants. According to the informants, the woody species that provide edible fruits were Cordia africana, C. monoica, Pappea capensis, Lannea schimperi, Grewia bicolor, G. velutina, Rhus natalensis, Ximenia americana, Opuntia ficus-indica, Ficus sycomorus, F. ingens and F. vasta. Out of the 141 plant species identified from the islands [10] , Acacia albida, A. tortilis, Aco- kanthera schimperi, Balanites aegyptiaca, Capparis tomentosa, Caylusea abyssinica, Celtis africana, Cleome gynandra, Coffea arabica, Commelina diffusa, Commiphora africana, Cordia africana, C. monoica, Cyperus esculentus, Ehretia cymosa, Erucastrum arabicum, Ficus ingens, F. sycomorus, F. thonningii, F. vasta, Flueggea virosa, Girardinia diversifolia, G. bicolor, G. velutina, Hypoestes forskaolii, Justicia schimperiana, Lannea schimperi, Maerua angolensis, M. triphylla, Olea europaea subsp. cuspidata, Pappea capensis, Pergularia daemia, Plectranthus lanuginosus, Rhamnus prinoides, Rhoicissus tridentata, Rhus natalensis, Rumex nervosus, Senna occidentalis, Urtica simensis, Ximenia americana and Ziziphus mucronata have already been reported as edible wild plants in Ethiopia [25] .

The local people used wild medicinal plants to treat various human and livestock ailments. According to the informants, Solanum incanum was used against snake bite, Withania somnifera against human and livestock ailments, Cordia monoica and Heliotropium steudneri against human “Mich” (a febrile disease in which the main symptoms are fever, headache and sweating), Asparagus africanus against anthrax, and Heliotropium aegyptiacum against goat infections. Out of the plant species identified from the islands [10] , Achyranthes aspera, Acokanthera schimperi, Asparagus africanus, Capparis tomentosa, Commicarpus plumbagineus, Cordia monoica, Croton macrostachyus, Heliotropium aegyptiacum, Pavetta gardeniifolia, Senna occidentalis, Solanum incanum and Withania somnifera have already been reported as medicinal plants used by the Zay people [26] .

The island communities were highly dependent on the natural vegetation for livestock grazing and browsing. The animals freely graze and browse in the natural vegetation, both in the dry and wet seasons.

The natural vegetation had a high potential for beekeeping as it possessed plants that provide bee feed. According to the informants, the woody species that are of great importance in providing bee feed were Acacia tortilis, Euphorbia abyssinica, E. tirucalli, Grewia velutina, Capparis fascicularis and Aeschynomene elaphroxylon. Among the herbs, Hypoestes forskaolii was an important source of bee feed. Out of the plant species identified from the islands [10] , 59 species have already been reported for their great values as bee forage [27] .

The Zay people have environmental friendly resource management systems and practices. Terracing is widely practiced on the islands (Figure 2). The Zay people construct the terraces from stone, and they plant trees, particularly Euphorbia tirucalli, to give strength to the terraces. Most edges of the lake were also terraced with stone primarily to promote the growth of pasture for livestock, as well as to prevent erosion by the strong lake waves and crop damage by hippopotamus. The Zay people have an excellent practice of traditional agroforestry system (Figure 3). They retain indigenous trees like Acacia tortilis and A. albida in farmlands and farm boundaries for erosion control, improvement of soil fertility and provision of various products (fuelwood, construction material, medicines, fodder, etc.).

The Zay people also have important traditional vegetation management systems and practices, which have contributed a lot for the maintenance of the vegetation resources in the absence or very little involvement of government bodies. They construct their housewall with stone and earth. This makes the house durable and thereby reduces the turnover of cutting trees for house construction. They use dried and fallen logs for fuelwood. They do not cut trees for fuelwood but for construction material, farm implements and other purposes. They use fuelwood mostly for cooking and only rarely for lighting. They do not sell wood products but use them only for

consumption. Charcoal production was insignificant on the islands. Absence of cutting and use of trees for sale is partly a reflection of low pressure on the natural vegetation.

These peculiar knowledge systems and practices have contributed a lot for the maintenance of the soil and vegetation resources on the islands for centuries. This can help the islands to remain unique areas in the region with their beautiful environment and cultural heritage. In the mainland areas surrounding the lake, in contrast, there is pronounced deforestation and soil erosion due to farmland expansion, overgrazing, urbanization, forest fires, and tree cutting for fuelwood, construction material, timber and charcoal (field observations; local people, personal communication).

The indigenous resource management systems and practices used by the Zay people are exemplary. Zegeye et al. [10] noted that they deserve special attention for scaling up to other rural areas since they have the potential to promote the conservation of biodiversity. Therefore, they supplement our knowledge on indigenous resource management systems and practices that exist in the country, such as soil and water management practices in Konso, resource management in Borana, traditional agroforestry practices in the south and southwest, and house construction with stone and earth in Tigray.

Galilla and Debre Sina had dense vegetation owing to the absence of settlement and thereby low human pressure. Tullu Guddo also had dense vegetation on the slopes, hills and rocky lake banks though lower flat areas were under settlement and cultivation. The vegetation in Funduro was slightly disturbed while the vegetation in Tsedacha was heavily disturbed due to the high population and suitability of the land for cultivation. At present, the vegetation resources on the islands are dwindling due to free livestock grazing, farmland expansion, soil erosion and tree cutting for various purposes, all of which are driven by human population growth.

According to the informants, soil erosion was insignificant on the islands until very recently because of the presence of well established terraces. At present, however, erosion has become a major problem due to damage on the terraces by livestock, particularly goats, and lack of maintenance. Rills started to form in some places, particularly on the slopes of Tullu Guddo. As a result of erosion, some individuals of trees became dry or uprooted, and rolling stones caused considerable damage on the natural vegetation. Thus, the terraces require maintenance in order to control soil erosion and thereby enhance vegetation development. Prevention of soil erosion is the priority action since the islands generally have slopy land. The damage caused by goats on the terraces and natural regeneration of trees needs special attention. As mentioned previously, the number of goats per household was high, indicating that it is a major threat to the vegetation resources.

There were livestock left to graze on their own in Galilla and Debre Sina, and also there was entry of goats by native inhabitants of the islands currently living in the shore areas. Thus, removal of livestock from the uninhabited islands and prevention of further entry are urgent actions. It is also advisable to limit the number of goats per household in the inhabited islands through provision of viable economic alternatives to the islanders.

Christianity is deep rooted in the islanders. Theft is a taboo. This was reflected by the fact that they leave their properties anywhere as deemed necessary and they don’t usually close their doors. Cutting trees from the sacred groves is also a taboo. This tradition has contributed to the maintenance of the sacred groves in particular and the vegetation resources on the islands in general. Moreover, as we have already reported [10] , the church has been involved in protecting the sacred groves, planting trees in churchyards and giving advice to the island communities on the importance of conserving the vegetation resources on the islands.

Trees such as Acacia tortilis, Euphorbia abyssinica, E. tirucalli, Opuntia ficus-indica, Cordia monoica, Pappea capensis and Ficus vasta were retained in churchyards and also trees like Melia azedarach were planted. Sacred groves provide various goods and services such as erosion control, protection of the church from strong winds, live fence, shade, construction material, edible fruits, medicines and plant material for religious purposes.

The recommendations forwarded by the clergymen for conservation, management and sustainable use of the vegetation resources on the islands were formation of control and management units, supply of seedlings and support from the government. From the survey it was found that the church, which is considered the house of God, has played a vital role in environment and development issues besides its religious service.

The survey showed that the involvement of stakeholders and their contributions in conservation and development activities on the islands was very limited (Table 3). Furthermore, the integration among the stakeholders involved was very poor. Limited involvement of stakeholders and poor integration will have negative impacts on conservation and development activities that can be carried out on the islands. In order to ensure the maintenance of the vegetation resources and bring socio-economic development on the islands, there is a need to promote the involvement of all relevant stakeholders with proper integration.