Prioritization and Selection of High Biomass Energy Producing Plant Species at Boset District, Central Ethiopia: An Ethnobotanical Approach

Background: In Ethiopia, about 92.3% of all the biomass energy is consumed by domestic households and the demand is growing from 10-14%. However, there are little/no practical experiences or documented indigenous knowledge on how traditional people identify and select high biomass producing plant species with short rotation periods at Boset District. Therefore, the present study was aimed at: (1) selecting and documenting high biomass energy producing plant species at Boset District; (2) identifying major predictor variables that inuence the prioritization and selection of species; and (3) develop a Generalized Linear Model (GLM) to predict the selection of species. Methods: A total of 96 informants comprising 59 men and 37 women between the ages of 18 and 81 were sampled. Data were collected using structured interviews, guided eld walk, discussions and eld observations. Results: Collected data indicated that 88.5% of the informants involved in rewood collection, while 90% practiced charcoal making. A total of 1533.60 Birr per household on average was earned annually from this activity. A total of 25 rewood and/or charcoal plant species were identied and documented at Boset District. Of these, Acacia senegal, Acacia tortilis and Acacia robusta were the three best prioritized and selected indigenous high biomass producing species. Prosopis juliora, Parthenium hysterophorus, Azadirachta indica, Calotropis procera, Cryptostegia grandiora, Lantana camara and Senna occidentalis further grouped under introduced fuelwood species. Prediction of GLM assured sampled Kebeles and source of income generated from fuelwood species positively and signicantly (p<0.001) related to selection of species. Higher eciency to provide energy and heat; little or no smoke or soot; easier to cut and split the wood and easier availability were some of the main selection criteria. Conclusions: This study provides valuable information in selection and documenting of high biomass producing plant species for proper management and sustainable use at Boset District. The three most selected species (A. senegal, A. tortilis and A. robusta) should be further evaluated at laboratory to determine their energy values.


Introduction
Wood energy is the major problems in east Africa both for domestic supply and commercial uses. Hence, it accounts for about 85% of the total energy consumed and for over 95% of the total wood products used in east Africa [1]. Out of this energy supply, the main source of wood energy is natural forests, which accounted for over 99% of the fuelwood consumed [1]. Consequently, wood energy is the main source of cooking, heating and lighting in the region. Almost 100% of the rural population as well as 80% of the urban population rely upon wood energy as their main source of domestic energy [1]. In line with this, a higher demand of energy in Ethiopia is growing from 10-14% [2]. However, according to the UNEPs study such energy source is mainly rely on biomass sources, which includes rewood and charcoal as well as agricultural crop residues and animal dung. As a result, a high demand for solid biomass ( rewood and wood. However, an ine cient and wasteful method of traditional open re cooking and the low e ciency cooking stoves accounts mainly for the consumption of relatively a higher proportion of fuel wood. At the same time, such traditional stoves causes a lot of smoke and soot which is associated with health problems. Women and children also spend a lot of time and energy to collect rewood and/or fuelwood from long distance. So, to combat the problem of deforestation designing e cient and fuel-saving improved stoves is one of the practical solutions in many developing countries. Although the majority of wild woody plant species can be used as a source of fuel for indigenous peoples, many species are recognized for particular burning qualities [7].
Charcoal is a valuable and a chief domestic fuel for cooking and heating [4,[8][9][10][11]. Due to this reason, it is a common source of fuel wood in urban centers. In the absence of fossil fuel, charcoal is more advantageous and much preferred fuel wood than rewood due to being of lighter weight, less bulky and more compact, thereby easier to store inde nitely and cheaper to transport [6,11]. It is more e cient and produces a steady heat with little or no smoke or soot [4][5][6][7][8]. Charcoal is also commonly used by blacksmiths and industrial fuel, which is served as reduction of metal and lters [11]. On the contrary, a lot of processes are required to make charcoal locally using simple traditional mound kilns. During charcoal preparation, about 50% of the wood's energy is wastefully burned away during carbonization process [6,9,11]. With this, one ton of charcoal is produced from about 5 tons of fuelwood [10]. Due to this reason, rewood is better than charcoal if the transport distance is short. The long distance transportation further makes charcoal more expensive compared to rewood. Consequently, extensive woodland has to be cleared to meet the high charcoal demand. High valued fuelwood species for charcoal production such as Acacia and other indigenous species are severely degraded and even endangered. Moreover, charcoal making causes many accidental res on forests and thereby devastates the forest resources associated with a huge loss of biodiversity. At the same time, both charcoal harvesting and accidental and/or deliberate forest re further contribute to deforestation, land degradation and climate change [12].
As a result, there are a number of limitations are found in optimum production and sustainable use of forest biomass energy in Ethiopia. Problems of forest biomass collection, transportation and storage as well as availability are some of the main factors. In addition, the ever-increasing demand for optimum and sustainable production of biomass coupled with efforts to mitigate greenhouse gas emissions and thereby adapt climate change as well as forest degradation especially for indigenous species has needs very urgent call and attention for the identi cation, selection as well as large scale development and promotion of forest plantation. Hence, in order to solve such problems producing su cient and sustainable quantities and expansion of forest biomass energy from fast growing fuelwood species with short-term rotation periods are an option for balancing the demand and supply of biomass energy. To achieve this objective, superior fuelwood species characterized by higher survival rate, better growth performance and disease resistance should be promoted for short-rotation biomass production [13]. This is because fuelwood will continue to be the most reliable source of energy in rural communities in Africa so that there is a need to expand its supply so as to satisfy the demand. As a result, a lot of effort has been done over the last a few decades to establish plantations particularly short-rotation fuelwood species such as Eucalyptus species. This, in turn, helps to solve the ever-increasing imbalance of demand and supply of fuelwood species associated with population pressure and expansion of urbanization. Thus, these short-rotation fuelwood species not only address the shortage of fuelwood demand for the long-term problem of the society but also they play a signi cant role in mitigate greenhouse gas emissions and thereby adapt climate change as well as forest degradation especially for indigenous species. Due to these and other related reasons fast growing fuel wood species having short-rotation periods currently rapidly expanding in various parts of Ethiopia in order to solve the fuelwood demand both in rural and urban areas. Consequently, many small-scale farmers in Amhara region widely plant Eucalyptus seedlings and expanding the Eucalyptus species (e.g. Eucalyptus globulus, Eucalyptus camaldulensis) and Acacia decurrens in their farmlands by converting from cultivation of crops. However, there is a knowledge gap on selecting these suitable forest biomass species to expand the plantation forests both in small-scale and large-scale plantations through the application of silviculture. Furthermore, selected species should be further evaluated under laboratory to check their energy value. Therefore, the present study was aimed at: (1) selecting and documenting high biomass energy producing plant species with short-rotation period to satisfy the high demand of biomass energy at Boset District; (2) identifying major predictor variables that in uence the identi cation, prioritization & selection of species; (3) develop a Generalized Linear Model (GLM) to predict or explain the selection & documenting of the most popular rewood and/or charcoal species; and (4) suggesting the best three prioritized and selected fuelwood species for further evaluation of their energy value at laboratory.

Study area
An ethnobotanical study was conducted in Boset District, East Shewa Zone of Oromia National Regional State, Ethiopia (Fig. 1). It is located in the Great east African Rift Valley. The capital town of Boset District, i.e., Olenchiti town is 25 km far from Adama town, while 99 km far from Addis Ababa, in the eastern Ethiopia. Olenchiti town is located between latitudes 37P 0547246 and longitudes UTM 0957166 within an altitude of 1465 m a.s.l.
The three study sites (Kebeles) are found around the Olenchiti town. Kebele is part of a District and the smallest administrative division or structure in Ethiopia. The three selected study Kebeles from Boset District (Borchota, Geri and Tedecha) are located around the Olenchiti town. These Kebeles are 12, 11 and ve km far from Olenchiti town in their respective orders. Based on the 2007 Census conducted by the CSA, Boset District has a total population of 141196 out of whom 73443 are men and 67753 are women [14]. Of these, a total of 114687 populations live in the rural setting that having 60107 male and 54580 women. The study area is generally practice mixed agriculture that comprising both livestock raising and crop production.
Boset District, which is located within the Great East African Ri t Valley, is characterized by semi-arid climate or Qolla Zone. Its mean annual rainfall is ranged from 600-900 mm, while the mean annual temperature is 26-34 o c [15]. The dominant soil types of the study area include brown (Dalecha) soil 30%, 13% black soil, 25% sand, 25% clay, 5% volcanic soil and the rest 2% other soil types. The main land use types are 28.7% agricultural land; 7% grazing land, 0.1% forest land, 51.9% uncultivated land and 1.47% construction and other uses [15]. The area is located within the Inter-Tropical Convergence Zone, which makes both temporal and spatial variability in rainfall, humidity and temperature [16]. Rainfall is bimodal with two distinct seasons, i.e., the short rains (Belig rain) between February and April and the long rains (Meher rain) between July and September [16]. The vegetation of the study area lies under the Somalia-Maasi center of endemism [17]. Sebsebe and Friis [18] further described that out of the nine vegetation types of Ethiopia, the vegetation type of the study area is classi ed under Acacia-Commiphora woodland. Accordingly, this vegetation type is characterized by drought-resistant trees and shrubs, either deciduous or with small, evergreen leaves. The trees and shrubs in this vegetation type include species of Acacia, Commiphora, Balanites, Capparis, Combretum and Terminalia.

Methodology
A two-stage sampling design was followed for conducting the in-depth ethnobotanical study at the study site. In the rst stage, a potential District, i.e., Boset District was purposively selected out of ten Districts from east Shewa Zone, Oromia National Regional State. The basis of selection mainly relied upon harvesting intensity of rewood collection and charcoal production in the area by rewood collectors and charcoal makers. Accordingly, the selection was conducted based on previous information/data by the east Shewa Zone Environment, Forest and climate change Authority. Following this, three potential Kebeles from Boset District were purposively selected out of 14 Kebeles. During the selection process, Boset District Agricultural and Natural Resources O ce Head, District Natural Resources expert, Kebele Development Agents (DA) and Kebele O cals were actively involved and gave their own suggestion. Three selected Kebeles were Borchota, Geri and Tedecha. These Kebeles were known with severe harvesting of rewood and charcoal production. In the second stage, a reconnaissance survey and pretest at three selected study sites was conducted in order to obtain an impression about commonly used high biomass producing plant species by charcoal makers, fuel wood collectors, pastoralists, farmers, religious and community leaders as well as local communities to identify and select informants [20]. Moreover, identi ed charcoal makers and fuel wood collectors were invited to suggest other charcoal makers and fuel wood collectors since these informants had better experience, knowledge and skills associated with their day-to-day activities [20]. Informants' selection was mainly based on their local knowledge, skills and daily practices on rewood collection and charcoal production, which was evaluated during pretest survey. In this insight, informants within different age, gender, occupation, wealth status and social groups were included from different households and considered as household heads in this particular ethnobotanical study. This is because indigenous knowledge considerably varies among age, gender, occupation, wealth status and different social groups [7,19,21,22]. At the same time, Kebele O cials and Development Agents (DA) were actively involved and participated during the selection process as they have a better experience and socio-economic information of the informants.
Then, identi ed and listed species from each Kebele were further ranked from 1-5 using simple preference ranking following Cotton [7] and Martin [25]. Following this, 10-15 key informants were selected and the paired comparison method was applied. Thereafter, the best three selected species from each Kebele after preference ranking were further prioritized again using paired comparison method following Cotton [7] and Martin [25]. Finally, the rst ranked potential species for rewood collection and charcoal making from each Kebele, i.e., three species from three Kebeles were prioritized and recommended for laboratory analysis to be evaluated their potential for biomass energy values. As a whole, this ethnobotanical eld method was effectively applied following Bahru et al. [19], [20] and [21], which are conducted for other related ethnobotanical studies with diverse species in and around the semi-arid Awash National Park. Eventually, collected ethnobotanical data were feed to computer excel sheet and summarized, quanti ed and presented using non-descriptive statistical methods such as graphs, tables and percentages.

Results And Discussion
This particular study was focused on providing scienti c evidence for ethnobotanical assessment, identi cation and prioritization of high biomass energy producing plant species with short-rotation period at Boset District. This, in turn, evaluates their energy values at laboratory so as to solve the high demand of fuelwood problem and contributes to the sustainable management and use of resources through the application of silviculture.

Socio-demographic characteristics of informants
During ethnobotanical study, data were collected from three selected potential rewood and charcoal producing Kebeles at Boset District namely Borchota, Geri and Tedecha that consisting of 7 Kebele villages (Gots). These were Addis Ketema, Hadhecha, Hadhecha the Second, Harabona, Sogido, Bekebishan and Tedecha the Second. A total of 96 informants comprising 59 men and 37 women between the ages of 18 and 81 were sampled and participated ( Table 1). Most of the informants (99%) were categorized under the medium wealth class, while the remaining were grouped under low income informants.
Out of sampled informants, the youth and adults comprised 90.6% ( Table 2). Out of this, 86.4% contributed by men, while 97.3% shared by women. This indicated that most of the informants were under productive age and hence actively involved in rewood collection and/or charcoal making as well as management and utilization practices. Selected informants in the studied District indicated that 67.7% of the informants were engaged on this activity for more than 10 years, while 19.8% of them involved up to 10 years. At the same time, above 78% of the informants were married, while the remaining were single. The average family size of the sampled respondents was 4.63 children, with minimum and maximum family size of 0 and 12, respectively. Of these, over 43% of the informants were illiterate in their educational background, while 19.8% of them attended elementary school (Grade 1-6). This was followed by 17.7% of them, who attended secondary school (Grade 7-12) education or who completed adult education, each. On the other hand, 72.9% of the informants were lived for more than 20 years in the areas and most of them were familiar to forest and forest resources. Overall, the study result indicated that the socio-demographic factors were considerably contributed to for rewood collection and/or charcoal making at Boset District.

Socio-economic characteristics of the informants
Ethnobotanical study conducted in three Kebeles at Boset District revealed that informants diversify their income from different sources besides to provide their household consumption. These mainly included income from agricultural products; animal husbandry as well as income from rewood collection and charcoal production ( Table 3). The study result indicated that among the studied Kebeles, Borchota Kebele had the highest annual cash income (35.89%) from different sources, followed by Geri Kebele, which accounted for 33.08%. The annual average informants' cash income per household and its percentage contribution earned from different sectors is listed down in Table 3 as follows.
Cash income from agricultural products and livestock raising Data analysis showed that nearly 99% of the informants were farmers and they generate income from different agricultural crops. In the same way, 12.5% of the informants also engaged on livestock husbandry side by side with farming activity. Therefore, most of the informants generated money by selling their agricultural products and livestock in addition to their household subsistence. They earned at least an average annual income of 275 and 142.71 Birr per household from agricultural crops and livestock sale, respectively. These agricultural products were agricultural crops (e.g. maize, teff (Eragrostis tef), sorghum, beans, barley, etc.) and vegetables and fruits (e.g. potato, sugar beet, carrot, onion, etc.). Source of income from livestock sale also included fattened ox, sheep, goat, cow, hen, horse, donkey and mule. Of the total informants, majority of them (64.6%) owned 1-13 ha of land for cultivation of different agricultural crops and raising livestock. In contrast, the remaining informants possessed less than 1 ha of land, while others didn't have their own land and cultivate crops by renting the land (contract). However, the area was frequently affected by recurrent drought and characterized by erratic rainfall. For instance, some of the informants 7.3% showed that for the last three or four years cultivated crops were failed due to frequent drought occurrence and shortage of rain. As a result, they often faced a problem to subsidize their household income and live with Government funded and other supporting aid. Likewise, a similar trend was investigated in the study area by Moroda et al. [26], who found that 26.5% of respondents were most food insecure and thereby they subsidize their food by borrowing (9.7%) or through aid (17.9%). Consequently, they look for other alternative income generating activities including rewood collection and/or charcoal production from the surrounding woodland vegetation. Due this reason, source of income generated from cultivation of agricultural crops was the second in Borchota and Tedecha Kebeles. Income source from livestock raising also contributed almost the least across all Kebeles.
Income diversi cation from rewood collection and charcoal production Analysis of eld data indicated that informants in the study area engaged on various income generating activities hand in hand with farming activities. These were mainly on forest and forest products such as timber harvesting, rewood collection and/or charcoal making, beehive hanging and honey collection, harvesting medicinal plants for traditional remedies as well as collecting gum and resin products. However, source of income generated from charcoal making ranked rst both in Borchota Kebele (33.35%) and Tedecha Kebele (29.17%). On the other hand, collection of rewood was the list income generating activity in Tedecha Kebele (29.17%), followed by Borchota Kebele (21.39%). Similarly, the same trend was observed for informants' preference to charcoal production (2 nd ranked) rather than rewood collection (least ranked) in Geri Kebele. This nding most probably suggests that informants in the studied Kebeles were mainly depending on charcoal production instead of rewood collection since they generate better income source. Furthermore, 97.9% of the informants in the studied Kebeles engaged on rewood collection and/or charcoal making. This gure showed that informants were directly relied on rewood and/or charcoal for cooking, heating and lighting purposes using traditional open re or low e ciency traditional cooking stoves. This nding is in agreement with other previous study by Feyisa et al. [27], who reported that all of the sampled informants at Gechi District rely on fuelwood for cooking and lighting. Consequently, these authors further reported that 6529.9 tons/ha fuelwood on average is consumed by the community in the study area. Likewise, electric access in the rural setting is around 5% so that fuelwood has a signi cant contribution to rural population [2]. However, 54.2% of them used other sources of energy such as electric, fossil fuel, solar, crop and animal residues as main or alternative energy sources. As a result, income generated from these sources had signi cantly contributed to rural households to subsidize their livelihoods. Table 4 showed that 88.5% of the informants at Boset District involved in rewood collection, while 90% of them practiced charcoal making. Of this, more than half of the informants (55.2%) were men, who engaged by providing rewood and charcoal to the market. However, most of the time women and children spend most of their time to collect rewood from long distances and less accessible areas. But in this particular study higher contribution of men than women probably suggests the task requires more labour intensive under harsh environmental conditions. On the other hand, men participated in charcoal making since it requires a lot of traditional processes and labor intensive as well. Among the sampled Kebeles, more rewood collection and charcoal making was contributed in Geri and Tedecha Kebeles.
The average annual income from rewood collection and/or charcoal making, in turn, indicated that a total of 1,533.60 Ethiopian Birr per household was earned by providing to market areas including their village, along the Addis Ababa asphalt highway or Olenchit town (Table 5). Of these, 36.7% of rewood collection and 46.9% of charcoal making was contributed by women households. In line with this, the highest collection of rewood (41.5%) as well as charcoal production (41.2%) was supplied to the market to satis ed fuelwood demand by Borchota Kebele. On the contrary, the least annual income from both sources (26.7% of rewood collection and 27.7% of charcoal production) was generated by Geri Kebele.

Informants attitude and perception towards rewood collection and charcoal production at Boset District
The study result showed that local communities depend on various forest and forest products from the surrounding woodland vegetation. These were rewood collection and charcoal making; timber harvesting; beehive hanging and honey collection; traditional medicinal plants harvesting; harvesting of bamboo, wild fruits as well as gum and resin products. Among these, almost all of the informants (97.9%) engaged on rewood collection and/or charcoal making as compared to other forest and forest products. Findings from the study area corroborate this investigation and showed that charcoal sale is the main source of income for 83% of respondents [28]. With this, majority of the informants (72.9%) engaged on this activity for both household subsistence and to diversify their source of income. In contrast, 23.9% of them were required it only for household subsistence. Furthermore, collection of rewood contributed 55.3% of the average annual source of income at Boset District (Table 4). Similarly, an earlier study conducted in and around the semi-arid Awash National Park by Bahru et al. [20] revealed that rewood was the major source of energy, which accounted for 73% and an income generating activity in the livelihoods of many rural dwellers. In turn, about 30% of charcoal making is accountable for the forest degradation [28]. Hence, the majority of the local communities use fuelwood to cook their food, heat and light up their houses [20]. At the same time, contribution of charcoal production (86.9%) ( Table  3) attributed to most probably due to higher potential of Acacia species in the studied Kebeles. A study conducted by Balemie et al. [29] in Fentalle area, in turn, found out that rewood collection and charcoal making contributed 17.9 and 18.5%, respectively. According to Zerihun and Mes n [30], the Rift Valley vegetation is an important source of charcoal making for the nearby towns and Addis Ababa. As a whole, a study from 2015 reported that wood is harvested for the supply of 115 million m 3 rewood and 5.4 million m 3 charcoal [2]. In addition, traditional and low e ciency cooking stoves and open cooking re in the rural areas further contributes for the high demand of fuelwood species and thereby depletion of forest resources. This is because open cooking re and poorly designed cooking stoves may have 3-5% lower energy e ciency than high e ciency improved cooking stoves [9]. Therefore, a high e ciency improved cooking stoves instead of traditional low e ciency stoves and open cooking re can save the loss of energy from fuelwood [9].
With this understanding, most of the documented fuelwood species were indigenous or native (76%) to the area, while the remaining species were introduced or exotic to the study area. More than 33% of the informants described that they used introduced species for fuelwood consumption, while 7.3% of them did not use it. Analyzed data further showed that 27% of the informants pointed out that they used these species so as to control their invasiveness and hence their spread to the area. Again, their easier availability, their importance for source of fuelwood species and shortage of preferred fuelwood species in the study area also made informants to use introduced species. According to various sources and informants suggestion, these exotic species were introduced to the study area due to various reasons at various time. For instance, Prosopis juli ora introduced to arid and semi-arid areas to rehabilitate the dryland areas. Parthenium hysterophorus also introduced through food aid with agricultural crops. Other introduced species, which are used for fuelwood species also comprised Azadirachta indica, Calotropis procera, Cryptostegia grandi ora, Lantana camara and Senna occidentalis. Out of these, P. juli ora is served as a good quality charcoal producing species. In the same way, A. indica and C. grandi ora often used as charcoal producing species, while the rest introduced specis were collected and used as rewood especially during dry season, when fuelwood was scarce. On the other hand, above 6% of the informants were further relied on other sources such as timber harvesting; honey collection; traditional medicinal plants harvesting as well as collecting gum and resin. During data collection, best quality parameters commonly practiced by the local communities to identify and prioritize species for rewood collection and/or charcoal making were listed. These included superior combustion characteristics (giving good energy, heat and light); higher amount of energy, heat and light produced per dry wood; lower pollution problems (little or no smoke or soot and ash contents); formation of little/no spark during heating and lighting; easier to cut and split the wood; production of high energy with longer time as well as heavy wood's dry weight per volume (density) with minimum moisture content; fuelwood species are easily accessible to the area and hence easier to collect rewood and make charcoal. This nding was corroborate with earlier study conducted by Bahru et al. [20], who indicated that selection of rewood mainly relies on availability, burning quality, little/no smoke/soot production and moisture content. Some of these fuelwood characteristics also reported by FAO [9][10] and ILO [11]. Overall, a total of 25 rewood and/or charcoal species were identi ed and listed at Boset District during this eld study (Appendix 1).

Management and sustainable utilization of rewood and/or charcoal species at Boset District
Informants' interview clearly showed that majority of them (83%) indicated that local communities widely collect rewood and produce charcoal from natural forests around the study area. Consequently, all informants (96 of them) agreed that the most preferred and selected rewood and/or charcoal species in the study area were declining in terms of their distribution and population size from time to time due to various anthropogenic factors. Of these, 78% of the informants mentioned two reasons as the main cause for species decline at Boset District. These were rst local communities use these species as the only energy source and the demand for rewood and/or charcoal use becomes increased. Second, local communities commonly practiced the traditional open re or poorly designed traditional cooking stoves for cooking, heating and lighting purposes. This is attributed to the loss of most of the fuelwood species due to the high fuelwood demand in the area. On the other hand, 26% of the informants stated that the population size of rewood and/or charcoal species was declined over time at alarming rate. This is because in the study area overexploitation of fuelwood species particularly Acacia species for charcoal production is commonly practiced. For instance, a study conducted by Bahru et al. [20] around the study area, showed that during both preference ranking and pairwise comparison for charcoal production, all species are classi ed under Acacia species. By contrast, according to Feyisa et al. [27] report at Gechi District, the most preferred and harvested fuelwood species are Syzygium guineense, Maesa lanceolata and Albizia gummifera. Others also listed that due to the high demand for rewood and/or charcoal, the supply was increased to satisfy the local communities need. However, other study showed that overgrazing/over browsing and deforestation for various uses are the major threats to fuelwood species [20].
Nevertheless, 29.2% of the informants explained that local communities manage and conserve the most preferred and selected rewood and/or charcoal species in the study area using various ways. Some of these were plant seedlings; protect species from cutting; replant the species around homesteads, farmlands and farm boundaries once cut/harvested for the required use; proper collection of the product as well as demarcating and protect/conserve the forest. For instance, some of the local communities satisfy their demand for rewood and/or charcoal products through planting Acacia tortilis, Eucalyptus species, Ziziphus mucronata, Acacia robusta and Azadirachta indica plant species, which is similarly reported for the conservation and management of some of the species by Bahru et al. [20], Balemie et al. [29] and Hunde et al. [31]. According to some informants this species can be harvested within 3-7 years after planted for rewood and/or charcoal use. Collected data as well as researcher observation during data collection indicated that local communities planted these species around homesteads and fences, farmlands and farm boundaries as well as other marginal lands. They selected these areas mainly due to the fact that it enhances soil fertility, soil and water conservation as well as easy for proper management of seedlings. Others also preferred to grow plants around homesteads and fences, farm boundaries and other marginal areas due to shortage of farmland or such tradition was commonly practiced by the local communities. In general, this trend revealed that local communities at Boset District have the traditional system to manage and conserve the natural resources, as also similarly reported by Hunde et al. [31].
Therefore, future plantation establishment and management through the application of suitable silvicultural practices (e.g. spacing, thinning, pruning and coppice management) will be helpful to address the high demand of short-rotation fuelwood species within three or four years.
Identi cation, prioritization and selection of the most popular rewood and/or charcoal species at Boset District During ethnobotanical study, simple preference ranking followed by species pairwise comparison indicated that the best three most popular or commonly used rewood and/or charcoal producing species were selected. Accordingly, A. senegal was the most commonly used high biomass energy producing species, which ranked 1 st with a total of 267 scores given by key informants (Table 6). This was followed by Acacia tortilis (244) and Acacia robusta, which was selected with 244 and 42 total scores.
Major opportunities and challenges for the plantation development, proper management and sustainable utilisation of rewood and/or charcoal species In Boset District, there are many promising opportunities for small-scale plantation development, management and sustainable utilisation on most preferred and selected rewood and/or charcoal species. Some of these opportunities listed during informants' interview were provision of alternative energy and income source; untapped fuelwood resource; fast growing and short-rotation fuel wood species as well as high demand and fair price of products. Of these, about 99% of the informants listed the rst three opportunities for small-scale plantation development, proper management and sustainable utilisation on most preferred and selected rewood and/or charcoal species. Despite this fact there are major challenges and constraints for plantation development, management and sustainable utilisation on the most preferred and selected rewood and/or charcoal species in the study area. These major challenges were listed as follows: limited awareness on management and conservation of the resources (training, education, experts support and supervision, etc.); shortage of land to expand the resource; lack of market access and value chains for the product. Others included limited awareness on the use of the resource; shortage of quality and amount of seeds and seedlings; shortage of labor for quality and quantity product; lack of facilities and logistics to produce the product; government limited focus on the resource; high cost of labour and budget for resource management and conservation as well as various anthropogenic (agricultural and investment expansion, charcoal production, overgrazing/browsing, forest re) and natural factors (drought). Some of the aforementioned threats to fuelwood species further reported by Bahru et al. [20] and Balemie et al. [29], in the semi-arid parts of the Rift Valley area. Of these challenges mentioned above, the rst three were chosen by 96.9, 54.2 and 50% of the informants, respectively (Table 7).
Model development on selection of high biomass producing species at Boset District Major predictor variables were identi ed and a GLM was developed to predict the correlation of various socio-economic and demographic features of informants' with the selection of high biomass producing plant species at Boset District. A response variable and 13 major predictor variables were listed in Table 8 and described in detail as follows.
The developed GLM demonstrated that sampled Kebeles and informant's source of income generated from rewood collection and/or charcoal making was positively and signi cantly (p<0.001) associated to identi cation, prioritization and selection of high biomass producing plant species (Table 8 & Fig. 2a&b). In the same way, informants' main source of livelihoods also signi cantly (p<0.01) correlated but negatively (Table 8 & Fig. 2c). On the other hand, source of energy, informants' age and experience were signi cantly related (p<0.05) although years of experience was negatively correlated (Table 8 & Fig. 2d-f).

Conclusions And Recommendations
An ethnobotanical study was conducted in Borchota, Geri and Tedecha Kebeles of Boset District. This particular study was focused on providing scienti c evidence for assessment, identi cation and prioritization of high biomass producing plant species with high biomass energy. A total of 96 informants comprising 59 men and 37 women between the ages of 18 and 81 were sampled and participated during the study. Field data indicated that 97.9% engaged on rewood collection and/or charcoal making as compared to other forest and forest products. Out of these, 88.5% of the informants involved in rewood collection, while 90% of them practiced charcoal making. As a result, source of income generated from charcoal making ranked rst both in Borchota Kebele (33.35%) and Tedecha Kebele (29.17%). The average annual income from rewood collection and/or charcoal making, in turn, indicated that a total of 1,533.60 Ethiopian Birr per household was earned. With this, Acacia senegal, Acacia tortilis and Acacia robusta were the three best prioritized and selected fuelwood species for high quality rewood and/or charcoal provision at Boset District. The GLM con rmed that sampled Kebeles and informant's source of income signi cantly related to the selection of species at p<0.001, while informants' main source of livelihoods correlated at p<0.01. By contrast, source of energy, informants' age and experience were signi cantly related at p<0.05. Most of the documented fuelwood species were indigenous or native (76%) to the area, while the remaining species were introduced or exotic to the study area. Some of these introduced species were P. juli ora, P. hysterophorus, A. indica, C. procera, C. grandi ora, L. camara and S. occidentalis. Analyzed data further showed that 27% of the informants pointed out that they used introduced species so as to control their invasiveness and hence their spread to the area. Higher e ciency to provide energy, heat and light; little or no smoke or soot, spark and ash contents; easier to cut and split the wood, heavy wood's dry weight per volume (density) with minimum moisture content as well as easier availability were some of the main selection criteria for rewood and/or charcoal species in the study area. Collectively, 29.2% of the informants explained that local communities manage and conserve the most preferred and selected rewood and/or charcoal species in the study area using various ways. At the same time, there is also a growing practice in the community to use improved cooking stoves for cooking, heating and lighting to save the energy. Limited awareness on management and conservation of the resources; various anthropogenic and natural factors as well as limited awareness on the use of the resource were the major challenges listed by informants. Local communities should also use improved cooking stoves such as Mirt and Gonzie for baking Injera while Tikikil and Lakech for other services instead of traditional open re cooking materials to save energy, rewood supply and/or charcoal production and even to avoid accidental re incidence. Furthermore, to save the loss of energy during carbonisation process, charcoal makers should practice improved earth mound kiln instead of traditional earth mound kiln. Future plantation establishment and management through the application of suitable silvicultural practices (e.g. spacing, thinning, pruning and coppice management) will be helpful to address the high demand of short-rotation fuelwood species within three or four years. The most preferred fuelwood species (A. senegal, A. tortilis and A. robusta) in the area should be further tested at laboratory to evaluate the energy value for further promotion and developing management strategy.

Declarations
Ethics approval and consent to participate: This study was conducted by involving only participants, who have a full consent to offer their traditional knowledge for research purpose. All the participants provided prior informed consent before the interviews. Accordingly, each informant accepted the request and signed for his/her consent before the interview on the informant's interview consent form. Therefore, "Informed consent was obtained from all individual participants included in the study." Consent for publication: Not applicable.
Availability of data and materials: Data in the current study are available from the corresponding author upon reasonable request from Central Ethiopia Environment and Forest Research Center (CEE-FRC)/Ethiopian Environment and Forest Research Institute (EEFRI).
Competing interests: The authors declare that they have no competing interests.
Funding: All the nancial cost and required research logistics of the project was fully funded by Central Ethiopia Environment and Forest Research Center (CEE-FRC)/Ethiopian Environment and Forest Research Institute (EEFRI). The authors also declare that the funding body has no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.
Authors' contributions: TB initiated and wrote the research activity, carried out the eld study and collected data and wrote the full write up manuscript. He also responsible for revision and for reading digital proofs. BK commented and revised the full write up research proposal and manuscript. AT commented the full write up manuscript. All authors read and approved the nal manuscript.

Figure 1
Location of Boset District at East Shewa Zone of Oromia National Regional State, central Ethiopia Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.