Ethnobotanical study of medicinal plants in the environs of Tara-gedam and Amba remnant forests of Libo Kemkem District, northwest Ethiopia

Background Remnant forests found in areas that have long been converted to agricultural landscapes are refuges of wild useful plants; and societies inhabiting them are custodians of rich indigenous botanical knowledge. This study was undertaken to document the medicinal plants used by the people living in and around Tara-gedam and Amba remnant forests, northwestern Ethiopia, together with the associated ethnomedicinal knowledge. Methods Data were collected from 105 informants through semi-structured interviews, guided field walk, market survey; and analyzed using standard ethnobotanical analytical tools including ranking and comparison. Results A total of 163 medicinal plant species in 145 genera and 67 families were recorded among which Zehneria scabra drew the highest community consensus. Seventy-one percent of the medicinal plants were those used for treating human ailments only, 21% for both human and livestock and 8% for livestock only. Asteraceae, with 14 species, had the highest number of medicinal plant species. The medicinal plants mainly (79.1%) belong to the shrub and herb categories and most of them were sourced from the wild habitats. Leaves and fresh plant materials were more frequently used for medicine preparation than other parts. Protected government and church forests as well as tree propagation in nurseries followed by planting them and local practices constitute the major forest conservation efforts that indirectly protect the medicinal plants in the area. Elders and healers knew more about the medicinal plants, their distribution, the local ethnomedicinal practices and knowledge transfer patterns. Though important for the local healthcare system and with potentials for modern drug discovery, both the plants and the knowledge pool are under threat. Conclusion The diversity of medicinal plants and the associated indigenous knowledge of Tara-gedam and its environs are of a considerable value to the local community and beyond. There is, therefore, a need for conservation of the vegetation and the medicinal plants along with preservation of the wealth of the indigenous knowledge.


Introduction
The relationship between plants and people is studied in ethnobotany, a field focusing on the study of the indigenous knowledge on how plants are perceived, used and managed [1,2]. Indigenous knowledge refers to the knowledge, rules, standards, skills and mental sets generated by and kept in custody of local people in a particular area [3]. It is the result of many generations and long years of experiences, careful observations and trial and error experiments [4]; and this study focuses on the medicinal plants and the associated ethnomedicinal knowledge in the environs of Tara-gedam forest. The cultural and spiritual identity of indigenous peoples is often linked to intact primary forests with their rich biodiversity [5]. Hence, plant resources possess and preserve cultural heritages, biological information and indigenous knowledge on plant identity and utility [6]. The ethnobotanical literature [7] underlines that both saving plant species and documenting and preserving indigenous knowledge associated with them are fundamental urgent concerns. There are around 6,000 species of vascular plants in Ethiopia, out of which more than 14% are said to have been used as traditional plant medicines (TPMs) [8], while more than 1,000 species have been documented at the National Herbarium (ETH) database. Despite their treasured contributions, in particular in Ethiopia, thus far TPMs have been offered very little attention in modern research and development, while less effort has so far been made to upgrade the traditional herbal medical practices [9]. For the most part, the potential of practitioners of traditional herbal medicine to serve as partners in the process of drug discovery and in providing healthcare services is not equitably acknowledged [10]. Hence, documenting traditional medicinal plants and the related traditional medical knowledge is important in order to facilitate the discovery of new sources of drugs and promote sustainable use of natural resources in Ethiopia [11]. Tara-gedam forest, selected for the study, is among the national priority forest areas in Ethiopia [12] and Amba forest is found adjacent to it. Both these remnant forests are known as species rich forests in Amhara Region, and the nearby local communities are in constant interaction with the plant resources [13,14], particularly so for those living in the forest fringes. Research revealed that urbanization in Ethiopia had tremendous impacts on the useful plants and the practice of traditional medicine [15]. Since Taragedam and Amba forests are found adjacent to the growing Addis Zemen Town, the impacts have already been alluded to by some researchers [14]. The local people, as in other parts of Ethiopia depend on traditional medicine, which mostly relies on medicinal plants, to fulfill their healthcare needs as pointed out by Zegeye [14]. Despite this fact, there are no studies on ethnomedicinal plants and the associated knowledge in the environs of Tara-gedam and Amba forests. Hence, this study was framed with the aim of documenting the medicinal plants and the associated ethnomedicinal knowledge of people living in the environs of Tara-gedam and Amba forests.

Material and methods
The study area and the demographic background The study was conducted in the general environment of Tara-gedam and Amba forests, located in Libo Kemkem District (Wereda) in the South Gondar Zone of the Amhara Regional State, northwestern Ethiopia located at around 12°04.351′-12°10.926′N and 37°44.266′-37°50.057′E. Tara-gedam forest ranges from 2062-2496 m a.s.l. and Amba from 2011-2541 m a.s.l. with the highest peak at Mt. Deboch. The climate data obtained from the National Meteorological Service Agency of Ethiopia shows that the mean annual maximum and minimum temperatures of the study area are 32.8°C and 8°C, respectively. The District receives a uni-modal rainfall of approximately 1300 mm per year and about 95.1% of the area is under moist weina dega (mid-highland) while the rest is under the wet Dega (highland) [16]. Medium and cold highland climatic features characterize the study area. The vegetation of the area belongs to the dry evergreen montane forest type consisting of forests, bushlands, shrublands and enrichment plantation interspersed with stands of natural vegetation [14]. Archival information [16] shows that forested land is about 4,429.5 hectares. Libo Kemkem District, in particular Tara-gedam, has several recreational sites. Mt. Kualla, along with diverse geographical features of the forest, Tara-gedam Monastery and many caves and forested churches are very useful for archaeological studies and for the tourism industry [17]. The 2007 census report of the Central Statistical Agency [18] of Ethiopia shows that Libo Kemkem District has an estimated population of 209,451 (106,564 males and 102,887 females). The inhabitants are mostly members of the Amhara ethnic community who speak the Amharic language with economies that are predominately based on rain-fed subsistence cultivation of crops mixed with livestock production [16]. There are 58 health services in the District [19]. Malaria, intestinal helminthiasis, and pneumonia were the top three human diseases and the major livestock ailments were pasteurllosis, anthrax, internal and external parasites, black leg, sheep pox, trypanosomiasis, respiratory tract infection, rabies and coccidiosis [20].

Site selection methods and procedures
Before starting the ethnobotanical study, contacts were made with various offices (District administration, tourism and culture, agriculture and rural development, traditional healers' association and health affairs) to seek permission to carry out the study by informing them about the aims and significance of the study. Letters authorizing the study were obtained from the relevant offices which were then presented to the concerned kebele (lowest administrative unit in Ethiopia) offices, forest scouts and informants in the study area. In this way, full legal procedures were followed and the informed consent of interested participants was obtained. Twelve rural villages, namely: Agamoch, Kidanemhret, Tibabosgie, Washa Indiras, Aguat Mafsesha, Mantogera, Abay, Kualla Yihuans, Yifag Akababi, Lomiye, Abuarra, Asiba Mariam and the town Addis Zemen were selected around the two forests. These villages are within the seven kebeles ( Figure 1) selected for the study. Relative distance, community-forest interactions and altitudinal differences were the basic site selection criteria. Relative distance and community forest interaction were taken as criteria after collecting information from forest scouts, kebele administrative offices and inhabitants of the area during the reconnaissance survey in order to compare the indigenous knowledge of the communities found nearest to the forest with those found relatively far away (reached after traveling for more than five kilometers). This was undertaken from November-June 2010.

Informant selection and approaches
One hundred five informants (85 males and 20 females) aged 19 to 84 were interviewed in this research. Among these, 45 (42 males and three females) were key informants and the rest 60 were general informants. Purposive and random sampling techniques were employed to select traditional herbalists and general informants respectively. The traditional association leaders, members of the tourism and culture office, elderly people and religious leaders helped to identify the key informants. In addition, the identified traditional practitioners and members who had earlier been treated by the healers also helped to identify other traditional experts. The general informants were randomly picked (from the list of inhabitants) during field and house visits (5-7 in each study site) by checking their names from the list of residents obtained from kebele offices. All interviews were administered after obtaining voluntary consent of each informant and assuring them that the data will be used only for academic purposes.

Ways of data collection and type of data collected
Ethnobotanical data were collected during three months from November to January 2010 by living in close contact with the community in the study area, following standard methods [2,4,21]. Accordingly, semi-structured interview, guided field walk, direct observation, market survey and focus group discussions with key informants and other knowledgeable community members were applied and their knowledge on medicinal plants gathered.
Interviews were held based on checklist of questions prepared before hand in English language and simultaneously translated into Amharic. Interviews focused to informant's demographic features including sex, age, marital status, occupation, religion, educational background, and duration of time an informant lived in the study area, and indigenous ecological knowledge (traditional ways of classifying vegetation, plants, landscapes and the soils in the area). The major part of the interviews were focused on the local names of medicinal plants used, their habits and habitats, plant part/s used, remedy preparation methods, materials used during preparation, condition of preparation, storage method, additives/ingredients used during preparation and administration, dosages administered, and route of administration. Likewise, side effect of the medicine (if any), use of antidotes for adverse effects, any taboos associated with medicinal plants, the season, month, dates and time of collection and preparation of plant medicines, and market value were also included. Further, the distribution (status) of medicinal plants, the interaction of healers with the District administration, threats and major problems, conservation methods, source of knowledge and ways of transfer and number of years of service as traditional healer were also the major interview points targeted, following the methods used by previous investigators [2,4,22].
The semi-structured interviews held with informants usually started at their sitting places and further broadened into field walk with interviewed informants in order to see the plants mentioned in their habitats and voucher collections following Martin [4]. This activity further helped to record growth habits of medicinal plants. Focus group discussions were done with traditional medicinal plant association members, other herbalists, monks and general informants to obtain additional information and to check the reliability. Informants were contacted two to three times and responses of an informant in harmony with each other were taken as relevant and used for data analysis. At times, the preparation methods of the medicinal plants were said to be secret and were not included during discussion. Most field observations were conducted with a single informant in order to keep the knowledge top-secret as this was what the healers in particular preferred. Some of the traditional healers were genuine herbalists, well-known by the local community and owned traditional home pharmacies derived from plant remedies. They were asked to demonstrate their work at their homes and in the field, which was recorded in order to check the consistency in knowledge and practice on the preparation of remedies and their effectiveness. The patients encountered at healers' homes were also asked about the traditional plant medicines they have used and their effectiveness when applied by healers.

Plant collection and identification
Voucher specimens were collected for each plant species during guided field walk with the informants. At times, the field activities included taking notes on plants and the associated indigenous knowledge with preliminary identification of the plants to family and sometimes to species levels. Photographic records were also taken in the field to capture the field sites, plants and other useful memories. The specimens were dried, deep-frozen, and determinations were made at the National Herbarium (ETH), Addis Ababa University, using taxonomic keys and descriptions given in the relevant volumes of the Flora of Ethiopia and Eritrea [23][24][25][26][27][28][29][30][31] and by visual comparison with authenticated herbarium specimens. Finally, the accuracy of identifications was confirmed by a senior plant taxonomist and the voucher specimens with labels were deposited at the ETH.

Data analysis
The ethnobotanical data were analyzed using Microsoft Office Excel spreadsheet (2007) and SPSS version 20 software. The former was used to calculate sum, percentages, tabulate and draw graphs whereas the latter was used to generate results of descriptive statistics, and perform t-tests as well as draw graphs and charts. Ethnobotanical ranking and scoring methods such as preference and direct matrix rankings as well as pair-wise comparisons and informant consensuses were employed to distinguish priority species and to check consistency.
Preference/priority ranking activities were employed on six most preferred and widely used medicinal plant species for the treatment of wound and the most threatened medicinal plants. Direct matrix ranking was employed for the six most widely utilized multi-purpose plant species and for the five factors considered most threatening to medicinal plants. Pair-wise comparison was made on six of the most preferred and commonly used medicinal plants against stomachache. To do this, the number of possible pairs was determined by applying the formula n(n-1)/2, where n is the number of medicinal plant species being compared. For all the above ethnobotanical ranking and scoring techniques, the same seven key informants who had long time practical experience in traditional plant medicine preparation, administration and collection were engaged. The strength of knowledge of the key informants was evident to the first author who witnessed the clarity of explanations and accuracy of actions. The overall procedures for these activities were conducted following standard ethnobotany texts [2,4,22]. Informant consensus factor (ICF) for different ailment categories was calculated to test agreements of the informants on medicinal plant knowledge of each category by using the formula ICF = Nur-Nu/Nur-1 where, nur is the number of uses reported in each category and Nu is the number of species reported in each category [32].

Ethical consideration
All data collections were done with special care on the base of the cultural view of the local communities in the study area. Informants were also informed that the objectives of the research were not for commercial purposes but for academic reasons. Since, ethnomedicinal indigenous knowledge is only obtained from traditional specialists within the community so any value that will obtain as a result of the research will benefit the community. According to ethnobiology code of ethics indigenous knowledge should be protected and a part of the value generated should be transferred back to the authors of the knowledge. Finally, informants were accepted the idea and came to reach an agreement.

Demographic features of the informants
Of the total informants, 46 were in the age group of 51-85; 51 were illiterate and the greater proportion (88) belonged to the married category. Almost all informants (101) belonged to the Ethiopian Orthodox Church. Parallel to the population structure, there were more males than females who were willing to be included among informants as indicated by the demographic profile in Table 1.
Most informants (70) were farmers, 11 of them were house wives, seven were students and other groups were represented by fewer numbers. Of the total informants, 99 lived in the study area since birth and the rest have lived there from six to 20 years.

Indigenous ecological knowledge of people in the study area
The inhabitants of the study area are owners of rich ethnobotanical and ethnoecological knowledge as demonstrated by their wide array of knowledge on environmental matters. They classified the land forms; vegetation and soil based on knowledge surviving from ancestral practices ( Table 2), now evident through their elaborate emic categorization systems.

Medicinal plant diversity and distribution
The study documented 163 species of medicinal plants belonging to 145 genera and 67 families. Three of the families had ten or more species each and the details are given in Table 3 and Table 4. The medicinal plant use reports showed that six species were cited by more than 20 informants each (Table 5). Twelve species were cited for the treatment of six and more ailments each (Table 6). Achyranthes aspera came out on the lists of both most effective and most cited medicinal plants and the details are tabulated (Table 4 and Table 5).
Among the reported medicinal plants of the area, some were also reported as wild edible plants (Table 4). Informants, during data collection, said that some of the species for example, the edible parts (fruits) of Rosa abyssinica are used to alleviate weakness or tension when eaten by children in the field. This is done without knowing the medicinal effects of the plants and those who eat it feel happy and accomplish their tasks effectively. Herbs accounted for 67 (41.1%) species followed by shrubs (62, 38.0%), trees (24,14.7%) and climbers (10, 6.1%). The medicinal plants occur in the wild, homegardens and in both premises. The forests, farmlands, margins, living plants on fences, roadsides, around homes, fallow lands and riversides are the habitats where the medicinal plants are found ( Figure 2).  Table 8).

Importance of the medicinal plants
Some medicinal plants were rated as important and used frequently by many, appearing in many formulations. Preferences for six common medicinal plant species said to be used for the treatment of the common ailment (wound) showed Cordia africana in the first rank order followed by Sida rhombifolia ( Table 9). The pair-wise comparison of medicinal plants used for the treatment of stomachache showed that Stephania abyssinica was the most reported and ranked first, while Otostegia integrifolia was the least ranked plant species (Table 10). Matrix ranking of six popular multipurpose medicinal plants showed that Cordia africana was the most useful multipurpose medicinal plant that was ranked 1 st while Croton macrostachyus was the least ranked one (Table 11).

Plant parts used and modes of remedy preparations
Out of the total plant parts used for remedy preparation, leaves were the highest (109, 31.2%), followed by roots (108, 30.9%) and lower values for other parts (Table 12). Information about the preparation of each plant has been included in Table 4. The results also showed that the majorities of remedies (89%) were prepared from single plant species and few (11%) were prepared from combinations of more than two medicinal plant species. Simple modes of preparation of medicine including crushing (90.5% informants), chewing, pounding, chopping and juice extraction were used ( Table 13).

Condition of preparation and storage of plant medicines
The results of the analyses showed that 70.94% of the plant medicines were prepared from fresh plant parts, 9.69% from dried and 19.37% from both fresh and dried parts. Healers explained that some of the stored remedies were kept for about one year, from September to September of the next year and discarded on the Ethiopian New Year and replaced with new preparations. When a particular medicinal plant could not be                       accessed easily, the previously stored remedy would be buried in the ground for one day (from the eve of the end of the first day of the New Year), after which time it is declared safe to be used. It was explained that remedies were stored secretly in a very secure place (mostly outside the living house at the top of the wall to keep them far from children) and no one is allowed to touch them without permission.

Route of remedy administration and dosage determination
It was found that the local people employ about 10 ways of medicine administration routes with varying frequencies.
Of the total, 157 (44.9%) prescriptions were mainly those said to be applied through oral route (   frequently mentioned by the traditional healers. Coffee and milk were mentioned for use as antidotes when formulations were made from Euphorbia abyssinica, for malaria, and Calpurnia aurea for diarrhea and anesthesia. Likewise, local beer (TELLA) is used as antidote when Asparagus africanus is used to treat impotence. The traditional healers indicated that they use the antidotes for dilution in cases of adverse effects.

Marketed medicinal plants in the study area
Survey of two towns in the proximity of the study sites (Addis Zemen and Yifag) did not show any medicinal plant mentioned during the interviews presented on the market. The respondents explained that most healers prepared and sold traditional medicinal plants in the home rather than in the open market. Healers usually had big signposts in front of their homes listing the health problems they treat. Some medicinal plants were marketed mainly for other use values (spices and food) but once bought they could be used as medicine at home as part of the common family home treatment. These include Allium sativum, Ruta chalepensis, Brassica carinata and Cicer arietinum usually traded for use as edible spices.

Taboos connected with handling and use of medicinal plants
Some of the taboos reported by experienced medicinal plant experts concern times of collection, ways of collection, preparation materials, administration and storage. Most of the medicinal plants were said to be collected on Wednesdays and Fridays in the early morning hours without contact and without talking to any other person and this is related to healers' beliefs that doing it otherwise would reduce the efficacy of the herbal medicine.
In the preparation of a single remedy, plant parts are mostly taken from individuals of the same species growing in three or seven different places. One healer said that this increases its remedial effectiveness. This could be a way of balancing the amount of phytochemical and pharmacological constituents based on habitat variation. Collection materials are KARA (kind of knife), ANKASIE/TORE (metallic spear), WEYRA EJETA MEKOFERIA (digger with handle made of Olea europaea ssp. cuspidata wood) and most of the time stationary stones are the preferred preparation places. It was mentioned that sexual intercourse is forbidden for healers and patients alike during any medicinal plant collection, preparation and application.

Variation of indigenous plant knowledge in the study area
Significant correlation (Spearman correlation test, r = −0.450, α = 0.05, p = 0.046) was observed between male and female informants on the number of medicinal plant species they knew. The test, however, did not indicate significant correlation between healers and general informants (Spearman correlation test, r = −0.002, α = 0.05, p = 0.991) regarding the number of medicinal plant species they reported. The comparison of knowledge and experience of age groups (35-50 and 51-84) showed significant differences (P < 0.05) while there was no significant difference between age groups 19-34 and 35-50 considering plant names and the respective medicinal uses (t = 0.05, two tailed and df = 52). Progressively increasing results were obtained with increasing age of informants ( Figure 3). Local community members in Washa Indiras, Kidanemhret and Kualla Yihuans gave 162, 95 and 91 medicinal plant names with 128, 95 and 86 medicinal uses respectively. Informants from Washa Indiras village reported the highest plant names (162) and uses (128), while those in Yifag Akababi and Asiba turned in the least numbers (58,56) and uses (52,50) respectively. However, not all communities living nearby the forests gave higher reports compared to distant villages. For example, Tibabosgie is the nearest village to the forest, but the report from informants showed relatively lower names (48) and uses (50) than the other villages found relatively far from the forest, namely Abuarra (92 names and 80 uses), Lomye (73 names and 80 uses) and Agamoch (69 names and 66 uses). On the other hand, Mantogera village is located nearest to the forest, but the results showed 61 names and 61 uses, which is less than other nearby villages in the same (woina dega) agroclimatic zone. Furthermore, in Aguat Mafsesha located at higher altitude of all villages found in dega agroclimatic zone, showed that informants could only recall a few species and uses (40 names and 43 uses). Generally, however, informants in villages near the forest knew more plants (38.5%) and uses (38.9%) than those located in towns (30.3%, 30.0%) and far away from forests (30.8%, 31.5%).

Indigenous medicinal plant knowledge development and sharing
Traditional knowledge of medicinal plants in most cases is passed along the family line from parents and other intimates, especially gifted family members (which they described as EJU YEMISEMRLET, meaning one whose hands are skillful and effectual). Some of the traditional knowledge is generated through the community by listening and practicing while some copied secretly and systematically by following and observing the knowledgeable individuals at times of medicinal plant collection and preparation. Others develop and transfer their medicinal plant knowledge to generations by following up healers after seeking treatment of their family members. In very few cases, individuals developed their medicinal plant knowledge upon careful observation of domestic carnivores, especially the cat, which immediately consumes medicinal plant parts upon preying on poisonous snakes, scorpions and spiders. One healer reported his discovery in this way of Vernonia adoensis for the treatment of snake poison. Medicinal plant experts have developed some traditional medicinal plant knowledge from observations of animal feeding to know the plants that are never consumed, which hints at plants not for internal use to ensure safety of the vital organs but rather used for the treatment of dermal ailments such as wounds because of their possible toxic nature. Furthermore, experienced medicinal plant experts create new medicinal knowledge by relating the plant odour with previously known medicinal plants. Some healers were seen recording ethnomedicinal knowledge in small notebooks during fieldwork, which may testify their curiosity and keenness to develop and transfer indigenous knowledge to the next generation.

Threats to and conservation of medicinal plants and associated indigenous knowledge
The study found that medicinal plants are faced with threats in their habitats. Informants claimed that long before the past ten to twenty years Tara-gedam and the surrounding areas were full of natural vegetation around the farmlands, riversides and grazing lands in addition to the wealth of plant species in number and diversity in the forests. They further asserted that in those days almost all the medicinal plants were easily accessible within short distances of the living place. Today, it is not an easy task to get medicinal plants out of Tara-gedam and Amba forests due to habitat modification. Most informants perceived that agricultural expansion was the main threat to medicinal plants, firewood collection the next and others follow (Table 15). Similarly, preference ranking of five most threatened medicinal plant species indicated that Withania somnifera and Huernia macrocarpa are the two most threatened medicinal plants (Table 16). Through further discussion and interview with informants, 63 plant species that were said to have become sparse in distribution were recorded along with five species restricted in occurrence and in most cases found in the homegardens in recent years ( Figure 4).
Conservation efforts specifically targeted to medicinal plants do not exist in the District. However, some of the medicinal plants are raised in the governmental nurseries for other purposes and conserved in the protected governmental and Orthodox Tewahedo church forests. The well known Tara-gedam and Amba natural forests and other relatively smaller patches of vegetation and plantations found in each kebele are nowadays being protected by the local people living around the forest fringes in collaboration with the government. Some of the medicinal plants occurring in the Orthodox Tewahedo church forests were Adiantum capillus-veneris, Clerodendrum myricoides, Juniperus procera, Millettia ferruginea, Schefflera abyssinica, Urera hypselodendron and Ziziphus spina-christi. The informants elaborated that some of the medicinal plants collected from the  Furthermore, the District administration has started considering the indigenous knowledge of the people as testified by the priority given to establish traditional health practitioners association along with the provision of some technical training and discussion on biodiversity conservation concepts. A good justification for the above scenario is the observation during our field study in the area the mutual exchange of knowledge and remedies at the time of monthly meetings. The first author had a chance to participate in two of their meetings and was kindly given permission to record the information.

Discussion
Despite the efforts made, only few women could take part in the study partly because of the tradition and being the usual case when the interviewers are men as in our case. Women are generally not expected to appear in public or discuss with stranger men both by society  and family (husbands deny permission in most cases) or other socio-cultural reasons, which our female informants refrained from describing openly. There were very few women practitioners in the community. More informants are expected to yield more knowledge of plants procured from the wild as was reported by other researchers [33][34][35]. The rich ethnoecological knowledge was revealed in their elaboration and categorization of the ecological units. They recognized six landscape, five soil and five vegetation types, reflecting their deep understanding of the differences and similarities in these key environmental components. This emanates from the ethnobotanical/ethnoecological knowledge that was shaped over generations and which they use for describing, managing and utilizing the land, the soil and vegetation. Their knowledge also stretches to the individual plants which they grouped into use categories, morphological classes and adaptive forms. Soils which were identified based on colour and texture are applied to determine and select those suitable for the type of crop varieties to be grown on a specific land. This knowledge shares similarities with the modern classification system [36] and the system used in another part of Ethiopia [37]. Such broad-based indigenous knowledge systems are indicative of prolonged experience, relationship and interaction of people with the biotic and abiotic components of the environment as rightly described for other areas in Ethiopia [38][39][40]. The top three families (Asteraceae, Fabaceae and Solanaceae) reported in this study are among those represented with higher number of taxa in the Ethiopian flora [39][40][41][42][43][44] and also found to have higher number of medicinal plants by other researchers working in other parts of Ethiopia [45][46][47]. This might be related to possession of more species that are widely distributed in almost all ecological areas and habitats since the Fabaceae and Asteraceae are respectively the first and third largest families of angiosperms in the Ethiopian flora [48]. These two families have many uses for the community as reported by other researchers [44][45][46]49]. The diversity of genera and families (29 with 2-14 species in many genera) is a good indication for the study area    [34,[39][40][41][42][43][44]46,[49][50][51][52][53][54][55][56][57][58][59][60] suggesting that while the knowledge is shared in some respects it also has some uniqueness to the study communities.
The finding that shrubs and herbs were the most abundant medicinal plants indicated that people rely more on such plants, which may relate to the fact that they are relatively common compared to other growth forms. Other researchers [41,47,53,59,61] also found that shrubs and herbs are the most frequent medicinal plant species. Most of the wild medicinal plants were accessed from Tara-gedam and Amba forests. Healers and some knowledgeable members of the local community were seen cultivating some medicinal plants in their homegardens for easy access and use of fresh parts at times of remedy preparation. The distribution of medicinal plants in the wild, homegardens and in both premises [39][40][41]62,58] as well as finding of more species in the wild environments were reported by other researchers [33,43,47,62] in Ethiopia and other countries [63,64].
Use of diverse plant species in the treatment of ailments implied that the people of the study area to date prevent and cure human and livestock ailments with plant materials collected from the surrounding areas. Less number of livestock diseases and medicinal plants were reported compared to those of humans, which could probably be due to the fact that the people give more attention to human ailments compared to livestock diseases. Generally, the local people affirmed that they first try to find medicines for human ailments and then search for remedies for livestock ailments as reported in other areas [38]. The healers also mentioned that they refer to the pharmacopeias (ancient herbals written on parchment) to learn about medicinal plants and treatments for human diseases. Traditional pharmacopeias have also helped to transfer the knowledge to more people. Treatment of human ailments like womb problem, sterility of females, prolonging the life of embryos in the uterus, expelling foreign particles from the eyes and ears, and livestock ailments like increasing sexual  Higher ICF values as in external parasites, beating with stick and sun stroke in the case of livestock, and febrile illness, headache, anemia, brain tension and malaria in human being are indicative of the presence of similar ethnomedicinal plant knowledge and their continued usage in similar ways among community members [32,64] as also reported from other parts of Ethiopia [39][40][41].
Cordia africana, the most multipurpose species as in other areas [62], would be imagined to be most threatened in the future. The clue to this is its rare occurrence with sparse distribution around farmlands and some homegardens. This scarcity was due to over harvesting not only for medicinal purpose, but also for other uses, notably for timber production. All of the medicinal plant species and the top ranking ones in particular need urgent conservation actions and adoption of a suitable system of sustainable use.
The preferences of leaves and roots to other plant parts could be attributed to ease of preparation, the presence of medicinally active secondary metabolites and accessibility at the required time in the same manner as described for western [34], southern [45][46][47]53,[59][60][61], northern [41,58], central [62] and eastern [65] Ethiopia and other countries [63,64]. The use of leaves for medicinal purposes is less likely to be destructive especially relative to the use of roots. The latter is likely to have negative influence on the survival of the plant. Cultural practices and beliefs requiring digging up of three or seven plants to prepare just a single remedy have been recorded. In some cases three or five or seven pieces each had to be removed from the same or different individual plants and applied to cure the disease, which would likely be unfavorable to conservation. Preparations made from all parts, three and two plant parts for remedy formulations (few in our case) may endanger the species unless mechanisms for sustainable utilization are put in place. Single plant preparations are easier to extract the curative chemical compounds as reported by others [33]. However, mixtures are expected to be more effective due to the additive effects of the combination of plants by increasing the compounds that could act on different pathogens.
Higher frequencies of crushed forms could be related to the ease of preparation at any place, using stones at most, which could be done by most local community members. Informants asserted that medicinal plant parts crushed and soaked in water lead to effective and immediate response to health problems. Crushing came out as the most frequent preparation method in other works [38]. A prescription that required crushed roots of Asparagus africanus concocted with honey and stored for seven days in a bottle was used for the treatment of impotency. Healers explained that such a preparation helps to extract the active chemicals and this is analogous to the methods used in modern phytochemical and pharmacological extractions using different solvents in the laboratory. This hints at a fair understanding of the local people about the science behind the traditional practices of herbal remedy preparation and treatment. About 71% of the medicinal plant remedies were prepared from fresh plant material highlighting that live medicinal plants have to be found near homes for instant use. Most herbalists advised that fresh material are more effective for treatment than dried forms further elaborating that drying could easily distort the efficacy of the medicine, and that stored plant medicine is culturally less liked and was also reported by other researchers [41,53,59] in Ethiopia. In modern herbal medicine, some secondary metabolites having active healing potentials are known to be quickly transformed to permanent compounds losing their healing power soon upon cutting [5,8]. The  use of dried plants and stored remedies were reported by very few healers, who said that they use dried plant material when availability of fresh material is seasonal. Dependency on fresh material is likely to throw the species to serious threats as had been warned by other sources [39]. Informants affirmed that after the New Year holiday, preparations from the past year could not have the potential to cure ailments if not buried on the eve of the holiday upto the next day to respect the cultural and religious beliefs. The newly prepared remedies are believed to have active constituents such as (volatile oils and other phytochemical and pharmaceutical ingredients) and these could be lost progressively due to factors including temperature, oxidation and reduction. This tradition of collecting most of the medicinal plant materials once in a year has the merit of minimizing overharvesting. Various sources from central [33], western [34], southern [46,[58][59][60], eastern [62] and northern [41] Ethiopia proclaim that oral route is most frequent. Some sources [33,34,58] that recorded measurements for remedies in a similar manner to ours noted the lack of precision and standardization as a drawback of the traditional herbal healthcare system. Additives are included in the medicines to minimize discomfort, improve the taste and reduce adverse effects such as vomiting and diarrhea, and enhance the efficacy and healing potential as explained by the informants. Mixing and using some medicinal plants with common foods and drinks is an easy way for effective treatment, particularly for children and facilitation of ingesting bitter tasting formulations as described in other sources [33,34,58].
The recorded taboos and other ritual-like actions related to the collection, preparation and administration of traditional medicine are beliefs carried over generations in the study area in a similar manner to the research results reported from Bale [52] in southeast Ethiopia. The  interpretations correspond to healers' perceptions of medicine and disease treatment whose scientific verification awaits further studies. Elderly members of the society (aged 51-85 years) had expectedly more knowledge on medicinal plants and their uses due to their long-lasting direct and regular contact with the forests and other plant resources. In contrast, the younger generation is more exposed to modern education and hence not interested in learning and practicing the ethnomedicinal wisdoms, which may affect the continuity of indigenous knowledge. Medicinal plant knowledge difference among age groups was also reported in other studies [2,45,59,66] but one study from southern Ethiopia [47] deviated from this.
People living far away from forests (Asiba and Yifag Akababi) knew relatively fewer species than those residing near the forests (Washa Indiras, Kualla Yihuans and Kidanemhret) showing that contact with the plant resources helps to preserve and continue using the knowledge. Tibabosgie village being close to the forest reported less knowledge due to being more dependent on a few highly knowledgeable healers for their healthcare delivery. Mantogera village is close to Addis Zemen Town and the people have better access to modern medical system than traditional medicine. On the high land area of Aguat Mafsesha, the people live concentrated within a specific compatible area and intensive cultivation is the norm. Here, biodiversity is considerably reduced and the possibility of finding medicinal plants has been minimized.
The study confirmed that variation exists in species preferences among sites, partly due to the wide array of ecological niches within short distances. This is in turn expected to bring about differences in indigenous knowledge among informants of different sites. Similar trends have been reported in a study conducted in eastern central Ethiopia [38]. Though results indicated relative variations between town and rural villages, indigenous medicinal plant knowledge difference was hardly noticeable indicating that even town dwellers living close to forests keep considerable ethnobotanical knowledge as reported in other studies [67,68].
It is no wonder that agriculture is the main culprit for the loss of medicinal plant habitats, vegetation and species because the communities in the study area depend more on mixed agriculture as their main economic activity with limited landholding and high human population [34,59,63,69]. Low living standards and lack of alternatives are major factors responsible for the decline of forest resources [14]. Cultivating the useful plants in homegardens is crucial, but conservation in the natural wild setting (in-situ) must also be considered since plants in their natural ecological area can grow at the limits of their potentials and provide the expected results including efficacy as medicine. Sustainable medicinal plant management and conservation are  imperative for rural people's healthcare and community well-being. The importance and conservation purposes of church forests have previously been reported [70]. Likewise, the governmental plant nursery in Addis Zemen Town is used as a germplasm source for the forest as well as the surrounding areas. The nursery is engaged in raising seedlings of selected species that are distributed for reforestation and afforestation programmes, which needs further enhancement and scaling up.

Conclusion
The present study showed that Tara-gedam and Amba forests harbour a high diversity of medicinally useful plants and the people living in the area have a long history of plant use, and that of medicinal plants is exceptionally notable and culturally rooted in the area. Despite the gradual socio-cultural transformation, the inhabitants have retained remarkable knowledge of the plants and their uses. Difficulties in knowledge transfer and the resulting generation gap in knowledge are threatening the continuity of the medicinal plants and the indigenous knowledge on them. On the other hand, the study provided evidence that medicinal plants will continue to play an important role in the healthcare system in the study area, given support through conservation and education. Knowledge and herbal medical practices for the treatment of various ailments among both rural and urban people are major parts of their livelihoods and culture. The traditional knowledge of the use and conservation of these plants is still being transferred from generation to generation, but appeared to be aging. The problem of transfer of knowledge from the elders to the young generation probably arose following the introduction of modern education, religious, spiritual and culture-related factors. Therefore, it is not only essential to conserve such a wealth of information hidden among the local people but also to apply modern science and technology to meet the ever increasing requirements of humankind. Furthermore, conservation of these biological resources is very important because their sustainable use can generate higher levels of employment and income.