Vascular plant species diversity in the HGs of the study areaVascular plant species taxa, richness and abundance in the study area

The HGs of Dawuro revealed the presence of high number of vascular plant taxa (345) compared to other areas from 30 to 258 species which is 159, 75 and 258 in south [6; 41; 42]. It also revealed the use of highest families and concentrated the same on use of Fabaceae, Asteraceae, and Lamiaceae compared to the study reported to Wolaita [41], Hawassa [43], Sebeta [17] and Gozamin of east Gojjam [44] in Ethiopia. This is due to the sharing of common culture in different ethnic groups of Ethiopia that enforces them to manage a lot of plants in their HGs. The other reason is that people focus on sustainable actions of health and food of their children and domestic animals.

Species richness is negatively correlated with education, farm size, and slope. This is because, the educated individuals give attention on professional works, which seeks for other job rather than agriculture including HG management; households with large-sized farm field focus on out field crop works and management that brings large amount of products for income and consumption rather than HG; and as the slope increases the degradation of fertile soil in the area also increases which consequently results in decreases of the growth and appearance of vascular plants.

Most of HGs were recorded with highest vascular plant species richness ranging from 13–59 (average 36) in the study area compared to the report ranging from 10 to 45 throughout the HGs to other areas [45, 83] of Ethiopia, Uganda [47] and Meghalaya of north-east India [1]. The highest species richness per HGs were recorded in mid altitude followed by highland and in lowland in that order which is different from the report to Kerala, India [46] that showed low elevation lands. This indicates in the midland region which can be attributed to the water availability due to the presence of different natural forests around as source for this and better soil fertility with lower slope of the lands.

The difference in species richness from place to place could be attributed to attitude, income difference, and personal preference of species, soil type and size of HG. The same report was suggested in study of Kerala, India [46] and Holeta Ethiopia [14]. However, more species richness records were seen in the HGs of female heads than males. This is because in male headed HG: 1. Culture enforces them to be worth wealth in plant agrobiodiversity: agroforestry (mainly enset, coffee and fruits- avocado, mango etc. with large size) and domestic animals (mainly cattle and equus for rich but sheep, goat and poultry for poor—at least one in each case) to sustain family life and the respect from community waits for him otherwise it is considered as taboo. 2. For this matter, he has to manage a lot of vascular plants with multipurpose in his homestead (HGs and farm fields) by planting intentionally, allowing the appearance of wild plants with multipurpose, domesticating the known wild edible and medicinal types of plants which are few in number because they need large space for management. He gives mandate for his family members, wife and children to closely manage; then after he follows every day it is in his entrance and out going from home. The same was reported to Hawassa city in Ethiopia [17]. In contrast, the higher species diversity in female headed homegardens is because of: 1. The owner’s interest, intentionally planted to get their multipurpose service 2. It may be accredited to enhanced and exhaustive effort of planting, weeding, watering, fencing, digging, applying animal dung and pruning and coppicing for the leaf, branches or canopy and height management by family labor (women and children) [16] 3. Culture enforces females to avoid some weeds and make clean around her home, leaving only managed or cultivated types like vegetables, spices, condiments and ornamental ones for immediate access and sustainable supply 4. She is also enforced to come up with multifood items in dining table; the staple food (in Dawuro case bread made from kocho of enset, wheat, maize and sorghum) with other cereals, root and tubers, vegetables, spices, condiments, boiled coffee leaf, milk, fruits or/and others for ease of eating; otherwise it is considered as taboo. These crops are herbs and shrubs those need small space and can be produced in large 5. Finally, she has the prior responsibility of a family member for care of family health to manage medicinal, nutritionally and economically important vascular plants in her HG for immediate access and sustainable harvest. The same was reported to Hawassa city Ethiopia [16].

The least species richness and abundance was recorded in few HGs due to size of HG, personal interest, attitude, busyness in other income generating job (daily laborer or professional worker), time of establishment (the newly established HG) and environmental factors like water stress, climate, soil type, elevation, slope, aspects, hillshade and toposhape layers. Some of them were the same factors reported to Hawassa city in Ethiopia [16] and to Ilam province of Iran [73].

The structure and composition of HGs

HGs of the study area are characterized by a structural complexity and multi-functionality which enables the provision of different benefits to people and ecosystems. For example, homegardens could be regarded as a relatively safe place for conserving specific endemic and threatened species. The horizontal and vertical structures of HGs, their composition, the richness, abundance and the size of vascular plants to be managed in the HG is determined at the beginning based on the size of the HG. A renowned structural characteristic of the HG was recorded with the great diversity of species varying from those creeps on the ground to tall trees. The identical was reported to homegardens of southern Ethiopia [48], West Java, Indonesia [61], Shan communities in Thailand [76] and elsewhere [62]. This is because; culture enforces the cleanness, neatness, and diversification of HG as well as the diet they eat which give the room for setting the type of HG. In spatial (vertical and horizontal) management of vascular plants immediately next to the clear area of the home, especially in sloppy areas, most of these plants with dwarf size were grown in the upper side or front-right side of home in order of height. The dwarf sized plants like spices, medicinal plants and ornaments were managed in the upper side of home and the long sized ones were at the lower side of home. This is because; 1. To protect contamination and to give well odder to the guests 2. To avoid the odor of animal pens in the house which is released/disposed to the lower side of the home 3. In order to protect the graving of species into sedimented materials those were eroded from the upper side of the resident 4. Those don’t need a high amount of manure. 5. Deeply rooted plants which make it hard to dig and pick the root from dregs in the lower part. 6. Those can be grown abundantly (small and thin) to protect or reduce erosion/flood.

Vascular plant species diversity in the HGs of the study area

The study result has revealed high Shannon’s diversity index (H') recorded in the homegardens from 1.3871 to 3.3956 compared to other study reports in central Ethiopia from 3.016 to 3.28 in Holeta area [14] and in Uganda ([47]. The shannon's diversity index (H') of beta diversity in different agroecology, in altitude gradient variation (lowland, midland and highland) has no significance differences were observed among themselves but the study reported to Kerala, India [46] showed that high vascular diversity in low elevation lands. The beta diversity of the study area is higher (3.97 to 4.08) than other areas HGs’ report to Hawassa city [16] recorded in four sites from 3.29 to 3.87 and Dilla area of Gedeo Zone [42] in seven sites from 3.34 to 3.52 in the country, Ethiopia.

The diversity of each plot (alpha diversity, H’) of the study area was recorded with higher range than the similar study reported elsewhere in the above comparison. This is because 1. The households were from the same ethnic group of a community governed by (practice) the same culture in the study area that forced them to diversify their HGs. 2. High species richness and abundance was recorded. 3. Suitable sociodemographic factors like age, education of household, family size, marriage, sex, traditional healer being the owner of household, and year of stay in the area were considered 4. Suitable surrounding factors like distance from natural forest and from urban areas, elevation, slope, soil and moisture availability were confidently predictable; these have an effect on the diversity of vascular plants in the study area.

The use of vascular plant species in the HGs of the study area

HG of the study area is a fixed plot of land comprising multipurpose nature plants which were harvested at different times to meet diverse people’s requirements and adapt to the environmental stress, climate change. These vascular plants were grown like for food security, nutritional, healthcare, economical, cultural value and to cope up the size of land they own. In the study area HG has use as site for food production economically that saves the expense on produce and food costs every season, shorten the commodity chain, save fuel-demanding transportation and reduce pressure on natural forests, health benefit, economic value, ecosystem service and provide a place for households to share knowledge and skills. The same was reported in Ethiopia [43], in Minneapolis of USA [65], in Sri Lanka [18; 66] and in Uganda [47].

HGs of the study area were enset with an agrobiodiversity-based agricultural system on landscape management which has great potential for ecological balance, climate change solution, carbon sequestration and subsidiary reimbursement as natural forest provides. The same was reported elsewhere [66]. Most of the recorded vascular plants in the study area were herbs followed by shrubs and trees, respectively. This is because, 1. They grow the freshly used and accessible vascular pants 2. The agrobiodiversity and agroforestry were encouraged by culture which enforces the household to grow in their HG 3. Individual interests of growing plants with multipurpose were some of the reasons. Most of them are used in combination but few vascular plants in the HG were used alone like leaf and whole parts. This is because the culture in the study area enforces to use fresh potherb species (seasoning, medicinal plants and vegetables) for daily consumption; using spoiled materials is taboo, called as “samaa”local saying meaning putrid/ stale.

Almost all householders’ manage vascular plants in their homegardens mainly for food use and others come next. However, in general, most of the recorded uses were with traditional medicinal value compared to other areas reported. HGs of the study area service as a source of traditional medicinal plants was assured for the study area [50; 80]. This study report is similar to the report of the study in Northeast India [57] and for keniya [79]. The reason why they manage a lot of vascular plants in their HGs is 1. Culturally they know that the food they eat is medicine by itself. 2. Most of them are from low status (the poor) and cannot afford the price either to buy the food with medicinal value from the market or to buy drugs from modern pharmacies 3. The multipurpose nature of the plant catches the attention of the interest of householders 4. The householder might be traditional healer who cultivated or allowed them to emerge there for immediate access for service delivery.

Enset ventricosum, C. arabica, Mangifera indica, Carica papaya and P. americana were considered important and most cultivated in the HGs of the study area. The same study report confirmed species composition in the HGs of Gamo in Ethiopia [67] and Uganda [47]. The perennial crop E. ventricosum among the dominant plant species existing in almost all sampled HGs and agroecology in the study area. Similar was reported to central Ethiopia [63; 65] and as it was reported to elsewhere [68]. This is because; these plant species serve as the main economic and food source of the daily diet of the livelihood of the farmers.

Based on the previous studies [52;69;70] and compilation of Institute of Biodiversity Conservation (Endemic plants of Ethiopia: Preliminary working list of Endemic plants of Ethiopia) was produced from published flora of Ethiopia and Eritrea and Gullele Botanic Garden (GBG) (http://gullelebotanicgarden.yolasite.com/endemic-species-in-ethiopia.php) there were more than 10 endemic vascular plant species recorded in the homegardens of the study area: namely Coccinia abyssinica, Crotalaria rosenii, Echinops kebericho, Erythrina brucei, Impatiens rothii, Milettia ferruginea, Pycnostachys abyssinica, Satureja paradoxa, Trifolium decorum, Vepris dainellii, Crassocephalum macropappum, Lippia adoensis. From this what can be drawn is homegarden plays the reservoir role of both native and introduced plant species for generation. Since this landscape is the area where domestication of the wilds, testing of modified species, introduction of exotic species and maintaining and propagation site of indigenous and land-races [10; 14; 15; 16] focus should be given for conservation and sustainable utilization of the resource at hand.

Therefore, its composition of various vascular plants including agrobiodiversity played a fundamental role in sustaining and strengthening food, nutrition, health, domestic energy needs and livelihood security, as well as environment. Because of these values, the plants in the HG were maintained and hence, HG is considered as a conservation site for rare and threatened species.

Vascular plant species conservation and management in the HGs of the study area Sociodemographic and labor division effect on management of vascular plants in the HGs of the study area

The statistics of socio-economic information indicated that most of the HG owners did not attend formal education; middle aged males married bearing more than 4 family members and stayed in the area by managing more than 2ha farm field for more than 10 years. This information indicates that the factors were conducive for households to apply HG management culture of the study area, to have more diversified vascular plant species and to pass the trend easily to the next generation. Similar was reported to Shewarobit District in Northeast Ethiopia [71]. Marriage, family size, age and year of stay in the area has positive correlation with the diversity of vascular plants of the study area. This is because, as the year of stay and age increases the marriage will happen and family size will increase; consequently to sustain family members and to fit with culture one has to collect a number of vascular plants with multipurpose either by growing and/or allowing the appearance which has contribution in diversity. In addition to this, the conditions make it an easy way of labor management to reduce the expense in the HGs management.

Based on sex and age, there is labor division in managing HGs. Males above 18 years were responsible to plant large-sized agroforestry plants including enset, coffee, mango, avocado, eucalyptus, bamboo tree and shade trees cordia, cupressus, ficus and others. Females and children were responsible to plant and manage small-sized vascular plants like spices, condiments, medicinal plants, vegetables and ornament ones. The same was reported in the Assosa area of Ethiopia [72] and in Bule Hora District, West Guji Zone, Southern Ethiopia [6]. Therefore, the well-managed HGs have contributed to the diversity of vascular plants apart from fulfilling the needs of the family. The same was reported in Nepal [21].

In plane area (flat surface), it is simply managed as needed and in order of height to protect wind and canopy stress as well as to protect their products from predatory birds and small mammals. Out crop plants like bean and tef were recorded in the HG because of dropping while preparing for either market (selling) or storing or, consuming at home and there was household waste. Most of the time, in educated household, plants on all sides of the home (in the HG) was manured in any way. In illiterate cases, plants that do not need more water were planted in the upper side of the home but the others in the lower part and hind part/side of the house.

Cultural effect on management of vascular plants in the HGs of the study area

The indigenous practice becomes a trend when its knowledge and skill is shared by others. The frequent application of trends for many years yields culture and the culture finally produces many social factors among the practitioners [56]. The strategy of diversification of vascular plants in the HGs has already been set in the culture (through taboos and some speeches) by coining life standard, dining table, marriage, labor division (family contribution) for the sake of daily family needs: nutrition, health, economy, and others. In Dawuro, HG is culturally considered as a symbol of social status. Households with no diversified agrobiodiversity in his/her HG, small HG or do not own it, otherwise bringing single or only two food item/s to the feeding table is considered as a lower social rank. Similar results were reported to Bule Hora [6], Holeta [14], Yayu (southwest) in Ethiopia [75], in European HGs [55] and sociocultural variables study elsewhere [77]. This is because beside culture, people develop a strong preference for managed plants for food, medicine and other benefits.

In Dawuro, the culture encourages people to have plants with multiple uses by planting intentionally, allowing the appearance of wild plants with multipurpose, domesticating the known wild edible and medicinal types of plants. The same was reported to Hawassa city in Ethiopia [16] and Kenya [74]. Appearance of wild edible plants in the HGs is encouraged in the study area for immediate access like for medicinal, food, shade and others. The same was reported to Gozamin District of east Gojjam in Northwest Ethiopia [44]. This might be because of 1. The owner’s interest, intentionally planted to get their multipurpose service. 2. HG owners might leave them for their multipurpose behavior while degrading others 3. HG owners might allow the appearance, 4. The household might be newly settled or encroached in the area nearby the natural forest 5. Dispersal of seeds from natural forests by self mechanism or by others like wind, rain water, or by birds, small mammals, domestic animals and children brought for eating or through fecal. HGs’ agrobiodiversity attracts a number of pollinator insects, bird species, and some small animal species like snake, frog, rats, and squirrel to collect their food and take shelter. Similar was reported elsewhere and Bangladesh, respectively [58; 60]. The HGs near the natural forest were documented with a large number of wild edible plants and can be taken as an opportunity to increase the diversity of HGs. However, dominating HG with weeds and wild species rather than intentionally managed types is strictly taboo. He/she has to ask (labor, seedlings, material, and other things) others/elders to help him/her to manage (avoid the dominated weed and planting multipurpose plants) in his/her HG otherwise having bare home is taboo and considered as thief (kayisuwa) or HG of migrated man (gangguwa/betiya). Because, they understand that multipurpose vascular plants in the HGs secure food, health and income, and make a conducive and attractive environment.

People of Dawuro know that the well-managed HG with diversified multi-purpose edible plants serve for both food security and as a source of micronutrients for the health of family members. The same was reported to rural households in Sri Lanka [18; 66]. They ask for multipurpose agrobiodiversity managed HG as criteria in case of marriage process; thinking that diversified HG is with secured life, prolonged life supplement.

Since it gives a viable solution for biodiversity conservation, the cultural practice and knowledge tied with management and utilization should be encouraged. In other words, ignoring the usable culture and indigenous knowledge of the community and managing a large number of invasive exotic species in homegardens might have long lasting negative effects [54].

Threats to vascular plants management in the HGs of the study areaEffect of the attitude of young generation on management of HGs in the study area

The negative effect of the attitude of the new generation for continuation of traditional practice on managing HG may be 1. The new generation focuses on academics not interested in participating in agricultural activities including HGs 2. They search for other job opportunities 3. The generation follows the new lifestyle due to urbanization and imposed from abroad due to globalization. The good value of conservation and management practice and associated knowledge of vascular plants in the HGs derived from culture falls into threat. It needs the national wide intervention of incorporating into curriculum, awareness creation of all households and the young generation and continuous supporting and supervision of implementation by agricultural development agents for ensuring food security and other needs and healthy life of people.

Perception on the Effect of invasive exotic species on vascular plants of HGs in the study area

HG vascular plant diversity is currently threatened by the growth of invasive exotic species, population growth, monoculturing expansion for food security, market and agricultural led industrialization, and urbanization. The same was reported to Hawassa in Ethiopia [16]. People in the study area manage landraces in the HG for different purposes both vertically and horizontally thinking that they defend against pests, diseases and environmental changes indirectly apart from direct uses. This study result is similar to the report elsewhere [76]. Though the introduction of exotic species for different purposes increases the richness in the homegardens, it has the potential to be invasive or inhibit the others’ growth under or nearby. Similar report of the study in the Assosa area of Ethiopia [72] supports this. Most of the inspected HGs were with some invasive exotic vascular plant species either in the homegardens or surrounding as live fence and wind break. Similar result was reported to Bule Hora District of West Guji Zone in southern Ethiopia [6]. The reasons might be 1. Their nature of multipurpose, especially timber production; similar to the present study, these species are also listed with 29 species as potential in timber production [17] 2. Due to lack of awareness, if the homegardens, live fences and farm fields were invaded by those species, the people tend to leave growing crops including staple ones like enset, wheat and maize, medicinal plants and other indigenous multipurpose plants. The consequences bring health problems, food insecurity and environmental change in near future unless intervention is taken in how to manage exotic invasive species. Those with their allelopathy chemicals had a negative effect on other plants’ growth as well as on their productivity that grew under or nearby to them. Most of the respondents have awareness of or argue that some of invasive exotic species E. camaldulensis, E. globules, C. lusitanica, G. robusta and A. indica tree growth in the HGs diminishes the land size of the productive part of HG, management of plants with multiple uses, and the product of enset and other plants (reduction of crop yields) in the HGs. Similar was reported to Sebeta-Awas [43], Hawassa [16]. Amhara region [59], and Assosa area [72] in Ethiopia and in Kenya [74; 83]. Consequently, this aggravates food insecurity and ecological shift in the area by putting enset and other crops growth, production and productivity under question. There was lesson from many of the forestry activities in eucalypt forests in eastern Australia which were not ecologically sustainable and many components of the forest biodiversity are threatened, including various biological and ecological processes, many vertebrate and invertebrate fauna, and ecosystem diversity [67].

In present study, the negative effect of the above exotic invasive species on ecology of the area was claimed. Because those species naturally have frond leaves encouraging the lowland agroecology, adapt water stress and have the ability to grow in all agroecologies; hence, they became means for ecological change. Consequently climate change is expected due to their use of large amounts of moisture resources. There is indication that the lowland crops like teff and maize were recorded in highland homegardens of the study area. Apart from this there are farmers’ claims on unproductivity of crops under or around those exotic invasive species, and on loss of some indigenous environmentally friendly species from the area. Furthermore, the live pharmacy, homestead that serves as a source of traditional medicine is losing its structure, diversity and system where the indigenous people of Dawuro practice their children on their culture, knowledge and skill [50].

The effect of distance of urbanization and settlement on management of vascular plant diversity in the HGs

Urbanization and settlement infrastructure is thought to be done at distant places from natural forest. There is an effect of natural forest on diversity of vascular plants which was contributed to the high diversity in the study area. The diversity of vascular plants decreases as we go far away from natural forest, as we approach urban areas. Therefore, the distance from urban areas has positive association with the diversity of vascular plants in the HGs of the study area (Fig. 4). The same was reported to Shan communities in Thailand [76], to the Nuba Mountains of Sudan [81], and to the Eastern Himalayan region of Mizoram, Northeast India [57]. This is because 1. The size of HG is diminished because of activities to sustain the blooming population in the process of settlement or urbanization 2. The fertility of soil which is important for plant growth becomes diminished due to the absence of natural forest nearby the urban area 3. Market oriented and those plants not found in the market, and spices and ornamental plants need small surface area were grown in the HG.

In another faucet, traditional knowledge (information on the type of plant, its uses and role) and local culture have developed in association with local resources over time [82]. The more the people living near urban areas, the more threat to his/her traditional practice and the associated knowledge will occur. The practice, management associated with community knowledge, culture and lifestyle tied with HG management diminish or will be lost with. This is because; the generation is more eager and aggravates the new lifestyle, not the traditional practice derived from culture. In addition to this, the growth of ornamental and the multi-use exotic plant species in the HGs was encouraged to show urban and the changed life style, modernity. They, elders’ claim that the negative effect of urbanization and resettlements for the continuation of their traditional practice of managing HG and others is considered as remote activity and enforces the knowledgeable persons to leave their traditional diversifying practice and managing knowledge. This study result agrees with the report to western Kenya [79] and Jimma in Ethiopia [78]. This is because; the lifestyle changes the pattern, composition and management system of HG.