Review on Selected Church Forests of Ethiopia: Implication for Plant Species Conservation and Climate Change Mitigation

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Introduction
Forests provide essential roles in the life support systems on our planet for both mankind and other living organisms [1][2][3][4][5]. Tey are the most productive ecosystems and important features in the landscape that provide critical and diverse ecosystem services and values to human society [6]. Tese ecosystem services include the provision of food, clean water, natural fbres and forest products, pollination, the regulation of climate, pests and diseases, and recreational opportunities. Furthermore, forests have roles as a home of several diversifed plant species in addition to ecological and economical values [7]. Ethiopia, located in the tropics, has a wide range of ecological settings; this wide ecological condition has created diverse and conducive environments for the development of various forms of life of fora. Tus, the country is one of the most biodiversity-rich countries in the world [8]. Shreds of evidence showed that Ethiopia owns the ffth-largest foral composition in tropical Africa [9].
Convention on Biological Diversity (CBD) reported that Ethiopia has heterogeneous fora that is estimated to contain around 6,027 vascular plant species of which 10% are endemic [8]. Te country is the ffth-largest foral diversity in tropical Africa [10]. Knowing the species' diversity and distribution patterns is crucial to assessing the complexity of biological resources [11]. Ethiopia is facing major problems including conservation and sustainable utilization of the remaining natural forests, expansion of plantation forests, and restoration of degraded lands [12]. Te natural vegetation types of Ethiopia are under harsh threats, and the coverage of forest ecosystems has been fragmented into small patches, and as a result, the structure of the forest and species composition has been degraded [13,14]. Tus, biodiversity has been exposed to a high level of degradation in Ethiopia [4,15]. Not only Ethiopia and also all types of the world's natural forests are degraded for searching forest products and agricultural expansion and settlement [16,17].
All over the world, the rate of deforestation is aggravated at very high rates in the last decades, with negative efects on ecosystems [18]. In Ethiopia, deforestation has a long history, especially in the Northern parts of the country where this activity is accelerated. Te increasing population has resulted in extensive forest clearing for agricultural use, overgrazing, and exploitation of existing forests for fuel wood, fodder, and construction materials. Due to these activities, the forest cover of the country was about 16% of the land area in the early 1950s and rapidly declined to 3.6% in the early 1980s and 2.7% in 1989 [13]. Diferent scholars reported deforestation status per year; as reported by [19][20][21], they estimated the rate of deforestation in Ethiopia as 141,000 ha·yr −1 , and a signifcant increase in the annual average deforestation rate was shown in 2015 as 210,000 ha per year. Te high rate of natural forest degradation led to undesirable and negative efects on species richness and diversity. Due to deforestation and degradation of forest ecosystems especially in the northern and central highlands of Ethiopia have been preserved in ancient Church and monastery grounds [1,3]. Te only areas where one can observe trees in Central Ethiopia are in the surroundings of churches [1,22]. Sacred forests have been recognized for their major efect on the conservation of natural resources, ecology, and climate mitigation in many parts of the world [23]. Sacred areas especially Ethiopian Orthodox Tewahido Churches (EOTC) serve as a means of preservation and management of biodiversity [1,3,4,24]. Abundant plant and animal species used sacred areas as a habitat [1,25]. Furthermore, religious areas are serving as conservation sites and hot spots area for biodiversity conservation, mostly indigenous trees and shrubs of Ethiopia [16]. Since trees and shrubs around the Church have a spiritual value attached to the churches, monasteries, and their sacred lands, the biodiversity islands of Church forests have well survived. Besides habitat for diversifed plant species, the conserved plant species are used for the reduction of atmospheric CO 2 concentration through both above-and below-ground biomass, soil, and litter falls [3,4,7,22]. Concerning the conservation and mitigation role of Ethiopian Church forests, numerous research studies and reports were done, and however, the outputs of those studies were scattered and do not provide comprehensive information. Tus, this review article tried to provide full and detailed evidence about the Ethiopian Church forests and their contribution to plant species conservation and mitigation of climate change.

Methodology
Tis review article is based on document analysis through a depth review of related literature from diferent sources. Data were obtained from the review of related literature on the Web of Published articles, researches, books, and reports. A total of 322 papers are searched from Scopus, Web of Science, and other indexed journals using keyword selections (Ethiopian Church forests, diversity, and carbon stock potential of Church forests) that have linkage with Ethiopian Church forests. However, from the total searched documents, thirty-eight publications focusing on plant species conservation and mitigation of climate change were chosen for a detailed review of their infuence on biodiversity conservation and climate change mitigation potential of Ethiopian Church forests. Tables and fgures are prepared by summarizing the outputs of selected publications.

Role of Church Forests
Tere are numerous sacred areas or forest patches in the world [2]. However, some of the remaining forest patches of Ethiopia are located in the areas of churches and monasteries under the protection of the Ethiopian Orthodox Tewahido Church [3,25]. In Ethiopia, numerous sacred churches (more than 35,000) persist in a degraded landscape and might contribute to the restoration and biodiversity conservation and provide many other economic and social benefts [1,22]. Sacred forests in Ethiopia are greater than sacred areas in Ghana (2,000 sacred forests) but lower compared to India, which is nearly 100,000 sacred forests [26]. In Ethiopia, most sacred areas are located near to churches and monasteries [27]. Ethiopia has more than 35,000 Church communities, and most of the churches from the total are located Northern and Central Highlands of Ethiopia [1,22,28]. Most part from the Church area is covered by diferent vegetation having a growth habit of trees, shrubs, and herbs [29]. In other directions, especially in the southwest of the country, Ethiopia the role of natural forests is replaced by shade cofee cultivation and home garden agroforestry systems [20]. Diverse plant species around the yard of the Church area have provided services to the communities as spiritual and medicinal values, and it ofers economic and ecological benefts to the local community ( Figure 1) [1,3,22].

Biodiversity Conservation Role of Some Church Forests in
Ethiopia. Te EOTC has a long history of planting, protecting, and conserving trees [1,[3][4][5]. Tus, churches and monasteries are not only considered religious spots but also biodiversity hotspot areas [28]. Churches and Monasteries in Ethiopia are often surrounded by patches of natural forest which are characterized by a high foral and faunal diversity with many indigenous and rare species [30,31]. As stated by Wassie [1], the main theological bases and religious perspectives in conserving forest resources were stated as the Church on the earth signifes and symbolizes the new heaven, the holy city, New Jerusalem coming down from God out of heaven, prepared as a bride, adorned for her husband. Te Church of Eden was so beautiful, and many plants, animals, and other organisms and the holy water/ streams infnitely had been surpassing from these forests that were believed as proceeding out of the throne of God. Te habit of ETOC in conserving plant species is coming from that history [1].
Even though the primary purpose of the EOTC is for worship, burials, and meditative religious festival, they also provide good and secure habitats for diverse plant and animal species [29] (Table 1). EOTC has a long history of planting, protecting, and preserving old-aged trees in churches and monasteries [20,21,43]. Tese tree species surrounding religious sites have a relationship with the term sacred groves and their combinations with Church forests [22]. Tus, forest resources around churches are important for biodiversity conservation and mitigating climate change [22]. Tree species richness, tree density, seedling species richness, and seedling density are signifcantly higher in Church forests with a wall than without a wall [44].
Church forests are serving as in-situ conservation of many indigenous species and exotic species (Table 1) [1,32]. However, the frequency and dominance of indigenous species are signifcantly higher than exotic species [3,4,22]. A study in 78 selected Church forests reported that from the recorded 148 plant species, all species were indigenous to Ethiopia [2], and another study in Church forests in the Highland landscape of Ethiopian also reported 160 plant species were indigenous, and the rest 8 species were exotic to Ethiopia from the recorded 168 plant species [21]. Te study by Wassie [1] showed that out of 125 woody species that have been registered for the South Gondar natural forests, 81 species occurred in eight Church forests in South Gondar, Ethiopia.
Te life form of vegetation in the Church forest consists not only of trees but also shrubs and herbs [29]. Moreover, Wassie and his groups [27] reported that a total of 168 woody species (100 trees, 51 shrubs, and 17 liana species) representing 69 families were recorded in 28 Church forests. Te contributions of Church forests to the conservation of diverse plant species in Ethiopia are summarized in (Table 1).

Dominate Family Categorization and Plant Species of Some Church Forests in Ethiopia.
Comparatively, as shown in Table 2, Fabaceae is the most conspicuous and abundant family categorization of Church forests in Ethiopia [34,35,37]. Terefore, this family categorization has high relative importance related to the degree of infuence on ecosystem components such as soils, plants, and animals and competition for resources (light, water, nutrients, and space) to adopt the area. Church forests in Ethiopia support the highest richness of trees and animal species that have almost disappeared in most parts of Ethiopia [1,2]. Juniperus procera Hochst. ex Endl., Podocarpus falcatus T., Olea europaea L., Croton macrostachyus Hochst. ex Delile., Calpurnia aurea Benth., Olea europaea subsp. cuspidata, Ziziphus mucronata Willd., and Hagenia abyssinica (Bruce) J. F. Gmel. are common native trees grown in Church forests (Table 3). Ethiopian Scholars also proved that Juniperus procera Hochst. ex Endl. and Olea africana Mill. were the most frequent and common species in the monasteries Goba District, Southeastern Ethiopia [55], Lasta Woreda, North Wollo Zone, Amhara Region, Ethiopia [33], and six selected Church forests in North Shewa Zone of Amhara Region, Ethiopia [22]. Summarized studies on dominant family categorization and dominant woody species of the studied Church forests in Ethiopia are presented in Tables 2 and 3.

Climate Change Mitigation
(Storing atmospheric CO 2 and limiting greenhouse gas emission)

Biodiversity Conservation (Habitat for diverse plant and animal species and act as in-situ conservation hot)
Household Uses (Medicine, fuel wood, honey production and building materials)

Benefits of Church Forests
Cultural and Spiritual values (Provide spiritual renewal and experience transcendence for worshipers) Climate Change Adaptation (Building public perception and altitude on causes and consequences of climate change and implementation of climate change adaptation strategies)  Note. H″: Shannon-Wiener diversity index; E: evenness index.

Church Forests for the Conservation of Treatened Plant Species.
Church and monastery forests provide ecosystem services through the critical conservation of plant species [56]. Around the churchyard comprise many threatened and unique species that make the preservation of these forests crucially important [53] (Table 4). Since the distribution and coverage of natural forests are reduced through diferent natural and human-induced factors, the distribution of a variety of plant species diversity also declines and goes to threatened. In such conditions, Church compounds are serving as in-situ conservation and hot spot sites for biodiversity resources including many endangered, threatened, and IUCN red lists plant species [1,22,32,57]. Juniperus procera L. and Prunus africana (Hook.f.) Kalkman. which are listed in the IUCN red list are mostly found in Church forests of Ethiopia [58]. Terefore, protecting the remaining forests, aforestation and wise use of exciting forest resources should be given attention [59]. Te roles of Ethiopia Church forests in the conservation of threatened plant species are presented in (Table 4).

Climate Change Mitigation Role of Some Church Forests in
Ethiopia. Climate is rapidly changing and global warming also increased due to increases in the concentrations of greenhouse gases (GHGs) in the atmosphere mainly caused by human activities, particularly the burning of fossil fuels, expansion of agriculture, and deforestation. Comparatively concentration of carbon dioxide in the atmosphere is one of the primary causes of climate change. Tis led to extreme hazards to animal and plant species diversity, human life, environmental health, agricultural productivity water, and air quality. For combatting the efect of climate change forests have a signifcant contribution to reducing atmospheric carbon dioxide through carbon sinks [60].
Climate change mitigation is a human intervention to reduce the sources or enhance the sinks of greenhouse gases [61,62]. Forest has a role in climate change mitigation through carbon sequestration in both above and belowground biomass and soil carbon stocks [63,64]. Compared with terrestrial ecosystems, forests have a high potential for sequestering carbon, through the process of tree growth and resultant biological carbon sequestration. However, forest coverage in Ethiopia is highly degraded due to diferent factors, simultaneously emission of CO 2 to the atmosphere also increased [65][66][67].
Forest coverage has a direct relationship with the amount of carbon stored but indirect relation with the amount of CO 2 concentration in the atmosphere. Now day's forest patches are highly concentrated around churchyards, especially in Ethiopia [28]. Tose forest patches which exist near and around Churches are very important in carbon sequestration and climate regulation (Tables 5 and 6) [32,49]. Since trees and shrubs around the Church area are well protected from different disturbances like illegal cutting, its carbon-storing potential through above-and below-ground biomass is signifcantly higher [49,68]. In addition due to the presence of vegetation cover, soil erosion is reduced and soil and water are well conserved, as a result, soil organic carbon stock is well enhanced [22,30]. Te contribution of Church forests to sequestering atmospheric CO 2 can be estimated by conducting studies in selected Church forests in diferent geographical locations in Ethiopia. Te potential of Church forests in storing CO 2 in above-and below-ground biomass, litter-fall, and soil carbon stock are summarized in Table 5.

Plant Species Having High Carbon Stock Potential in
Some Church Forests of Ethiopia. Te performances of trees also afect the amount of carbon stored means that healthy International Journal of Forestry Research  International Journal of Forestry Research  [41] Note. AGBC: above-ground biomass carbon; BGBC: below-ground biomass carbon; SOC: soil organic carbon; LC: litter carbon. 8 International Journal of Forestry Research  [41] International Journal of Forestry Research and larger-diameter trees have good potential in sequestering carbon. Tus, trees around the Church have long ages and have a high diameter class so their ability in absorbing carbon dioxide is higher [33,46,48]. Due to the presence of those best-performed tree species, soil organic carbon (SOC) in Church forests is higher due to the addition of diferent organic materials into the soil, and this helps as a greenhouse gas mitigation activity under the Kyoto Protocol [64,72,73]. Lists of plant species having high potential in terms of carbon sequestration are presented in Table 6.

Challenges to the Church Forests of Ethiopia
Ethiopia faced diferent challenges in the development and conservation of forests [22,27,42,74,75]. Tus, habitat and species are being lost rapidly as a result of the combined efects of environmental degradation, agricultural expansion, deforestation, and over-harvesting of species [3,4,30]. Te loss of plant species is aggravated by human and livestock population increase thus hastening the overall rural livelihood impoverishment and loss of the biological diversity in Ethiopia [3,22,30]. Population increment led to a decrement in economic opportunities, and this puts positive energy for land conversion of forest to agriculture and grazing, and timber exploitation for frewood and construction [30].
Even though Ethiopian Orthodox Tewahido Churches are considered sanctuaries for diferent plant and animal species, evidence revealed that over time decreasing both in size and density, with visible losses in biodiversity [2,43]. Te most commonly listed challenge by scholars is the grazing of seedlings and saplings [22,29]. Ethiopia has the largest livestock population in Africa [75]; however, the livestock nutrition and the population's livestock are imbalanced. 75% of Ethiopian livestock is depending on free grazing as a feed source [76]. In addition, poor management of livestock in the feld led to the disturbance of the Church area by livestock searching for feed. Livestock grazing has a direct and indirect efect on the conservation of plant species [22,29,42,55].
Mainly challenges on Church forests have direct and indirect efects; the direct disturbance of Church forests through livestock grazing is the most critical challenge that signifcantly reduced plant species diversity. Tis is through browsing and trampling of small understory vegetation, so this signifcantly reduced plant species diversity around the Church areas. Indirectly, livestock has an indirect efect through the distraction of physical structures like soil degradation [46] when the stricter detached soil is washed by runof and its nutrient availability is also reduced as a result of the suitability of the site for germination and initiation of seedling highly decline [77]. Ten, the diversity of plant species also reduced simultaneously over time. According to studies by Wassie and his Colleagues [1], Ethiopia Church forest reported that grazing had a strong negative efect on germination, seedling survival, and growth. In addition to free grazing, wood harvesting, human encroachment, removal of forests for building for religious aspects, and replacement of indigenous trees with Eucalyptus species are recorded as challenges that faced forests in Church areas [1,2,22,31]. Te other big challenge is the replacement of indigenous herbs and shrub species with invasive species like lantana camera, and this led extinction of species [22].
Te study by Cardelu's and his friends [31] found that human disturbance was high in more than half of the 44 studied Church forests in northwest Ethiopia, resulting in reduced tree species richness, biomass, and density. Furthermore, Church forests degradation is ongoing, as logging and tree dieback of species such as Juniperus procera L. and Olea europaea spp. cuspidata lead to community shifts, from dry Afromontane forest towards shrubland [78,79]. Overall, the protection of Church forests from diferent disturbances is important for the conservation of biodiversity in areas threatened by deforestation and fragmentation [78][79][80][81][82]. Summarized studies on challenges to Ethiopian Church forests in diferent geographical locations in Ethiopia are presented in Table 7.

Conclusion
Te comprehensive review of published works indicated that churches and monasteries of the EOTC are often surrounded by small natural forests characterized by a high foral and faunal diversity with many indigenous, endemic, and threatened species. Te conservation roles of Church forests are the substantial contribution of EOTC, and this is due to religious thought and local people's willingness to protect and conserve them. In addition to their biodiversity conservation benefts of Church forests, they have a significant contribution to mitigating atmospheric CO 2 . Tis is due to the presence of diverse plant species around yards of the Church areas also having a major role in the remarkable carbon stock potential to sequester atmospheric carbon dioxide. Te nature of Church forests in terms of woody species composition is diverse, and stand parameters are also well-kept so they have high biomass carbon sequestration potentials. Even though Church forests have an important role in conservation and climate change mitigation, their potential is highly disturbed by diferent natural factors and anthropogenic encroachment. Grazing of Church areas is a frequently existing challenge listed in Ethiopia. Local people must work integrally with Church administrative workers for efective conservation and management of Church forests. Free grazing must be replaced by a cut-andcarry system to enhance the regeneration status of Church forests healthy. Apart from this, the boundary Church area must be demarcated and fenced for reducing diferent disturbances.

Data Availability
Te data supporting this review are from previously reported studies and datasets, which have been cited.

Conflicts of Interest
Te author declares no conficts of interest.