Exploration of Species Diversity as Ecological Conditions Vary to Determine the Possible Areas for Collecting Tree Seeds in Amhara Region, Ethiopia

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Introduction
Biodiversity encompasses the variety and variability of life forms, ecosystems, and ecological processes, at all levels of biological organization, and is the foundation of human survival and economic well-being [1].Ethiopia is one of the top 25 richest biodiversity tropical countries in the world due to its huge variety of forest types [2].Tis country is endowed with a variety of geographical features and biodiversity hotspots [2].Such land features are high altitudinal variation, mountains, fat plateaus and deep gorges, river valleys, and rolling plains, as well as water bodies [3].Generally, biodiversity of the forest ecosystem is determined by the diversity of the tree components because trees hold habitats and supply resources for all the other related species in the forest [4].
Almost 85% of the population in Ethiopia lives in rural areas and most of this population directly or indirectly depends on natural resources [5].Forests fulfll human demands for goods such as food, fodder, fuel, medicine, timber, resins, and oil [5] and services such as climate regulation, pollution control, soil and water conservation, nutrient cycling, pollination, and recreation [6].Forest comprises the resource base upon which the providence of our outlook generation depends.Preservation and periodic assessment of diverse ecosystems and the whole of biological diversity therein are, therefore, vital for the long-term continued existence of human beings [7].Te conservation of species allows regulating fresh air and water quality, shaping ecosystems and managing the climate, and suppling food, medicine, clothes, shelter, and the raw materials from which several other yields are prepared.Tus, trees are both a fundamental part of the world's biological diversity and an important economic resource for human survival [8].
In Ethiopia, there are enormously complex vegetation due to its high variations in moisture, temperature, and altitude [9].Te Ethiopian highlands comprise more than 50% of the land area with Afromontane vegetation, with the dry evergreen Afromontane forests (DAFs) and grassland complex forming the largest part [10].Te most highland part of the country such as northern, northwestern, central, southern, southeastern, and southwestern areas are the dry Afromontane forests with altitudes between 1800 and 3000 m [9].Most of the natural dense forests are fragmented, mostly represented by the Afromontane dry evergreen forest formed by riparian vegetation and pastures [9].
However, the rich biodiversity and vegetation of the country are under serious threat from overexploitation, overgrazing, expansion of cultivation, and settlements that are accompanied by excessive deforestations, invasions of alien species, and pollution [11].Te country had experienced substantial deforestation and soil degradation and an increase in bare land over the years.Te use of fuel wood, arable land, and grazing areas have been specifed as the major causes of forest degradation, continually leading to loss of forest cover and diversity, erosion, desertifcation, and reduced water resources [12].
Terefore, assessment of the species richness, structure, and regeneration status is essential to create the successful forest resources management and conservation [13].Forest species variety protection and conservation are essential for continuous sectors as deferent as energy, agriculture, forestry, fsheries, wildlife, industry, health, tourism, commerce, irrigation, and power.Te trends of Ethiopia for the future are persisting to depend upon the inspiration given through current assets and retaining species diversity [14].Te regeneration status of species in a community can be accessed from the total population dynamics of seedlings and saplings in the forest community [15].Regeneration is a central part of forest ecosystem dynamics and reestablishment of degraded forest lands.Proper forest utilization is merely possible if there is sufcient information on the regeneration dynamics and causes infuencing vital canopy tree species are obtainable [7].
A study on the remnant-fragmented forest of Ethiopia is urgently needed as baseline information for ensuring the sustainable use of natural vegetation, its conservation, and ecological management practices [16].However, baseline information on the status of regeneration is still lacking in some dry evergreen forests, in particular for the Fudi forest vegetation.Tus, the aim of this study was to determine the forest species trees and shrubs that occur in the Amhara region, Ethiopia, for determining the possible areas for collecting seeds and propagules to meet genetic conservation and use programs, as well as the recovery of degraded areas.

Description of the Study Area.
Te study was conducted at Fudi Natural Forest in Fagta Lekoma district, Amhara region, northwestern Ethiopia, which was selected based on its representativeness of the potential protected natural forest with altitudinal gradient variation and since it is among the least studied natural forest site.Fagta Lekoma district is 460 km away from Addis Ababa, and its geographical location lies between 10 °57′23″ and 11 °11′21″N and 36 °40′01″ and 37 °05′21″E (Figure 1).Te altitudinal gradient is 1887-2902 m a.c.l.Te annual average rainfall is around 2000 mm and 1154-2829 mm, and the gradient of air temperature is 11 °C-25 °C according to the altitudinal variation [11,17].In areas where altitude changes occur, changes in air temperature occur, as there is a strong inverse correlation between altitude and temperature.Hypothetically, for every 100 m of altitude, there is a decrease of 1 °C in temperature [18,19].As the altitude of the region varies, temperature changes up to 10 °C may occur between areas of lower and higher altitudes [11] due to the large variation in the altitude, also infuencing the loss of water from the system soil-plant atmosphere and, therefore, on the water balance.In areas with greater water defcit, the vegetation size tends to be smaller, as well as the species diversity.
Te main soil classes in the district are Vertisols, Nitosols, and Cambisols.Te main agricultural practices are mixed farming (crop production and livestock raring) and the land-use systems are cropland, grazing land, forest land, and woodlot [20].Te ecosystem of the study area is the Afromontane dry evergreen forest, composed of two types of agroecological systems, Dega and Weyna Dega, represented by tree, shrub, and herbaceous species [20].

Methods.
Te woody species measurements and aspect data were collected feld data collection system inventory.Te rectangular nested-quadrat design is used to incorporate the variable tree sizes.Te sample plot size was taken as 10m * 20m (200 m 2 ).Terefore, systematically 59 sample plots were established from the total area of 590ha of the forest by using 10% of sampling intensity.
Te transect line was laid out from the lowest altitudinal elevation to the highest against altitudinal gradients to capture representative samples of the forest.Quadrats were laid out systematically at every 100 m distance between each plot along the transect lines, and the distance between transect lines was 100 m apart from each other.To avoid the edges' efects, all the sample plots were established at least 50 m from the forest edges or roads inside the forest [13].For saplings and seedlings data collection and inventory, the two subquadrats at opposite corners (5m * 5m) and fve subquadrats with four at corners and one at the middle (2m * 2m) were laid without overlapping each other, respectively, as the nested plot system in the main quadrats ([21]).

International Journal of Forestry Research
In each main sample plot, all adult woody individual trees and shrubs with DBH of ≥5 cm and height of ≥2.5 m were measured by using caliper and hypsometer, respectively.Te woody species individuals were recorded and counted with DBH <5 cm and height <2.5 m ≥1.5 m as saplings and individuals with DBH <5 cm and height <1.5 m as seedlings [21].Te slope, elevation, and geographical coordinates of the quadrats were measured using Suunto clinometer and Garmin GPS64.All woody plant species encountered in each sample plot were recorded using local and vernacular names.Plant identifcation was carried out at the feld with the help of diferent Flora of Ethiopia and Eritrea [4,22,23].
Te data for this study were obtained from feld inventory in 2021.All data are restricted to the phytogeographic domains of Ethiopia.Tis procedure was performed using the geographic information system (GIS) in Arc Map software [24].
Species presence points were plotted on the USGS SRTM map (GTOPO30) at the 1 : 250,000 scale [25] using the geographic information system (GIS), Arc GIS 10.1 software [24].Te maps were presented only for the municipalities with species presence points.Te fgures were generated in the JPG format for each species individually, showing the distribution of each one according to the altitude of the area (Figure 2).Te maps were elaborated through multiple linear regressions, correlating the bioclimatic variables with the numerical models of latitude, longitude, and altitude (Figure 2).Descriptive statistical analysis was initially performed.Tis was followed by performing a normality test to observe the data distribution.For the comparison among tree height, diameter at breast height and average canopy diameter between the species were applied.Tese statistical analyses and graphs were performed and built in software R [26].

Results
Te Fudi Natural Forest in Fagta Lekoma district, Amhara region, northwestern Ethiopia, comprises many families of tree and shrub species (Table 1).In the region, 1250 individuals were sampled from 32 families and 46 species.Te most common families in the northeast, north, northwest, southwest, southeast, east, and west regions were Mimosoideae, Euphorbiaceae, Celastraceae, and Rubiaceae (Figure 3).Te frst three regions were the ones with the highest number of species.Te formation of relief afects the amount and daily cycle of solar radiation received at different times of the year, which infuences the species diversity.Te areas of the forest located to the north, northeast, and northwest receive less solar radiation, which results in a cooler and more humid climate, supporting plant species that like moisture (Figure 4).Solar radiation and air temperature are related to the loss of water from the soil-plant system to the atmosphere.Its increase represents greater water loss, increasing the risk of water defcit, which may be related to the smaller size of vegetation and species diversity (Figure 5).Conversely, in other areas, humidity is lower due to greater solar radiation and, consequently, greater evaporation, resulting in a lower species diversity.
Albizia gummifera (J.F. Gmel.), Croton macrostachyus (Del.),Maytenus arbutifolia (A.Rich.), Rytigynia negligence (Hiern), Vernonia auriculifera (Del.),Prunus africana (Hook.f.), and Justicia schimperiana (Hochst.Ex Nees) were  6).Te species that presented the highest growth rate in height and diameter were A. gummifera, Bersama abyssinica, P. africana, Ficus sur, Ehretia cymosa, and Ekebergia capensis (Figures 7 and 8).Te southeast and west regions were the ones that presented individuals with greater development in height and diameter at breast height, evidencing the relationship between these parameters and the type of relief and, therefore, with the predominant climate of the region and soil attributes.Tus, individuals sampled in areas located in the southwest and west of the forests were larger, with greater height and diameter, and had lower population density compared to individuals sampled in the area located in the north of the forest.Te higher population density in a forest community implies individuals with the smaller diameter and height due to the efect of competition for nutrients and solar radiation.

Discussion
Knowledge of species diversity is necessary to establish proper strategies for conservation programs.Although Ethiopia is a diverse country, its forests face challenges such as high rates of deforestation (especially by indiscriminate exploitation of forest resources and changes in land use from expansion in agricultural and livestock operations), fres, hydroelectric power plants, mining activities, construction of highways, and urbanization [29].Furthermore, fragmenting forests afects the efciency of pollinators as well as dispersers, reducing gene fow and favoring genetic drift and greater inbreeding within populations as described by Souza et al. [28].Tere have been major eforts on the botanical characterization of forests populations and species in Ethiopia [29][30][31][32][33][34][35][36][37][38].Despite advances in this feld, these eforts have fallen short, considering the huge number of forest species present.Strong eforts in terms of resources and research are still required to understand the species from biological, silvicultural, and genetic points of view, particularly in areas including species distribution, reproductive systems, inbreeding mechanisms (dioecy, protandry, protogyny, heterostyly, and self-incompatibility), crossing rate, gene fow (ranging in scope from pollen to seed migration), pollination and seed dispersion agents, degree of inbreeding, seed germination, silviculture, and species ecology.
In general, by diminishing forest health and decreasing habitat, the forest fragmentation shows the way to biodiversity loss, invasive plants expansion, pests, and pathogens and decline the water quality.Te abundance of seedling depended on the local existence of big, mature trees and on the geographic distance to potential seeds source populations, which strongly recommends that metapopulations dynamics likely are vital [29].Biodiversity corridors should also be utilized as a strategy in conservation projects for areas with intense fragmentation.Tis strategy is intended to increase the connection of remnants and allow gene fow (of animals and plants) in the long term.Tere are three main recognized biodiversity corridors, for example, the Central Atlantic Forest Biodiversity Corridor (CCMA) and the Northeast Biodiversity Corridor (CBN) [34].

International Journal of Forestry Research
Te concept of metapopulations can also increasingly be applied to overcome the problem of Ethiopia's extremely fragmented regions.Joining small populations with individuals from neighboring populations has been used as a strategy to neutralize genetic erosion and make populations viable.Trough such processes, many populations may be viable as metapopulations, which consist of populations structured in interconnected demes, considering extinction events and decolonization [35,36].Many important tree species such as P.africana, O. capensis, C. macrostachus, E. capinesis, C. africana, A. demidiata, A. gummifera, A. abyssinica, and T. nobilis which had a low number of species could beneft from this strategy.Te Ethiopian action plan and strategy on the conservation of biodiversity objectives has been formulated as efcient systems are recognized that make sure the wise use of Ethiopia's biodiversity, which give for the equitable sharing of the costs and benefts arising there from and that contribute to the well-being.
Forests are the main sources of terrestrial species variety, which covers approximately one-third of the earth parts [5].Forest species variety protection and conservation are essential for continuous sectors as deferent as energy, agriculture, forestry, fsheries, wildlife, industry, health, tourism, commerce, irrigation, and power.Te trends of Ethiopia for the future are persisting to depending upon the inspiration given through current assets and retaining species diversity [37].Tere are basic strategies to conserve biodiversity in Ethiopia as well as in the Amhara region.Tese strategic goals deal with improvement of the status of biodiversity by safeguarding ecosystems, species, and genetic diversity.Ecologically representative and efciently supervised protected areas need to be designed as conservation methods to increase forest area coverage, conservation of  International Journal of Forestry Research agrobiodiversity, wild plants, animals, and microbes and enhance the standard by improving ex situ conservation of existing ones as well as increasing in situ conservation sites/ ecosystems and species/breeds and improving the existing ones [2].Plant richness in high mountains is one of the most important issues in biodiversity conservation due to global climate change.It is well-known that species richness and endemism change along environmental gradients [38,39].However, the associated patterns in the variation of species diversity have not been adequately addressed [40].In addition, the high species richness and diversity in the forest indicated that it would be a good source of forest products if it is sustainably used.Since the forest harbors endemic species, it needs conservation priority [41].Ethiopia is the origin of diversity and agricultural product, which is one of the eight world's centers of biodiversity.It is partly because of the in situ conservation of plants traditionally grown in homegardens.Currently, homegardens are threatened mainly due to genetic erosion, loss of traditional knowledge of management practices, housing changes, and drought [42,43].Boz and Maryo [44] carrying out an inventory of the vegetation in Wurg forest, southwest Ethiopia, found the presence of diferent species.Tey observed trees, shrubs, herbs, and climbers, noticing that the family Fabaceae was the most species-rich family due to families' preference for these species on their farmland.
Te species diversity analysis permits a comparison of the species in each location with other forests.Tese analyses can also indicate the dominance of one species over the others in a specifc area.Terefore, vegetation characterization and description allow the ranking of the species regarding management and conservation priority.In general, species with a smaller natural distribution and low density need high conservation eforts.On the other hand, species that are dominant in the forests and have a wide geographic distribution should monitor for sustainable management [45,46].Boz and Maryo [44] observed in Wurg forest (Ethiopia) a relatively rich diversity of woody species (76 species) and high species diversity and evenness values as compared to many of the Afromontane forests of Ethiopia.Four plant community types were identifed by cluster analysis using the presence/absence value of each species in each plot and Syzygium guineense, Maytenus arbutifolia, and Elaedendron buchananii were the dominant tree/shrub species of Wurg forest.
Te species richness of woody and herbaceous plants in forests is expected to be afected by environmental variation, forest canopy, and anthropogenic disturbances [47].Woody plants are probably more strongly infuenced by large-scale environmental variations, such as changes in moisture, temperature, or altitude, than herbaceous plants [48].For example, Zhou et al. [49] argued that the diference in humidity between the southeast and northwest slopes of Mount Kenya has a higher infuence on the species richness of woody plants.In the same way, the authors point out that the density of the forest canopy infuences the light intensity, moisture, and temperature in the understory.
Te vegetation structure is the distribution of individuals of each species to determine the overall regeneration profle   International Journal of Forestry Research of the forest vegetation based on the tree/shrub density, frequency, height, DBH, and basal of the species [50].Te structure of tree and shrub species on population information shows the history of previous interruption to the species and environment.It forecasts the future trend of a particular species, providing information for conservation and management strategies [51].Analysis of the Alemsaga forest structure (northwestern Ethiopia) indicated that several species have abnormal population structures.In the lower diameter classes, there was small-sized individual's predominance that indicates good potential of reproduction and unusual amount of large individuals.Moreover, when the analyses of population structure in a forest indicate that some tree species have no or few individuals at lower size classes, it needs urgent conservation measures to promote natural regeneration.Masresha et al. [7]'s analysis also shows that the aspect and slope are among the major factors determining the species distribution patterns and plant community formation.Albizia gummifera occurs in greater density in the various sampled regions and is the most dominant.Amhara, Ethiopia, is a region with a high altitude gradient, which infuences the edaphoclimatic attributes and, consequently, the diversity of species.In the north region, the diversity of species and the size of the vegetation are lower due to the lower water supply, which occurs due to the greater solar radiation and air temperature.

Figure 5 :
Figure 5: Number of species per forest aspect in the Amhara region of Ethiopia.

Figure 6 :
Figure 6: Proportion of sample individuals per forest in the Amhara region of Ethiopia.

Table 1 :
List of species described in the Amhara region of Ethiopia with information regarding their number of stems per each species and distribution in the forest.
Figure 1: Map of the study area.International Journal of Forestry ResearchFigure 2: Maps that identify the study area.
found with the highest population density.It is believed that due to their commercial value, mainly C. macrostachyus and P. africana are more conserved in the sampled area and that, for this reason, man may have introduced them in the region.Albizia gummifera occurs in all areas.Te other species present a higher population density in the north, northeast, northwest, west, southwest, and southeast regions (Figure
Bold values diferentiate sub and grand totals from detail values.
Number of families found per forest aspect in the Amhara region of Ethiopia.
Average diameter of tree species in a forest in the Amhara region of Ethiopia.Fudi Natural Forest in Fagta Lekoma district, Amhara region, northwestern Ethiopia, comprises 32 families and 46 species.Te most common families in the northeast, north, northwest, southwest, southeast and, west regions were Mimosoideae, Euphorbiaceae, Celastraceae, and Rubiaceae; International Journal of Forestry Research.Conclusion