The Effect of Closed Area on Woody Species Regeneration: A Case study in Loma Bosa Woreda, Dawuro zone, Southern Ethiopia

This study examines the effect of closed area on woody species regeneration by comparing the woody species regeneration among closure, open woodland, and degraded land areas in Loma Bosa district, zone in southern Ethiopia. Results show that Simpson's Diversity Index was 7.24 for woody species in closed area, 6.01 in open woodland and 3.40 in open degraded land area. Shannon-Weiner Diversity Index(H') was 2.26 for woody species in closed area, 2.38 in open woodland area and 1.56 in open degraded land area. The results of Sorenson's similarity coecients indicates woody species composition in closed area are highly correlated with open woodland areas. Wood species density were 2,225 ha -1 , 1,642 ha -1 , and 297 ha -1 for closed area, open woodland area, and open degraded land area, respectively. The results indicate that closed area development enhanced species composition, richness, diversity, woody vegetation regeneration, inverted J shape Diameter at Breast Height (DBH) and height class and higher woody species density and crown cover class percentage compared to open degraded area. Overall results from this study indicated that area closure is important for improvement of woody species regeneration in the study area. ha, species regeneration, crown cover than open

The major consequences of land degradation in Ethiopia include low or declining agricultural productivity, increase in food insecurity, loss of biodiversity, drying up of springs and water bodies, increased incidence of water-borne diseases, climate change, and deserti cation (Taddese, 2001;Abebe et al., 2014;Gashaw et al., 2018). The diagram in Fig. 1 summarizes the causes and consequences of land degradation that negatively affect the economy, environment and livelihoods of people in the country.
To combat the deforestation and land degradation problems, Ethiopia has initiated extensive number of rehabilitation programs, including establishment of closed areas and soil and water conservation activities.
Particularly, the establishment of area closure considered an important tool to rehabilitate the degraded land, improve agricultural productivity, restore natural vegetation, reduce soil erosion, improve hydrological cycles and microclimate in the country (Betru et al., 2005;Mekuria et al., 2013;Teketay et al., 2018).
Following Betru et al. (2005), the operational de nition of closed area in this study context is "the degraded communal land that has been excluded from livestock and human interference for rehabilitation". The main purposes of area closure in country is to improve agricultural productivity, restore vegetation, species composition, biomass, richness, diversity, and providing overall ecological functions to local communities (Kasim et al., 2015;Mekuria et al., 2018;Teketay et al., 2018). In principle, human and livestock interference is limited or completely restricted in closed areas to encourage rehabilitation of degraded lands and regeneration of natural vegetation in Ethiopia; however, several challenges are facing to make it fully realize. Because, in practice, in several places, local communities allow their livestock to free graze in the closed areas. Moreover, cutting grass and collection of fuel woods from dead trees are continued (Nedessa et al., 2005). Therefore, despite government efforts to combat land degradation and deforestation, natural forests in Ethiopia are declining rapidly due to their conversion to arable lands coupled with inappropriate and excessive utilization triggered by increasing population growth (Senbeta et al., 2002). This situation has continued in the country. For instance, a report by FAO (2015) on Global Forest Resource Assessment (GFRA) indicates that the forest resource and other wooded land area change rate in the country is negative 104,000 ha per years since years 1990 to 2015. They suggest that the remaining high forests and biodiversity under threatened and will disappear within a few decades in the country. Hence, the major task facing Ethiopia includes protection and sustainable utilization of the remaining natural forests, expansion of tree plantation and restoration of degraded lands by establishing area closure in several parts of the country. Particularly, establishing area closure on degraded land is considered as a cheap and convenient means of rehabilitating degraded areas, and convenient for economically poor countries such as Ethiopia. Because in a closed area, rehabilitation of land or restoration of natural vegetation cover is primarily a natural process and human inputs are very limited to offering protection against interference. As a result, some call it 'zero management' strategy for rehabilitation of degraded land and restoration of natural vegetation. This process makes area closure economically the cheapest method of rehabilitation of degraded area (Teketay et al., 2018). Now a day, closed area become very common and important tool to rehabilitate of degraded lands especially in the southern Ethiopia including Dawuro zone, Loma Bosa district because of the impressive changes in terms of ecological restoration, improve ecological succession, regeneration of different plant diversity, improvement of productivity, reduction of runoff and soil erosion and over all agro-ecological stabilization. Therefore, this research is to examine the effect of closed area on woody species regeneration by comparing the woody species regeneration between closure, open woodland and degraded land area in the Zima Waruma kebele of Loma Bosa district in Dawuro zone, Southern Ethiopia.

Description of study area
The study area of this study is Loma Bosa district located in Dawuro zone of the Southern Nation Nationalities and Peoples Regional State (SNNPR) of Ethiopia. The geographical location of Loma Bosa district is between 6°42'13"-6°53'48"N lat. and 37°00'20"E-37°15'48"E long. The elevation of the district ranges from 700 m to 2600 m above sea level (masl). District is composed of three agro-ecological zones namely high land, midland, and low land.
The topography of Loma Bosa district varies from undulating landscape to an extended, steep slope and mountains. The district is a source of many perennial and seasonal rivers, which ow to Omo river, the largest river in southern Ethiopia. Those rivers are Karata, Koma, Bokoli, Ugumono, Tone, Wuni, Maula, Koranto and Manta. Currently, Omo river the main source of electric power to the Ethiopia. Different hydroelectric dams such as Gibe I, II, III and Koyisha (Gibe IV-under construction) are station on Omo river.
The soil characteristics of the district varies with its agro-ecological zones and landscapes of the catchments area. In high land agro-ecological zone, the soil is the deeper than other two agro ecological zones; but fertility states is less because of steeper slope of the farmland and high rainfall. As result the farmer in high land agro-ecology are using commercial fertilizer, farmyard manure and compost for crop production. In the low land, the depth of the soil is very less and stone is frequent in farmland, as result stone bund constructed on farming land and closed area in communal land. However, in all three agro-ecological zones of the district, deforestation, soil erosion and land degradation are the major problem due to topographic future and misuse of forest resources.
Zima Waruma (Fig. 2), the study site, is located in Loma Bosa district of the Dawuro zone. The altitude of Zima Waruma lies 720 to 1800 masl, and has an annual rainfall of 1000-1300 mm. The climatic condition of the area is lowland agro climatic zone; the amount of rainfall distribution through the year is erratic. The study area receives less rain than the other Kebeles in the Loma Bosa distirct. The temperature range in the area is 15.1-27.5 °C with the higher temperature in the lower part of the watershed or Omo river. The soil of the study site is classi ed under Orthic Acrisols. The population of Zima Waruma is about 3,724, of which 1879 male and 1845 is female. Mixed agriculture (crop production and livestock rearing) is the main economic activity in the study site. The major crops are grown in the areas include, Zea mays L., Sorghum bicolor, Eragrostis tef, Phaseolus vulgaris, Ipomoea batatas and Manihot esculenta are widely cultivated (Wolka et al., 2013).

Sampling and data collection techniques
Since this is the rst investigation after establishment of the closed area, it is challenge to explain the full process of the vegetation dynamics in study site. However, changes after the establishment of closed area were described using some important parameters such as woody species composition (relative contribution of individual species; density and cover) and diversity measurements (e.g., richness and evenness) in the study site (Seid et al., 2020) compared with the open woodland and adjacent open lands. The assumption in this study is that the closed area and open areas had similar conditions before establishment of the closed area.

Sampling techniques
To obtain overviews of the closed area activities and woody species regeneration, the reconnaissance survey was made in 2018 before the actual eldwork in the study area. Contacts were made and consent had reached with the Dawuro zone Agriculture and Natural Resource and Department of environment, forest and climate change at Loma Bosa district before starting actual eldwork. Accordingly, they assigned the technical experts who have experience on natural resource data collection to assist and facilitate the data collection process. Speci c training and orientation on collecting the data and on lling the questioners were given for all experts involved in the data collection. Moreover, a brief introduction about the purpose of the study was given for the kebele ( The Simpson's Diversity Index was developed by Simpson (1949) and given as

( )
Where D is Simpson's diversity index, which ranges the value between zero and one. The zero value represents in nite diversity and one represents no diversity. That is, the bigger the value of D, the lower the diversity of The Shannon-Weiner index (Barnes et al. 1998) assumes that all species are represented in a sample and that the sample was obtained randomly. The index obtained from the following equation Where pi is is the proportion of individuals that belong to species i; R is the number of species in the sample, and ln is the natural logarithm. The term in the parenthesis equal to the true diversity (i.e., D) and H'=ln(D). A limitation for Shannon-Weiner index is that its value usually biased toward measuring species richness in a sample.
Evenness index (J) or equitability of species was calculated using the Shannon Evenness index equation as Where H'Max is equal to ln(R); H' represents Shannon diversity index; lnR represents the natural logarithm of the total number of species in each community, and R represents the number of species in each community (Shannon and Weiner, 1949). The higher the values of Shannon evenness (J), the more even the species are by their distribution. Likewise, the higher the value of Shannon diversity index (H'), the more diverse the community are. If the community has one species, the index will be close to zero. If all species in the data set are equally common, all pi values will be equal to 1/R and the Shannon-Weiner index equals ln(R). The collected data from each closed area, based on the parameters indicated above, ware compared to its adjacent open land to evaluate the effect of closed area on species richness and diversity.

The similarity between the closed area and open areas in their woody species vegetation was analyzed using
Sørenson's Similarity Coe cient (SSC) (Krebs, 1999;Tamrat, 1993).
Where a represents number of plant species common to both habitats (i.e., closed and open areas); b represents number of species in the rst habitat but absent in the second; and c represents number of species preset in the second habitat but absent in the rst.  *Seedlings indicate less than 0.5 m height only of which their numbers were counted. Seedling is less than 2.5 cm at DBH and below 1.5 m in height, saplings at DBH 2.5 cm and height between 1.5 cm to 2 m above ground, shrubs all multi-stem woody plants below stump height with DBH more than 2.5 cm and height more than 0.5 m, and trees at DBH above 2.5 cm and height more than 2 m.

( )
No. Scienti c name of species *Seedlings indicate less than 0.5 m height only of which their numbers were counted. Seedling is less than 2.5 cm at DBH and below 1.5 m in height, saplings at DBH 2.5 cm and height between 1.5 cm to 2 m above ground, shrubs all multi-stem woody plants below stump height with DBH more than 2.5 cm and height more than 0.5 m, and trees at DBH above 2.5 cm and height more than 2 m. as illegal cutting of trees, free or over grazing, and absence of effective keeping system. This result is consistent with the studies that concluded as humans modify the oristic composition and structure of forests during the process of utilization for their immediate purpose of best goods and services (Wiersum, 1997), but activities such as establishment of the closed area are among other factors that assist in improving the overall ecological conditions of degraded land areas (Mengistu et al., 2005) and allowed regeneration of woody species.

Species richness, diversity and evenness
A combination of the number of species and their relative abundance de nes the species diversity in general and woody species in particular. The value of woody species diversity depends on the level of species richness and evenness. This study has shown species richness in the closed area is the higher than among other corresponding habitats.
The diversity value was tested in both Simpson's and Shannon Weiner Diversity index ( area reveals that the areas are dominated by a few woody species. This is because, of an illegal cutting of naturally regenerated seedling with grass, planting of a few tree species by the development program, and protection of existing shrubs and trees from illegal cutting which resulted dominance of a few woody species in the closed area. Hence, dominance is inversely related to evenness, the closed areas are considered to be dominated by few species but with higher species richness than other habitats (see Table 4). The result is consistent with the studies by (Giday, 2002 andMengistu et al., 2005) that showed closed area enhanced species richness, diversity and vegetation regeneration. This higher proportion of woody vegetation in the closed area suggests the existence of an active regeneration and succession of woody vegetation's. This resulted due to restriction of humans, animal interference and effective keeping system. The result showed that the species richness, diversity and density of woody species were signi cantly higher in the closed area than open degraded land suggesting closed area enhanced woody species regeneration in relatively short periods by avoiding or minimizing human and livestock interference in the degraded areas. Similar results were reported by Birhane (2002), Giday (2002) and  (Table 5). There is similarity of woody species regeneration across the closed area and woodland of study sites. This similarity may be due to altitudinal range, geographic location, climatic conditions and the woody vegetation composition. There is variation of woody species composition between closed area and open degraded and. This in turn may be due to a closed area developments, which increases the species regeneration by protecting from human and livestock interferences. The composition of woody species similarity across the sites is also not even. woodland and degraded land. Less seedling density were counted in closed area may be because much seedlings were cut down due to grass cutting system. The density per ha of seedling in open wood land was higher than that of the closed area, but its growth potential to the next generation was less than closed area due to sever disturbance regime (87% the seedling not survived to sapling). Therefore, closed area resulted in the best growth potential to the next generation and highest percentage of tree in study site. This indicating the effect of closed area management and effective protection of land promoted woody vegetation density and regeneration in closed area. This result is in harmony with a study by Birhane (2002) who concluded that closed area increased woody species density in Ethiopia.   (Table 6 and Fig. 3).
Based on the regeneration status of 23 different woody species composition within closed area the seedling, sapling and trees or shrubs occurred species has 12 (52.2%) out of 23 woody species (Fig. 4). Taking seedlings into consideration 4 woody species for examples Dedonaea viscosa, Flacourtia indica, Strychos innocua, and Ficus sycomorus not found by seedling stage in closed area. Taking sapling in the consideration 10 woody species for examples Aloe vera, Flacourtia indica, Strychos innocua, Vitex doniane, Hagiluwa (in local name), Teema (local name), Dobiya (local name), Atiya (local name), Kasiyo (local name) and Ficus sycomorus not represented by sapling stage in closed area. Taking trees/shrubs in to consideration Aloe vera, Vitex doniane, Teema, Atiya (local name) and Kasiyo woody species not represented by trees/shrubs stage in closed area (see , Table 1). Sobowa and Conbretum collinum are the two most dominating trees and Dichrostrachys cinocera the most dominating woody species at seedling stage in closed area (Fig. 4).
Based on the regeneration status of 22 different woody species composition in open woodland of study site the seedling, sapling and trees or shrubs occurred species is 8(36.4%) out of 22 woody species (Fig. 5) (Table 2 and Fig. 5).
The regeneration status of 8 different woody species composition in open degraded land of Zima Waruma study site the seedling, sapling and trees or shrubs occurred species is 4 (50%) out of 8 woody species (Fig. 6) Albizia granibracteate, Dichrostrachys cinocera, Grewia bicolor and Prosopis juli ora are example of woody species found at both stages. Conbretum molle, Strychos innocua and Conbretum collinum are not found in seedling stage at degraded land. Taking  The density of woody species in closed area was the highest from other habitats and all DBH classes except the rst and last class (Fig. 7). This indicates that closed area activity enhanced woody species regeneration. Closed area promoted species density and protection from interference improved diameter size. Other study supports that management of closed area ensures the probability of plant growth to high diameter size which will enhance the probability of seed-bearing plants for seed dispersal and germination to seedlings (Teketay, 1997), which enhance future regeneration. Accordingly, the woody vegetation frequency distribution in closed area and open woodland showed inverted J shape pattern of distribution indicating high degree of woody vegetation heterogeneity (Shibru & Balcha, 2004). Open woodland a sharp decline of rst DBH class to the second class affected the inverted J shape slightly. However, the density distribution of vegetation in open degraded lands has not shown inverted or normal J shape pattern of distribution due to higher level of disturbance (Fig. 7).
Height classes were divided into four height classes from 0.1-2m to 10.1-15m classes based on measurement results (Fig. 8). All the seedling, saplings and some of the shrubs less than 2 m height were recorded in lower height classes in both study habitats. In closed area from the total 2,225 ha − 1 woody species, 38% density of woody species constituted the rst height class, 28% woody species 2-5 m height class, 21.3% woody species 5. The tree height analysis result has shown that the density of woody species in closed area constituted the highest density distribution from other habitats and in all height classes except 0.1 to 2 m class (Fig. 8). The tree height percentage density distribution decreased with an increase in height class showing inverted J shape pattern of distribution in closed area. Open woodland has shown the highest number of density per ha in the lowest height class only. However, open woodland higher height class from 5.1-15m trees distribution has shown much declined density and signi cantly affected by disturbance. This shows illegal cutting of tree affected open woodland which affect seed bearing woody species and future regeneration at risk. This has indicated closed area development and management enhancing woody species regeneration and important means of solution for rehabilitation of degraded vegetation (Fig. 8).

Woody vegetation crown cover classes
In this study the horizontal crown distribution covered the surface of closed area to reduce erosion and vegetation degradation. Woody vegetation cover reduced the rain drop impact on soil as well as the velocity of erosion. The litter fall in the surface was decomposed and added nutrient to the soil which increases the regeneration of species and enhance succession. Seven crown cover classes prepared and crown cover of horizontal surface by woody species data collected by format absent or less than 1% cover, 1 to 5% cover, 6 to 10% cover, 11 to 25% cover, 26 to 50% cover, 51 to 75% cover and 76 to 100% cover classes used and data collected from each habitat of study sites.
The research was conducted in Zima Waruma site of Loma Bossa district in Dawuro zone, Southern Ethiopia with the aim of understanding the effect of closed area on woody species regeneration through eld vegetation assessment of woody species and comparing among closed area, open Combretum-Terminalia woodland area and open degraded land in the study site.
The results of this study showed that closed area had the highest woody species compositions, richness, density per ha, woody species regeneration, and crown

Recommendations
Closed area should be one of the development options to solve the land and woody vegetation degradation in the study site. The effect of closed area on woody species regeneration enhanced natural regeneration, woody species composition and richness compared to other habitats in study area. As a result, closed area development and conservation options should be practiced at similar agro-ecological zones to sustainably manage, utilize vegetation resource in general and conserve the endangered woodland area species in particular. As a result, additional plantation with indigenous and fast-growing species, integrating soil and water conservation, water harvesting trenches and micro-basin should be introduced to improve the natural regeneration status and maximize diversity of woody species. Plantation of fast-growing multipurpose tree and shrubs, agroforestry in homestead area for household energy, construction material and forage should be considered for future sustainability of closed area for more success of regeneration.
Finally, further detailed study is needed on the effect of closed area on soil environment and soil seed bank, water shade development, wildlife, sustainable use of wood and non-wood products from closed area, as well as ethno-botanical value and different uses of regenerated woody species in closed area.

Declarations
Ethics approval and consent to participate Authors declare that there is no information related with an experiment on humans and/or the use of human tissue samples in this paper. Plant woody species data were collected from led following agreed consent with Dawuro zone and Loma Bosa district agriculture and natural resource o ces.