A Comparative Study of Indigenous Woody Species Diversity and Regeneration Status Among Plantations of Three Exotic Tree Species and Natural Forest, in Gomma District, South-western Ethiopia

doi:10.21203/rs.3.rs-4340190/v1

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A Comparative Study of Indigenous Woody Species Diversity and Regeneration Status Among Plantations of Three Exotic Tree Species and Natural Forest, in Gomma District, South-western Ethiopia

https://doi.org/10.21203/rs.3.rs-4340190/v1

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Diversity, density and species composition of naturally regenerated indigenous woody species under three selected exotic tree plantations (Eucalyptus camaldulensis, Grevillea robusta and Cupressus lusitanica) and the adjacent natural forests were investigated in Gomma district. The objective of this study was to verify the hypothesis that the diversity and regeneration status of indigenous woody species differ among plantations of the three exotic tree species and the adjacent natural forest patches. Three sites (kebeles) were purposively selected from three altitudinal ranges (agroecological zones). Four quadrats of size 10 m × 10 m were established for each of stand at all sites, and generally 48 quadrats were laid down along transect line with 50m interval between plots. Within each main plot, five 1m x 1m subplots were also laid. All matured trees/shrubs of indigenous woody species were identified, measured and counted from each main plot, while saplings and seedlings were collected from subplots. A total of 49 woody plant species belonging to 41 genera and 27 families were identified from all plantations and natural forest stands. The highest number of species was recorded for natural forest patches followed by Eucalyptus camaldulensis, Grevillea robusta and Cupressus lusitanica plantation stands. Similarly, highest density was recorded for the Eucalyptus camaldulensis among plantation stands. The Eucalyptus camaldulensis stands showed the highest Shannon diversity (H’ = 2.67) and Cupressus lusitanica showed the least (H’ = 2.05) among plantation stands. Almost the population structure of all stands in the present study showed an inverse J-shape. This implies that the population is composed of numerous individuals at the seedling stage, and decreases continuously or gradually as height increases, and hence indicates healthy regeneration. The study revealed that regeneration and diversity of indigenous woody species were significantly different under the canopies of exotic plantations. E. camaldulensis and G. robusta plantation stands showed higher density and diversity than C. lusitanica stands, but for successful regeneration, there should be seeds sources and seed dispersal agents (e.g., animals) and knowledge of biodiversity management.

indigenous woody species

regeneration

stands

diversity

natural forest patches

Forest lands, agricultural lands, marginal lands, and other types of land use are being converted to exotic tree plantations in Ethiopia as a result of population pressure, irresponsible resource usage, and strong demand for fast-growing exotic tree species. According to FAO [1] and FRA [2], the majority of the forest plantations in Ethiopia are monocultures of exotic species such Eucalyptus camaldulensis, Eucalyptus globulus, Cupressus lusitanica, Grevillea robusta, Casuarina cunninghamiana, Pinus patula, and Pinus radiata. In particular, the only practical option to initially reforest the degraded areas, then to transform them into permanent forest [3], appropriate monoculture plantation of fast-growing species like Eucalyptus species, Acacia, Teak, Poplar, etc., has proven to be one of relevant approaches for afforestation programs, both in economic and ecological purposes.

Controversial ideas were raised among many scholars on regeneration and diversity of native woody species under exotic tree plantations. Some regeneration studies on plantations of Eucalyptus globulus, Eucalyptus saligna, Eucalyptus grandis, Pinus patula, Pinus radiata, Cupressus lusitanica and Grevillea robusta established at localities with high amounts of rain-fall and in relatively high altitudes of Ethiopia, proved a surprising catalytic role of these monocultures with regard to habitat recolonisation by native woody plants [4–7]. On the other hand, some studies have shown exotic tree species could hamper the regeneration of native species by different mechanisms such as completion for nutrient, allelophatic effects, etc [1, 8].

Most studies also revealed that the regeneration and diversity of indigenous woody species are significantly different under the canopies of different exotic tree species. For example, Eucalyptus species play a significant role in fostering for the regeneration of indigenous woody species diversity, while, the Cupressus lusitanica has relatively less indigenous woody species diversity, which could be due to high shading conditions and less litter decomposition [6]. On the other hand, another studies have shown that the understory woody species diversity were higher in Cupressus lusitanica than Eucalyptus species [9, 10] and Grevillea robusta plantations [11].

Even though the regeneration status and diversity of indigenous woody species under exotic tree plantations were studied, comparative study among the exotic tree species and relating to the current landscape management is necessary and need continuous study for sound landscape management. And also, there are still controversial ideas among many scholars on the exotic tree species whether they have significant positive impact for regeneration and diversity of indigenous woody species under their canopies or not and the comparative study among the exotic tree species needs extra investigations. Therefore, this study would give insights on regeneration status of indigenous woody species growing under three exotic tree plantations and adjacent natural forest patches.

The study was conducted to satisfy the following specific objectives:

To determine the composition, density, and diversity of indigenous woody species under the canopy of each exotic tree plantation/stand and the adjacent natural forests
To assess the regeneration status of indigenous woody species under the canopy of each exotic tree stand and compare the species composition (similarity) between stands/forests

2.1 Description of the Study Area

The study was conducted in Gomma District, Jimma zone, Oromia National Regional State, South-western Ethiopia. It is located at 395 km south west of Addis Ababa and about 45 km west of Jimma town. It is bordered on the south by Seka Chekorsa, on the southwest by Gera on the northwest by Setama on the north by the Didessa, on the northeast by Limmu Kosa and on the east by Manna. The district lies approximately between 7^o 40’00’’ − 8^o 03’30’’ N latitudes and 36^o 25’00’’ − 36^o 45’00’’E longitudes (Fig. 3.1); altitudinal ranges from 1,380 to 2870 meters above sea level. The mean annual rainfall is about 1524 mm with bi-modal distribution.

2.2 Sampling Technique and Sample Size

The study was conducted among from 36 rural kebeles where plantations/stands of the selected three exotic tree species (Eucalyptus species, Cupressus lustannica and Grevillea robusta) exist. The preliminary assessment showed that the three selected exotic tree species plantations/stands exist in 15 kebeles mostly on individual farmers’ land (Fig. 2.1).

From the total 15 kebeles (colored kebeles in Fig. 2.1), in which the plantations/stands of Eucalyptus species, Cupressus lustannica and Grevillea robusta exist, three sites/kebeles were purposively selected based on agroecology, availability of natural forests adjacent to each stand, availability of the plantations/stands more or less around the same site, accessibility of road, etc (Fig. 2.1). Accordingly, the three sites/kebeles were selected from three agroecological zones; one site/kebele from each agroecological zone. The three sites/kebeles selected were Yachiaurache, Aomafantule and Aomobeko from Kola/lowland, Woina Dega/midland and Dega/highland agroecological zones respectively. From each site/kebele, three plantations/stands (one plantation/stand for each selected exotic tree) and adjacent natural forest stand/patch were identified. Then, the total stands were 12; nine exotic tree plantations and three natural forest patches. The plantations/stands in each site/kebele were adjacent to one another.

Following a reconnaissance survey, actual sampling of vegetation was done focusing on appropriate sampling methods. Hence, systematic sampling design was employed. For each plantation/stand and forest patch, quadrats with 10mx10m were laid at 50m intervals using line transect survey method considering edge effect as described by Bullock (1996). Four square plots (quadrats of size 10mx10m) were laid in each stand. Within each main plot, five 1m x 1m subplots were laid to collect data regarding seedlings and saplings. A total of 48 plots (36 plots for exotic tree plantations and 12 plots for natural forest patches), 16 plots at each site/kebele were laid. GPS Garmin 60 was used to take site characteristics and quadrats points.

2.3 Method of Data Collection

From a total of 48 plots, all of the naturally regenerated woody species were identified, measured and counted. The indigenous woody plant species were categorized into three based on their height as seedlings (height ≤ 1m), saplings (height > 1m and ≤ 2m) and matured shrub/tree (height > 2m). The diameter at breast height (DBH) of all matured trees and shrubs (height > 2m and/or ≥ 2.5 cm DBH) within the main plot was measured using measuring tape and height was measured using centimetre marked stick, measuring tape and ruler with help of trigonometric calculation.

The height and collar diameter (diameter at the ground level) of seedlings and saplings within the subplot were measured using a centimetre marked stick and measuring tape, respectively. The identification of all indigenous woody plant species was carried out in the field with help of local elders who are experienced in knowing more plant names in local language. Then, the identified local names were crosschecked and matched using identification keys of Useful trees and Shrubs of Ethiopia: identification, propagation, and management for 17 agro climatic zones [12].

2.4 Method of Data Analysis

The data obtained from the three exotic tree species of nine plantations/stands and three adjacent natural forest patches about diversity and regeneration status of indigenous woody species were merged into four stands as Eucalyptus, Grevillea, Cupressus and Natural forest stands for analysis and interpretation.

The diversity, density, evenness, and richness of indigenous woody species were analysed using commonly used biodiversity measuring formulas and methods. Shannon diversity index (H′) and Shannon evenness index (J’) were used to measure diversity of naturally regenerated indigenous woody species in the different plantations and adjacent natural forests [13, 14]. These help to measure diversity of naturally regenerated indigenous woody species in the different plantations. And the similarity index of understory regenerated native woody species in the different stands was calculated using Jaccard’s Coefficient of Similarity (JCS) [13, 14].

The Species richness is measured to know how much number of different kinds of woody species presents in each stand; and from the results to compare between stands species composition. Species richness computed simply by counting the number of types of indigenous woody species (taxa) regenerated in a stand (S’). And the Margalef index, was used to compute the species richness for each stand. This index takes the total observed individuals ‘N’ as one factor in the computation. And the formula is as follows:

R=(S’-1)/lnN “Eq. 1”

Where, R is Margalef index of species richness; S’ is number of taxa or species; N is number of individuals.

Thus, the higher the R index value, the richer is the stand in species.

The diversity of species is computed to know how diverse (in item and abundance) the species present in each stand. Or to know how much is the average degree of uncertainty in predicting to what species an individual chosen at random is from the population of a collection of species. Species diversity is analyzed by using the most popular of metrics Shannon-Wiener Diversity Index (H’) and Simpson’s Index, D [13, 14, 15].

Shannon diversity index (H’) is a non-parametric index based on the proportional abundance of species taking into account both species richness and evenness [14]. It can be determined using the equation:

𝐻′ = − ∑ 𝑝𝑖 𝑙𝑛𝑝𝑖 “Eq.2”

Where 𝑝𝑖 represents the proportion of the population that belonging to the i^th species

Evenness is a measure of how similar species are in their abundances. And as a heterogeneity measure, it describes the equitability of species abundance in the community [14]. Evenness is calculated using Shannon Evenness index (E’) [13]. And the formula of evenness index is described as follows:

\({E}^{{\prime }}= \frac{H{\prime }}{H{\prime }max}\) “Eq. 3”

Where, H’ is observed diversity (Shannon diversity index); H′max is equal to natural logarithm of richness, ln S.

Thus, an assemblage in which most species are equally abundant is one that has high evenness. And it is conventional to equate high diversity with high evenness (equivalent to low dominance of one or few species) [14].

The Density of species expresses how many members of that particular specie are found in the forest. Or it expresses the abundance of the specie in that forest. And it is computed as the division of the number of plants of a certain species by the area sampled expressed in hectare.

Basal area is the cross-sectional area of tree stems at breast height. It is measured through diameter, usually at breast height that is 1.3 m above ground level. It measures the relative dominance (the degree of coverage of a species as an expression of the space it occupies) of a species in a forest [16]. It is calculated as:

𝐵𝐴 = 𝜋 𝑥 (𝐷𝐵𝐻)² “Eq.4”

Where, BA = basal area (m2), DBH = diameter at breast height (cm); π = 3.14

Dominance refers to the degree of coverage of a species as an expression of the space it occupied in a given area. Usually, dominance is expressed in terms of basal area of the species [15]. Two set of dominance: dominance (the sum of basal areas of the individuals in m2/ha), and relative dominance, which is the percentage of the total basal area of a given species out of the total measured stem basal areas of all species.

\(Dominance= \frac{Total basal area}{Area sampled}\) “Eq. 5”

\(Relative dominance= \frac{Dominance of species A}{Total dominance of all species}x100\) “Eq. 6”

Frequency is defined as the probability or chance of finding a species in a given sample area or quadrant [18]. Thus, it shows the presence or absence of a given species within each sample plot. Frequency will be computed for each woody species encountered within the study plots:

\(Frequency of species = \frac{Number of plots in which that species occurs}{Total number of plots}\) “Eq. 7”

\(Relative frequency= \frac{Frequency of species A}{Total frequency of all species} x 100\) “Eq. 8”

The Similarity analysis is used to identify the highly similar and or dissimilar stands in their understory plant composition. The similarity is analysed using a statistical measure of similarity Jaccard’s Similarity Coefficient (JSC) [13, 14]. The Jaccard index for two sets, set A and set B, is defined as the cardinality of their intersection divided by the cardinality of their union. Mathematically, this can be is described as follows:

J(A,B)=[AnB]/[AUB] “Eq. 9”

Where, A and B are assumed as stand 1 and stand 2.

Or,

C_j=j/(a + b-j) “Eq. 10”

Where, j = the number of species found in both sites and a = the number of species in stand 1 with b the number of species in stand 2.

The status of natural regeneration of indigenous woody species in a stand or in a forest as a whole can be determined from population structures. Population structure refers to the distribution of individuals in arbitrarily defined by diameter or height classes. In this study, the height class category of regeneration was followed based on seedlings, saplings and mature trees [18], as shown in the following manners:

Seedling > sapling > tree/shrub state, pattern represents good regeneration
Seedling outnumbers sapling and tree/shrub state but sapling less than tree/shrub state pattern fair regeneration
Seedling < sapling < tree/shrub state, this pattern shows poor reproduction and hampered regeneration
With no individual in seedling and sapling stages but relatively many individuals in matured tree/shrub stage pattern shows poor reproduction and hampered regeneration

Then the values evaluated by using height class histograms, (Height class vs. % proportion of density). And from the population structure one of the two types of regeneration status will be determined: good regeneration status or poor or hampered regeneration status in determining regenerating ability of both a stand and a species. Those Species which possess high number of individuals in the lower height category, particularly in the first two categories, are considered to have good regeneration potential; whereas, other species which possess either no or few number of individuals are in poor regeneration status. From this analysis, the species which show good regeneration or hampered regeneration status in each stand or for the forest as a whole were described.

A computer program, Microsoft Excel, and R Statistical software were employed for data analysis. To make computation and analysis for diversity, evenness, abundance and status of growth and to draw graphs, curves and tables, a computer program, Microsoft Excel was employed while R Statistical software was employed for all statistical analyses.

Density and species richness as well as co-variables affecting density and species richness of IWS were analysed using a generalized linear model (GLM) specifying negative binomial distribution with log link function (using the R MASS package). Chi-square and correlation tests were used to test the significance of distribution of density and species richness of different stands among agro-ecologies/altitudinal ranges and to test the interdependence or relationship between density and species richness of IWS and other co-variables respectively.

For basal area (BA), Shannon diversity index, Richness index and evenness, one-way ANOVA (with log transformation to account for the large variation in the standard deviations) was used. Significant results (alpha ≤ 0.05) were compared using the glht function of the R multcomp package for GLM and ANOVA models.

3.1 Results of Descriptive Statics of Study Variables

3.1.1 Density and Structure of Species Regeneration

The status of the natural regeneration under the canopies of forests can be revealed from the DBH class distribution histograms of the species of each stand. DBH class distribution of the naturally regenerated understory indigenous woody species showed similar rends almost in all stands (Fig. 3.1). The proportion of individuals showed a typical inversed J- shaped curve with many small individuals and few or no large individuals in most of the plantation stands, indicating a maximum number of seedlings, lower proportion of saplings and relatively few mature trees/shrubs (Fig. 3.1). Thus, the result shows the presence of more seedlings than saplings and saplings than mature trees, which indicates successful regeneration status of species almost in all stands. But, important timber species such as Pouteria adolfi-friedrichi and Podocarpus falcatus and most other woody species were not regenerated in the plantation stands which might be attributed to scarcity of seed sources or the ecological requirements for seed germination or absence of seed dispersal agents and seedling growth of the species.

3.1.2 Frequency distribution

The most frequently occurred indigenous woody species (IWS) under plantations/stands are given in Fig. 4 below. In all stands, the three types of indigenous woody species most frequently occurred are Vernonia auriculifera, Croton macrostachyus, and Maesa lanceolata with relative frequency (and number of plots in which the species is occurred) of 14.87% (29), 14.36% (28), and 8.72% (17) respectively while the relative frequency (and number of plots in which the species is occurred) of top five most frequently occurred woody species in natural forest stands were Coffee arabica (100%(12)), Clausenia anisata (75%(9)), Syzygium guineense (67%(8)), Croton macrostachyus (58%(7)) and Albizia gummiffera (58%(7)). This result showed that Coffee Arabica was the most frequent and abundant species evenly distributed throughout the natural forests in the study district. Generally, from the cumulative plots of all plantation and natural forest stands (from 48 quadrat plots), the relative frequency (and number of plots in which the species is occurred) of the top five most frequently occurred indigenous woody species from the study area were Croton macrostachyus (73%(35)), Vernonia auriculifera (71%(34)), Maesa lanceolata (46%(22)), Albizia gummiffera and Calpurina aurea each 42%(20) (Fig. 3.2).

3.2. Inferential Analysis of variables

3.2.1. Species Diversity

Species diversity is generally assessed by using diversity index, which incorporates information on species richness and evenness. Diversity measures or heterogeneity measures can also be analysed using rank/abundance plot. The result of Species diversity indexes (H′) of stands revealed that generally Natural forest was more diverse (3.29) and C. lusitanica was the least (2.05). Among plantation stands, the natural regeneration of native woody species in the Eucalyptus plantation was more diverse (2.67) than the other two plantations. Generally, the results of Shannon diversity index in the present study showed moderate values for all stands. This condition might be happened due to the prehistory of the plantation sites might be forest land or have seed bank.

Statistically, there were significant differences among plantations on their Shannon diversity index and richness index. But, there was no statistically significant difference on evenness among plantations (Table 3.1).

Table 3.1

Mean variation analysis for different parameters among plantation types and sites
Plantation types	Means for parameters
Plantation types	Number of individuals (N)	Number of species (S’)	Marglef Species richness index (R)	Diversity index (H’)	Evenness index (J’)
Natural forest	26^a	12.92^a	3.58^a	2.17^a	0.89^a
Eucalyptus	11.92^b	6.92^b	2.42^b	1.92^b	0.96^b
Grevillea	9.75^c	5.50^c	2.17^b	1.5^c	0.92^b
Cupressus	5.67^d	3.83^d	1.67^c	1.33^d	0.95^b
Sites
Yachiaurachi	15.56^e	7.69^e	2.50^d	1.81^e	0.91^c
Aomafuntule	12.25^f	7.94^e	2.75^d	1.93^e	0.95^c
Aomobeko	12.18^f	6.25^f	2.13^e	1.43^f	0.93^c

Different letters with in a column show that means are significantly different among particular plantation types or sites at p < 0.05

3.2.2. Species evenness (J’) and richness (R)

The evenness (or similarity in proportion of abundance of naturally regenerated native woody species in a stand; or the equitability of species), as a heterogeneity measure, results is indicated in the Table 3.2. Here the result shows the abundance of regenerated species under Eucalyptus stands are relatively even (0.91) than other stands. And cumulative evenness under that of the natural forest stands is the least (0.85). This was due to the wide abundance range (8-417 individuals Ha^− 1) of regenerates exhibited in natural forest stands than other stands. So, the width of the range in abundance do have an effect on the evenness, J’ of a stand. The presence of extremely dominant (abundant) species can affect the evenness. The more the relative abundance of species differs, the lower the evenness. Low evenness in abundance distribution of species for natural forest was reported from Plantation Stands of Yeraba Priority State Forest [10] which was similar with present study. The result showed that, the natural forest stand is richer in regenerated species than plantation stands (R = 8.36). And from plantations stands E. camaldulensis is richer than others (R = 3.63).

Table 3.2

Summary of average stand value of Richness, Shannon diversity, Evenness and Density in four types of forest stands.
No	Stand	#total	Density Ha-1	Richness		Diversity (H’)	Evenness (J’)
No	Stand	#total	Density Ha-1	S’	R	Diversity (H’)	Evenness (J’)
	Natural forests	312	2600	49	8.36	3.29	0.85
	Eucalyptus	143	1192	19	3.63	2.67	0.91
	Grevillea	117	975	17	3.36	2.47	0.87
	Cupressus	68	567	10	2.13	2.05	0.89

#total = total number of individuals encountered from 12 quadrats for each type of stands; S’=number of species; R = Margalef species richness index.

Cupressus lusitanica is the least stand in species richness (R = 2.13) (Table 3.2). In this estimator, as He and Gaston [19] indicated, the presence and distribution (abundance) of rare species affects the species richness estimate. The existence of these rare species made the richness result higher. For example the Natural forest stands have contained 22 rare species which are not found on the plantation stands. This might show the species are habitat or site specific or absence of seed dispersal agents and/or due to the nature of those species’ seeds.

Among plantation stands, the E. camaldulensis stands contained six rare species which are not found on the other two plantation stands and most of these rare species have high abundance. So the result becomes higher in E. camaldulensis stands than other two plantation stands. Similar results were reported in species richness where E. camaldulensis and G. robusta had higher species richness than the other plantation stands and E. camaldulensis had higher in species richness than C. lusitanica which has been reported by Tesfaye and Wendawek [20], whereas E. globulus and J. procera, each with 27 species, had higher number of species than the remaining plantation stands at Menagesha Suba forest [5]. Unlike different previous reports [6, 9, 10]; where C. lusitanica had the highest species richness among plantation stands, it was found to be lowest in terms of species richness in the present study.

3.3. Similarity in Species Composition between Stands

Jaccard’s Coefficient of Similarity in species composition of naturally regenerated woody species between stands is presented in Table 3.3.

Table 3.3

Jaccard’s Coefficient of Similarity in species composition of naturally regenerated woody species between stands
Stand	E. camaldulensis	G. robusta	C. lusitanica	NF
E. camaldulensis	1.00	0.52	0.21	0.39
G. robusta		1.00	0.29	0.35
C. lusitanica			1.00	0.20
NF				1.00
NF = Natural Forest

Among all stands the maximum Jaccard’s similarity index value in number of regenerated indigenous woody species is exhibited between E. camaldulensis and G. robusta stands which is 0.52, while the least (JCS = 0.20) is exhibited between C. lusitanica and natural forest stands. When we examine the similarity of plantations with the natural stand, E. camaldulensis stand showed higher similarity (JCS = 0.39), and C. lusitanica showed the least (JCS = 0.20) (Table 3.3).

The present study indicated lower similarity (less than 40%) of woody species composition between the adjacent forest stands and plantation stands. This dissimilarity in species composition between plantation stands and natural forests shows that are not ecologically connected. This might be due to the available species pool in the surrounding natural forest, distance between adjacent natural forests and plantation stands, interference or management in plantation stands, the absence of seed dispersal agents and/or impact of the plantations in their underneath woody vegetation. The findings of this study resonate with former studies conducted in Ethiopia [5, 6], which reported low similarity among different plantations and adjacent natural forests.

The results of this study indicated that there is difference on diversity and regeneration status of IWS naturally grown under the canopies of exotic tree species; but, generally they might allow regeneration of indigenous woody species where there are seed sources in the vicinity of the plantations and the area should be protected from grazing and human interference. And appropriate management of the regeneration is very crucial to maintain succession. The difference in the type of taxa, diversity, and density of naturally regenerated native species among the plantation stands of exotic species might be due to their crown architecture/canopy covers, distance of a stand from adjacent forest or source of seeds, and age of stands.

Higher density and diversity of naturally regenerated indigenous woody species were observed in Eucalyptus plantations than in Grevillea and Cupressus plantation stands at all sample sites. This implies Eucalyptus camaldulensis play a significant role in allowing for the regeneration of indigenous woody species diversity than the other two exotic tree stands.

The absence of regenerating important timber species of Pouteria adolfi-friedrichi and Podocarpus falcatus from the plantation stands can be attributed to scarcity of seed sources or the ecological requirements for seed germination or absence of seed dispersal agents and seedling growth of the species.

The findings of this study provide recommendations for the use of tree plantations as a means of facilitating the regeneration of indigenous woody species; but the need to have seed sources in the purlieu to facilitate the regeneration of indigenous woody species under the canopies of tree plantations is a pre-requisite. Therefore, it is very crucial issue to keep sufficient natural forest to maintain seed sources in the vicinity allowing ecological connectivity of natural forest and plantation stand and provide habitats for seed dispersing agents/animals. However, more investigation should be carried out for better understanding of the effects of exotic tree plantations on successional processes such as the dynamics of seeds, i.e. germination of seed, as well as seedling establishment and growth. It is also necessary to investigate how the established native woody species can be manipulated to develop a secondary forest.

Conflict of Interest:

The author declares that there is no conflict of interest and this work my original work

ACKNOWLEDGEMENT

First and foremost, I thank the almighty God for helping me in all my duties. Next, I would like to express my deepest gratitude to my advisor Prof. Kitessa Hundera and co-advisor Mr. Dereje Bekele for their exhaustive review and constructive comments to the finalization of this thesis. Without their guidance and comments, the study would have remained incomplete. Moreover, their gracious care and lovely approaches have far-reaching positive impact on my life and initiated me for further work and I am very grateful to them for that too.

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The authors declare no competing interests.

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A Comparative Study of Indigenous Woody Species Diversity and Regeneration Status Among Plantations of Three Exotic Tree Species and Natural Forest, in Gomma District, South-western Ethiopia

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Abstract

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I. INTRODUCTION

II. RESEARCH METHODOLOGY

III. RESULTS AND DISCUSSION

IV. CONCLUSION AND RECOMMENDATION

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