Comparative Study of Woody Species Composition, Diversity, Structure and Regeneration Status in Traditionally Managed Coffee Agro-forestry System Adjacent to Natural Forest in Gimbo District, Southwest Ethiopia

doi:10.21203/rs.3.rs-2333619/v1

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Comparative Study of Woody Species Composition, Diversity, Structure and Regeneration Status in Traditionally Managed Coffee Agro-forestry System Adjacent to Natural Forest in Gimbo District, Southwest Ethiopia

https://doi.org/10.21203/rs.3.rs-2333619/v1

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Diversity of woody species in natural forests has been threatened by unwise use of forest resources globally. This study was conducted to assess the woody species diversity, structure and regeneration status in the traditionally managed coffee agro-forestry system adjacent to natural forest. The study used vegetation inventory, focus group discussion and key informant interview. Vegetation data were collected from 60(sixty) sample plots (30 from natural forest and 30 from traditionally managed coffee agro-forestry). A sample plot of 20 mx20 m was used for tree and five sub plots in the main plot were used to collect seedling/sapling and shrubs. The result revealed that a total of 75 (53 from natural forest and 22 from coffee agro-forestry system) woody species belonging to 33 were found in the study area. Rubiaceae, Rutaceae and Euphorbiaceae were the dominant families in natural forest while Euphorbiaceae, Rubiaceae, Araliaceae, Moraceae and Boraginaceae are dominant families in coffee ago-forestry system. Sorensen’s coefficient of similarity (SS) (42.76%) indicated similarity of species composition between natural forests and traditionally managed coffee agro-forestry was low. Diversity indices revealed that evenness, Shannon’s and Simpson diversity in natural forest were significantly higher than (p < 0.001) in traditionally managed coffee agro-forestry system. The result also shows that the traditionally managed coffee agro-forestry system has negatively influenced the composition, diversity, and structure and regeneration status of woody species in the study area. Thus, appropriate shade tree management need to be implemented to simultaneously improve the productivity of coffee and conserve woody species diversity in traditionally managed coffee agro-forestry system.

coffee agro-forestry system

diversity

natural forest

regeneration status

Ethiopia has a diverse flora, accounting for 6,200 of the 7,850 floral species found in East Africa (IBC, 2009, 2010). According to Friis et al.,(1982) forest ecosystems, especially the moist evergreen Afromontane forests are the most diverse in terms of species and are the origin and diversity center of Coffea arabica., including the wild gene pool of all farmed arabica coffees (Anthony et al., 2002).

On the other hand, in moist evergreen Afromontane forests of Southwest Ethiopia (Friis 1992), local people have historically managed these Afromontane moist forests for traditional coffee production, as coffee is a major source of income for many rural areas (Gole 2003; Senbeta and Denich 2006; Schmitt et al. 2009). Traditional coffee farm management system such as forest coffee (FC) system, semi-forest coffee (SFC) system, and semi-plantation coffee (SPC) system in the region has a long history of flora diversity and regeneration performance (Senbeta and Denich 2006).

In semi-forest and sub-forest coffee, farmers managed their farms traditionally involve removing all competing vegetation, including canopy tree seedlings and saplings on an annual basis in order to boost coffee yield, (Hundera, 2013).

But the recent report revealed that increased demands for traditional coffee management to produce coffee products through traditional management, like situational based thinning and regular slashing of tree seedlings and saplings has resulted in a constant decline in forest biodiversity and native forest composition on quality, structure and diminishing the native flora diversity, regeneration potentials and fragmentation of tree species (Hundera, 2013).

Besides, there is a deficiency of scientific evidence on how these pressures influence on the tree composition, structure, and regeneration potential of natural forests, as well as the significance of traditional coffee agro-forestry management system of this district.

Therefore, the research aimed to assess the composition, diversity, structure and regeneration status of woody species in traditionally managed coffee agro-forestry system adjacent to natural forest.

Description of the Study Area

The study was conducted in Gimbo district, Kaffa Zone, Southwestern Ethiopia. Gimbo district is located at altitudes between 1000 and 3500 m above sea level. It is located 432 km far from Addis Ababa. Geographically, it is found within 07°4’00”- 7°35’00”N latitude and 36°1’30”-36°31’00”E longitude (Figure. 1).

The forest in this district are fragmented with some undisturbed forest parts and large areas of degraded and disturbed forest. Forest in the study area is classified in the vegetation of Ethiopia referred to as moist evergreen Afromontane forests and located within altitudinal range of 1100–2700 m. above sea level. The forests in this area was normally the richest in species (Friis et al. 1982) and a source of fuel wood, charcoal and timber (Ensermu and Teshome, 2004). The major land cover of district is forest and agriculture associated with human settlement. The forests found in the study area are among the remnant forests in Ethiopia where, different kinds of mammals and birds dwell. The major land use types such as natural forest, agro-forestry, coffee and tea investments, grazing land, wetland, and settlements occupy these zones (Tadesse and Fite, 2011). The main sources of livelihood are forest utilization, livestock rearing and agriculture, (Aklilu et al. 2014). The most income sources of the population are from small-scale agriculture, wild coffee and other non-timber forest products (Melaku and Tsegaye, 2005).

Funding and Conflict of interest.

For this research, researchers (ourselves) funded all needed finances and Logistics thus, there is no conflict of interest for this research for the data or for the whole manuscripts.

Methods

Study Site Selection

Based on the objective of the study, two different land use types namely, coffee agro forestry system and natural forest were selected and assessed. Site selection was carefully determined so that they are representative of traditionally managed coffee agro forestry system adjacent to natural forests, their accessibility to carry out this study and similarity of environmental conditions. Among the sites that fulfilled the required criteria, two representative site were selected purposely. The association of traditionally managed coffee agro forestry system to adjacent natural forests was intended to minimize the effect of environmental factors on vegetation diversity.

Vegetation data collection

Prior to vegetation data collection, reconnaissance survey was carried out at each site to overview the biophysical nature of the sites such as forest types and accessibility.

Systematic sampling strategy was employed to place transect and sampling plot. Four transect along which sample plots laid were placed from lower altitudinal up to higher altitude at a distance of 500m apart and the distance between samples plots were 300m. A total of 60sample plots (30 from agro forestry and 30 from natural forest) were inventoried. The first transect and sample plot were located randomly and subsequent transect and sample plots were lied systematically.

A plot size of 20m × 20m (400m²) was laid along transect and used for floristic inventory, (Kelbessa, 2012; Hundera & Gadissa, 2008; Senbeta &Denich,2006) in Ethiopia’s Afromontane forests. Accordingly, all tree/woody with diameter at breast height (DBH) greater than 2.5 cm was measured within 20 m x 20 m (400m²) while sapling, seedling and shrubs were collected within 5 m x 5 m (25m²) sub-quadrant placed at four corners and one at the middle of main quadrant (20 m x20m). In this study individuals having < 1.5m height and < 2.5cm DBH are counted as seedlings, individuals having > 1.5 m height and DBH less than 10cm was counted as sapling (Ensermu and Teshome, 2004). The height of tree was measured using Suunto clinometers while circumstances is measured using caliper and meter tape. However, tree with height less than 3m was measured by graduated stick. Altitude and geographical point of each main plot was recorded by geographical positioning system (GPS).

Plant identification was done in field by the local name and converted to scientific and vernacular names. Then specimens were identified and confirmed according to flora of Ethiopia and Eritrea by following Edwards et al. (1995, 1997), Asrat and Tesfaye, 2019 and Hedberg et al. (2003, 2006, 2009a).

Data Analysis

The woody species diversity of Shannon’s diversity index (H’), Simpson’s diversity index (1-D), and Shannon’s evenness index (E) was determined by using adopted formula (Kent and Coker, 1992). This is because of compound indices are preferred and effective for diversity analysis and interpretation (Morris et al., 2014). Shannon’s diversity index places more weight on the rare species in the sample, whereas Simpson’s diversity index gives more weight to the most abundant species (Krebs, 1999).Sorensen’s coefficient of similarity index was also used to examine the floristic similarities among land uses (traditionally managed coffee agro forestry system and adjacent natural forest sites) (Kent, 2012).

The status of woody species structure was examined by estimating stem density, importance value index (IVI), forest structure, population structure and diversity pattern (Fisseha, 2008). The ecological importance of tree species (IVI) was calculated using relative density (RD), relative frequency (RF) and relative dominance parameters (RDO) of each species.

Regeneration status was designated as: “Good” if seedlings > saplings > adults; “Fair” if seedlings > or < saplings ≤ adults; “Poor” if the species survives in only in sapling stage, but no seedlings (saplings may be <,> or = mature individuals); and “Not regenerating” if a species is present only in adult form (Dhaulkhandi et al., 2008). Finally, a significance test was made with independent t-test software to compare species diversity.

Woody Species Composition

The result in table 1. indicated a total of 75 woody species belonging to 49 genera and 33 families were recorded in both traditionally managed coffee agro forestry system and adjacent to natural forest (Table. 2). Out of 75 woody species, 22 species belongs to 18 families were recorded in traditionally managed coffee agro forestry system whereas 53 species belongs to 33 families were recorded from natural forest adjacent to agro forestry.

The Sorensen’s coefficient of similarity (SS) (42.76%) indicated similarity of species composition between natural forests and traditionally managed coffee agro forestry system was low. The study also revealed, from the total recorded tree species, 31 (62.26%) of the tree species was found only in natural forests, whereas absent in traditionally managed agro forestry system. This indicated that woody species composition in traditionally managed agro forestry system affected by intensive coffee management as compared to natural forest..

Of all families with Rutaceae and Rubiaceae are the most dominant families each contributing 5 (15% and 4 species 12%) followed by Euphorbiaceae with 3(9%) species in natural forest, whereas in coffee ago forestry system with Euphorbiaceae was the most dominant with each contributing 3 (17%) species followed by Rubiaceae,Araliaceae, Moraceae and Boraginaceae each contributed 2(11%) species. The result also showed that Rubiaceae and Rutaceae were the most dominant family with the more number of species in natural forest than traditionally managed coffee agro-forestry system.

Therefore; low species composition under traditionally managed coffee agro-forestry system as compared to adjacent natural forest.

The difference is due to intensive management in traditionally managed agro-forestry system, like tree cutting, selective harvesting and slashing of undergrowth. On the other hand, presence of protection and conservation nearby forest from disturbance and illegal harvesting tree helped natural forest to have more species than that of traditionally managed agro-forestry system. The result revealed that coffee farm management practices had negative influence on the woody species composition. Similar management effects were reported in Ethiopia (Senbeta and Denich, 2006; Schmitt et al., 2009) and in Latin America ( Philpott et al. 2008).

Table.1 Tree species encountered in traditionally managed coffee agro forestry system and natural forest

Family	Number of species
Family	Traditionally managed coffee agro forest	Natural forest
Araliaceae	1	2
Fabaceae	2	2
Euphorbiaceae	3	3
Dracaenaceae	1	1
Arecaceae	1	1
Boraginaceae	2	2
Moraceae	2	2
Alangiaceae	0	1
Sapotaceae	0	2
Meliaceae	0	2
Simaroubaceae	0	1
Pittosporaceae	0	1
Rutaceae	0	4
Rubiaceae	2	5
Strerculiaceae	0	1
Rosaceae	1	2
Myrsinaceae	1	1
Asteraceae	1	1
Combretaceae	0	1
Oleaceae	1	2
Lauraceae	0	1
Ranunculaceae	1	2
Apocynaceae	0	2
Piperaceae	0	1
Flaacourtiaceae	1	1
Acanthaceae	1	2
Sapindaceae	0	1
Icacinaceae	0	1
Melianthaceae	0	1
Rhizophoraceae	1	2
Rhamnaceae	0	1
Myrtaceae	0	1
Menispermaceae	0	1
Total	22	53

The growth habit of woody species in natural forest indicated 64.1%, 22.64% and 13.2% trees, shrubs and lianas respectively. Similarly, trees, shrubs and lianas composition of traditionally managed coffee agro-forestry system were 65%, 25% and 10% respectively (Fig. 2).

The total number of tree, shrub and lianas are different in both natural forest and traditionally managed coffee agro forestry system and higher distribution under natural forest.

Woody Species Diversity

The highest of evenness, Shannon’s diversity and Simpson diversity index was recorded in natural forest with the values of 0.62, 2.08 and 1.72 respectively, which are significantly higher (p < 0.001) than the similar diversity indices (E = 0.32, H’=0.73 and1-D = 0.53) computed for traditionally managed coffee agro forestry system (Table.2). The diversity value for traditionally managed coffee agro forestry system indicated that the species diversity and distribution of individuals of each species were uneven.

Table.2.Woody species richness, Shannon diversity, Simpson’s diversity & Shannon’s evenness
Diversity indices	Mean (± STD)				t	P value	Confidence interval
	Traditionally managed coffee agro-forestry		Natural forest				Confidence interval
	Mean	STD	Mean	STD			Lower	upper
Richness	9.54	2.33	23.26	4.45	-9.43	0.000^***	16.69	10.73
Shannon index	0.53	0.29	2.08	0.86	-5.73	0.000^***	-2.11	-0.99
1-D	0.73	0.44	1.72	0.62	-4.66	0.000^***	-1.42	− .55
Evenness	0.32	0.19	1.62	0.38	10.43	0.000^***	-1.56	-1.04
*** indicates highly significantly different at p < 0.001

The low diversity and abundance in traditionally managed coffee agro forestry system is due to high human disturbance such as selective cutting of woody/tree for coffee plantation and other local consumptions like for construction and agricultural tools, trees logging for timber, beehive and fuel wood, and seasonal pruning and slashing of woody/tree to lower the effect shade on coffee productivity. According to field observation, strict access to natural forest and low disturbances in the natural forest contributed for high diversity value and thereby natural forest area to conserve its high diversity of species. The result revealed traditionally managed coffee agro-forestry system in Gimbo district has low potential to conserve woody species as compared to adjacent natural forest. Similar studies in Ethiopia (Senbeta and Denich, 2006; Schmitt et al. 2009) also verifies that intensively management of coffee have a negative impact on the species diversity.

Woody Species Structure

Density

The average density of woody species was 401 and 689 individuals per hectare in traditionally managed coffee agro forestry and natural forest respectively.

In natural forest species such as Schefflera abyssinica (Hochst.ex.A. Rich.)Harms (88 individual ha^-1), Coffea arabica L (78 individualsha^-1), Croton macrostachyusDel (62 individuals ha^-1), Millettia ferruginea (Hochst.) Baker (54 individualsha^-1), Clausenaanisata (Wild.) Benth (52 individual’s ha^-1and Margaritaria discoidea (Baill.) Webster(45individualsha^-1) had highest density. Similarly, Coffea arabica L(157individuals ha^-1), Croton macrostachyus Del (42individuals ha^-1), Millettia ferruginea (Hochst.) Baker (25individuals ha^-1),Ehretia abysslnica (33 individuals ha^-1), Ehretia cymosa(Thonn) (24 individuals ha^-1) and Margaritaria discoidea (Baill.)Webster (19individual ha^-1) had highest density in traditionally managed coffee agro forestry system (Fig. 3).

Species contributed low density in natural forest were Ocotea kenyensis (Chiov.) Robyns & Wilc z (5individuals ha^-1), Alangiumchinens (Lour). Harms (4 individuals ha^-1) and Brucea antidysentrica J.F. Mill (3 individuals ha^-1). Similarly, under traditionally managed coffee agro forestry system species such asVernonia amygdalina Del (1 individual ha^-1), Albizia gummifera (Gmel.) C.A.Sm (5 individuals ha^-1), Piper capense (4 individuals ha^-1), Clematis simensis Fresen (3 individual ha^-1), Acanthopale ethio-germanica Ensermu (3 individuals ha^-1), Acanthus eminens C.B. Clarke (2 individuals ha^-1), Albizia gummifera (Gmel.) C.A.Sm (5 individualsha^-1) and Olea welweitschii (Knobl.),Gilg (1 individuals ha^-1) shared low density.

The difference in traditionally managed coffee agro forestry system is due to continuous slashing of seedlings and saplings, reducing canopy covers and selective cutting mother trees for local consumptions, like fuel wood, construction materials having high influence on the density of woody species under natural forest than coffee agro forestry system were observed during field survey. Other studies (Yeshitela, 2001; Abreham et al., 2013; Dejene, 2020) reported that high human pressure for expansion of tea and coffee plantation investment had high impact on species diversity and density species in managed coffee forest area of Southwest Ethiopia.

DBH Distribution

The DBH class distribution of tree/shrubs from 10-20cm shared 46.2% in natural forest followed by 21–40 (23.85%). In traditionally managed coffee agro forestry system, the share was about44.88% and 21.42% for DBH10-20cm and 21–40 respectively (Figure.4).On other hand, DBH class for 41–60 cm in coffee agro forestry system was 17.96% whereas 19.57% was in natural forest, which is higher. Similarly, DBH class greater than 60cm, traditionally managed coffee agro forestry system had proportionally higher (13.8%) than natural forest (11.73%). The highest proportion of individuals in low DBH class between 10–20 cm indicated the predominance of small sized individuals in the both land uses. However, progressive increment in the proportion of individuals with higher DBH in agro-forestry system was the indicator the removal of small tree than large tree. Gobeze et al. (2009) reported the same result at Bonga Forest, southwest Ethiopia.

The species with highest basal area in natural forests are Millettia ferruginea (Hochst.)Bakerwith 3 m² ha^-1 (22.39%) followed by Margaritaria discoidea (Baill.) Webster, Croton macrostachyus Del 2.58m² ha^-1 (18.66%), Sapium ellipticum (Krauss) Pax 1.4m² ha¹ (9.6%) and Cassipourea malosana (Baker) Aliston1.4 m2 ha^-1 (9.6%), Whereas Schefflera abyssinicahas highest basal area 14.672 m² ha^-1 (64.977%) followed by Croton macrostachyus Del 3.4m2 ha^-1 (15.15%), Margaritaria discoidea (Baill.) Webster 1.8m2 ha^-1 (8.2%), Millettia ferruginea (Hochst.) Baker 3.6m² ha^-1 (15.52%) and Albizia gummifera (Gmel.) C.A.Sm are highest basal area in traditionally managed coffee agro forestry system.

The lowest basal area recorded by Cassipourea malosana (Baker), Ilex mitis (L.) Radlk and Phonex reclinata in natural forest. Similarly the lowest basal area recorded by Ehretia cymosa Thonnand and Ilex mitis (L.) Radlk in traditionally managed coffee agro forestry system.

The total basal area of coffee agro forestry system and natural forest was 200.17m² ha^-1 and 468.12m²ha^-1respectively. The result indicates that the total basal area of woody species in natural forest is higher than basal area of woody species in traditionally managed coffee agro forestry system. The diameter distribution of individuals in natural forest and coffee agro forestry system indicates inverted J-shape implying that there is greater number of individuals in lower DBH class. However, proportion of individual at DBH > 60cm for traditionally manage coffee agro forestry system, were less than that in forest indicating effect of management such as removal of small tree, shrubs, seedling and sapling coffee farm and leaving bigger tree with larger DBH. The larger diameter was dominated by Alibizia gummifer, Croton macrostachyus Del, Millettia ferruginea (Hochst.) Bake, Phonex reclinata, Schefflera abyssinica and Ficus vastaunder traditionally managed coffee agro forestry system, whereasSchefflera abyssinica (Hochst.ex.A. Rich.) Harms, Millettia ferruginea (Hochst.) Bake, Croton macrostachyus Del, Cordia africana Lam,Prunes Africana and Apodytes dimidiate E.Mey.ex Arnin natural forest..

Frequency

The result showed, from the total 53 species, 6 species were frequently observed for more than 50% under natural forest and 2 species were frequently observed for more than 50% in traditionally managed coffee agro forestry system. Among the species frequently observed in both traditionally managed coffee agro forest and natural forest were Coffea arabica L, Phonex reclinata Jacq, Schefflera abyssinica (Hochst.ex.A. Rich.) Harms, Millettia ferruginea (Hochst.) Baker, Croton macrostachyus Del, Cordia africana Lam, Albizia gummifera (Gmel.) C.A.Smand Margaritaria discoidea (Baill.) Webster(Table. 3).

Table 3

Most frequently observed species in natural forest and traditionally managed coffee agro forestry system
Species name	Frequency (%)
Species name	Natural forest	Traditionally coffee AF system
Phonex reclinata	78.94	27.23
Schefflera abyssinica	68.42	18.21
Millettia ferruginea	68.42	63.63
Croton macrostachyus	57.87	45.45
Margaritaria discoidea	63.15	19.3
Albizia gummifera	28.43	36.36
Coffea Arabica	75.4	81.1
Cordia Africana	42.1	27.27

The overall result indicates that species in the natural forest were observed highly frequent as compared to traditionally managed coffee agro forestry system. This is because of human disturbance, management practices and economic importance of the species in traditionally managed coffee agro forestry system affected the abundance of species. Similar result indicated by Belay et al. (2018) that human disturbance and preference of species in modified land uses affected the frequency species.

Important Value Index (IVI)

Importance value index (IVI) is valuable indicator to relate the environmental importance of species (Lamprecht, 1989). It also characterizes the vegetation and help to rank species for management.Species such as Millettia ferruginea (Hochst.) Baker(19.14%), Schefflera abyssinica (Hochst.ex.A. Rich.) Harms(15.87%),Croton macrostachyus Del(13.26%), Coffea Arabica (12.99%), Cordia Africana (10.98%) and Phonex reclinata(10.88%) had highest IVI value. In traditionally managed coffee agro forestry system highest IVI value were recorded for Millettia ferruginea (Hochst.) Baker(26.92%), Croton macrostachyus Del(25.5%)Ehretia cymosa Thonn (14.8%), Ficus vasta(12.99%) and Cordia africana(10.13%), (Table.4).

On other hand, species with low IVI value Acanthopale ethio-germanica Ensermu, Acanthus eminens C.B. Clarke, Bersama abyssinica Fresen in traditionally managed coffee agro forestry system, whereasAlangium chinens (Lour). Harms,Brucea antidysentrica J.F. Mill, Pittosporum viridiflorum Sims, Ilex mitis (L.)Radlk,Rothmaniaurcelliformis (Hiern) Robyns, Ficus vasta, Fagaropsis angalensis(Engl.) Dale and Ocotea kenyensis (Chiov.) Robyns & Wilcz species with low IVI value in natural forest.

Table.4. Species with IVI in natural forest and traditionally managed coffee AF system

Name of Species	Trad. Coffee agro forestry				Natural forest
Name of Species	RF	RD	RDO	IVI	RF	RD	RDO	IVI
Schefflera abyssinica (Hochst.ex.A.	1.12	6.66	8.29	16.07	3.73	6.66	5.48	15.87
Millettia ferruginea (Hochst.)	12.51	7.66	6.75	26.92	6.18	6.66	6.3	19.14
Croton macrostachyus Del	12.51	6.66	6.33	25.5	6.23	3.33	3.7	13.26
Ehretia cymosa Thonn	3.75	6.66	4.39	14.8	1.24	2.11	2.52	5.87
Phonex reclinata Jacq	3.25	2.12	4.63	10	5.48	3.12	2.28	10.88
Cordia africana Lam	4.5	2.54	3.09	10.13	4.73	4.51	1.74	10.98
Ficus vasta	0	0	0	0	3.24	0.15	1.77	5.16
Coffea arabica L.	23	13.29	25.1	61.39	1.18	6.66	5.15	12.99

The species with lower IVI values indicated the need to give high priority for their conservation than with higher IVI value. Those species (with low IVI) are sensitive to intensive management and human influenced environment (traditionally managed coffee agro forestry system) needs conservation priority. Species with high IVI value are considered ecologically more important (Lamprecht, 1989) than those with low IVI value indicating they are relatively highest ecological dominant species.

Regeneration Status

Regeneration status of the vegetation is one of the important criteria to establish conservation priority classes among species in natural forest and traditionally managed agro forestry. The average number tree seedling, sapling and matured tree species recorded under natural forest were 2919, 2845and 689 per hectare respectively. In coffee agro forestry system, it was 1443, 1023 and 401 seedling, sapling and matured woody per hectare respectively (Figure. 5).

Coffee arabica had highest seedling and sapling in both traditionally managed coffee agro forestry system(600 and 303) and adjacent natural forest(1297 and 518)compared to matured stand followed by Phonex reclinata in natural forest (181 and 341) and Croton macrostachyus (107 and 97) in traditionally managed coffee agro forestry system.

The result indicats a good regeneration status of the study area that might be associated with limited disturbance of the woody species. Generally, the pattern of both in natural forest and traditionally managed coffee agro-forestry system of the seedling, sapling and adult indicates that the current study are in a good regeneration and reproduction potential of seedling > sapling > adult.

Woody species like Coffea arabica, Croton macrostachyus, Prunes Africana, Bersama abyssinica, Clausena anisata (Wild.) Benth, Aframomu corrorima, Ehretia cymosa and Vepris dainellii Kokwarospecies have contributed highest number of regeneration status in natural forest. Similarly woody species like Coffea arabica, Croton macrostachyus Del, Prunes Africana, Phonex reclinata Jacq, Vepris dainellii Kokwaro, Cordia Africana, Millettia ferruginea, Clausena anisata (Wild.) Benth ndEhretia cymosa has the species contributed highest number of regeneration status under traditionally managed coffee agro forestry system.

The tree species like Vangueria madagascariensis, Combretum paniculatum, Polyscias fulva, Ekeberigia capensis, Rothmannia urcelliformisandVernonia amygdalina Del are low regeneration status under natural forest, whereas Apodytes dimidiata E.Mey.ex Arn, Piper capense, Ficus surand Psychotria orophila are low regeneration status in traditionally managed coffee agro forestry system.

Generally three regeneration level in both traditionally coffee AF and natural forest, namely 46.15% of the species were in good regeneration and reproduction status of seedling > sapling > adult; 32.69% of species were in fair regeneration and reproduction potential of seedling < sapling < adult; 21.15% of the species were in poor regeneration were only in sapling stage or sapling > adult in traditional coffee agro forestry system; whereas 37.5% of species were in good regeneration and reproduction status of seedling > sapling > adult; 54.16% of species were in fair regeneration and reproduction potential of seedling < sapling < adult; 12.6% of the species in poor regeneration in poor regeneration were only in sapling stage or sapling > adult in natural forest, indicating that natural for had better regeneration status than traditional coffee agro forestry. This may be due to human disturbance with continuous tree cutting and slashing of tree seedling and saplings. Those species with low regeneration status of the endemic species will needs priority for conservation. This conveys with Hundera et al (2013): Beer et al. (1998); Gordon et al., (2007) reported that the structure and regeneration of the Ethiopian Moist evergreen Afromontane forest affected by coffee management intensity.

Conclusion

A total of 75 (53 from natural forest and 22 from coffee agro forestry system) woody species belongs to 33 were found in the study area. Rubiaceae, Rutaceae and Euphorbiaceae were the dominant families in natural forest Euphorbiaceae, Rubiaceae, Araliaceae, Moraceae and Boraginaceae are dominant families in coffee ago forestry system. Sorensen’s coefficient of similarity (SS) indicated similarity of species composition between natural forests and traditionally managed coffee agro forestry was low. Diversity indices revealed that evenness, Shannon’s and Simpson diversity in natural forest were significantly higher than (p < 0.001) in traditionally managed coffee agro forestry system. Intensive coffee shade management in agro forestry that involving cutting of tree for coffee plantation, selective harvesting and slashing of undergrowth for reducing canopy to easily access sun light had negative effect on diversity, structure and regeneration of woody species in the study area. The study generally revealed traditionally managed coffee agro forestry system in Gimbo district has low potential to conserve woody species compared to adjacent natural forest. The study highlighted that current shade tree management in traditionally managed coffee agro-forestry system had negatively influenced the composition, diversity, and structure and regeneration status of woody species in the study area. Therefore, appropriate shade tree management need to be implemented to reduce its effect on diversity and regeneration of woody species.

Recommendations

Based on the result of this study, the following recommendations are forwarded

Awareness creation training and continuous extension services on coffee shade tree management for coffee growing community is crucial to reduce the current management effect on diversity and regeneration status of woody traditionally managed agro forestry system.
Rehabilitation of lost species through planting and promoting natural regeneration is important in traditionally managed agro forestry system.
Traditional knowledge of woody species management should be documented and harmonized with scientific knowledge.

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No competing interests reported.

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Comparative Study of Woody Species Composition, Diversity, Structure and Regeneration Status in Traditionally Managed Coffee Agro-forestry System Adjacent to Natural Forest in Gimbo District, Southwest Ethiopia

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