Species richness and composition
A total of 230 vascular plant species belonging to 183 genera and 76 families were identified from the study area. From the total plant families, ferns were represented by 1 family (1.32%), gymnosperms by 1 family (1.32%), and angiosperms by 74 families (97.37%) (dicots by 66 families, 86.84%; monocots by 8 families, 10.53%). The family with the highest number of species was Fabaceae (28 species, 12.17% of all species), followed by Asteraceae (18 species, 7.83%), Poaceae (13 species, 5.65%), Acanthaceae and Euphorbiaceae (9 species each), Celastraceae and Lamiaceae (8 species each), Rutaceae (7 species), Anacardiaceae, Malvaceae, Moraceae and Rubiaceae (6 species each), and Asclepediaceae (5 species). Two families were represented by 4 species each, 6 families by 3 species each, 20 families by 2 species each, and the rest 35 families by only 1 species each. From the total species, 45 (19.57%) were trees, 62 (26.97%) trees/shrubs, 37 (16.09%) shrubs, 13 (5.65%) woody climbers, 10 (4.35%) herbaceous climbers, and 63 (27.39%) herbs. Seventeen species (7.42%) were endemic to the country. Twenty eight trees, shrubs and treelike herbs (12.17%) were cultivated plants (most are exotic and some indigenous).
Taxa (family, genera, species) and endemic richness of Fach forest were higher than or comparable to that of some other DAFs of Ethiopia, for example, Tara Gedam and Abebaye forests (57 families, 114 genera, 143 woody species, 6 endemics) (Zegeye at al. 2011), Ambo (58 woody species) (Melaku 2012), Zegie (52 families, 113 woody species) (Alelign et al. 2007), Zengena (31 families, 50 woody species) (Tadele et al. 2014), Kuandisha (40 families, 66 woody species) (Berhanu et al. 2017), Kahtassa (47 woody and 34 herbaceous species) (Gebeyehu et al. 2019), Yegof (43 families, 66 genera, 76 woody and herbaceous species) (Woldearegay et al. 2018), Denkoro (66 families, 174 woody and herbaceous species, 12 endemics) (Ayalew et al. 2006), Wof Washa (40 families, 54 genera, 62 woody species) (Fisaha et al. 2013), Menagesha Amba Mariam (76 families, 182 genera, 219 woody and herbaceous species, 16 endemics) (Tilahun et al. 2011), Munessa (41 families, 61 tree species) (Muhammed and Elias 2020), Kimphee (74 families, 136 woody and herbaceous species) (Senbeta and Teketay 2003), Dodola (55 families, 95 genera, 113 woody and herbaceous species, 15 endemics) (Hundera et al. 2007), and Dindin (43 families, 72 genera, 81 woody species) (Shibru and Balcha 2004). Variation in species composition among different forests is attributed to topographic, edaphic and climatic differences, as well as degree of human disturbance.
Diversity and evenness of woody species
The diversity (H') and evenness (E) values of woody species were 3.53 and 0.72, respectively. The high diversity is attributed to habitat diversity and low human disturbances (as slopy terrain limits human exploitation and livestock grazing/browsing). The high evenness showed that there is more or less balanced distribution of individuals among the different species. The diversity value implies the need to conserve the forest from floristic diversity perspective.
The diversity and evenness of woody species in Fach forest were higher than or comparable to that of most other DAFs, for example, Tara Gedam (2.98 and 0.65, respectively) and Abebaye (1.31 and 0.31, respectively) (Zegeye et al. 2011), Ambo (2.73 and 0.67, respectively) (Melaku 2012), Zegie (3.72 and 0.84, respectively) (Alelign et al. 2007), Zengena (2.74 and 0.70, respectively) (Tadele et al. 2014), Kahtassa (2.06 and 0.53, respectively) (Gebeyehu et al. 2019), Yegof (2.26 and 0.57, respectively) (Woldearegay et al. 2018), Wof Washa (3.25 and 0.8, respectively) (Fisaha et al. 2013), Munessa (2.6 and 0.39, respectively) (Muhammed and Elias 2020) and Kimphee (2.92 and 0.66, respectively) (Senbeta and Teketay 2003).
Density and frequency of woody species
The total density (inclusive of seedlings) of woody species was 4938.24 individuals ha−1 (Table 1). The species with the highest density was Dodonaea angustifolia (605.15 individuals ha−1), followed by Maytenus serrata (482.35), Calpurnia aurea (481.62), Euclea racemosa subsp. schimperi (258.82), Acokanthera schimperi (232.35), Carissa spinarum (180.15), and Vernonia myriantha (177.94). These seven most abundant species contributed about 49% of the total density. The high density of the species is attributed to suitable environmental conditions for regeneration, high reproductive capacity of the species, and the relatively better protection of the forest from human exploitation and livestock grazing/browsing as it is a protected area and the presence of sacred places within the forest area. Ten species had the lowest density (0.74 individuals.ha−1 each), and thus were poorly represented in the forest.
Table 1
Density (D, number of individuals ha-1), relative density (RD, %), frequency (F, %), relative frequency (RF, %), basal area (BA, m2 ha-1), relative basal area (RBA, %) and IVI (%) of woody species (arranged alphabetically by scientific name)
No.
|
Scientific name
|
D
|
RD
|
F
|
RF
|
BA*
|
RBA
|
IVI**
|
1
|
Abutilon longicuspe
|
1.47
|
0.03
|
2.94
|
0.13
|
0.00
|
0.01
|
0.16
|
2
|
Acacia abyssinica
|
5.88
|
0.12
|
5.88
|
0.25
|
0.63
|
3.31
|
3.68
|
3
|
Acacia lahai
|
16.18
|
0.33
|
5.88
|
0.25
|
0.16
|
0.82
|
1.39
|
4
|
Acacia pentagona
|
3.68
|
0.07
|
2.94
|
0.13
|
-
|
-
|
-
|
5
|
Acacia pilispina
|
90.44
|
1.83
|
70.59
|
3.02
|
0.61
|
3.17
|
8.02
|
6
|
Acacia polyacantha
|
1.47
|
0.03
|
2.94
|
0.13
|
0.01
|
0.07
|
0.23
|
7
|
Acacia senegal
|
9.56
|
0.19
|
17.65
|
0.75
|
0.19
|
0.99
|
1.94
|
8
|
Acacia seyal
|
3.68
|
0.07
|
5.88
|
0.25
|
0.01
|
0.03
|
0.36
|
9
|
Acanthus eminens
|
4.41
|
0.09
|
5.88
|
0.25
|
-
|
-
|
-
|
10
|
Acanthus polystachius
|
164.71
|
3.34
|
44.12
|
1.89
|
-
|
-
|
-
|
11
|
Acanthus sennii
|
58.09
|
1.18
|
26.47
|
1.13
|
-
|
-
|
-
|
12
|
Acokanthera schimperi
|
232.35
|
4.71
|
70.59
|
3.02
|
0.21
|
1.08
|
8.81
|
13
|
Albizia gummifera
|
46.32
|
0.94
|
17.65
|
0.75
|
0.85
|
4.45
|
6.14
|
14
|
Albizia schimperiana
|
1.47
|
0.03
|
2.94
|
0.13
|
0.01
|
0.04
|
0.20
|
15
|
Allophylus abyssinicus
|
2.21
|
0.04
|
2.94
|
0.13
|
0.03
|
0.14
|
0.32
|
16
|
Apodytes dimidiata
|
2.21
|
0.04
|
2.94
|
0.13
|
0.01
|
0.08
|
0.25
|
17
|
Asparagus africanus
|
12.50
|
0.25
|
29.41
|
1.26
|
-
|
-
|
-
|
18
|
Barleria ventricosa
|
2.21
|
0.04
|
2.94
|
0.13
|
-
|
-
|
-
|
19
|
Bersama abyssinica
|
44.12
|
0.89
|
17.65
|
0.75
|
0.08
|
0.43
|
2.08
|
20
|
Bothriocline schimperi
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
21
|
Bridelia micrantha
|
1.47
|
0.03
|
2.94
|
0.13
|
0.02
|
0.08
|
0.24
|
22
|
Brucea antidysenterica
|
2.94
|
0.06
|
2.94
|
0.13
|
-
|
-
|
-
|
23
|
Buddleja polystachya
|
7.35
|
0.15
|
11.76
|
0.50
|
0.05
|
0.27
|
0.92
|
24
|
Calotropis procera
|
2.94
|
0.06
|
2.94
|
0.13
|
-
|
-
|
-
|
25
|
Calpurnia aurea
|
481.62
|
9.75
|
88.24
|
3.77
|
0.29
|
1.52
|
15.05
|
26
|
Canthium sp.
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
27
|
Capparis tomentosa
|
39.71
|
0.80
|
47.06
|
2.01
|
-
|
-
|
-
|
28
|
Carissa spinarum
|
180.15
|
3.65
|
79.41
|
3.40
|
0.19
|
0.99
|
8.03
|
29
|
Celtis africana
|
19.12
|
0.39
|
29.41
|
1.26
|
0.25
|
1.29
|
2.93
|
30
|
Clausena anisata
|
5.88
|
0.12
|
5.88
|
0.25
|
0.01
|
0.04
|
0.41
|
31
|
Clematis longicauda
|
52.94
|
1.07
|
50.00
|
2.14
|
-
|
-
|
-
|
32
|
Clerodendrum myricoides
|
11.03
|
0.22
|
20.59
|
0.88
|
0.01
|
0.04
|
1.14
|
33
|
Clutia lanceolata
|
156.62
|
3.17
|
52.94
|
2.26
|
-
|
-
|
-
|
34
|
Combretum molle
|
152.94
|
3.10
|
76.47
|
3.27
|
3.62
|
18.89
|
25.26
|
35
|
Cordia africana
|
1.47
|
0.03
|
5.88
|
0.25
|
0.14
|
0.72
|
1.00
|
36
|
Croton macrostachyus
|
66.18
|
1.34
|
58.82
|
2.52
|
0.46
|
2.42
|
6.28
|
37
|
Cussonia ostinii
|
2.94
|
0.06
|
5.88
|
0.25
|
0.05
|
0.24
|
0.55
|
38
|
Cussonia sp.
|
7.35
|
0.15
|
2.94
|
0.13
|
0.05
|
0.24
|
0.51
|
39
|
Dichrostachys cinerea
|
62.50
|
1.27
|
32.35
|
1.38
|
0.13
|
0.67
|
3.32
|
40
|
Dodonaea angustifolia
|
605.15
|
12.25
|
82.35
|
3.52
|
0.39
|
2.03
|
17.80
|
41
|
Dombeya torrida
|
25.00
|
0.51
|
20.59
|
0.88
|
0.09
|
0.49
|
1.87
|
42
|
Dovyalis abyssinica
|
3.68
|
0.07
|
5.88
|
0.25
|
0.02
|
0.10
|
0.43
|
43
|
Ekebergia capensis
|
5.15
|
0.10
|
11.76
|
0.50
|
0.14
|
0.71
|
1.32
|
44
|
Embelia schimperi
|
2.21
|
0.04
|
2.94
|
0.13
|
-
|
-
|
-
|
45
|
Entada abyssinica
|
3.68
|
0.07
|
5.88
|
0.25
|
0.04
|
0.23
|
0.55
|
46
|
Erythrina abyssinica
|
2.94
|
0.06
|
5.88
|
0.25
|
0.01
|
0.03
|
0.35
|
47
|
Euclea racemosa subsp. schimperi
|
258.82
|
5.24
|
70.59
|
3.02
|
0.20
|
1.02
|
9.28
|
48
|
Euphorbia abyssinica
|
2.94
|
0.06
|
2.94
|
0.13
|
0.09
|
0.47
|
0.66
|
49
|
Euphorbia tirucalli
|
3.68
|
0.07
|
2.94
|
0.13
|
0.02
|
0.13
|
0.33
|
50
|
Ficus lutea
|
1.47
|
0.03
|
2.94
|
0.13
|
0.06
|
0.31
|
0.46
|
51
|
Ficus palmata
|
2.21
|
0.04
|
2.94
|
0.13
|
-
|
-
|
-
|
52
|
Ficus sur
|
1.47
|
0.03
|
2.94
|
0.13
|
0.54
|
2.84
|
2.99
|
53
|
Ficus sycomorus
|
0.74
|
0.01
|
2.94
|
0.13
|
0.00
|
0.00
|
0.15
|
54
|
Ficus thonningii
|
1.47
|
0.03
|
2.94
|
0.13
|
0.01
|
0.05
|
0.20
|
55
|
Ficus vasta
|
2.21
|
0.04
|
2.94
|
0.13
|
2.11
|
10.99
|
11.16
|
56
|
Flueggea virosa
|
1.47
|
0.03
|
2.94
|
0.13
|
0.00
|
0.01
|
0.17
|
57
|
Gardenia ternifolia
|
0.74
|
0.01
|
2.94
|
0.13
|
0.00
|
0.01
|
0.16
|
58
|
Gnidia glauca
|
8.82
|
0.18
|
5.88
|
0.25
|
0.01
|
0.08
|
0.51
|
59
|
Grewia ferruginea
|
100.74
|
2.04
|
67.65
|
2.89
|
0.21
|
1.07
|
6.01
|
60
|
Gymnema sylvestre
|
0.74
|
0.01
|
2.94
|
0.13
|
-
|
-
|
-
|
61
|
Helinus mystacinus
|
39.71
|
0.80
|
35.29
|
1.51
|
-
|
-
|
-
|
62
|
Hibiscus macranthus
|
52.21
|
1.06
|
32.35
|
1.38
|
-
|
-
|
-
|
63
|
Hibiscus micranthus
|
0.74
|
0.01
|
2.94
|
0.13
|
-
|
-
|
-
|
64
|
Hippocratea africana
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
65
|
Hypericum quartinianum
|
5.15
|
0.10
|
8.82
|
0.38
|
-
|
-
|
-
|
66
|
Indigofera tinctoria
|
11.76
|
0.24
|
8.82
|
0.38
|
-
|
-
|
-
|
67
|
Jasminum abyssinicum
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
68
|
Jasminum grandiflorum subsp. floribundum
|
65.44
|
1.33
|
64.71
|
2.77
|
-
|
-
|
-
|
69
|
Juniperus procera
|
1.47
|
0.03
|
2.94
|
0.13
|
0.19
|
0.99
|
1.14
|
70
|
Justicia schimperiana
|
11.03
|
0.22
|
2.94
|
0.13
|
-
|
-
|
-
|
71
|
Lannea schimperi
|
12.50
|
0.25
|
20.59
|
0.88
|
0.15
|
0.76
|
1.90
|
72
|
Lippia adoënsis
|
75.74
|
1.53
|
38.24
|
1.64
|
0.00
|
0.01
|
3.18
|
73
|
Maesa lanceolata
|
2.21
|
0.04
|
2.94
|
0.13
|
0.00
|
0.01
|
0.18
|
74
|
Maytenus arbutifolia
|
27.94
|
0.57
|
20.59
|
0.88
|
0.02
|
0.12
|
1.57
|
75
|
Maytenus cortii
|
0.74
|
0.01
|
2.94
|
0.13
|
0.03
|
0.15
|
0.29
|
76
|
Maytenus obscura
|
2.94
|
0.06
|
2.94
|
0.13
|
0.03
|
0.14
|
0.32
|
77
|
Maytenus senegalensis
|
2.21
|
0.04
|
2.94
|
0.13
|
0.02
|
0.09
|
0.26
|
78
|
Maytenus serrata
|
482.35
|
9.77
|
76.47
|
3.27
|
0.01
|
0.05
|
13.09
|
79
|
Maytenus undata
|
0.74
|
0.01
|
2.94
|
0.13
|
0.00
|
0.01
|
0.16
|
80
|
Millettia ferruginea
|
1.47
|
0.03
|
2.94
|
0.13
|
0.04
|
0.19
|
0.34
|
81
|
Mimusops kummel
|
0.74
|
0.01
|
2.94
|
0.13
|
0.37
|
1.93
|
2.07
|
82
|
Myrica salicifolia
|
2.21
|
0.04
|
5.88
|
0.25
|
0.01
|
0.06
|
0.36
|
83
|
Myrsine africana
|
22.79
|
0.46
|
5.88
|
0.25
|
0.00
|
0.01
|
0.73
|
84
|
Nuxia congesta
|
22.79
|
0.46
|
23.53
|
1.01
|
0.41
|
2.14
|
3.61
|
85
|
Ocimum lamiifolium
|
19.12
|
0.39
|
14.71
|
0.63
|
-
|
-
|
-
|
86
|
Olea europaea subsp. cuspidata
|
92.65
|
1.88
|
70.59
|
3.02
|
3.12
|
16.29
|
21.19
|
87
|
Opuntia ficus-indica
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
88
|
Osyris quadripartita
|
20.59
|
0.42
|
20.59
|
0.88
|
0.04
|
0.20
|
1.50
|
89
|
Otostegia integrifolia
|
23.53
|
0.48
|
8.82
|
0.38
|
-
|
-
|
-
|
90
|
Otostegia tomentosa
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
91
|
Pavetta abyssinica
|
1.47
|
0.03
|
2.94
|
0.13
|
0.01
|
0.05
|
0.20
|
92
|
Pavetta oliveriana
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
93
|
Pavonia urens
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
94
|
Periploca linearifolia
|
2.21
|
0.04
|
2.94
|
0.13
|
-
|
-
|
-
|
95
|
Phragmanthera regularis
|
4.41
|
0.09
|
2.94
|
0.13
|
-
|
-
|
-
|
96
|
Phytolacca dodecandra
|
2.21
|
0.04
|
2.94
|
0.13
|
-
|
-
|
-
|
97
|
Piliostigma thonningii
|
0.74
|
0.01
|
2.94
|
0.13
|
0.07
|
0.38
|
0.52
|
98
|
Premna schimperi
|
101.47
|
2.05
|
67.65
|
2.89
|
0.19
|
0.99
|
5.94
|
99
|
Protea gaguedi
|
2.21
|
0.04
|
2.94
|
0.13
|
0.01
|
0.07
|
0.24
|
100
|
Prunus africana
|
2.21
|
0.04
|
2.94
|
0.13
|
0.07
|
0.38
|
0.55
|
101
|
Pterolobium stellatum
|
169.85
|
3.44
|
82.35
|
3.52
|
-
|
-
|
-
|
102
|
Rhoicissus tridentata
|
36.76
|
0.74
|
41.18
|
1.76
|
-
|
-
|
-
|
103
|
Rhus glutinosa
|
80.88
|
1.64
|
61.76
|
2.64
|
0.33
|
1.71
|
5.99
|
104
|
Rhus retinorrhea
|
0.74
|
0.01
|
2.94
|
0.13
|
0.00
|
0.00
|
0.14
|
105
|
Rhus vulgaris
|
149.26
|
3.02
|
79.41
|
3.40
|
0.79
|
4.10
|
10.52
|
106
|
Ritchiea albersii
|
4.41
|
0.09
|
5.88
|
0.25
|
0.02
|
0.10
|
0.44
|
107
|
Rosa abyssinica
|
14.71
|
0.30
|
23.53
|
1.01
|
0.01
|
0.07
|
1.37
|
108
|
Rubus steudneri
|
2.21
|
0.04
|
2.94
|
0.13
|
-
|
-
|
-
|
109
|
Rumex nervosus
|
3.68
|
0.07
|
2.94
|
0.13
|
-
|
-
|
-
|
110
|
Ruttya speciosa
|
2.21
|
0.04
|
2.94
|
0.13
|
-
|
-
|
-
|
111
|
Sapium ellipticum
|
1.47
|
0.03
|
2.94
|
0.13
|
0.02
|
0.10
|
0.26
|
112
|
Satureja punctata
|
2.94
|
0.06
|
2.94
|
0.13
|
-
|
-
|
-
|
113
|
Schefflera abyssinica
|
1.47
|
0.03
|
2.94
|
0.13
|
0.06
|
0.31
|
0.46
|
114
|
Schrebera alata
|
38.97
|
0.79
|
41.18
|
1.76
|
0.52
|
2.72
|
5.27
|
115
|
Scolopia theifolia
|
4.41
|
0.09
|
5.88
|
0.25
|
0.01
|
0.04
|
0.39
|
116
|
Senna didymobotrya
|
2.94
|
0.06
|
2.94
|
0.13
|
-
|
-
|
-
|
117
|
Senna singueana
|
21.32
|
0.43
|
26.47
|
1.13
|
0.02
|
0.08
|
1.64
|
118
|
Sida schimperiana
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
119
|
Solanum incanum
|
39.71
|
0.80
|
8.82
|
0.38
|
-
|
-
|
-
|
120
|
Steganotaenia araliacea
|
4.41
|
0.09
|
8.82
|
0.38
|
0.02
|
0.11
|
0.58
|
121
|
Stereospermum kunthianum
|
12.50
|
0.25
|
26.47
|
1.13
|
0.33
|
1.71
|
3.10
|
122
|
Syzygium guineense
|
3.68
|
0.07
|
2.94
|
0.13
|
0.14
|
0.74
|
0.95
|
123
|
Tapinanthus globiferus
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
124
|
Teclea nobilis
|
13.24
|
0.27
|
11.76
|
0.50
|
0.03
|
0.18
|
0.95
|
125
|
Tephrosia elata
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
126
|
Terminalia schimperiana
|
2.94
|
0.06
|
5.88
|
0.25
|
0.02
|
0.11
|
0.42
|
127
|
Triumfetta tomentosa
|
2.94
|
0.06
|
2.94
|
0.13
|
-
|
-
|
-
|
128
|
Urera hypselodendron
|
2.21
|
0.04
|
2.94
|
0.13
|
-
|
-
|
-
|
129
|
Vernonia adoensis
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
130
|
Vernonia amygdalina
|
0.74
|
0.01
|
2.94
|
0.13
|
0.02
|
0.10
|
0.24
|
131
|
Vernonia myriantha
|
177.94
|
3.60
|
26.47
|
1.13
|
0.03
|
0.13
|
4.87
|
132
|
Vernonia rueppellii
|
1.47
|
0.03
|
2.94
|
0.13
|
-
|
-
|
-
|
133
|
Woodfordia uniflora
|
7.35
|
0.15
|
2.94
|
0.13
|
0.00
|
0.02
|
0.30
|
134
|
Ximenia americana
|
2.21
|
0.04
|
5.88
|
0.25
|
0.01
|
0.03
|
0.33
|
|
Total
|
4938.24
|
100.00
|
2338.24
|
100.00
|
19.17
|
100.00
|
251.15
|
* Values are absent (-) since DBH measurement was not taken for the plants; all values indicated as 0 represent values very close to, but above zero |
** Had it not been missings in BA (thus RBA), the total IVI would have been 300% than 251.15% |
The total density of woody species in Fach forest was higher than that of most other DAFs, for example, Tara Gedam (3001 individuals ha−1) and Abebaye (2850 individuals ha−1) (Zegeye et al. 2011), Zegie (3318 individuals ha−1) (Alelign et al. 2007), Zengena (2202 individuals ha−1) (Tadele et al. 2014), Yegof (1768 individuals ha−1) (Woldearegay et al. 2018), Hugumburda (1218 individuals ha−1) (Aynekulu 2011), Wof Washa (699 individuals ha−1) (Fisaha et al. 2013), Gedo (782 individuals ha−1) (Kebede et al. 2014), Munessa (481 individuals ha−1) (Muhammed and Elias 2020), Kimphee (3059 individuals ha−1) (Senbeta and Teketay 2003), Adelle (898 individuals ha−1) and Boditi (498 individuals ha−1) (Yineger et al. 2008), Dodola (761 individuals ha−1) (Hundera et al. 2007) and Dindin (1750 individuals ha−1) (Shibru and Balcha 2004), but lower than Debre Libanos (18508 individuals⋅ha−1) (Hordofa 2013).
The species with the highest frequency was Calpurnia aurea (88.24%), followed by Dodonaea angustifolia and Pterolobium stellatum (82.35% each), Carissa spinarum and Rhus vulgaris (79.41% each), and Combretum molle and Maytenus serrata (76.47% each) (Table 1). The high frequency indicates regular horizontal distribution of the species in the forest. On the other hand, 66 species had the lowest frequency (2.94% each), and thus were infrequent in the forest.
Density and frequency of the woody species varied considerably among the species. The variation in density and frequency between species is attributed to habitat differences, habitat preferences among the species, species characteristics for adaptation, conditions for regeneration, and degree of human disturbance (Tesfaye and Teketay 2005; Zegeye et al. 2006, 2011).
Dominance / basal area of woody species
The total basal area of woody species was 19.17 m2 ha−1 (Table 1). The species with the highest basal area was Combretum molle (3.62 m2 ha−1), followed by Olea europaea subsp. cuspidata (3.12), Ficus vasta (2.11), Albizia gummifera (0.85), Rhus vulgaris (0.79), Acacia abyssinica (0.63), and Acacia pilispina (0.61). These seven most dominant woody species accounted for about 61% of the total basal area. Ficus vasta and Acacia abyssinica had high basal areas because of their larger diameters, though they had low densities. The basal areas of all other woody species were negligible. Dodonaea angustifolia, Maytenus serrata, Calpurnia aurea, Euclea racemosa subsp. schimperi, Acokanthera schimperi, Carissa spinarum and Vernonia myriantha had high densities but their basal areas were less than that of the aforementioned species due to their smaller diameters. It indicated that the total basal area of woody species was low since most species having high densities were shrubs and small-sized trees, and big-sized trees were absent or represented by very few numbers of individuals (this is due to slopy terrain, rocky land and shallow soil, as well as human exploitation). The presence of high numbers of small-sized trees and inadequate numbers of big-sized trees indicates that Fach forest is at the stage of secondary development. Similar results were reported by Kebede et al. (2014), Teketay et al. (2016) and Woldearegay et al. (2018).
The relative ecological importance and/or dominance of tree species in a forest ecosystem can better be depicted from measurements of basal area than stem counts (Cain and Castro 1959). Woody species with the largest contribution in basal area can be considered as the most important species in a forest. Accordingly, Combretum molle, Olea europaea subsp. cuspidata and Ficus vasta were the most dominant tree species in Fach forest.
The total basal area of woody species in Fach forest was lower than that of most other DAFs, for example, Tara Gedam (115.36 m2 ha−1) and Abebaye (49.45 m2 ha−1) (Zegeye et al. 2011); Zengena (23.3 m2 ha−1) (Tadele et al. 2014); Denkoro (45 m2 ha−1) (Ayalew et al. 2006); Wof Washa (101.8 m2 ha−1), Menagesha (36.1 m2 ha−1) and Chilimo (30.1 m2 ha−1) (Bekele 1993); Wof Washa (64.32 m2 ha−1) (Fisaha et al. 2013); Gedo (35.45 m2 ha−1) (Kebede et al. 2014); Munessa (91.75 m2 ha−1) (Muhammed and Elias 2020); Adelle (26.39 m2 ha−1) and Boditi (23.34 m2 ha−1) (Yineger et al. 2008); Dodola (129 m2 ha−1) (Hundera et al. 2007); and Dindin (49 m2 ha−1) (Shibru and Balcha 2004); but higher than Kuandisha (15.3 m2 ha−1) (Berhanu et al. 2017), Yegof (15.85 m2 ha−1) (Woldearegay et al. 2018), and Hugumburda (9.23 m2 ha−1) (Aynekulu 2011).
Importance Value Index (IVI) of woody species
The species with the highest IVI value was Combretum molle (25.26%), followed by Olea europaea subsp. cuspidata (21.19%), Dodonaea angustifolia (17.80%), Calpurnia aurea (15.05%), Maytenus serrata (13.09%), Ficus vasta (11.16%), Rhus vulgaris (10.52%), Euclea racemosa subsp. schimperi (9.28%), Acokanthera schimperi (8.81%), Carissa spinarum (8.03%), and Acacia pilispina (8.02%) (Table 1). These 11 most important woody species contributed about 59% of the total IVI value. The high IVI value of F. vasta was because of its high relative basal area, though it had low relative density and relative frequency. Rhus retinorrhea had the least IVI value (0.14%). Thirty four species (including R. retinorrhea) had low IVI values (˂ 0.5% each), and thus were ecologically less important in the forest.
The IVI is an important parameter that reveals the ecological importance and/or dominance of species in a given ecosystem (Cain and Castro 1959; Lamprecht 1989). Species with high IVI values are considered more important than those with low IVI values. According to Curtis and McIntosh (1951), a given species is said to be dominant if it had the highest IVI value compared to other plant species within an area. In a very general sense, the higher the IVI value of a species, the more successful it is in that pariticular habitat (Peters 1996). Accordingly, Combretum molle, Olea europaea subsp. cuspidata, Dodonaea angustifolia, Calpurnia aurea, Maytenus serrata, Ficus vasta, Rhus vulgaris, Euclea racemosa subsp. schimperi, Acokanthera schimperi, Carissa spinarum and Acacia pilispina were ecologically the most important species in Fach forest. In other words, these species were more abundant, frequent and dominant in the forest.
The IVI values can also be used to prioritize species for conservation: species with high IVI values need less conservation efforts whereas those with low IVI values need high conservation efforts (Shibru and Balcha 2004). The results suggest that species with low IVI values such as Rhus retinorrhea, Ficus sycomorus, Maytenus undata, Gardenia ternifolia, Abutilon longicuspe, Flueggea virosa, Maesa lanceolata, Albizia schimperiana, Pavetta abyssinica and Ficus thonningii should be given high priority for conservation.
Population structure and regeneration status of woody species
The DBH class distributions of woody species exhibited different patterns (Fig. 3), and showed that there are species with high number of individuals in the lower classes and some species in the middle classes. The patterns of DBH class distributions indicated the general trends of population dynamics and recruitment processes of the species. From the DBH class distributions of the species, two broad types of regeneration status were determined: good and poor regeneration. Some species possessed high number of individuals in the lower DBH classes, particularly the first class (DBH ˂ 2 cm, i.e., seedlings), and this suggests that they have good regeneration potential. This implies that dying adult individuals will be replaced by the growth of individuals from the smaller size classes and seems to be a self-sustaining plant population. The species with good regeneration potential were Olea europaea subsp. cuspidata, Combretum molle, Calpurnia aurea, Euclea racemosa subsp. schimperi, Acokanthera schimperi, and Acacia pilispina. Here it is important to note that Acacia pilispina had high number of individuals in the first DBH class (though less than the second class), indicating that the species has a relatively good regeneration potential. Most of the species, however, possessed low number of individuals in the lower DBH classes, particularly the first class, and this suggests that the species are in poor regeneration status (demonstrated hampered natural regeneration). The species with poor regeneration status were Rhus glutinosa, Premna schimperi, Albizia gummifera, and Shrebera alata. Hampered or poor regeneration is due to human disturbances, particularly livestock grazing/browsing and tree cutting for various purposes, as well as unfavourable environmental conditions such as soil erosion and climate change. The aforementioned factors have been reported as the major reasons for hampered or poor regeneration (Wassie and Teketay 2006; Zegeye et al. 2006, 2011; Teketay et al. 2016).
The DBH class distributions of Olea europaea subsp. cuspidata, Calpurnia aurea, Combretum molle, Euclea racemosa subsp. schimperi and Acokanthera schimperi showed a reverse “J” distribution. The DBH class distributions of all woody species showed a reverse “J” distribution, in which there is high number of individuals in the first class with decrease towards the middle and higher classes. It is interesting to see that Olea europaea subsp. cuspidata has shown good regeneration potential, unlike the poor regeneration status of the species in many other forests, for instance, Tara Gedam (Zegeye et al. 2011).
A reverse “J” distribution is considered as an indication of stable population structure or good regeneration status (Silvertown and Doust 1993; Bekele 1993; Teketay 1997; Zegeye et al. 2006, 2011; Teketay et al. 2016). The natural regeneration potential of Fach forest was promising, provided that appropriate conservation and management interventions could be employed. But here it is important to note that some of the species (Rhus glutinosa, Premna schimperi, Albizia gummifera, Shrebera alata) are in poor regeneration status and thus require due attention from conservation point of view.
Socio-economic importance of the forest to the local communities
The responses from the key informants indicated that Fach forest is the major source of fuelwood (most of the woody species), construction material (several woody and some herbaceous species, e.g., Juniperus procera, Olea europaea subsp. cuspidata, Cordia africana, Scolopia theifolia, Justicia schimperiana, Clematis longicauda, Hyparrhenia hirta), charcoal (e.g., Combretum molle, Acacia lahai, A. pilispina, Dichrostachys cinerea, Rhus glutinosa), timber (e.g., Juniperus procera, Cordia africana, Apodytes dimidiata, Schefflera abyssinica, Ekebergia capensis, Albizia gummifera, Bridelia micrantha), and farm implements (e.g., Olea europaea subsp. cuspidata, Acacia spp., Rhus glutinosa, Albizia gummifera, Croton macrostachyus, Ficus sur). It is also the source of food (edible fruits) (e.g., Syzygium guineense, Mimusops kummel, Cordia africana, Ximenia americana, Carissa spinarum, Rosa abyssinica, Rhus vulgaris), medicines (e.g., Vernonia amygdalina, Phytolacca dodecandra, Justicia schimperiana, Brucea antidysenterica, Ocimum lamiifolium, Gymnema sylvestre, Stephania abyssinica, Verbascum sinaiticum, Datura stramonium, Cucumis ficifolius), fodder, and bee forage (a total of 27 woody and herbaceous species were identified, e.g., Acacia spp., Cordia africana, Croton macrostachyus, Carissa spinarum, Dombeya torrida, Pterolobium stellatum, Guizotia scabra, Andropogon abyssinicus). From the 230 plant species identified from the study area, 122 (53%) had already been identified by Fichtl and Adi (1994) for their great values as bee forage. Some farmers living around the forest practice beekeeping to get honey for domestic consumption (food and medicine) and mainly income generation through selling. Forest management has created employment opportunities for the forest guards (currently a total of 9) and workers of the seedling nursery. Moreover, the forest has a potential value for tourism/ecotourism.
Conservation and management of the forest
The conservation and management of Fach forest is a tripartite venture: the conservation efforts of local communities, religious institutions (churches and monasteries), and governmental institutions. Moreover, indigenous (sacred grove) and modern (protected area system) conservation methods have been merged to conserve and manage the forest – a vital synergy. The integration of the conservation methods and the integration of the relevant stakeholders are crucial for conserving the biodiversity.
Role of local communities
The local people have environmentally friendly resource management systems and practices. Terracing and traditional agroforestry are widely practiced in the area. The major reason for constructing terraces is to control soil erosion and improve soil fertility and thereby increase crop production. In addition, the farmers construct terraces on farm boundaries to serve as demarcation lines between adjacent farmlands of different farmers. The local people retain and/or plant indigenous trees (e.g., Acacia abyssinica, Cordia africana, Combretum molle, Croton macrostachyus, Sapium ellipticum, Ficus thonningii, F. sur, F. vasta) in and around the farmlands, and plant Euphorbia tirucalli as a hedge along the edges of crop fields, yards, and roads. They also plant exotic species (e.g., Eucalyptus globulus, Jacaranda mimosifolia, Melia azedarach, Spathodea campanulata subsp. nilotica) in the homesteads, farm woodlots, and roadsides. Besides control of soil erosion and improvement of soil fertility, trees retained and/or planted in the agroforestry systems provide various forest products (fuelwood, construction material, timber, farm implements, food, medicines, fodder, bee forage), and serve as shade and live fence. Thus, the agroforestry systems reduce the pressure on the natural forest, showing the indirect contribution of local communities in conserving the forest.
The maintenance of the sacred groves in the study area is attributed to the strong religious belief and respect of the followers to the church, which is considered the house of God. Cutting trees from the sacred groves is taboo. If a person cuts trees from the sacred sites, the followers of the church inform the case to the religious fathers, and the doer is condemned. The followers of the church actively participate in the religious, conservation (e.g., tree planting in church/monastery yards) and development activities of the churches and monasteries. The majority of the Ethiopian people have respect and trust for the Ethiopian Orthodox Tewahedo Church (EOTC) and it is this spirit that supported the church to maintain forest resources till this generation (Wassie 2002).
The communities in the study area were involved in the conservation activities of the government like construction of terraces and tree plantation programs. The local communities were also instrumental in controlling the forest fire incidences that have occurred in Fach forest at different times.
Role of religious institutions (churches and monasteries)
Although the main role of the churches and monasteries is to give religious service to the followers of the church, they are also involved in protecting the sacred groves, planting trees in church/monastery yards, and giving advice to the followers about the importance of conserving the sacred groves. The EOTC has a long history of conserving sacred groves, i.e. patches of natural vegetation conserved on sacred sites. The EOTC has over 30 million followers, 400,000 clergies and 35,000 churches in Ethiopia (Wassie 2002). Churches and monasteries have played a great role in the conservation of sacred groves in particular and forest resources of the country in general (Wassie et al. 2005; Zegeye et al. 2006).
Role of governmental institutions
As Fach forest is a protected area, it is managed by governmental institutions, particularly Libo Kemkem District Agricultural Development Office. Governmental institutions enforce legal protection of the forest. As such, a total of 9 forest guards have been employed on contractual basis to protect the forest from human and livestock interferences. The forest guards are trying their best to control tree felling and livestock grazing/browsing and enforce the existing forest law. Indeed, the existence of the forest is largely attributed to the remarkable efforts of the forest guards. Though it is very limited, enrichment tree planting has been carried out in the forest (exotic as well as indigenous tree species). Four firebreaks (fire control gaps) have been established in the forest by removing woody vegetation so as to control the spread of fire incidence and thus reduce its impacts. Moreover, there is a minor seedling nursery near Ambo Meda. The nursery produces seedlings of exotic and indigenous trees and distributes to users (model farmers, shcools, youth associations, churches and monasteries, institutions). Governmental institutions are promoting tree planting (reforestation, afforestation, agroforestry) in the study area, and this reduces the pressure on the natural forest. In fact, a rigorous tree planting is needed in the study area and beyond.
Threats to the forest
Fach forest is a protected state forest and contains sacred places, but it has been dwindling from time to time due to livestock grazing/browsing, tree cutting for various purposes (fuelwood, construction material, charcoal, timber, farm tools), farmland expansion to the peripheral areas of the forest, rural settlements expansion, urbanization (expansion of Ambo Meda town), fire incidences (seven major fire incidences have occurred since the establishment of the protected forest; also a minor fire incidence has occurred during the data collection of this study), exotic species plantations (mainly Cupressus lusitanica and Eucalyptus globulus) at the expense of the natural forest, and road construction across the forest (Addis Zemen–Ebenat main road; minor gravel roads built during the Derg regime for transport of wood harvested from the forest), as well as soil erosion and climate change. The forest will diminish in the near future unless appropriate and immediate measures are taken. The loss of the forest will lead to loss of biodiversity, particularly the endemic plant species. This calls for strengthening the conservation and management of the forest, as it harbours high number of plant species including endemics, and is a refuge for different plants and animals that have disappeared from most parts of northwestern Ethiopia. A proper forest management plan should be developed and implemented to reverse or at least stabilize the present trend in the forest.