3.1 Woody Species Composition
A total of 48 woody species belonging to 46 genera and 35 families were recorded from Zijje Maryam Church Forest. Among the collected species, many of the woody species were shrubs, trees, and climbers, respectively (Fig. 3). Fabaceae was the most dominant family and ranked first; it was the most species rich family contributing 5 (10.42%) species followed by Rosaceae. Rosaceae ranked second next to Fabaceae, which contributed 3(6.25%) species to the total woody species. Then, Asteraceae, Celastraceae, Cupressaceae, Lamiaceae, Moraceae, Sapindaceae, and Urticaceae in which each of the above families contributed 2 (4.17%) species for the total woody plant species, and these all were the third ranked families next to Rosaceae. Each of the rest 26 families contributed 1(2.08%) species to the total woody species of Zijje Maryam church forest (Table 1).
Table 1
Top nine families with number of genera and species in Zijje Maryam church forest
Family | No. of Genera | % | No. of Species | % |
Fabaceae | 5 | 10.87 | 5 | 10.42 |
Rosaceae | 3 | 6.52 | 3 | 6.25 |
Celastraceae | 2 | 4.35 | 2 | 4.17 |
Asteraceae | 2 | 4.35 | 2 | 4.17 |
Cupressaceae | 2 | 4.35 | 2 | 4.17 |
Lamiaceae | 2 | 4.35 | 2 | 4.17 |
Moraceae | 2 | 4.35 | 2 | 4.17 |
Sapindaceae | 2 | 4.35 | 2 | 4.17 |
Urticaceae | 2 | 4.35 | 2 | 4.17 |
Others | 24 | 52.17 | 26 | 54.17 |
Total | 46 | 100.00 | 48 | 100.00 |
The findings from this study are helpful in providing the new information on the status of sacred forests in Ethiopia that has great contribution to the scientific community. The findings can provide baseline information on Ethiopian sacred groves status in composition, density, diversity, structure, regeneration, and anthropogenic disturbances and their potential for biodiversity management where Ethiopia is missed from the 12 African countries having sacred groves as reviewed by [19].
3.2 Species Diversity and Evenness
The results of the present study showed that the species diversity and species evenness of woody plants in the study area was found to be 3.29 and 0.85, respectively. This comparatively high diversity and evenness reflect the more stable the ecosystem and the better efforts on forest conservation and management in the sacred church forests of the study area. According to [36], the Shannon-Weiner diversity index normally varies between 1.5 and 3.5 and it rarely exceeds 4.5. According to [39], the Shannon diversity index is high when it is above 3.0, medium when it is between 2.0 and 3.0, low when between 1.0 and 2.0 and very low when it is smaller than one. Therefore, the Shannon-Wiener Diversity Index (H') in this study was 3.29 which was high indicating the forest was rich in diversity. Communities with a large number of species that are evenly distributed are the most diverse, and communities with few species that are dominated by one species are list diverse as noted by [40]. The Shannon Wiener diversity index and evenness value of this study was higher than Boda forest diversity (1.79) and evenness (0.1) of northwest Ethiopia of Montane forest [41]. Similarly, the diversity and evenness of woody species of Zijje Maryam Church forest was higher than 2.98 and 0.65, respectively of Tara Gedam and Abebaye forests, northwestern Ethiopia [42]. The possible reason is suggested be the larger wall fencing of the forest which remained with active conservation efforts of the stakeholders. Therefore, the individuals of woody plant species diversity and evenness in the study area were reflected as more; diverse and evenly distributed in the forest.
3.3 Vegetation Structure
3.3.1 The Diameter at Breast Height (DBH)
The vegetation structure of trees, shrubs, and lianas/ climbers of Zijje Maryam Church forest were stratified using DBH class. The patterns of DBH class distribution indicated the general trends of population dynamics and recruitment processes of the species. The distribution of woody plant species in different DBH classes were analyzed by classifying them into 10 DBH classes. Different patterns of species population structure can indicate variation in population dynamics as noted by [43].
The results revealed that the distribution of woody plant species in the present study showed a high number of individuals in the first DBH class. Plants with DBH class 2 ranked second as far as the number of individual woody plants were concerned. As shown in the graph of DBH class, the second most abundant individual trees were recorded in DBH class 2. Plants with DBH class 3 were the third most dominant based on the number of individual plants available. Whereas small values were registered in the rest DBH classes (Fig. 4). The list dominant DBH class of this study was DBH class 9, which was represented by only 4 individual plants. The DBH class map of this study was inverted J-shaped (Fig. 4). This pattern indicates that the majority of the species had the highest number of individuals with lower DBH and a gradual decrease towards the higher class. This in turn shows that the forest vegetation has good reproduction and recruitment potential. Differently, the DBH class map of Weiramba forest was bell shaped [44], and similar results to the current study were reported by [45–46]. Such DBH pattern in the forest is a normal population structure and shows the existence of species in healthier conditions as indicated by [47].
3.4 Height Class Distribution
The result indicated that height class 4 contained the highest number of individual woody species of plants that was 21.82% (177 individuals). Therefore the majority of the height classes were distributed under height class 4. Height class 3 was the second highest height class which was represented by 21.09% (171 individuals). Height class 1 was represented by 19.73% (160 individuals). There were a higher number of tree/shrub/climber individuals in the height classes 1, 2, 3, and 4, which accounted 79.78% (647 individuals) of the total height class. This is due to distribution pattern; showing that the higher number of individuals at height class 1 occupied better niche i.e. microenvironment compared with the lower number of individuals at the other height classes. The majority of the woody species (trees, shrubs and climbers) individuals of this study were distributed in the first DBH class. Different patterns of species population structure can indicate variation in population dynamics as noted by [48]. The rest height classes (height class 5, 6, 7, 8, 9, and 10) were 20.22% (164 individuals) of the total 10 height classes. The last fewer height classes were occupied by fewer numbers of individual species as shown in the graph of height class distribution (Fig. 5). The height class distribution map of Weiramba forest was bell shaped [44]. Similar results to the current study were reported by [48], and [49].
3.5 Basal Area
The total basal area of woody plants in Zijje Maryam Church Forest with DBH ≥ 2.5 cm was about 83.03m2 ha− 1. Basal area provides a measure of the relative importance of the species rather than a simple stem count [25, 50, and 51]. The basal area of the study sites compared with some other studies was higher, but still some other studies had a higher basal area. For instance, the BA ha− 1 of the present study was higher than the studies conducted in YemrehaneKirstos Church Forest, Weiramba Forest, Magda Forest, and Gedo Forest. That means the basal area per hectare of the present study was higher. The reason for higher basal area in this study would be due to the provision of higher comparative importance of the woody plant species to the study area. Basal area provides the measure of the relative importance of the species rather than simple stem count [25 and 29]. However, the BA ha− 1 of the present study was less than BA ha− 1 of Menna Angetu forest (Table 2). The total basal area of the current study was higher when compared with the previous studies conducted in Magda Forest, YemrehaneKirstos Church Forest, Weiramba Forest, and Gedo Forest (Table 2). Species with higher basal area could be considered as the most important species in the study of vegetation. Therefore, species with the largest contribution to the BA can be considered as the most important species in the forest following [51].
Table 2
Basal area comparison of the current study with some other studies conducted in Ethiopia where the vegetation data were collected in the same DBH.
Study sites | DBH | Basal Area (ha− 1) | Source |
Zijje Maryam Church Forest | --- DBH > 2.5 cm --- --- --- | 83.03m2 | Current study |
YemrehaneKirstos Church Forest | 72m2 | [25] |
Menna Angetu | 94.22 | [52] |
Weiramba Forest | 32.10m2 | [44] |
Magda Forest | 68.52 | [16] |
Gedo Forest | 35.45 | [53] |
In the study conducted in Zijje Maryam church forest, basal area analysis across individual species indicated that there was high domination by very few or small woody species. Thus, species with the largest basal area can be considered the most important woody species in the study area. Those individual woody plant species which contributed more to higher basal area in this study include J. procera Hochst. (54%), O. europaea L. (23.65%), V. abyssinica (Hochst. Ex Benth) K. and B. (5.14%), M. undata (Thunb.) Blakelock (3.38%), P. abyssinicum Del. (2.37%), H. abyssinica (Bruce) J.F.Gmelin (1.88%), G. saxifrage (Hochst.)Bridson (1.58%) and M. ovatus Schweinf. (1.41%) respectively. As far as BA was concerned, J. procera, O. europaea, V. abyssinica ranked first, second, and third, respectively (Table 3). This suggests that the aforementioned species of Zijje Maryam church forest had better growth and potential to retain higher biomass.
Table 3
List of woody plant species with high basal area and their percent contribution of BA m2 ha− 1 in Zijje Maryam church forest.
Species | BA | BA (m2ha− 1) | % | D (ha− 1) | % | |
Juniperu procera Hochst. | 42.04 | 44.84 | 54.00 | 152.53 | 17.63 | |
Olea europaea L. | 18.41 | 19.64 | 23.65 | 118.40 | 13.69 | |
Vachelia abyssinica (Hochst. Ex Benth) K. and B. | 4.00 | 4.27 | 5.14 | 36.27 | 4.19 | |
Maytenus undata (Thunb.) Blakelock | 2.63 | 2.80 | 3.38 | 20.27 | 2.34 | |
Pittosporum abyssinicum Del. | 1.85 | 1.97 | 2.37 | 40.53 | 4.69 | |
Hagenia abyssinica (Bruce) J.F.Gmelin | 1.47 | 1.56 | 1.88 | 11.73 | 1.36 | |
Galiniera saxifrage (Hochst.)Bridson | 1.23 | 1.31 | 1.58 | 28.80 | 3.33 | |
Maytenus ovatus Schweinf. | 1.10 | 1.17 | 1.41 | 45.87 | 5.30 | |
Others 40 species | 5.13 | 5.47 | 6.59 | 410.67 | 47.47 | |
Total | 77.84 | 83.03 | 100 | 865.07 | 100 | |
Where: BA = Basal Area, BA (m2ha− 1) = Basal Area m2 per hectare and D (ha− 1) = Density per hectare.
3.6 Importance Value Index (IVI)
According to [36], the importance Value Index combines data from three parameters which include RF, RD, and RDO. It is crucial to compare the ecological significance of species [51]. It was also described that species with the greatest importance index are the leading dominant of specified vegetation following [54].
The hierarchies of importance value indices of this study were calculated and ranked. The highest IVI value of the present study was contributed by J. Procera which was ranked first. As indicated by [51], IVI is used for comparison of ecologically significant species in which high IVI values indicate that the species structure in the community is high. Hence, J. procera in this study was high in structure. Its IVI and %IVI were 27.67 and 9.22, respectively. O. europaea was the second dominant species of this study. It’s IVI and %IVI was 23.09 and 7.70, respectively. As the output of IVI analysis showed that the top 10 woody plant species of this study were J. procera Hochst. (9.22%), O. europaea L. (7.7%), M. ovatus Schweinf. (3.49%), P. abyssinicum Del. (3.1%), V. abyssinica (Hochst. Ex Benth) K. and B. (2.63%), E. arborea L. (2.59%), G. saxifrage Hochst.)Bridson (2.34%), M. undata Schweinf. (2.32%), D. torrid(J.F.Gmel) Bamps (2.24%), and U. hypselodenderon A.Rhi. (2.07%) (Table 4).
Table 4
Importance Value Index (IVI) of the top ten woody plant species of the study area
Species | RD | RF | RDO | IVI | %IVI | Rank |
Juniperus procera Hochst. | 17.63 | 9.74 | 0.29 | 27.67 | 9.22 | 1 |
Olea europaea L. | 13.69 | 9.09 | 0.31 | 23.09 | 7.70 | 2 |
Maytenus ovatus Schweinf. | 5.30 | 4.55 | 0.63 | 10.48 | 3.49 | 3 |
Pittosporum abyssinicum Del. | 4.69 | 3.90 | 0.73 | 9.31 | 3.10 | 4 |
Vachelia abyssinica (Hochst. Ex Benth) K. and B. | 4.19 | 2.60 | 1.10 | 7.89 | 2.63 | 5 |
Erica arborea L. | 4.07 | 2.60 | 1.10 | 7.76 | 2.59 | 6 |
Galiniera saxifrage (Hochst.)Bridson | 3.33 | 2.60 | 1.10 | 7.02 | 2.34 | 7 |
Maytenus undata Schweinf. | 2.34 | 3.90 | 0.73 | 6.97 | 2.32 | 8 |
Dombeyatorrida Dovyalis (J.F.Gmel)Bamps | 2.59 | 3.25 | 0.88 | 6.71 | 2.24 | 9 |
Urera hypselodenderon A.Rhi. | 2.10 | 3.25 | 0.88 | 6.22 | 2.07 | 10 |
Others 38 species | 40.07 | 54.55 | 92.25 | 5.92 | 62.29 | 11 |
Total | 100 | 100 | 100 | 300 | 100 | |
Where: RD = Relative Density, RF = Relative Frequency, RDO = Relative Dominance, IVI = Important Value Index and %IVI = percentage of Importance Value Index.
3.7 Frequency
The present study revealed a high percentage of species in lower frequency classes and a relatively low percentage of the number of species in high frequency classes. Thus, the result verifies the existence of a high degree of floristic heterogeneity in Zijje Maryam Church Forest. The relative frequency revealed that J. procera Hochst. was the most frequent species with a frequency of 100, followed by O. europaea L., M. ovatus Schweinf., P. abyssinicum Del., and M. undata Schweinf. Similar result was reported from the study conducted in Yemrehane Kirstos Church Forest results of [25].
Frequency is the number of quadrates in which a given species occurred in the study area. The five most frequently observed woody plant species of this study were J. procera Hochst. which occurred 100 times out of 15 quadrates which were having 9.74 relative frequencies. The relative frequencies of some most frequent woody plants were O. europaea L. 9.09, M. ovatus Schweinf. 4.55, P. abyssinicum Del. 3.90, and M. undata Schweinf. 3.90. The rest 43 frequently occurred species together contributed 68.83% of the total relative frequency of the forest (Table 4). The least occurred species were R. myricoides (Hochst.), A. retinoides, R. abyssinica Lindley., C. simensis Fresen., R. nervosus (vahl), R. prinoides L'Herit., O. ficus indica (L) Miller, F. carica L. and D. abyssinica (A. Rich.) Warb. each having 0.65 relative frequencies and total 5.84 relative frequencies. The possible reason the authors mentioned could be due to less competitiveness and less seedlings and sapling to reach maturity stage of these species compared with most frequent once.
Table 5
Frequency distribution of dominant woody species in Zijje Maryam church Forest
Species | No. of quadrats | F | RF |
Juniperus procera Hochst. | 15 | 100 | 9.74 | |
Olea europaea L. | 14 | 93.33 | 9.09 | |
Maytenus ovatus Schweinf. | 7 | 46.67 | 4.55 | |
Pittosporum abyssinicum Del. | 6 | 40 | 3.90 | |
Maytenus undata Schweinf. | 6 | 40 | 3.90 | |
Others 43 species | 106 | 706.67 | 68.83 | |
Total | 154 | 1026.67 | 100.00 | |
Where: F = Frequency and RF = Relative Frequency |
3.8 Regeneration status of Zijje Maryam Church forest
The density of Seedling (15555.56) was greater than saplings (3833.33) and mature trees (865.07) (Table 6 and Table 7). Saplings were also greater than mature trees, although they were less than seedlings. As noted by [38], if seedling > sapling > mature tree, it is "good" regeneration status. Because of the density of seedlings was > the density of saplings > the density of mature trees, the regeneration status of the present study was good.
Table 6
Abundance and density per hectare of saplings of Zijje Maryam Church forest
Species name | No. of saplings | Sampled area by ha | Density ha− 1 | %Density ha− 1 |
Erica arborea L. | 9 | 0.018 | 500 | 13.04 |
Maytenus ovatus Schweinf. | 8 | 0.018 | 444.44 | 11.59 |
Ocimum lamiifolium Hochst.ex.Benth. | 5 | 0.018 | 277.78 | 7.25 |
Euclea schimperi SchI. | 1 | 0.018 | 55.56 | 1.45 |
Myrsine afrcana L. | 17 | 0.018 | 944.44 | 24.64 |
Rosa abyssinica Lindley. | 2 | 0.018 | 111.11 | 2.90 |
Mimusops kummel A.DC | 2 | 0.018 | 111.11 | 2.90 |
Laggera aurita (L.f.)Benth. ex C.B.Clarke | 9 | 0.018 | 500 | 13.04 |
Dodonaea viscosa L. | 1 | 0.018 | 55.56 | 1.45 |
Myrica salicifolia A. Rich. | 1 | 0.018 | 55.56 | 1.45 |
Ficus sycomorus L. | 2 | 0.018 | 111.11 | 2.90 |
Pentas schimperiana Schi. | 2 | 0.018 | 111.11 | 2.90 |
Pittosporum abyssinicum Del. | 3 | 0.018 | 166.67 | 4.35 |
Dombeyatorrida Dovyalis (J.F.Gmel)Bamps | 7 | 0.018 | 388.89 | 10.14 |
Total | 69 | | 3833.33 | 100 |
Based on the results of this study, 9 species (18.75%) of the total woody plant species were represented by both seedling and sapling stages. These species showed ‘good’ regeneration status. Those plants that were represented by both seedlings and saplings were E. arborea, M. ovatus, O. lamiifolium, R. abyssinica, M. kummel, D. viscosa, F. sycomorus, P. abyssinicum and D. torrid (Table 5 and Table 6). There were 3 species (6.25%) that were represented by saplings but not seedlings (Table 6). Those species were E. schimperi, L.aurita, and M. salicifolia. These species showed ‘poor’ regeneration status. The two other species (4.17%) were available in seedlings but not in saplings. These species were C. aurea (Ait.) Benth. and A. abyssinicus (Table 7). These species showed ‘fair’ regeneration status (Fig. 6).
Among the total woody plants, 37 species (77.08%) were not represented by seedlings and 36 species (75%) of the total woody plants were not represented by sapling stages. Others were such as without seedlings and those without sapling stages. Therefore these woody plants have lower regeneration status, which may suggest that these species are either under the threat of local extinction or may prefer coppices or sprouts as the strategy of survival. If a species is absent both in sapling and seedling stages, but present as mature, it has no regeneration potential as noted by [38]. Thirty four species (70.83%) of the total woody plant species were represented by neither seedlings nor saplings. These 34 species (70.83%) were not regenerating. There were also new species that were represented by seedling and sapling stages but not in mature stages. M. africana and P. chimperiana were new species which were not available in the mature stage but in seedlings and saplings. These species showed ‘new regeneration’ status in Zijje Maryam church forest (Fig. 6).
Table 7
Abundance and density per hectare of seedlings of Zijje Maryam church forest.
Species name | No. of seedlings | Sampled area by ha | Density ha− 1 | %Density ha− 1 |
Erica arborea | 11 | 0.0045 | 2444.44 | 15.71 |
Maytenu sovatus | 8 | 0.0045 | 1777.78 | 11.43 |
Ocimum lamiifolium | 3 | 0.0045 | 666.67 | 4.29 |
Calpurnia aurea | 2 | 0.0045 | 444.44 | 2.86 |
Allophylus abyssinicus | 2 | 0.0045 | 444.44 | 2.86 |
Myrsine Africana | 27 | 0.0045 | 6000 | 38.57 |
Rosa abyssinica | 4 | 0.0045 | 888.89 | 5.71 |
Mimusops kummel | 2 | 0.0045 | 444.44 | 2.86 |
Dodonaea viscosa | 1 | 0.0045 | 222.22 | 1.43 |
Ficus sycomorus | 2 | 0.0045 | 444.44 | 2.86 |
Pentas schimperiana | 2 | 0.0045 | 444.44 | 2.86 |
Pittosporum abyssinicum | 4 | 0.0045 | 888.89 | 5.71 |
Dombeyatorrida Dovyalis | 2 | 0.0045 | 444.44 | 2.86 |
Total | 70 | | 15555.56 | 100 |
From the total of 50 woody plant species found in Zijje Maryam Church forest, 13 species (26%), 14 species (28%), and 48 species (96%) have seedlings, saplings, and matured woody plants, respectively. The following species had the largest contributions to the seedling counts D. abyssinica, P. africana, M. ferruginea, M. ovatus, M. Kummel, and C. tomentosa. The study of the regeneration potential of a forest is one of the major means to assess its conservation status.
The overall regeneration status of the forest was not satisfactory. Most of the woody plants were not regenerated (70.83%). Such conditions might have been occurred due to existing disturbances in the study site like over grazing, firewood collection, and poor biotic potential of tree species which either affect the fruiting or seed germination or successful conversion of seedlings to sapling stage following [28]. The possible reasons for insufficient seedlings and saplings for the above tree species in the forest might be seed predation, grazing and browsing, lack of safe sites for seed recruitment, nature of seeds of certain trees which seek dormancy period, litter accumulation, pathogens, species specificity, and moisture stress or might have other alternative adaptations for propagation and reproduction rather than seed germination [57].
3.9 Comparison of disturbances based on their impact
The relationship between the disturbances and species diversity was determined. This is because a higher species diversity help the forests to have a more stable ecosystem functioning and enhances both productivity and stability [29]. In this study the least disturbed the quadrats of the sacred forest were found to have the highest the species diversity. The total area coverage by all disturbance type was 2075 m2 among 9375m2 area of quadrats studied in the forest. Thus 2,207m2ha− 1 of forest land was disturbed. Nearly 22.13% of the areas of the forest get disturbed. This is very low compared to the study of [27] on disturbance coverage of 44 church forests in South Gonder that were 56.2%. This could be because of some of the conservation effort observed in the study area via religious thoughts, religious supports, its inviolability, and legal safeguard (the civil law and guards).
There was a significant difference (P < 0.05) between the types of human disturbances and the quadrat distance from the church (Table 8). The result revealed that Gathering area (Mahiber) was the highest among the ten human disturbances occurred in the church forest which covers nearly 21% of all disturbed area (Fig. 7). The impact of gathering area is due to ceremonial effect throughout the year. This causes lack of safe site for seed recruitment, affect nature of seeds of certain trees which seek dormancy period, affect litter accumulation, affects species specificity, and moisture stress [55]. Probably church forests might have other alternative adaptations for propagation and reproduction rather than seed germination [55], therefore impacts the species diversity and evenness. Wind had the least effect followed by logging (clearing), and grazing (Fig. 7). The amount of natural disturbances (rocky area and wind fallen trees) was insignificant which affected only 1.6% of the area of the forest compared to human disturbance which was 21%. Thus, the total disturbance can be taken as human disturbance due to the insignificance of natural disturbance. This is analogous to the result of [27].
Quadrats near the edges of the church forest were disturbed critically higher than the inner quadrats by human disturbances (Fig. 8). Similar result was found by [54] that the edge effect was significantly higher affecting the soil nutrients near the edge of the church forest quadrats. Similarly, [57–58] also found exotic plantation disturbances across quadrats were significantly different.
Table 8
ANOVA results determining the types of human disturbance and disturbances across quadrats number inside the church forest (P < 0.05)
Source of Variation | SS | df | MS | F | P-value | F crit |
Types of Human disturbance | 6157 | 7 | 879.6 | 14.1 | 0.00001 | 2.10 |
Disturbances across quadrats | 9741.9 | 14 | 695.8 | 11.2 | 0.00001 | 1.79 |
Error | 6106.2 | 98 | 62.3 | | | |
Total | 22005 | 119 | | | | |
The rate of human disturbance critically affected the amount of basal area (m2/ha), diversity, evenness, and the number of seedling found in the quadrats (Fig. 8). These disturbances reduced the vegetation density, diversity, evenness, and number of seedlings of woody plants in the forests.