https://orcid.org/0009-0009-6281-7079
Figures
Abstract
Ethiopian Orthodox Tewahido Churches preserve remnants of native woody species around their premises, playing a vital role in biodiversity conservation and carbon sequestration. This study assesses woody species diversity and carbon stock potential of church forests in the Gamo Zone, South Ethiopia. We examined woody species diversity and carbon stock in six Orthodox Church forests classified by age (Old, Middle, and Recent). Standard vegetation sampling techniques were employed to record species composition, while allometric equations were used to estimate aboveground, belowground, and deadwood carbon stocks. Species richness, evenness, and the Shannon diversity index were calculated, and statistical analyses were conducted to evaluate patterns across age gradient. Data collection was carried out using approximately 40 plots (20m × 20m). Litter and soil carbon samples were collected using 1m × 1m subplots, and their contents were determined using the Walkley-Black and ignition methods, respectively. A total of 62 woody species were recorded across all forest age classes, with species composition varying significantly along age gradient. Fabaceae dominated lowland flora (17.64%), while Euphorbiaceae was the most prevalent in highland flora (11.1%). The Shannon-Wiener diversity indices were 1.91 for lowland forests and 2.89 for highland forests, with corresponding evenness values of 0.61 and 0.72, respectively. Older church exhibited higher aboveground, belowground, and deadwood carbon stocks compared to younger forests. Carbon stock density and CO₂ equivalents were significant in lowland and highland forests, measuring 139.06 tons/ha and 234.42 tons/ha, respectively. The study indicates a decline in woody species diversity and total carbon stock with increasing forest age, although older forests contribute more to carbon storage. These findings underscore the importance of age-specific management strategies for conserving biodiversity and maximizing carbon sequestration in church forests. The government should prioritize church forests as focal points for biodiversity conservation and advocate for their inclusion in carbon markets.
Citation: Sitotie YM, Gatew S (2025) Diversity of woody species and carbon stock potential in Orthodox Church forests in Gamo Zone, Southern Ethiopia. PLOS Clim 4(7): e0000661. https://doi.org/10.1371/journal.pclm.0000661
Editor: Muhammad Irfan Ashraf,, University of Sargodha, PAKISTAN
Received: February 24, 2025; Accepted: May 31, 2025; Published: July 23, 2025
Copyright: © 2025 Sitotie, Gatew. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: The raw data used in this manuscript is available at: https://doi.org/10.5281/zenodo.15651301.
Funding: The author(s) received no specific funding for this work.
Competing interests: The authors have declared that no competing interests exist.
1. Introduction
Church forests are small patches of forest preserved by communities for their spiritual, cultural, or religious values. These forests play a crucial role in conserving biodiversity and maintaining essential ecosystem services [1,2]. They exist as small, isolated patches, often located on mountain tops and at the heads of streams surrounding churches [3,4]. However, anthropogenic activities such as uncontrolled agricultural expansion, overgrazing, and urban development are contributing to the decline in church forest coverage [4,5]. The forests linked to church land are well-documented in empirical literature and are recognized as climate ambassadors [6,7].
Climate change is a significant environmental issue, requiring extensive discussion, deliberation, and negotiation at both national and international levels [8]. It presents numerous hazards and threats, leading to altered global warming, natural disasters, biodiversity loss, and rising ocean levels [9–11]. Greenhouse gas emissions continue to accumulate in the atmosphere, and without effective management, global temperatures could rise between 1.4°C to 5.8°C by 2100 [12]. Currently, global forest coverage stands at 31%, yet factors such as population growth and urbanization are causing rapid forest degradation [13]. Forests’ play a critical role in the carbon cycle, sequestering more carbon than any other terrestrial ecosystem in response to increased atmospheric CO2 concentrations [14].
The Ethiopian Orthodox Tewahedo Church (EOTC) has a long-standing tradition of planting, protecting, and preserving ancient trees within its premises. These forests serve as vital biodiversity hotspots, particularly for Ethiopia’s indigenous trees and shrubs [15–17]. The grounds of ancient churches contain natural forest vegetation, offering more complex habitat than non-church forests [18,19]. Oldest churches are surrounded by primary forest, while newly established churches are bordered by secondary forests. This indicated that older church forests harbor a higher variety of floral and fauna indigenous species, reinforcing respect for religious sites, while serving as sanctuaries for endemic, rare, and vulnerable species [15,20,21] Church forests play a vital role in mitigating climate change by enhancing carbon sequestration from both environmental and economic perspectives [22]. The major carbon pools measured in forest carbon estimation included plant biomass (both above and below ground), soil organic carbon (SOC), litter, herbs, and grass (LHG) and deadwood [23]. Various research has been conducted on the conservation and mitigation role of Ethiopian Church forests [15,24]. However, the impact of EOTC forests on biodiversity conservation; particularly in terms of species evenness, richness and carbon stock has not been adequately addressed in study area especially regarding deadwood carbon stock. Hence, this study aims to investigate the diversity of woody species and carbon stock potential of Orthodox Church forests in Gamo Zone of Southern Ethiopia.
2. Materials and methods
2.1 Site description
The study was carried out in selected Orthodox Church forests in Chencha and Arba Minch district, Gamo Zone, Southern Ethiopia. Chencha district is located between latitude 6°15′14.03”N and 6°15’17.06”N and longitude 37°34′55.77”E and 37°34′56.08”E, with an altitude range of 2425–2732 meter above sea level. In contrast, the Arba Minch district is situated between latitude 5o51’23.06”N and 6°03′33”N and longitude 37°32′55’‘E and 37o 37’04”, with an altitude ranging from 1200 m to 1320 meters above sea level (Fig 1).
The Chencha district has a bimodal climate pattern, with maximum mean temperature ranging between 18°C and 26°C, while the minimum mean temperature varies from 11°C to 13°C [25]. The district receives high mean annual rainfall of 1,600 mm, primarily between April and October. The lowest amount of rainfall was recorded from January to February and from November to December, with a mean annual total of 810 mm [26].
In contrast, the Arba Minch district experiences a dry season from November to March. Rainfall is bimodal, with short rains occurring from March to May and long rain from September to October. The average annual rainfall ranges from 650 mm to 830.7 mm [27]. The maximum mean temperature varies between 30°C and 33°C, while the minimum mean temperature ranges from 12°C to 17°C. The lowland agro-climatic area of Arba Minch has an average annual temperature of 28°C and an average annual rainfall of 895 mm [27].
Chencha District, situated at higher elevations, experiences a highland climate characterized by cooler average temperatures and greater rainfall. The area’s natural vegetation originally consisted of Afromontane forests. Subsistence agriculture dominates land use in Chencha, with a particular focus on the cultivation of Enset (Ensete ventricosum), barley (Hordeum vulgare), and potatoes (Solanum tuberosum), complemented by home garden agroforestry systems [28].
Arba Minch district, located at a lower elevation, has a tropical savanna climate with higher annual average temperatures. The vegetation consists of primarily of dry woodland and savanna patches. Land use is mainly agricultural, with large areas devoted to irrigated banana plantations, maize, and cash crops, along with urban development in and around Arba Minch town [28].
Ethiopian Orthodox Tewahedo Church forests are protected under the Church’s authority, with local clergy and communities actively involved in their preservation. To access the church forests in the Gamo Zone, we submitted permission letter to the office of the Bishop of the Gamo Zone and received permission granted by Abune Eliyas, Bishop of the Gamo Zone.
2.2 Sampling design and data collection
In our study area small-sized forests that belong to Ethiopian Orthodox Churches. These forests were established during different government eras, dating back more than a century.
A reconnaissance was conducted, and six church forests were purposively selected based on their representativeness, accessibility, budget and time constraints (Table 1). Churches were classified into three categories based on governance periods. Stratum I comprise churches established before the reign of Emperor Haile Selassie (pre-1974), Stratum II includes those founded during Ethiopia’s military rule (1975–1991), and Stratum III consists of churches established under the current administration (1992–2019). To ensure adherence to scientific standards, we employed a systematic sampling approach, collecting data through transects and plots.
The forest patches within each church boundary were measured, and their areas were summed to determine the total church forest coverage. A total of 14 transects were laid based on the church forest distribution and coverage, six transects in the lowlands and eight in the highlands. We established 40 quadrats measuring 20 × 20 m (400 m²), and within each main quadrat, five sub-quadrats of 1 × 1 m (1 m²) were created, with one placed in the center and four at the corners (Fig 2). After placing the first sample in the initial quadrat, we moved 30 meters inward to minimize age-related effects. Subsequent quadrats were positioned along transect lines at 150-meter intervals. The number of sample plots varied depending on forest size and area coverage. The floristic data such as diameter at breast height (DBH) of all woody species with DBH ≥ 5 cm was measured in each plot along the transects. All woody species encountered in the sampling plots were documented and assigned vernacular names. Plant growth forms (trees and shrubs) were recorded, dried, pressed, and transported to the National Herbarium (ETH) of Addis Ababa University for formal identification with the help of the Flora of Ethiopia and Eritrea in comparisons with authenticated specimens [29].
DBH measurements were recorded at a height of 1.3 m from the ground using a caliper, while woody species’ heights were assessed using clinometers. For trees with branches at or below breast height, the diameter of each branch was measured separately, and an average value was calculated. In cases where trees had multiple stems exceeding 1.3 m in DBH, the longest stem was measured.
2.3 LHG and soil sampling
LHG samples were collected from church forests using the composite sampling method as described by Daba and Soromessa [30]. Samples were taken from five sub-quadrats: one at the center and four in the corners of the main quadat.The litter within 1m2 sub-quadrats of each major quadrat was weighed and labeled. The wet weight of the composite samples was measured and recorded in the field before being transported to the lab for litter biomass calculation. A total of 100g of dry weight from each sample was sent to Arba Minch University for laboratory analysis. The total dry weight was determined in the laboratory after the samples were oven-dried at 70 °C for 24 hours, following the methodology out lined by Tura et al. [31] and Solomon [32]. Additionally, soil samples were collected from sub quadrats designated for litter sampling. Using soil auger, soil sample were taken from the four corners and the center of each sub-quadrat at depth of 30 cm, in accordance with the methods of Muluken et al. [33].
2.4 Analysis of woody species diversity
2.4.1 Shannon-Wiener diversity index.
Woody species diversity was assessed using various indices, including the Shannon diversity index (H0), Shannon equitability/ evenness index (E), density (D) and species richness (S). These indices provide essential information about the rarity and commonness of woody species in church forests. Both the abundance and evenness of species within the church forests were measured to ensure a comprehensive analysis of biodiversity. Evaluating the diversity of woody species in each church forest within the study area was a critical component of the research [34]. The Shannon diversity index can be calculated as follows.
Where, H is Species diversity index, S is total number of species, Pi is relative frequency of species, and ln is natural logarithm.
The Jaccard Similarity Coefficient (SJ) was used to compare the similarity of woody species in church forests from lowland and highland agro ecology zones based on species composition. SJ is calculated using the formula:
Where: SJ = Jaccard similarity coefficient,
a=Number of species that occur in highland area
b=Number of species that occur in lowland area
c=Number of common species that occur in site a and b
2.5 Church forest structure analysis
The vegetation structure was characterized by measuring density, diameter at breast height (DBH), frequency, dominance, basal area, and important value index (IVI). A complete inventory was conducted in each church forest to record floristic variables and parameters, following a methodologies of Yilma and Derero [17].
2.6 Carbon stock data analysis
2.6.1 Aboveground and belowground biomass carbon stock estimation.
Many scholars have developed and used various mathematical allometric formulas to estimate the aboveground biomass of trees. These formulas vary based on species, geographical location, forest stand type, and climate [35,36]. After reviewing published allometric equations for tropical regions and dry tropical forests, the equation developed by Chave et al. [37] model was taken to estimate the above ground biomass of the woody tree species of church forests.
Where, AGB = aboveground biomass and DBH, diameter at breast height, WD = Wood density 0.5 g/cm3 and H = height of tree species.
Where BGB is belowground biomass, AGB is aboveground biomass, 0.50 is the conversion factor (50% of BGB). Belowground tree biomass is converted into BGC by multiplying BGB by 0.50 [38].
2.6.2 Deadwood carbon stock estimation.
The estimation of standing deadwood biomass was conducted using an allometric equation, which was validated by REDD+ through a similar study with Siraj [39].
The recommended allometric equation was used to calculate the biomass of fallen deadwoods in accordance with [40] REDD+(2009).
Where: BSDW = Biomass of fallen deadwood (kg), H = Height of Standing Deadwood (m), D = Diameter of Breast Height Standing Deadwood (cm) and p = Deadwood density.
According to Pearson [41], the biomass in leaf litter was estimated using the formula:
Where: LHGs = litter, herbs, grass (biomass of LHGs t ha-1), Wfield = weight of wet field sample of litter within an area with size of 1 m2 (g), A = size of the area in which LHGs were collected (ha), Wsub sample (dry)= oven-dry sub-sample weight of LHGs used to determine moisture content (g), and W sub-sample (fresh) =, Fresh sub-sample weight of LHGs used to determine moisture content (g).
Carbon stocks in LHGs biomass were calculated as follow:
Considering that 58% of the carbon is found in ash-free litter material
Where: C = biomass carbon stock,
W1 = weight of crucible, W2 = weight of the oven-dried ground sample and crucible, and W3 = Weight of ash and crucible.
Total carbon stocks in dead litter were determined using:
Where: CL = total carbon stocks in the dead litter (tons ha-1), % C = Carbon content determined in the laboratory
2.6.3 Estimation of soil organic carbon.
The carbon stock density of soil organic carbon was calculated based on soil volume and bulk density, following the methodology recommended by Pearson [41]. The volume of soil in the core sampler was determined using:
Where: V = the volume of the soil in the core sampler (cm3), H = height of core sampler (cm), and r = radius of core sampler (cm). Moreover, the bulk density of a soil sample was calculated:
Where: BD = the bulk density of the soil sample (g cm ⁻ ³), Wav, dry = the average air-dry weight of soil sample per the quadrat (g), V = volume of the soil sample in the core sampler (cm3).
Soil organic carbon (SOC) stock per unit area was determined using:
Where: SOC = Soil organic carbon stock per unit area (tons ha-1), BD = soil bulk density (g cm-3), D = total sampling depth (30 cm), and %C = Carbon concentration (%).
2.6.4 Total carbon stock estimation (TCSE).
Belowground biomass of trees in tropical forest was estimated by multiplying aboveground biomass by a specific coefficient factor. To stream line estimating belowground biomass, root-to-shoot ratio of 1:5 was recommended [41]. Additionally, biomass stock densities were converted to carbon stock densities using a default carbon fraction of 0.5 as dry biomass contains 50% organic carbon [42].
The total carbon stock estimation of the church forests was calculated by summing the carbon stock densities of the individual carbon pools, Using the formula provided by Gedefaw et al. [43].
Carbon stock density of the forest was calculated as follow.
Where: C density = Carbon stock density (tons ha-1), CAGB = Carbon in aboveground tree biomass (tons ha-1), CBGB = Carbon in belowground biomass (tons ha-1), CLHG = Carbon in dead litter, herbs, grass (tons ha-1), TBDWC = total biomass dead wood carbon (tons ha-1), SOC = Soil organic carbon.
According to Pearson [41], The total carbon stock was converted into CO2 equivalent by multiplying by 44/12 or 3.67.
2.7 Statistical analysis
The data were assessed for normality and outliers before analysis. Parametric tests were conducted using the Statistical Package for Social Sciences (SPSS), version 20. Two independent t-tests were performed to examine differences in carbon stock between highland and lowland church forests, while two-way ANOVA was used to assess mean differences among the age groups.
Descriptive statistics, including mean, standard deviation, frequency, maximum, and minimum values, were calculated. Additionally, density, dominance, diameter at breast height (DBH), species richness, Shannon diversity index, and biomass carbon were quantified using the specified equations in the methodology part. All statistical tests were conducted at a significance level of p < 0.05.
3. Results
3.1 Floristic composition
A total of 62 woody species, belonging to 28 families and 43 genera, were identified in the church forests of Gamo zone. The most dominant family was Fabaceae, represented by six species. Woody species in lowland areas exhibited greater diversity compared to those in the highland region, where species composition tended to be more homogeneous. The second most abundant families across both areas were also Moraceae, Meliaceae, Euphorbiaceae, Malvaceae, and Asteraceae.
In highland church forests Malvaceae and Euphorbiaceae were the most dominant families, each represented by four species. The least dominant families, with only one species each, included Cupressaceae, Myrtaceae, Rubiaceae, and Asteraceae. Additionally, Moraceae, Cannabaceae, Araliaceae, and Peraceae were represented by just two species each (Table 2).
The presence of common species in highland and lowland church forests is crucial for calculating Jaccard similarity index, facilitating comparative analysis between districts and provide valuable insights to strengthen regional conservation strategies (S1 Fig).
The distribution of woody species increases in highland church forests but declines in lowland church forests. As forest age increases, species diversity also rises, enhancing ecological interrelationships among species (Table 3).
3.2 Species diversity and evenness
The woody species richness in the studied church forests ranges from 15 to 21species. The highest richness was recorded in Zeyse Kidane Mihiret church forest, while the lowest was observed in Debre selam Kidus Gebreal church forest. The Shannon-Wiener diversity and evenness indices for wood species in church forests are 2.4 and 0.68, respectively.
In lowland church forest, species diversity and evenness ranged from 1.91 to 0.61, while in highland church forests, they ranged from 2.89 to 0.72 (Table 4). The highland church forest exhibits a higher Shannon diversity index compared to the lowland forest, indicating a greater biodiversity in the highland area.
The highest species diversity was recorded in old church forests, whereas the lowest was found in recently established church forests (Table 5).
3.3 Woody species structure in lowland and highland church forest
3.3.1 Important value index.
The Important value Index (IVI) serves as a key tool for conservation, helping to identify species that require immediate protection and management to maintain the ecological health and biodiversity of church forests. The dominant and ecologically significant species in these areas include Vachellia abyssinica (41.3%), Ficus benjemina (10.1%), and Terminalia brownie (4.4%). Conversely, species with lower IVI scores are considered rare and should be prioritized for conservation efforts. Research has highlighted the ecological significance of certain species based on their IVI scores. Among them Celtis africana holds the highest IVI (14.03%), followed by Pavetta oliveriana (8.3%) and Macaranga capensis (8.5%). These species play essential roles in ecosystem structure and function. Additionally, Vernonia auriculifera and Premna schimperi are identified as rare species, with IVI values of 0.4% and 0.2%, respectively, underscoring their conservation importance.
3.3.2 DBH class distribution.
The diameter at breast height (DBH) class distribution exhibited a skewed pattern, with the highest number of individuals concentrated in the mid-sized diameter classes, while lower and higher diameter classes showed a decline in abundance (Fig 3). This distribution pattern indicates limited regeneration and recruitment potential among species within the study area, suggesting potential ecological constraints affecting population dynamics and forest sustainability.
3.4 Carbon stock potentials
The average total carbon biomass stored in the church forests within the study area was 337.3 ton ha-1. Highland church forests exhibited the highest carbon stocks, with aboveground carbon values ranging from 100.1 to 367.8 tons per hectare. In contrast, lowland church forests showed lower belowground carbon values, ranging from 15.6 to 57.4 tons per hectare (Table 6). Variations in aboveground carbon were primarily associated with differences in diameter at breast height (DBH) and tree height. Smaller DBH and tree height values in the lower altitudinal gradient correlated with reduced biomass and carbon stock. Consequently, the mean carbon stock of lowland forests showed a statistically significant difference (P ≤ 0.05).
The total carbon stock in the Gamo church forests was determined by summing the contributions of various carbon pools. Aboveground carbon (AGC), representing the biomass stored in trees and vegetation above the soil surface, accounted for 160.3 tons per hectare. Belowground carbon (BGC), which includes root biomass, contributed 34.4 tons per hectare. Litter carbon (LC), derived from decomposing plant material, was minimal at 0.03 tons per hectare. Soil organic carbon (SOC), which plays a critical role in long-term carbon sequestration and soil health, amounted to 154.7 tons per hectare. Lastly, deadwood carbon (DWC), stored in fallen and decaying woody debris, was estimated at 23.75 tons per hectare. These carbon pools illustrate the significant role of church forests in carbon storage and their importance for conservation and climate regulation.
The study revealed a significant correlation between the year of establishment, species composition, carbon stock (P < 0.05), and carbon density (P < 0.05). Older forests and plantations tend to accumulate higher carbon stocks and densities due to extended growth periods and greater biodiversity. Additionally, species diversity plays a crucial role in carbon storage, with favorable agro-climatic conditions such as optimal temperature, rainfall, and soil quality, enhancing carbon sequestration, while harsher environmental factors may limit it (Fig 4).
The two way ANOVA reveals significant effect of altitude, age and their interaction on total biomass carbon in Gamo zone church forests. Highland forests store more carbon than lowland forests likely due to favorable climatic condition enhancing tree growth. Old and middle aged forests accumulate more biomass than the recent forests, consistent with ecological succession (S1 Table). the interaction indicates that age effects are more pronounced in lowland forests, where middle aged forests have substantially higher total biomass carbon than recent ones, possibly due to management practice or disturbance history. In highland church forests total biomass carbon is less variable across ages, suggesting stable carbon storage.
4. Discussion
4.1 Woody species composition
The number of woody species identified and recorded in the church forest of the Gamo zone was lower than that reported in [44] who documented 70 woody species in the Debre Libanos church forests, and by [45] who recorded 91species in Dangila district, Similarly, [17] documented 90 species in Addis Ababa church forests. However, the result for the Gamo zone church forests was higher than those reported in [46] who documented 41 species in the Tara Gedam Church. Variations in woody species around church forests are influenced by several environmental factors, including altitude, disturbance levels, management practices, soil type and fertility, forest age.
The church forests in the Gamo district exhibit a species diversity index (H’) of 2.4 and an evenness (E) of 0.68. These values are higher than those reported in [17,47] who found lower diversity indices of 1.57 and 2.27, with corresponding evenness values also 0.52 and 0.71, respectively. However, the woody species diversity in the highland church forests of Gamo remains is lower than that reported for other sites, including Debre Libanos Monastery (H’ = 3.17; [44]), Zijje Maryam (H’ = 3.29 [48]), and SaledaYohannes Church forest (H’ = 3.82 [49]). Similarly, a higher diversity index of(H’ = 2.88) and an evenness value (0.79) were reported for Yemrehane Kirstos Church Forest [9].
The study area exhibited relatively low species richness and a heterogeneous distribution of individuals across species. For instance, Embelia schimperi and Celtis africana each had a density of only two individuals per hectare, whereas Vachellia abyssinica exhibited significantly higher abundance of 148 individuals per hectare in the surveyed church forests. The observed variation in Shannon diversity and evenness, compared to similar studies, are likely attributed to differences in management practices, church establishment age, levels of urbanization, site condition, microclimatic factors, selective logging, and the spread of exotic species, such as Eucalyptus spp. and Grevillea robusta.
Woody species with the highest important value indexed (IVI) require less conservation effort, whereas species with lower IVI values demand higher conservation priority [21].Therefore, species such as Embelia schimperi, Juniperus procera, and Hagenia abyssinica, which exhibited low IVI should be prioritized for conservation in the study area. Similar findings were reported for Dangila District church forest [45].
4.2 Carbon stock potentials
The average total biomass carbon stock of the church forests within the study area was 373.45 ton ha-1. Globally, the aboveground biomass for tropical dry forests ranges between 30 and 270 ton ha-1 [50]. The finding of this study was higher than values reported for Sekela Mariam and Addis Ababa church forests [31] as well as for Zuqualla Monastery [38,51] (Table 6). It also exceeded the carbon stock estimate of 126 ton ha-1 for tropical forests and 72 ton ha-1 for open sub-Saharan African forests [52]. Similarly, open forests in sub-Saharan Africa reported lower values, with AGC at 30 ton ha-1 and BGC at 12 ton ha-1 [53].
The aboveground and belowground carbon stock density in the church forests exceeds that of open forest in sub-Saharan African countries. Variations in carbon stock density can be attributed to a range of biophysical and anthropogenic factors, including diameter at breast height (DBH), tree height, the year of church establishment, species composition, forest management practices, and site-specific environmental conditions. Trees with larger diameter at breast height (DBH) at high altitudes are critical for carbon storage, generally storing greater aboveground carbon than those at lower altitudes [54]. In contrast, trees with smaller DBH and reduced height at lower altitudes exhibit lower biomass and aboveground carbon stock [54].
Most lowland church forests in Gamo zones are located in urban areas, which experience frequent litter removal, selective cutting and specific management practices. As a result, the mean carbon stock in both church forests showed a statistically significant difference.
The carbon content of litter in the study area ranged from 0.01 to 0.02 tons per hectare, which is notably lower than litter fall estimates for tropical forests, typically ranging from 2.5 to 3.69 tons per hectare [55]. Additionally, the litter carbon stock in church forests was lower than values reported for Zequala Monastery forest [38], Addis Ababa church forests [31], and selected church forests in Northern Ethiopia [23], which recorded 1.8 ton ha-1. Human activities such as grazing, fuel wood collection, and forest clearing reduce litter input and increase disturbances, thereby decreasing the amount of carbon stored in the litter layer compared to the more protected biomass pools.
Soil organic carbon plays a crucial role to the global carbon cycle [56]. According to Raty, t The average soil organic carbon content in Ethiopia ranges from 94 to 133 tons ha-1 [57], while the IPCC default values for different tropical soils range from 31 to 130 ton ha-1 [42]. The SOC value recorded in this study was 77.5 ton ha-1, which is lower than 179.9 ton ha-1 reported for Sekela Mariam. [58] and the 135.9 tons per hectare recorded for Addis Ababa church forests Tura et al. [31]. However, it was higher than the SOC values reported for Zequala Monastery forest [38]. Overall, lower SOC levels in this study may be attributed to variation in soil types, soil texture, woody species and agro climate conditions.
The total carbon stock in the study area was estimated 1373.68 CO₂ equivalents. According to [59], the average market value for carbon sequestration projects is approximately USD $15.41 per ton of CO₂ equivalent. Based on this rate, the Gamo church forests could generate an estimated carbon offset value of approximately USD $21,168.4088 per hectare.
5. Conclusion and policy implications
This study identified 62 woody species, representing 28 families and 43 genera, within the church forest of Gamo Zone, underscoring their significant role in biodiversity conservation. Orthodox Church forests serve as vital sanctuaries for native woody species, offering both ecological resilience and economic value. The findings revealed that older church forests exhibit higher Shannon diversity indices and greater species richness compared to more recently establish. The total carbon stock potential of Gamo church forest was estimated at 1373.68 CO₂ equivalents, highlighting their substantial contribution to carbon sequestration. Despite their relatively small size, remnant forest patches provide essential ecosystem services and play a vital role in climate mitigation efforts.
Given the increasing anthropogenic pressures on forest ecosystems, integrating the conservation of sacred groves into broader climate policies and land management strategies would enhance their ecological function and long-term sustainability. Further research on investigating the long-term carbon dynamics and the socio-cultural aspects of church forest conservation are needed. Moreover, understanding the interaction between traditional ecological knowledge and scientific conservation approaches will be essential in developing comprehensive strategies for preserving church forests.
Supporting information
S1 Fig. Species composition in lowland and highland church forest.
https://doi.org/10.1371/journal.pclm.0000661.s001
(DOCX)
S1 Table. Two-way ANOVA mean total biomass carbon by altitude and site factors.
https://doi.org/10.1371/journal.pclm.0000661.s002
(DOCX)
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