Study of the Soil Seed Bank Composition in Arjo-Diga Humid Afromontane Forest under Different Land Use Types and Its Implications for the Restoration of Degraded Lands in Western Ethiopia

Berihun, Tariku; Bekele, Tamrat; Lulekal, Ermias; Asfaw, Zemede

doi:https://doi.org/10.1155/2024/5119487

International Journal of Ecology

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Abstract Materials and Methods Discussion Conclusions Data Availability Conflicts of Interest Acknowledgments Supplementary Materials References Copyright Related Articles

Research Article | Open Access

Volume 2024 | Article ID 5119487 | https://doi.org/10.1155/2024/5119487

Study of the Soil Seed Bank Composition in Arjo-Diga Humid Afromontane Forest under Different Land Use Types and Its Implications for the Restoration of Degraded Lands in Western Ethiopia

Tariku Berihun,^1,2Tamrat Bekele,²Ermias Lulekal,²and Zemede Asfaw²

Academic Editor: Xunfeng Chen

Received26 Apr 2023

Revised21 Dec 2023

Accepted21 Jan 2024

Published06 Feb 2024

Abstract

The soil seed bank present in forests serves as a crucial indicator of soil resilience following disturbances. The objective of this study was to investigate the composition, density, and vertical distribution of the soil seed bank in the Diga District of Western Ethiopia across four land use types: forestland, grassland, bare land, and shrubland. Soil samples were collected from plots measuring 225 square centimeters with a depth of 9 cm. A total of 108 soil samples were collected, representing the four land use types. Each plot was sampled at three different soil layers: 0–3 cm, 3–6 cm, and 6–9 cm depths. From the soil seed bank, 51 plant species were identified, with 46 (90.2%) being herbs, 3 (5.88%) trees, and 2 (3.92%) shrubs. The Asteraceae (13.30%), Poaceae (11.53%), and Fabaceae (9.61%) families exhibited the highest species composition, accounting for 38.44% of the total. Species richness varied significantly across all land use types and soil layers (), with shrubland having the highest species richness and bare land having the lowest count. The total seed bank density in the soil across all plots was 92153 seeds/m², with the highest density observed in the top 3 cm of the soil layer. The first and second soil layers exhibited a high Jaccard similarity coefficient of 0.76. Forestland and shrubland displayed the highest Jaccard coefficient of similarity (0.72), while the lowest was observed between bare land and shrubland (0.43). There was greater species similarity between the first and second soil layers (0.76) and lower similarity between the middle and bottom layers (0.32). The study found limited similarity between aboveground vegetation and the soil seed bank due to the low regeneration of woody species. Forestland and shrubland exhibited a high Jaccard similarity coefficient to aboveground vegetation, while grassland had the lowest similarity coefficient. Based on the findings, it can be concluded that the shrubland land use types had high soil seed bank composition and density. Therefore, the conservation of shrubs in the Arjo-Diga Forest should be considered for the restoration of degraded areas, taking into account the soil seed bank in the shrubland ecosystem.

1. Background of the Study

Globally, forest cover was reduced to 420 million hectares between 1990 and 2020 through conversion to agricultural land and other uses [1, 2]. Tropical forests in particular continue to be destroyed by natural and human intervention [3–6]. As a result, 75% of tropical forests are being cleared, degraded, and converted to cropland [6–8] and human habitation, which is common in the tropics, e.g., Ethiopia [9, 10]. In these cases, while soil seed banks have the potential to recruit regeneration, they are continuously eliminated by weed control and eventually completely depleted [11, 12].

Ethiopia is recognized as one of the most biodiverse countries in Africa due to its diverse climate, topography, and soil variability [13]. However, many natural resources have been reduced and overused through degradation for decades. This degradation is the result of rapid population growth, extensive forest clearance for cultivation, and livestock grazing [14]. Forest fires and illegal harvesting of forest products also reduced the forest area [15–17]. Recent land use changes are likely to affect biodiversity and the ability of plant species to regenerate or recover in rural ecosystems [16, 18, 19]. In addition, the increase in the human population has led to the depletion of the soil seed bank [20, 21]. When the population grows rapidly, land is needed for agriculture, urbanization, and development, resulting in the loss of native vegetation and soil seed banks [22]. Likewise, changes in land use resulting from human population growth in the Chilimo forests and the Buska Mountain forests of Ethiopia led to the depletion of seeds naturally preserved in soil seed banks [23]. Therefore, a nature-based solution to land degradation has long been considered a cost-effective solution for remediation and vegetation restoration to increase the sustainability of degraded land [24, 25]. As a result, a soil seed bank study has been proposed as a promising method for vegetation restoration.

Soil seed banks are viable seeds present on the soil surface or buried in the soil [26, 27] and can serve as a “memory” of past plant communities by containing seeds from previous vegetation in the area and enhancing future plant communities [28]. It is widely believed that the soil seed bank contains native seeds for native vascular plants and provides the majority of seedlings for natural vegetation restoration [29]. However, the feasibility of vegetation restoration using the soil seed bank is highly dependent on seed density and species composition. The density and composition of the soil seed bank have been influenced by disturbances such as humans, grazing, and fires [30]. Soil seed bank density may have increased or decreased with increased human disturbance [20]. Livestock grazing alters the composition of the soil seed bank due to continuous grazing during the flowering and seeding periods [31] and can provide better opportunities for seed germination through trampling manure pellets [32], which can result in minimizing seed retention in the seed bank. Therefore, understanding the effects of grazing on the seed bank is crucial for conservation and grazing management in the tropics [33]. For this reason, the effect of fire on the soil seed bank in various grassland areas has been extensively studied [34, 35], and it has been reported that fire can affect vital processes such as flowering, fruiting, and seed germination.

Obtaining adequate information on natural forest restoration potential as well as threat factors is now urgently needed to implement appropriate forest management measures that could minimize forest loss [36, 37]. Therefore, determining the state of the seed bank is crucial for ecological stability and the restoration of degraded forests. Current habitat destruction and fragmentation (land use change) in the study area poses a significant challenge, as it threatens seed formation and maturation as well as seedling production under vegetation. In addition, no previous ecological survey of the soil seed bank in the area was conducted.

The current study was conducted in the Arjo-Diga Forest in Diga District, Western Ethiopia, in different land use types that help to establish conservation approaches for both the present and the future. Therefore, the objectives of this study were (1) to study the horizontal and vertical distribution and density of soil seed banks under different land use types and soil layers and (2) to assess the similarity in species composition between the soil seed bank and the standing vegetation of the Arjo-Diga Forest, Western Ethiopia.

2. Materials and Methods

2.1. The Study Area

Arjo-Diga Forest is located in Diga District, East Welega Zone, Oromia Regional State. It is located 234 kilometers southwest of Addis Ababa between latitudes of 9°59′00″ and 9°6′30″ and longitudes of 36°18′30″ and 36°24′30″ with altitudinal ranges between 1360 and 2,220 meters above sea level (Figure 1).

The study area features a diverse landscape that includes plains, slopes, gentle slopes, and steep hills [38]. Three main types of soil are present in the study area: Dystrian Nitrosols, Dystrian Gleysols, and Orthoclastic Acrisols [38]. Geologically, the study area is characterized by Precambrian rocks of high origin and migmatites [39]. The monthly maximum and minimum temperatures in the study area are recorded as 25.7°C and 10.2°C, respectively. The mean annual rainfall in the study area is 1997 mm, following a unimodal rainfall pattern. Monthly rainfall data show that the highest precipitation occurs in July, June, and August, while the period from November to February is relatively dry.

Jaleta and Debella [40] classified the study area into six different land use types, including arable land (71%), grassland (11%), dense forest (10%), bushes and shrubs (2%), woodland (5%), and bare land (1%). The vegetation type of the study area is humid Afromontane forest characterized by broadleaf evergreen plant species. The lowland area also includes solid lowland bamboo thickets and Combretum species.

2.2. Site Selection, Sampling, and Data Collection

Four land uses, i.e., forestland, shrubland, grassland, and bare land, were used for the collection of soil samples. Due to frequent and uncontrolled disruptions, cultivated and rural areas were not included in the present study because cultivation has no role in the restoration of vegetation [41]. Soil samples were collected in late October 2018 at the end of the growing season (after seed dispersal). To compare the seed bank flora with the standing vegetation in the Arjo-Diga Forest, a total of 36 plots with standing vegetation were randomly selected (three successive vertical soil layers 36 plots). A plot of size 15 cm × 15 cm was purposefully laid in each land use type following the methods in [22]. Soil samples were collected from five smaller subplots measuring 15 cm × 15 cm (one from the center and four from the corner) of each of the 36 sample plots. The soil samples were collected from three successive layers: the top (0–3 cm), middle (3–6 cm), and bottom (6–9 cm), using a marked metal rod following the methods in [20]. Soil from similar layers was mixed to form a composite, and approximately one kilogram of composite soil samples was transferred to cotton bags and kept separately in plastic trays. Finally, a total of 108 soil samples (3 layers × 4 land use types × 9 sample replicates) were collected and transported to the Ethiopian Biodiversity Institute (EBI) greenhouse for seed germination by the germination method.

2.3. Seedling Emergence Methods

Soil samples were air-dried and sieved with a 2 mm·mesh to remove plant matter, including roots, leaves, and stones. Soil samples were then spread in plastic trays, perforated at the bottom, watered to three days per week, and incubated in the greenhouse for seed germination. Seedlings that were easy to identify by their scientific names were counted and recorded following standard methods [42]. Seedlings that were difficult to identify were transplanted into pots and grown until they produced diagnostic characteristics that were easy to identify [43]. Seedling emergence was recorded for at least six months [44]. All specimens were pressed, dried, and identified from the Flora of Ethiopia and Eritrea and deposited in the National Herbarium, Addis Ababa University, Ethiopia.

2.4. Data Analysis

Soil seed bank density, species composition, abundance, and vertical distribution in each land use type and soil layer data were organized in an Excel spreadsheet (version 2010). The composition and density of the seeds in the soil were obtained from the combined data from the germination experiment. Soil seed bank density was calculated based on the number of seeds recovered from the soil samples. On the other hand, the vertical distribution of seeds was obtained from the combination of similar layers and converted to density of seeds/m² according to the methodology applied in [45]. In this study, R software version 4.2.3 was utilized to investigate the impact of land use types and soil layers on the mean species diversity (H′), species richness (S), and evenness (E) of soil seed banks. A two-way ANOVA was used to investigate how different types of land use and soil layers affect soil seed bank density. In addition, the mean differences in soil seed bank species compositions among the land use and aboveground vegetation were computed using one-way ANOVA, with a post hoc Tukey HSD test with a significance level of 0.05.

The similarity of soil seed bank composition among different land uses and soil layers was examined using the Jaccard similarity coefficient [46]. The coefficient is calculated using the following equation:where Sj = Jaccard similarity coefficient; a = number of species shared by both types of land use and soil layers; b = number of species that are only found in the soil layer or land use type b; and c = number of species unique to land use type c/soil layer c. The coefficient has a value from 0 to 1, where 1 indicates complete similarity and 0 shows dissimilarity.

3. Result

3.1. Seedling Composition

In this study, a total of 51 plant species belonging to 44 genera and 24 families were identified in the soil seed bank (supplementary appendix 1). The number of species varied across land use types within each family. Among the 24 families recorded in the soil seed bank, shrubland had 17 families (31 species), forestland had 14 families (27 species), grassland had 13 families (24 species), and bare land had 11 families (22 species) (refer to Figure 2). Similarly, among the 24 families recorded in the soil layers, the first upper layer (0–3 cm) had 22 families (45 species), the middle layer (3–6 cm) had 19 families (33 species), and the bottom layer (6–9 cm) had 17 families (28 species) (supplementary appendix 2).

The three most common families in the study area were Asteraceae, Poaceae, and Fabaceae, which contributed 9 (17.30%), 6 (11.53%), and 5 (9.61%) species to the soil seed bank, respectively. Conversely, 32.7% of species were contributed by the families Cyperaceae, Euphorbiaceae, Acanthaceae, Amaranthaceae, Caryophyllaceae, Rubiaceae, and Tiliaceae, while 1.92% of species were contributed by the remaining 14 families (supplementary appendix 1).

Herbs were represented by the highest number of species in all land use types (46, 90.2%), followed by trees (3, 5.88%) and shrubs (2, 3.92%) (supplenentary appendix 1). The number of species collected from different land use types ranged from 22 to 31. Shrubland had the highest number of species (31 species), followed by forestland (28 species). However, the bare land soil had the lowest number of species (22 species) in the soil seed bank. Achyranthes aspera, Hypoestes triflora, Ficus sur, Ipomoea eriocarpa, and Mitracarpus hirtus were found only in shrubland and forestland soil samples. In addition, Oldenlandia herbacea only germinated from soil samples taken from bare land soil samples. In contrast, Eragrostis schweinfurthii and Hygrophila schulli were discovered exclusively from soil samples from grassland land use types. Vernonia auriculifera, Croton macrostachyus, Entada abyssinica, Ficus sur, and Calpurnia aurea were woody species recovered from forest and shrubland land use types.

3.2. Species Diversity, Richness, and Evenness of Seedlings in Different Land Use Types

According to this study, species richness was significantly different in all land use types in the soil seed banks (), but the Shannon‒Wiener diversity index and Shannon evenness index were not () (Table 1). In shrubland (6 ± 0.39), higher species richness was observed among seedlings. However, bare land had the lowest species richness (3.81 ± 0.31). The same table shows that forestland (2.52 ± 0.14) had the largest Shannon‒Wiener diversity index, followed by grassland (2.42 ± 0.9), shrubland (2.40 ± 0.9), and bare land (2.39 ± 0.08). The highest evenness value was found in grassland (0.78 ± 0.03), while the lowest evenness value (0.71 ± 0.04) was observed in forestland.

3.3. Soil Seed Bank Density for Different Land Use Types

The present study investigated the variations in soil seed bank density among different land use types, as outlined in supplementary appendix 3. The results revealed that shrubland exhibited the highest mean soil seed bank density (1320.2 ± 2.1), while forestland had the lowest mean soil seed bank density (539.9 ± 2.3). The corresponding table also indicated that the maximum and minimum numbers of seedlings per square meter were observed in shrubland and forestland, respectively.

Additionally, the two-way ANOVA results presented in Table 2 demonstrated that different land use types had a significant and strong impact on soil seed bank density (F = 15.901, ) across soil layers. However, the analysis indicated that the interaction between land use types and soil layers did not have a statistically significant effect on soil seed bank density (F = 0.952, ).

The result of Tukey’s pairwise comparisons of means of soil seed density revealed significant differences between land use types 3-1, 3-2, and 4-3 (). However, there was no significant difference in soil seed bank density between land use types 2-1, 4-1, and 4-2 (Table 3).

According to this study, soil layers with depths of 0–3 cm, 3–6 cm, and 6–9 cm contained 45, 33, and 28 seedling species, respectively (Table 4). In the 0–3 cm soil layer, herbaceous species accounted for 91.1% of the seedling population compared to trees (6.7%) and shrubs (2.2%). Herbaceous species accounted for 90.9% of the seedling population in the 3–6 cm soil layer, compared to 6% for trees and 3% for shrubs. Furthermore, herbaceous species accounted for 82.14% of the seedling population in the 6–9 cm soil layer, while shrub species (two species) and tree species (three species) accounted for 7.15% and 10.71% of the seedling population, respectively.

The results of the soil seed density analysis indicated a significant decrease in soil seed bank density as the soil layer depth increased, as shown in Table 5. Specifically, the top layer (0–3 cm) exhibited the highest density, with 39,333 seedlings per square meter. The 3–6 cm and 6–9 cm bottom layers followed with slightly lower densities. Among the herbaceous species, the 0–3 cm layer had the maximum density of 144,687 seedlings per square meter. In contrast, the layer of 6–9 cm had the lowest density, with 21,220 seedlings per square meter.

The frequency of soil seed bank species in soil samples taken from each of the three soil layers can vary significantly from layer to layer (Table 5). In the 0–3 cm soil layers, Ageratum conyzoides, Cardamine trichocarpa, Commelina benghalensis, Centella asiatica, Cyperus fischerianus, Oplismenus hirtellus, and Veronica javanica represented a high number of seedlings (>13 seedlings each). Adenostemma mauritianum, Eragrostis schweinfurthii, Oldenlandia herbacea, and Triumfetta brachyceras had the lowest number of seedlings (<2 seedlings each). Cyperus fischerianus, Oldenlandia herbacea, and Oplismenus hirtellus were dominant in the 3–6 cm soil layer with seedlings (>6 each), while Eleusine indica, Laggera crispata, and Mitracarpus hirtus together accounted for 8.1%. Cyperus fischerianus, Veronica javanica, and Centella asiatica were the dominant seedlings in the 6–9 cm soil layers, accounting for approximately 55.5%, 52.7%, and 38.8%, respectively. Furthermore, Achyranthes aspera, Psilotrichum elliotii, Euphorbia rothiana, Triumfetta rhomboidea, Cynoglossum lanceolatum, Eragrostis schweinfurthii, Tagetes minuta, and Persicaria nepalensis only germinated from the 0–3 cm soil layers. Ipomoea eriocarpa and Hygrophila schulli were found only at a soil depth of 6–9 cm. In contrast, Hypoestes triflora was found only from the 3–6 cm soil layers (appendix 2).

Soil seed bank species richness was significantly different across soil layers () (Table 6). However, the Shannon diversity index and species evenness showed no significant differences between soil layers (). The 0–3 cm soil layer had a mean Shannon diversity index higher than that of the other soil layers (2.46 ± 0.1a). In addition, the 6–9 cm soil layer had the highest mean species uniformity of seedlings (0.77 ± 0.02a) compared to the other soil layers. In the topsoil layer, species uniformity had the lowest value (0.72 ± 0.03a). In most cases, the diversity of seedlings across soil levels decreased with increasing soil layer.

A pairwise comparison of soil layers for significant differences was conducted using Tukey’s linear contrast hypothesis. The results of the pairwise comparisons of the mean indicated significant differences in seed density between the 3–6 cm and 0–3 cm soil layers, as well as between the 6–9 cm and 0–3 cm soil layers. However, no significant differences were observed between the 6–9 cm and 3–6 cm soil layers, as shown in Table 7.

3.4. Similarity in Species Composition between Land Use Types, Soil Layers, and Standing Vegetation

In terms of species composition, forestland and shrubland had the highest Jaccard similarity coefficient value (0.72), followed by forestland and grassland (0.62), while bare land and shrubland had the lowest similarity value (0.43) (supplementary appendix 4).

The degree of Jaccard similarity between the soil seed bank layers, on the other hand, showed that the first and second layers were more similar. Conversely, the first and third layers showed the least similarity (supplementary appendix 5).

According to the study, there were 234 different species of aboveground plants in the main plots. Only 65 plant species were present in both the standing vegetation and the soil seed bank (supplementary appendix 6). The soil seed bank contained only 9.1% of the woody plants that made up the aboveground vegetation. However, the standing vegetation contained all herbaceous species found in the soil seed bank. In addition to common species present in both the seed bank and aboveground flora, 234 aboveground species and 80 seed bank-identified species were used as comparisons for the Jaccard and between the soil seed bank and standing species. However, the soil seed band and aboveground vegetation in the shrubland had a comparatively higher similarity index than the other land use types. The output of one-way ANOVA showed the variation in soil seed bank species composition and standing vegetation. Accordingly, the findings revealed that there was a significant difference between the land use types as well as a notable distinction between the seed bank and existing vegetation (Table 8).

4. Discussion

4.1. Species Composition in the Soil Seed Bank

The study of species composition, distribution, and density of soil seed banks in different land uses reflects in part the history of the standing vegetation [47]. Our results showed that the soil seed bank contains a high proportion of herbaceous species and a low proportion of woody species. The dominance of herbaceous species and species of the Asteraceae and Poaceae plant families in the soil seed bank could be due to species seeds being small, light, and winged [48]. This characteristic makes seeds more durable and dispersible through a variety of mechanisms, contributing to their high species composition in the soil seed bank [42, 49, 50]. Another possible reason is that herbaceous species have a better chance of recovering from disturbance because they produce many seeds quickly and spread over long distances [4, 43]. In contrast, only five woody species (e.g., Vernonia auriculifera, Croton macrostachyus, Entada abyssinica, Ficus sur, and Calpurnia aurea seeds) emerged from the soil seed bank of shrubland and forestland use types in this study. This number is lower than the number of woody species identified in the Arjo-Diga Forest aboveground vegetation survey because of the difficulty of incorporating their larger seeds into the soil to form seed banks [51], and they are more susceptible to fungal infections and predators [52]. The results of this study were consistent with soil seed bank studies in Ethiopia [45, 49, 53–56]. Larger, moist seeds of woody species are adapted for rapid germination, seedling formation, and survival under a forest canopy [57, 58]. Similarly, Senbeta and Teketay [3] reported that the lack of soil seed banks for woody plants affects the number of seedling populations on the forest floor.

4.2. Soil Seed Bank Species Richness and Density among Land Use Types

The results showed that both species richness and soil seed density were highest in shrubland land use types. This could be due to shrubland creating suitable conditions for the growth of many seeds under their canopies by increasing the moisture content of the soil [59] and encouraging plants to produce large numbers of viable seeds [60]. Similarly, previous work by the authors of [61, 62] has shown that shrubs have a significant impact on the movement of wind or water in an area and thus can trap seeds or act as a barrier to movement. Shrubs can also serve as perches for birds to transport and deposit seeds [63], resulting in increased seed deposition. In addition, by improving accessible soil conditions, shrublands can create favorable conditions for herbaceous plants under their canopy, which can facilitate the colonization and growth of herbaceous species [64, 65] and can increase seed production of these species. In addition, shrubs act as effective seed traps and can provide safe microsites for the germination and establishment of certain suppressed species (e.g., palatable species) by providing refuge in overgrazing areas [61]. Therefore, this study emphasizes the need to conserve and restore shrublands, which are crucial for sustaining biodiversity and ecosystem function. In contrast, bare land has lower soil species richness and seed bank density because there is no mature aboveground vegetation that can produce and deposit seeds in the soil. Additionally, bare land is susceptible to erosion, which can remove soil and seeds from the site [66]. Soil disturbances due to natural processes such as landslides or human activities can further reduce soil seed species richness and seed bank density by damaging the soil surface and removing seeds [67]. Our findings suggest that shrubland serves as a nursery, in comparison to other land use types, for maintaining the species richness and diversity of the soil seed bank.

4.3. Vertical Distribution of the Soil Seed Bank among Soil Layers

Our study found that viable soil seed density, species richness, and the Shannon diversity index decreased significantly with increasing soil depth, with the highest values observed in the layers. This could be due to several factors, including greater availability of nutrients, light, and moisture content, that promote seed germination in the upper soil layers [66, 68, 69]. Furthermore, the upper soil layers are dominantly covered with herbaceous species and hence have high diversity attributes (i.e., richness, diversity, and evenness) due to the better chances of recovery from the soil seed banks [23, 49].

Although the vertical distribution of soil seed banks varies by species, the overall pattern suggests that the seed density and seed richness of soil seed banks were highest in the top 3 cm of soil and gradually decreased with depth. The high seed density in the top layer of soil can be attributed to several factors, such as light availability, oxygen, temperature, and moisture [70]. These conditions promote successful germination and the establishment of seeds in the upper soil layers. This general trend toward higher seed bank density in the soil and higher species richness in the upper soil layers is commonly observed in our study. However, it is important to remember that species can vary because different plants have different seed characteristics and dispersal abilities. Some species may have adaptations that allow their seeds to survive and germinate at deeper soil depths, while others may have specific requirements for shallower soil depths [71]. In our study, some woody plants, such as Vernonia auriculifera, Croton macrostachyus, Entada abyssinica, Ficus sur, and Calpurnia aurea, sprouted from the 3–6 cm and 6–9 cm soil layers. This is associated with several adaptive strategies, such as the ability to sprout from dormant buds underground or long-lived seeds, which allow them to survive and thrive in different soil conditions.

4.4. Similarity in Species Composition among Land Use Types and Aboveground Vegetation

Despite differences in species composition in the soil seed bank, different land use types shared many common species, including Ageratum conyzoides, Anagallis arvensis, Cardamine trichocarpa, Centella asiatica, Cyperus brevifolius, Cyperus fischerianus, Digitaria abyssinica, Eleusine indica, Galinsoga parviflora, Laggera crispata, Oplismenus hirtellus, and Veronica javanica. The highest Jaccard similarity coefficient between forest and shrubland could be because both land use types have a similar number of common plant species and have similar ecological conditions, such as climate, soil type, and topography. The lowest Jaccard similarity coefficient was observed between shrubland and bare land use types due to variation in soil nutrient content and microclimate between these land use types [72–74].

Low similarities in species composition between the soil seed banks and the aboveground vegetation are associated with poor regeneration of woody species from soil seed bank samples. In this study, it was found that only 9.1% of woody species occur in both seed banks and aboveground vegetation. These findings suggest that the seeds of woody species are rapidly decomposed and heavily eaten by small mammals, leading to a significant deterioration in the composition of the seed bank in the soil [67, 75, 76]. Another possible reason for the different species compositions between soil seed banks and aboveground vegetation is that most woody plants produce seeds that sprout a few days or weeks after dispersal [75]. In addition, seedling emergence methods underestimate the density of the soil seed bank due to seed dormancy and the specific environmental conditions needed for germination [65, 77], which leads to a decrease in the density of the seed bank. This result is also consistent with the results of several studies conducted in Ethiopia [49, 53, 78].

Understanding soil seed banks is important for maintaining and repairing degraded ecosystems [29]. For example, seeds buried in the ground cannot fully regenerate the standing plant from anthropogenic or natural damage. This has significant management implications. Similarly, the Arjo-Diga Forest has been degraded as a result of charcoal production, animal grazing, expansion of agricultural land, and tree felling for housing. Consequently, most tree and shrub species have a minimal regenerative capacity [3]. Therefore, the soil seed bank would be essential to recover the previously existing vegetation that has been degraded.

4.5. Soil Seed Bank and Its Impact on Biodiversity Conservation

The presence of viable seeds in the soil is an important trait for making conservation measurements because it indicates the plant’s ability to recover. Herb seedlings abound in the research area. Because herbaceous vegetation produces large number of long-lived seeds, it has a better chance of recovery [49, 53]. Few seedlings of woody species have been found in soil seed banks. This indicates that trees and shrubs have low regeneration potential, which could be related to various disturbances, such as humans, livestock grazing, and fires, in the study area. Therefore, planting native seedlings and preserving existing trees are crucial for tree recovery. This also applies to bare land, which has a low seedling density and a low regeneration potential.

5. Conclusions

The study examined soil seed banks in different land use types and their potential for natural plant regeneration. Herbaceous seedling density was high across all land use types due to small, light, and winged seeds. However, only a few woody species such as Vernonia auriculifera, Croton macrostachyus, Entada abyssinica, Ficus sur, and Calpurnia aurea seeds have emerged from the soil seed bank of shrubland and forestland use types. This is primarily due to the challenge of incorporating their larger seeds into the soil to form seed banks. Active restoration strategies, such as no-till practices and planting native species in nurseries, were recommended.

Shrubland had high species richness, diversity, and seed density due to its role as a bird perch, facilitating seed deposition. Conserving and restoring shrubland ecosystems were emphasized for biodiversity and ecosystem functioning. Bare land had low species richness and seed density, attributed to erosion susceptibility. Vegetation establishment was suggested to improve the soil seed bank.

Vertical distribution of seed banks varied with soil layers, influenced by seed properties and environmental conditions. Dissimilarities were found between aboveground vegetation and soil seed banks, indicating challenges in natural regeneration. Establishing nurseries and producing seedlings were recommended for sustainable management of native plant species.

In conclusion, the study highlights the importance of soil seed banks for natural plant regeneration. Active restoration, shrubland conservation, vegetation formation in bare areas, and nursery establishment were identified as effective strategies. Understanding seed bank dynamics and its relationship with aboveground vegetation is crucial for ecosystem management and biodiversity conservation.

Data Availability

The data supporting the findings of this study are available upon request from the corresponding author.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

The first author would like to thank the Diga District Department of Agriculture for providing the needed data and the local community for their generous support and cooperation during data collection. The authors also thank the staff of Addis Ababa University National Herbarium, Ethiopia, for their help in identifying soil seed bank flora.

Supplementary Materials

This section consists of list of identified soil seed bank species in Diga district, percentage frequency of soil seed bank species and their density across soil layers, mean (±SD) densities (m⁻²) of soil seed recovered from different land use types, similarity of the Jaccard coefficient in species composition between land cover types, and Jaccard’s coefficient of similarity (JCS) among soil layers and between the soil seed bank and aboveground vegetation. (Supplementary Materials)

References

F. Belete, M. Maryo, and A. Teka, “Land use/land cover dynamics and perception of th local communities in Bita district, south western Ethiopia,” International Journal of River Basin Management, vol. 21, pp. 1–12, 2021.
View at: Google Scholar
Fao and Global Forest Resource Assessment, FAO Forestry Paper 140, Food and Agriculture Organization, Rome, Italy, 2001.
F. Senbeta and D. Teketay, “Soil seed banks in plantations and adjacent natural dry Afromontane forests of central and southern Ethiopia,” Tropical Ecology, vol. 43, no. 2, p. 22242, 2002.
View at: Google Scholar
A. Popradit, T. Srisatit, S. Kiratiprayoon et al., “Anthropogenic effects on a tropical forest according to the distance from human settlements,” Scientific Reports, vol. 5, no. 1, Article ID 14689, 2015.
View at: Publisher Site | Google Scholar
Fao and Unep, “The state of the world’s forests 2020,” Forests, Biodiversity and People, FAO, Rome, Italy, 2020.
View at: Google Scholar
H. K. Gibbs, A. S. Ruesch, F. Achard et al., “Tropical forests were the primary sources of new agricultural land in the 1980s and 1990s,” Proceedings of the National Academy of Sciences, vol. 107, no. 38, pp. 16732–16737, 2010.
View at: Publisher Site | Google Scholar
C. Brown and J. Ball, “World view of plantation grown wood,” Oceania, vol. 2, pp. 0-01, 2000.
View at: Google Scholar
R. Trancoso, J. Syktus, A. Salazar et al., “Converting tropical forests to agriculture increases fire risk by fourfold,” Environmental Research Letters, vol. 17, no. 10, Article ID 104019, 2022.
View at: Publisher Site | Google Scholar
F. Senbeta and D. Teketay, “Regeneration of indigenous woody species under the canopies of tree plantations in Central Ethiopia,” Tropical Ecology, vol. 42, no. 2, pp. 175–185, 2001.
View at: Google Scholar
F. Pendrill, U. M. Persson, J. Godar et al., “Agricultural and forestry trade drives large share of tropical deforestation emissions,” Global Environmental Change, vol. 56, pp. 1–10, 2019.
View at: Publisher Site | Google Scholar
T. Demel, “Soil seed bank at an abandoned Afromontane arable site,” Feddes Repertorium, vol. 109, no. 1-2, pp. 161–174, 1998.
View at: Publisher Site | Google Scholar
S. Wakshum, D. Sebsebe, and B. Tamrat, “Ecology of soil seed banks: implications for conservation and restoration of natural vegetation: a review,” International Journal of Biodiversity and Conservation, vol. 10, no. 10, pp. 380–393, 2018.
View at: Publisher Site | Google Scholar
M. Asefa, M. Cao, Y. He, E. Mekonnen, X. Song, and J. Yang, “Ethiopian vegetation types, climate and topography,” Plant Diversity, vol. 42, no. 4, pp. 302–311, 2020.
View at: Publisher Site | Google Scholar
F. K. Tola, “Drivers of forest cover changes in and around jorgo wato forest, west wallagga, Oromia, Ethiopia,” Heliyon, vol. 9, no. 8, Article ID e19053, 2023.
View at: Publisher Site | Google Scholar
T. B. Egziabher, “Vegetation and environment of the mountains of ethiopia: implications for utilization and conservation,” Mountain Research and Development, vol. 8, pp. 211–216, 1988.
View at: Google Scholar
T. Soromessa, D. Teketay, and S. Demissew, “Ecological study of the vegetation in Gamo Gofa zone, southern Ethiopia,” Tropical Ecology, vol. 45, no. 2, pp. 209–222, 2004.
View at: Google Scholar
X. Hu, J. S. Næss, C. M. Iordan, B. Huang, W. Zhao, and F. Cherubini, “Recent global land cover dynamics and implications for soil erosion and carbon losses from deforestation,” Anthropocene, vol. 34, Article ID 100291, 2021.
View at: Publisher Site | Google Scholar
O. E. Sala, F. Stuart Chapin, J. J. Armesto et al., “Global biodiversity scenarios for the year 2100,” Science, vol. 287, no. 5459, pp. 1770–1774, 2000.
View at: Publisher Site | Google Scholar
R. J. Wilson, Z. G. Davies, and C. D. Thomas, “Insects and climate change: processes,patterns and implications for conservation,” in Insect Conservation Biology Proceedings of the Royal Entomological Society’s 22nd Symposium, CAB International Publishing, Wallingford, UK, 2007.
View at: Google Scholar
M. Lemenih and D. Teketay, “Changes in soil seed bank composition and density following deforestation and subsequent cultivation of a tropical dry Afromontane forest in Ethiopia,” Tropical Ecology, vol. 47, no. 1, pp. 1–12, 2006.
View at: Google Scholar
D. Taiwo, O. J. Oyelowo, T. C. Ogedengbe, and A. I. Woghiren, “The role of soil seed bank in forest regeneration,” Asian Journal of Research in Agriculture and Forestry, vol. 1, no. 4, pp. 1–10, 2018.
View at: Publisher Site | Google Scholar
C. Li, B. Xiao, Q. Wang, R. Zheng, and J. Wu, “Responses of soil seed bank and vegetation to the increasing intensity of human disturbance in a semiarid region of northern China,” Sustainability, vol. 9, no. 10, p. 1837, 2017.
View at: Publisher Site | Google Scholar
B. Assefa, T. Bekele, and S. Nemomissa, “Impact of land use type on soil seed bank flora in Chilimo forest, Ethiopia: implications for natural restoration of vegetation,” Ethiopian Journal of Biological Sciences, vol. 13, no. 2, pp. 117–133, 2014.
View at: Google Scholar
J. L. Nel, D. C. Le Maitre, D. C. Nel et al., “Natural hazards in a changing world: a case for ecosystem-based management,” PLoS One, vol. 9, no. 5, Article ID e95942, 2014.
View at: Publisher Site | Google Scholar
S. Keesstra, J. Nunes, A. Novara et al., “The superior effect of nature based solutions in land management for enhancing ecosystem services,” Science of the Total Environment, vol. 610-611, pp. 997–1009, 2018.
View at: Publisher Site | Google Scholar
C. Douh, K. Daïnou, J. Joël Loumeto et al., “Soil seed bank characteristics in two central African forest types and implications for forest restoration,” Forest Ecology and Management, vol. 409, pp. 766–776, 2018.
View at: Publisher Site | Google Scholar
T. M. Sloey and M. W. Hester, “The role of seed bank and germination dynamics in the restoration of a tidal freshwater marsh in the Sacramento–San Joaquin Delta,” San Francisco Estuary and Watershed Science, vol. 17, no. 3, 2019.
View at: Publisher Site | Google Scholar
D. A. Levin, “The seed bank as a source of genetic novelty in plants,” The American Naturalist, vol. 135, no. 4, pp. 563–572, 1990.
View at: Publisher Site | Google Scholar
R. R. Warrier, R. R. Warrier, and C. Kunhikannan, “Significance of soil seed bank in forest vegetation—a review,” Seeds, vol. 1, no. 3, pp. 181–197, 2022.
View at: Publisher Site | Google Scholar
M. Ma, X. Zhou, and G. Du, “Role of soil seed bank along a disturbance gradient in an alpine meadow on the Tibet plateau,” Flora-Morphology, Distribution, Functional Ecology of Plants, vol. 205, no. 2, pp. 128–134, 2010.
View at: Publisher Site | Google Scholar
M. Sternberg, M. Gutman, A. Perevolotsky, and J. Kigel, “Effects of grazing on soil seed bank dynamics: an approach with functional groups,” Journal of Vegetation Science, vol. 14, no. 3, pp. 375–386, 2003.
View at: Publisher Site | Google Scholar
M. Fraser, V. J. Theobald, M. S. Dhanoa, and O. D. Davies, “Impact on sward composition and stock performance of grazing Molinia-dominant grassland,” Agriculture, Ecosystems & Environment, vol. 144, no. 1, pp. 102–106, 2011.
View at: Publisher Site | Google Scholar
A. F. Fernandes, Y. Oki, G. W. Fernandes, and B. Moreira, “The effect of fire on seed germination of campo rupestre species in the South American Cerrado,” Plant Ecology, vol. 222, no. 1, pp. 45–55, 2021.
View at: Publisher Site | Google Scholar
H. Snyman and A.-E. van Wyk, “The effect of fire on the soil seed bank of a semiarid grassland in South Africa,” South African Journal of Botany, vol. 71, no. 1, pp. 53–60, 2005.
View at: Publisher Site | Google Scholar
M. Bashmaghi, R. Erfanzadeh, and M. Abedi, “Effect of fire intensity on soil seed bank density of plant functional groups (case study: golestan national park),” Journal of Range and Watershed Managment, vol. 70, no. 1, pp. 43–55, 2017.
View at: Google Scholar
D. A. DellaSala, A. Martin, R. Spivak et al., “A citizen's call for ecological forest restoration: forest restoration principles and criteria,” Ecological Restoration, vol. 21, no. 1, pp. 14–23, 2003.
View at: Publisher Site | Google Scholar
J. Wang, L. Huang, H. Ren, Z. Sun, and Q. Guo, “Regenerative potential and functional composition of soil seed banks in remnant evergreen broad-leaved forests under urbanization in South China,” Community Ecology, vol. 16, no. 1, pp. 86–94, 2015.
View at: Publisher Site | Google Scholar
T. Megersa, D. Nedaw, and M. Argaw, “Combined effect of land use/cover types and slope gradient in sediment and nutrient losses in Chancho and Sorga sub watersheds, East Wollega Zone, Oromia, Ethiopia,” Environmental Systems Research, vol. 8, 2019.
View at: Publisher Site | Google Scholar
P. A. Mohr, The Geology of Ethiopia, Haile Selassie I University Press, Addis Ababa, Ethiopia, 1971.
G. Jaleta and H. J. Debella, “The impact of large scale agriculture on forest and wildlife in Diga Woreda, Western Ethiopia,” Asian Journal of Agriculture, vol. 1, no. 2, pp. 100–113, 2017.
View at: Publisher Site | Google Scholar
M. R. Wade, G. M. Gurr, and S. D. Wratten, “Ecological restoration of farmland: progressand prospects,” Philosophical Transactions of the Royal Society B: Biological Sciences, vol. 363, no. 1492, pp. 831–847, 2008.
View at: Publisher Site | Google Scholar
Z. K. Tessema, W. F. de Boer, R. M. T. Baars, and H. H. T. Prins, “Influence of grazing on soil seed banks determines the restoration potential of aboveground vegetation in a semi-arid savanna of Ethiopia,” Biotropica, vol. 44, no. 2, pp. 211–219, 2012.
View at: Publisher Site | Google Scholar
C. Álvarez-Aquino, G. Williams-Linera, and A. Newton, “Disturbance effects on the seed bank of Mexican cloud forest Fragments¹,” Biotropica, vol. 37, no. 3, pp. 337–342, 2005.
View at: Publisher Site | Google Scholar
L. López-Toledo and M. Martínez-Ramos, “The soil seed bank in abandoned tropical pastures: source of regeneration or invasion?” Revista Mexicana de Biodiversidad, vol. 82, no. 2, pp. 663–678, 2011.
View at: Publisher Site | Google Scholar
G. Tesfaye, D. Teketay, Y. Assefa, and M. Fetene, “The impact of fire on the soil seed bank and regeneration of Harenna forest, Southeastern Ethiopia,” Mountain Research and Development, vol. 24, no. 4, pp. 354–361, 2004.
View at: Publisher Site | Google Scholar
A. E. Magurran, “Measuring biological diversity,” Current Biology, vol. 31, no. 19, pp. R1174–R1177, 2021.
View at: Publisher Site | Google Scholar
T. Solomon, H. Snyman, and G. Smit, “Soil seed bank characteristics in relation to land use systems and distance from water in a semiarid rangeland of southern Ethiopia,” South African Journal of Botany, vol. 72, no. 2, pp. 263–271, 2006.
View at: Publisher Site | Google Scholar
B. Liu, Q. Liu, C. Zhu et al., “Seed rain and soil seed bank in Chinese fir plantations and an adjacent natural forest in southern China: implications for the regeneration of native species,” Ecology and Evolution, vol. 12, no. 1, p. e8539, 2022.
View at: Publisher Site | Google Scholar
A. Wassie and D. Teketay, “Soil seed banks in church forests of northern Ethiopia: implications for the conservation of woody plants,” Flora-Morphology, Distribution, Functional Ecology of Plants, vol. 201, no. 1, pp. 32–43, 2006.
View at: Publisher Site | Google Scholar
R. Erfanzadeh, M. Hadinezhad, and H. Ghelichnia, “Soil seed bank characteristics in relation to different shrub species in semiarid regions,” Authorea Preprints, vol. 32, 2020.
View at: Google Scholar
B. Reubens, M. Heyn, K. Gebrehiwot, M. Hermy, and B. Muys, “Persistent soil seed banks for natural rehabilitation of dry tropical forests in northern Ethiopia,” Tropicultura, vol. 25, no. 4, p. 204, 2007.
View at: Google Scholar
J. Obiri, J. Healey, and J. Hall, “Species representation in the soil seed bank under two invasive woodland trees species. indicators and tools for restoration and sustainable management of forests in east africa,” Working Paper, vol. 14, 2005.
View at: Google Scholar
M. Bekele, S. Demissew, T. Bekele, and F. Woldeyes, “Soil seed bank distribution and restoration potential in the vegetation of Buska Mountain range, Hamar district, southwestern Ethiopia,” Heliyon, vol. 8, no. 11, Article ID e11244, 2022.
View at: Publisher Site | Google Scholar
L. Birhanu, T. Bekele, B. Tesfaw, and S. Demissew, “Soil seed bank composition and aboveground vegetation in dry Afromontane forest patches of Northwestern Ethiopia,” Trees, Forests and People, vol. 9, Article ID 100292, 2022.
View at: Publisher Site | Google Scholar
M. Girmay, T. Bekele, and S. Demissew, “Soil seed bank study of Hirmi woodland vegetation: implications for restoration and conservation of natural vegetation, in tigray, northern ethiopia,” Trees, Forests and People, vol. 8, Article ID 100249, 2022.
View at: Publisher Site | Google Scholar
S. A. Chengere, C. Steger, K. Gebrehiwot, S. Wube, B. W. Dullo, and S. Nemomissa, “Quantifying shrub encroachment through soil seed bank analysis in the Ethiopian highlands,” PLoS One, vol. 18, no. 8, Article ID 0288804, 2023.
View at: Publisher Site | Google Scholar
D. Teketay, “Seed and regeneration ecology in dry Afromontane forests of Ethiopia:Seed production-population structures,” Tropical Ecology, vol. 46, no. 1, pp. 29–44, 2005.
View at: Google Scholar
Y. Teklu and T. Bekele, “Composition study of soil seed bank at gera moist evergreen afromontane forest, jimma zone of Oromia regional state, southwest Ethiopia,” International Journal of Scientific Engineering and Research, vol. 10, no. 6, pp. 1480–1495, 2019.
View at: Google Scholar
F. I. Pugnaire and R. Lázaro, “Seed Bank and understorey species composition in a semi-arid environment: the effect of shrub age and rainfall,” Annals of Botany, vol. 86, no. 4, pp. 807–813, 2000.
View at: Publisher Site | Google Scholar
M. Debussche and P. Isenmann, “Bird-dispersed seed rain and seedling establishment in patchy Mediterranean vegetation,” Oikos, vol. 69, no. 3, pp. 414–426, 1994.
View at: Publisher Site | Google Scholar
A. Filazzola, A. R. Liczner, M. Westphal, and C. J. Lortie, “Shrubs indirectly increase desert seedbanks through facilitation of the plant community,” PLoS One, vol. 14, no. 4, 2019.
View at: Publisher Site | Google Scholar
I. Iladi, M. Segoli, and E. D. Ungar, “Shrubs and herbaceous seed flow in a semi‐arid landscape: dual functioning of shrubs as trap and barrier,” Journal of Ecology, vol. 101, no. 1, pp. 97–106, 2013.
View at: Google Scholar
R. Erfanzadeh, R. Shahbazian, and H. Zali, “Role of plant patches in preserving flora from the soil seed bank in an overgrazed high-mountain habitat in northern Iran,” Journal of Agricultural Science and Technology A, vol. 16, no. 1, pp. 229–238, 2014.
View at: Google Scholar
P. Niknam, R. Erfanzadeh, H. Ghelichnia, and A. Cerdà, “Spatial variation of soil seed bank under cushion plants in a subalpine degraded grassland,” Land Degradation & Development, vol. 29, no. 1, pp. 4–14, 2018.
View at: Publisher Site | Google Scholar
R. Erfanzadeh, A. A. Shayesteh Palaye, and H. Ghelichnia, “Shrub effects on germinable soil seed bank in overgrazed rangelands,” Plant Ecology & Diversity, vol. 13, no. 2, pp. 199–208, 2020.
View at: Publisher Site | Google Scholar
M. Mndela, C. I. Madakadze, F. Nherera-Chokuda, and S. Dube, “Is the soil seed bank a reliable source for passive restoration of bush-cleared semiarid rangelands of South Africa?” Ecological Processes, vol. 9, no. 1, pp. 1–16, 2020.
View at: Publisher Site | Google Scholar
P. Savadogo, L. Sanou, S. D. Dayamba, F. Bognounou, and A. Thiombiano, “Relationships between soil seed banks and above-ground vegetation along a disturbance gradient in the W National Park trans-boundary biosphere reserve, West Africa,” Journal of Plant Ecology, vol. 10, no. 2, pp. 349–363, 2017.
View at: Google Scholar
R. Erfanzadeh, J. Pétillon, J.-P. Maelfait, and M. Hoffmann, “Environmental determinism versus biotic stochasticity in the appearance of plant species in salt-marsh succession,” Plant Ecology and Evolution, vol. 143, no. 1, pp. 43–50, 2010.
View at: Publisher Site | Google Scholar
K. Tiebel, F. Huth, and S. Wagner, “Soil seed banks of pioneer tree species in European temperate forests: a review,” iForest: Biogeosciences and Forestry, vol. 11, no. 1, pp. 48–57, 2018.
View at: Publisher Site | Google Scholar
Á Tóth, B. Deák, K. Tóth et al., “Vertical distribution of soil seed bank and the ecological importance of deeply buried seeds in alkaline grasslands,” PeerJ, vol. 10, Article ID e13226, 2022.
View at: Publisher Site | Google Scholar
T. Mašková and P. Poschlod, “Soil seed bank persistence across time and burial depth in calcareous grassland habitats,” Frontiers in Plant Science, vol. 12, Article ID 790867, 2021.
View at: Publisher Site | Google Scholar
J. C. Chambers, J. A. MacMahon, and J. H. Haefner, “Seed entrapment in alpine ecosystems: effects of soil particle size and diaspore morphology,” Ecology, vol. 72, no. 5, pp. 1668–1677, 1991.
View at: Publisher Site | Google Scholar
K. Rusvai, B. Wichmann, D. Saláta, V. Grónás, J. Skutai, and S. Czóbel, “Changes in the vegetation, soil seed bank and soil properties at bait sites in a protected area of the central European lower montane zone,” Sustainability, vol. 14, no. 20, Article ID 13134, 2022.
View at: Publisher Site | Google Scholar
M. Girmay, T. Bekele, S. Demissew, and E. Lulekal, “Ecological and floristic study of hirmi woodland vegetation in tigray region, northern Ethiopia,” Ecological Processes, vol. 9, no. 1, 2020.
View at: Publisher Site | Google Scholar
D. Teketay, Seed ecology and regeneration in dry afromontane forests of Ethiopia, Swedish University of Agricultural Sciences, Uppsala, Sweden, 1998.
N. Wang, X. He, F. Zhao, D. Wang, and J. Jiao, “Soil seed bank in different vegetation types in the Loess Plateau region and its role in vegetation restoration,” Restoration Ecology, vol. 28, no. S1, pp. A5–A12, 2020.
View at: Publisher Site | Google Scholar
R. Erfanzadeh, M. Daneshgar, and H. Ghelichnia, “Improvement of the seedling emergence method in soil seed bank studies using chemical treatments,” Community Ecology, vol. 21, no. 2, pp. 183–190, 2020.
View at: Publisher Site | Google Scholar
D. Sileshi and B. Abraha, “Assessment of soil seedbank composition of woody species in hgumbirda national forest priority area, northeastern Ethiopia,” Momona Ethiopian Journal of Science, vol. 6, no. 1, pp. 25–44, 2014.
View at: Publisher Site | Google Scholar

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