Status of Soil Physicochemical Properties in Forests and Savannas Restored Using the Ecosystem-Based Adaptation Approach in Eastern Rwanda

Abstract

The concept of soil quality was developed to describe the capacity of soil to perform ecosystem functions properly. Nowadays, soil quality is affected by climate change effects. To remediate the problem, the ecosystem-based adaptation approach (EbA) was initiated to restore degraded ecosystems. In Rwanda, the approach was initiated in 2016 to restore degraded wetlands, savannas, and forests. However, nothing is known about how the restoration improved soil quality. This research aims to reveal the status of soil physicochemical properties in restored forests and savannas in Eastern Rwanda. Soil cores were collected and analyzed for soil pH, electrical conductivity, ammonium, nitrates, total nitrogen, organic carbon, available phosphorus, calcium, magnesium, potassium, sodium, cation exchange capacity, structure, texture, and soil water content. Results indicated that the restored and natural forests offer better conditions of soil properties. The restored forest (plot A) had lower level of soil pH and had higher electrical conductivity, total nitrogen, organic carbon, available phosphorus, calcium, potassium, magnesium, cation exchange capacity, and sandy loam soil type. The nonrestored forest (plot B) was rich in ammonium, silt, water content, and sandy loam soil type, while the natural forest (plot C) was rich in soil pH, electrical conductivity, total nitrogen, organic carbon, calcium, magnesium, cation exchange capacity, and soil water content and had loam soil compared to plots A and B. In savannas, all plots were similar in vegetation type and tree species. Higher levels of ammonium were found in plots A and C. The available phosphorus and potassium content was significantly higher in plot A than in the plots B and C. In all savanna plots, soil was sandy loam. Like in the forests, sodium was the same in all plots. We recommend future studies to validate these findings.

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

Soil is a complex ecosystem comprising living organisms like animals and plants as well as nonliving components such as organic matter and minerals that interact in various ways, especially via the biogeochemical cycles [1]. Furthermore, soil consists of pore systems [2] that are essential for soil health and soil quality [3] defined as the capacity of soil to sustain soil air and soil water quality, leading to proper soil functioning and maintenance of plant health and productivity [4]. Furthermore, soil is essential for soil microbial metabolic pathways [5] that fix greenhouse gases and degrade organic pollutants [6]. Many soil ecosystem services inherently depend on soil health and soil biota such as soil ecosystem engineers that create galleries and pores essential for soil aeration and soil water retention [7]. Recent research showed the key regulators of soil quality and functions. These are but not limited to soil physical, chemical, and biological properties [8].

Soil quality and function are constantly affected by climate change and variations, particularly the ecosystem services supporting human wellbeing [9] and human activities [10, 11]. Reported impacts of climate change effects on soil occur through droughts, flooding, and heat waves [10] as a result of changes in temperature and precipitation [11]. These effects accelerate changes in soil quality and function [12], such as changes in soil structure [13], porosity [14], water infiltration [15], bulk density [16], plant root deepness [17, 18], cover of the soil surface [19], soil temperature [12], soil electrical conductivity [20], soil cation exchange capacity [16], soil nutrient availability [21], soil organic matter [22], soil carbon-nitrogen ratio (C/N), soil mineralizable carbon and nitrogen, soil enzyme activity [19], soil respiration [23], and microbial biomass [6].

Changes in soil properties reduce the ability of the soil to properly sustain quality and quantity of plant growth and production [19, 24, 25]. Countries affected by these changes are those relying on low-income climate patterns-dependent economy. Most of these countries rely on rain-fed agriculture [26, 27], and variations in precipitation affect food security due to changes in crop and livestock production [11, 28]. Effects of climate change are further expanded to land degradation [19] coupled with limited potentials of lands to provide enough crop yield [29]. In sub-Saharan countries for example, continuous changes in temperature and precipitation alone will decrease rain-fed cereals (rice, wheat, and maize) by 12% in 2080 [11, 30]. Effects of climate change shall go beyond of these projections if there are no sustainable measures in place.

One of the solutions taken to mitigate challenges imposed by changes in soil properties from climate change effects is the use of ecosystem-based adaptation (EbA) approach [31]. This consists of the use of biodiversity and ecosystem services to help people adapt to adverse effects of climate change [32]. In other words, EbA approach was developed as a solution to increase the resilience of local people to climate change [33]. The EbA was identified as a suitable approach to adapt and mitigate adverse effects of climate change on social-ecological systems [34] and has gained significant consideration in the fields of environmental development policies [35]. As a result, many projects have been implemented using the EbA approach worldwide [31, 36]. In Rwanda, the use of EbA is recent. It was introduced in 2016 to establish buffer zones and restore wetland, savanna, and forest ecosystems. The approach was also used to remove invasive species and construction of terraces for erosion control [37]. The recent assessment of the impacts of EbA interventions in Rwanda has indicated positive outcomes as restoration activities supported local people living around restored areas through direct ecosystem services and employment [32].

Despite the strong promotion and use of the EbA approach, building evidence of its environmental, social, and economic benefits in practice remains work in progress. There is a lack of demonstrable evidence of EbA approach in delivering indirect ecosystem services, such as pollination, soil quality, and soil function. Assessing effectiveness of EbA interventions to improve soil quality in restored lands using soil properties is an important tool, but it is understudied in Rwanda. There is a need to assess the contribution of EbA restoration activities on soil physicochemical properties. To fill the gaps, this study assessed the current levels of soil pH, soil electrical conductivity, ammonium and nitrate ions, total nitrogen, organic carbon, available phosphorus, calcium, magnesium, potassium, sodium, cation exchange capacity, soil structure, soil texture, and soil water content in savannas and forests of Eastern Rwanda restored using the EbA approach.

Findings serve as baseline for further assessment of the EbA approach impacts as this is the first study assessing the levels of soil properties in forests and savannas restored using the EbA approach in Rwanda. The specific objective was to assess the current levels of soil properties in the restored lands of Ibanda-Makera forest and Eastern savannas. Due to different vegetation cover and the current land use among the sampled plots at Ibanda-Makera site, we hypothesized that (i) there are differences in the levels of soil physical and chemical composition among the natural, restored, and nonrestored forests. Contrarily, because of similar vegetation type and land use at the Eastern savanna site, we predicted (ii) similar soil physicochemical composition among the sampled plots. Similarly, as a result of different vegetation cover and land use, we finally expected (iii) significant differences in soil properties between the restored savannas and restored forests.

2. Methodology

2.1. Description of the Area of Study

Data were collected at Ibanda-Makera (Kirehe district) forest and in savannas (Nyagatare district) located in Eastern Rwanda (Supplementary Figure 1). At Ibanda-Makera forest, data were collected in three plots named A (2°6′28″S, 30°51′24″E, altitude: 1306 m), B (2°6′9″S, 30°51′30″E, Altitude: 1365 m), and C (2°6′26″S, 30°51′4″E, altitude: 1307 m). At Nyagatare, data were also collected in three plots named A (1°16′ 35″S, 30°26′12″E, altitude: 1422 m), B (1°16′24″S, 30°26′42″E, altitude: 1379 m), and C (1°13′18″S, 30°28′22″E, altitude: 1305 m). According to USDA soil classification, Ibanda-Makera forest has Ultisol, while the Eastern savannas have Oxisol soil types [38]. In savannas, all plots were similar in vegetation type and planted tree species (Supplementary Figure 2, Photo a). Plots A and B were at higher altitudes, while plot C was located at lower altitude and near the Karangazi River. At Ibanda-Makera, plot A was in restored forest at high altitude on the hill dominated by Lantana camara (family: Verbenaceae) weeds (Supplementary Figure 2, Photo a). Plot B was in nonrestored pasture forest used for cow herding also dominated by Lantana camara weeds (Supplementary Figure 2, Photo b), while plot C was at the low altitude in nondisturbed natural forest gallery near the swamp and river (Supplementary Figure 2, Photo c). Furthermore, each plot was subdivided into eight subplots totaling 48 subplots.

Ibanda-Makera is made of a gallery natural forest called Ibanda associated with woodland and savanna in East. It is also made of papyrus swamp in the south known as Makera. The gallery forest is dominated by Markhamia lutea (family: Bignoniaceae), Vepris nobilis syn. Teclea nobilis (family: Rutaceae), Ficus vallis choudae (family: Moraceae), and Dracaena afromontana (family: Asparagaceae) tree species. The area endured complete pressure from farmers, and only the Ibanda forest remained. The other part of the forest, which was degraded, was later restored in 2017 using indigenous tree species, namely, Acacia polyacantha (family: Fabaceae), Markhamia lutea (family: Bignoniaceae), and Ficus sp. (family: Moraceae). The current surface area of the forest is 163 ha (Makera: 74 ha, Ibanda: 89 ha) inhabited by different amphibians, reptiles, and birds, which are not yet fully studied, and hence, the knowledge of their diversity remains limited.

Besides, Eastern savannas were part of Akagera National Park dominated by Hyparrhenia grasses (family: Poaceae), and it was mainly used for hunting. Due to human pressure, the area was converted into pastureland after 1994. To reinforce their sustainability, Rwanda Environment Management Authority (REMA) restored the pastureland by using the Grevillea robusta (family: Proteaceae), Cedrella serrata (family: Meliaceae), Maesopsis (family: Rhamnaceae), Casuarina equisetifolia (family: Casuarinaceae), Senna siamea (family: Caesalpinioideae), and Acrocarpus fraxinifolius (family: Fabaceae) tree species. The restoration was initiated in 2020. The restored lands are the farmlands owned by local community members and still used for cow herding. They are mixed with the native Hyparrhenia grasses, which are dominant compared with other grasses.

2.2. Soil Sampling Design

Each plot was subdivided into eight subplots of 50 m × 50 m each (Supplementary Figure 3). Within the subplot, soil samples were taken in nine sampling points as indicated in Supplementary Figure 2. Soil cores were collected from soil columns using a 2-cm-diameter soil auger to a 0–5 cm soil depth and pulled together to make a representative sample of the subplot [39]. Because of short soil depth, it was not possible to go deep and collect soil layers beyond of 5 cm. Collected soil cores were sieved using 2 mm mesh size to remove debris and for homogenization [40]. A total of 24 soil samples (8 × 3) were taken in savannas and 24 soil samples (8 × 3) were taken from the forest, totaling 48 soil samples.

2.3. Laboratory Analysis

Soil samples were analyzed in the laboratory of soil, plant, and water analysis of Rwanda Agriculture and Animal Resources Development Board (RAB). Each sample was first air-dried [41] and analyzed for soil pH, electrical conductivity, ammonium and nitrate ions, total nitrogen, organic carbon, available phosphorus, calcium, magnesium, potassium, sodium, cation exchange capacity, soil texture (sand, silt, clay), and soil water content. Measurements followed the laboratory methods of soil and plant analyses [42]. Specifically, soil pH was measured at 1 : 2.5 soil : water ratio using the pH 3110 SET 2. Electrical conductivity was measured from 1 : 5 soil : water ratio using Cond 3310 SET 1 electrical conductivity meter, total nitrogen was calculated by the Kjeldahl method [43], ammonium ${\text{NH}}_4^{+}\text{\hspace{0.17em}and\hspace{0.17em}nitrate\hspace{0.17em}}{\text{NO}}_3^{-}$ were measured by calorimetric method using the UV-6300PC Double Beam spectrophotometer, and the exchangeable sodium and potassium were measured by flame photometry using PfP7 Flame Photometer (JENWAY), while calcium and magnesium were measured using the atomic absorption spectrophotometry. Furthermore, the organic carbon was measured using Walkley and Black method by oxidizing aqueous mixture of potassium dichromate in the presence of sulfuric acid [44]. Available phosphorus was measured by ultraviolet-visible spectrophotometry at 884 nm wavelength [45], while water content was measured by the oven-drying method [46]. Furthermore, soil texture was determined using the Bouyoucos hydrometer method and the textural classification was done using the soil texture triangle [47].

2.4. Statistical Data Analysis

Data from laboratory analysis of the soil physicochemical properties were all statistically analyzed by using the Paleontological Statistics Software (PAST) version 4.03. Specifically, the means and standard deviations [48] were calculated for soil samples from A (n = 8 samples), B (n = 8 samples), and C (n = 8 samples) plots in savannas and forests, respectively. Findings were given in a table, and significant differences were indicated by letters according to the $P$ values. Furthermore, the ANOVA for several sample tests [49] using the Kruskal–Wallis test for equal medians [50] at $P<0.05$ was calculated to compare the variations in soil properties between plots of the individual sites and between sites. In addition, nonmetric multidimensional scaling (NMDS) was used for unconstrained ordination of soil physicochemical properties. Results from this analysis were quantitatively evaluated using the Euclidian distance [51]. Furthermore, the Bray–Curtis similarity indices were also used to test significant differences in the composition of soil properties between plots and between sites. The conclusion was taken following R value whereby values closer to zero indicate high similarity, while values closer to one indicate low similarity. Furthermore, the similarity percentage analysis (SIMPER) was used to determine soil properties, which contributed more to similarity. High percentage implied high contribution to similarity in soil properties [52].

3. Results

3.1. Status of Soil Properties in the Restored Forest

Row data of this study are presented in Appendix 2. The analysis indicated that the forest (Supplementary Table 1; plot A) had higher level of soil pH (5.3 ± 0.4) and higher values of electrical conductivity (440.1 ± 175.7 µS/cm), total nitrogen (0.3 ± 0.1%), organic carbon (3.0 ± 0.9%), available phosphorus, calcium (4.6 ± 1.8 meq/100 g), potassium (0.5 ± 0.3 meq/100 g), magnesium (2.0 ± 1.0 meq/100 g), and cation exchange capacity (14.7 ± 4.6 meq/100 g) and had sandy loam soil (60.4 ± 4.7% sand, 28.1 ± 4.8% silt, and 11.5 ± 4.0% clay). These were in comparison with the nonrestored forest (Supplementary Table 1; plot B), which had higher levels of ammonium (55.9 ± 8.8%), silt (34.5 ± 3.2%), and water content (11.5 ± 2.1%). Besides, the natural forest (Supplementary Table 1; plot C) had higher levels of soil pH (6.7 ± 0.6), electrical conductivity (944.8 ± 286.0 µS/cm), total nitrogen (0.5 ± 0.1%), organic carbon (3.8 ± 0.4%), calcium (28.1 ± 7.8 meq/100 g), magnesium (5.6 ± 1.8 meq/100 g), cation exchange capacity (29.3 ± 7.2 meq/100 g), soil water content (12.5 ± 2.9%), and loam soil (55.0 ± 6.9% sand, 30.5 ± 6.4% silt, and 14.5 ± 2.6% clay) compared with plots A and B (Supplementary Table 1). The levels of sodium (0.1 ± 0.0 meq/100 g) did not change in all forest types (Supplementary Table 1). Within plots, significant differences ($P<0.05$) were found for soil pH (${\chi }^2$ = 16.0), electrical conductivity (${\chi }^2$ = 15.0), ammonium (${\chi }^2$ = 17.3), total nitrogen (${\chi }^2$ = 12.5), calcium (${\chi }^2$ = 15.6), magnesium (${\chi }^2$ = 17.0), sodium (${\chi }^2$ = 19.5), cation exchange capacity (${\chi }^2$ = 12.3), and soil water content (${\chi }^2$ = 16.3).

3.2. Status of Soil Properties in Restored Savannas

Even though all plots were similar in vegetation type and tree species, there are differences in the levels of some soil properties. Higher levels of ammonium (51.3 ± 5.8 mg/kg) were found in plots A and C without significant differences (Supplementary Table 1). Available phosphorus and potassium content were significantly higher ($P<0.05$) in plot A than in plots B and C. The soil texture in all plots was sandy loam (Supplementary Table 1). Furthermore, the levels of nitrates (6.2 ± 3.3 mg/kg) were higher in plot C. Like in the forest, the levels of sodium (0.1 ± 0.0 meq/100 g) were the same in all studied plots of the restored savannas. Within plots, statistically significant differences ($P<0.05$) were found in soil pH (${\chi }^2$ = 12.9), organic carbon (${\chi }^2$ = 11.9), calcium (${\chi }^2$ = 15.4), magnesium (${\chi }^2$ = 8.6), cation exchange capacity (${\chi }^2$ = 10.5), silt (${\chi }^2$ = 7.7), clay (${\chi }^2$ = 12.4), and water content (${\chi }^2$ = 6.0).

3.3. Comparison of the Status of Soil Properties between Restored Forest and Savannas

Within the sites, significant differences ($P<0.05$) were found in soil pH (${\chi }^2$ = 18.5), electrical conductivity (${\chi }^2$ = 9.0), total nitrogen (${\chi }^2$ = 14.1), soil organic carbon (${\chi }^2$ = 17.9), calcium (${\chi }^2$ = 27.0), magnesium (${\chi }^2$ = 23.5), cation exchange capacity (${\chi }^2$ = 20.3), clay (${\chi }^2$ = 6.0), and soil water content (${\chi }^2$ = 13.7). The NMDS indicated dissimilarities in soil physicochemical properties between plots (stress = 0.06, axis 1 = 0.97, axis 2 = 0.07; Supplementary Figure 4) and between sites (stress = 0, axis 1 = 0.97, axis 2 = 0) restored using the EbA approach. The overall distance measured using Euclidian distance for all plots showed the overall dissimilarity (average dissimilarity (AD): 21.09; $P<0.05$) between sites and plots (AD: 26.9, $P<0.05$). Within plots, soil properties that contributed to the dissimilarity ($P<0.05$) were the electrical conductivity, available phosphorus, silt, sand, and ammonium ions. Within sites, the electrical conductivity, available phosphorus, silt, sandy, and ammonium ions more contributed to the dissimilarities. Between sites and plots, dissimilarities were found for organic carbon, pH, potassium, total nitrogen, and sodium (Supplementary 1).

4. Discussion

Results of this study (Supplementary 2) have indicated significant differences between plots and sites in savannas and forests restored using the EbA approach (Supplementary Table 1; Supplementary 1). Generally, restored and natural forests offer better conditions in soil properties.

4.1. Variations of Soil Physicochemical Properties in the Forest

Studies showed that soil pH is influenced by soil nutrients [53], water content [54], and plant diversity [55]. Higher levels of soil pH in natural and restored forests are due to plant heterogeneity and soil nutrients from the leaf-litter decomposition [56, 57]. The observed differences between restored and natural forests are associated with the stability and locality of the natural forest. Observations during field data collection indicated that natural forest was more heterogeneous, had a well-developed forest canopy, and is located near the river and wetland. The restored forest is made of scattered planted trees, which are not yet heterogeneous and mature enough to form the canopy. Furthermore, it is dominated by the Lantana camara weeds. Studies have indicated that these weeds change the concentration and balance of soil nutrients resulting in changes of soil nutrients in detriment of native plant species [58, 59]. Therefore, changes in soil nutrients are the major causes of soil differences in soil pH under restored forest compared with the natural forest [60].

Besides, the electrical conductivity explains the accumulation of essential salts for plant growth [61], which is also revealed by the cation exchange capacity commonly known as the ability of the soil to retain cations as they move in the soil [62]. In this regard, cations (calcium, magnesium, potassium, and hydrogen) are held by the negatively charged clay and organic matter particles in the soil through the electrostatic forces [63]. They are easily exchangeable with other cations and hence made available for plants [64]. Even though the plot C was rich in silt soil structure, the levels of clay soil (Supplementary Table 1) were also enough to have an influence on soil cation exchange capacity. [65]. In addition, silt and clay soil types affect the maximal carbon and nitrogen storage levels in soil [66] and have an influence on cation exchange capacity and the electrical conductivity when associated with soil water content [67, 68].

Furthermore, there is a relationship among soil pH, total nitrogen, organic carbon, and water content [69]. Soil pH increases the solubility of soil organic matter (carbon and nitrogen in this study) by increasing the dissociation of acid functional group and reducing the binds between the organic constituents and clays [60]. This explains the strong effects of alkaline soil pH conditions on the leaching of dissolved organic carbon and dissolved organic nitrogen [70]. In relation to water content, pH is controlled by the leaching of basic cations (Ca, Mg, K, and Na) far beyond their release from weathered minerals, leaving H⁺ ions to dominant exchangeable ions. The dissolution of CO₂ in soil water produces acidic carbon, which dissociates and releases H⁺ ions [71]. Furthermore, H⁺ ions are produced by the dissociation of high-density carboxyl and phenolic groups formed from the humification of soil organic matter [72]. Furthermore, H⁺ ions can be produced from the nitrification of ammonium to nitrate ions (${\text{NH}}_4^{+}$ to ${\text{NO}}_3^{-}$) [73]. However, further studies are needed to confirm to make this affirmation. We conclude that soil pH in the presence of water contributes to the removal of nitrogen in plant and animal products [60]. Besides, silt soil can hold low to medium soil water content [54] and soil nutrients [66] that essential for plant growth [74].

4.2. Variations of Soil Physicochemical Properties in Savannas

Higher levels found in available phosphorus, ammonium, and potassium in plot A, and clay in plot B were associated with other environmental factors. It is known that ammonium and potassium ions can bind so that none of them can be easily replaced by another kind of cation [75]. The ammonium fixation and release are essential for the health of the environment as it plays the role for efficiency of nitrogen fertilizer with impacts on indigenous soil nitrogen supply toward crop nitrogen uptake [76]. In addition, nitrogen, phosphorus, and potassium are the main nutrient needed by plants [77]. Of them, soil available phosphorus and available potassium can be directly used by plants. Therefore, they are effective indicators of soil fertility and plant growth in studied areas [78].

Furthermore, soil available phosphorus is influenced by many factors including the soil parent material, geographic location, and other soil physicochemical properties [79]. On the other hand, soil available potassium is influenced by clay soil type due to a high adsorption capacity [80]. Higher levels of available phosphorus and potassium found in plot A might be associated with soil parental material and the land use system. We suspect that it was due to dungs from cows as indicated by the results of other studies [81, 82]. Besides, high levels in clay soil found in plot B were found to be associated with soil aggregation [83]. However, we cannot make a deep discussion as we did not measure the soil aggregation in this study. Next study may focus on both clay and aggregate stability to conclude about their relationships. Furthermore, plot C located in savannas was rich in nitrates and sandy soil type. The plot was located at low altitude and near the river, and hence, there might be relationships between soil nitrates, sandy soil type, and water content.

In the literature, nitrates are the main source of nitrogen, and they are constantly changing in different forms in the environment [84]. Changes that have influences on nitrogen management in sandy soils are the process known as nitrification [85]. It occurs when ammonium nitrogen is added to warm and moist soils [86]. Nitrifying bacteria converts ammonia to nitrate ions. Because these ions are negatively charged, they are not held by soil particles, but they are readily leached as water flows through the soil [87]. Nitrates leach more rapidly from sandy soils than finer-texture soils because sandy soils have a lower water-holding capacity [53]. This means that the same amount of water from rainfall or irrigation will leach ions deeper in sandy soils than fine-textured soils [88].

4.3. Comparison of the Status of Soil Properties between Restored Forest and Savannas

In all sites, the levels of sodium were constant and had low levels, which is a sign that the studied soil is normal [89] due to less soluble salts [90]. Sodium is not part of nutrients needed by plants. Its small quantity is an advantage for plant growth and development [91]. Higher levels of sodium are detrimental to soil structure, soil permeability, and plant growth [92]. This is in line with a study focusing on partial to near-complete replacement of potassium, nitrates, ammonium, or potassium by sodium in soil [91]. Results showed that when plant growth is stimulated in low concentrations of potassium supply for example, plants cannot grow properly due to the concentrations of sodium compared to potassium [93]. The same trend was observed when nitrates and ammonium ions are reduced and replaced by sodium [94]. Reference to our observations, all studied plots had different types of plantations, exception for plots located in savannas. Differences in vegetation types particularly in the forests might be associated with other factors rather than soil sodium availability.

The NMDS indicated dissimilarities in soil physicochemical properties between plots and between the two sites that have been restored using the EbA approach. Differences in the levels of soil properties might be associated with the land use history, land location, and vegetation types [95]. All plots in savannas were dominated by Hyparrhenia, and they were part of Akagera National Park. The three types of forests (plots A, B, and C) are different in terms of tree species, shrubs, and bushes and have different levels of disturbance and location. As discussed in the previous sections, differences in land use and structure [96], soil characteristics, vegetation diversity, and structure [97], and other abiotic factors such as nutrient availability [96] are the drivers of differences in soil properties as it was found in other studies [96, 98, 99].

5. Conclusion and Recommendation

The restored forest (plot A) had lower level of soil pH and was rich in electrical conductivity, total nitrogen, organic carbon, available phosphorus, calcium, potassium, magnesium, cation exchange capacity, and sand soil. The nonrestored forest (plot B) was rich in ammonium, silt, and soil water content, while the natural forest (plot C) was rich in soil pH, electrical conductivity, total nitrogen, organic carbon, calcium, magnesium, cation exchange capacity, soil water content, and silt compared to plots A and B. In savannas, all plots were similar in vegetation type and tree species. Plot A was rich in ammonium and potassium, plot B was rich in clay, and plot C was rich in nitrates and sandy soil. Sodium levels did not change in all studied areas. Unfortunately, we cannot conclude about the positive or negative effects of restoration on soil physicochemical properties by using the EbA approach. This is because there is no baseline data, which may serve as reference. We recommend the use of the findings of this research as baseline data for future studies in the studied savannas, forests, and other areas restored using the EbA approach in Rwanda and to add more other soil properties.

Authors’ Contributions

VN designed the study, analyzed data, and wrote the manuscript. MM, JDH, and FU contributed to soil sampling and reviewed the manuscript. CSI, YB, and FN reviewed the manuscript.

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