Soil organic carbon stock in Abune Yosef afroalpine and sub-afroalpine vegetation, northern Ethiopia

Abstract Introduction Soil is the major reservoir of organic carbon. There is a paucity of soil organic carbon (SOC) stock data of afroalpine and sub-afroalpine vegetation in Ethiopia. Hence, this study was conducted to estimate the SOC stock and correlate it with soil physicochemical properties in Abune Yosef afroalpine and sub-afroalpine vegetation. Systematic sampling was employed to collect soil samples from upper 30 cm. Dry bulk density soil pH (1:2.5 water); organic carbon (Walkley and Black), and total nitrogen (Kjeldahl) were the methods used for soil analysis. Pearson correlation and linear regression analysis were performed in SPSS 24 statistical software. Results The SOC stock of the study area was found to be 79.57 t C ha−1. Soil organic carbon stock showed statistically significant positive correlation with vegetation type (r = 0.522, p < 0.01), bulk density (r = 0.62, p < 0.01), total nitrogen (r = 0.41, p < 0.01), and altitude (r = 0.468, p < 0.01) and negative correlation with slope (r = − 0.298, p < 0.05). The present study revealed similar soil organic carbon stock (SOCS) with the Intergovernmental Panel on Climate Change (IPCC) default estimate for similar regions. Positive correlation of SOCS and altitude could be resulted from the variations in anthropogenic disturbances, temperature, and precipitation vegetation types. The negative correlation between SOCS and slope is the result from the predictably higher soil erosion at steeper slopes. Temporal livestock trampling increased the bulk density but never affected the SOCS to decline. Aspect did not show any significant relationship with SOCS due to either the under surveying of all aspects or similar solar radiation found in the study area. Moreover, gazing, aspect, and soil pH did not show statistically significant impact on SOCS. Conclusion The SOCS of Abune Yosef afroalpine and sub-afroalpine vegetation is similar to the IPCC default estimate for similar regions. This is a great contribution both to the global and local terrestrial carbon sink

Result of Monte Carlo test using function Adonis of environmental variables.

Result of Monte Carlo test using function Adonis of environmental variables.</p

Descriptive statistical analysis of the topography and soil variables of each community.

Descriptive statistical analysis of the topography and soil variables of each community.</p

Kruskal-Wallis test.

Detailed information on plant community types, distribution, and their relationships with various environmental gradients is crucial for understanding forest dynamics and sustainable forest management because plant community types are influenced by various environmental factors. Thus, this study was conducted to investigate plant community types and species diversity in relation to various environmental gradients in Geramo Forest, which is a remnant forest in the western escarpment of the Rift Valley of Ethiopia. Vegetation data were collected in 96 nested plots (20 × 20 m2 and five 1 ×1 m2) laid systematically at a distance of 250 m along 16 line transects, which were laid 300 m apart. Environmental and disturbance variables were also collected from each main plot. Agglomerative hierarchical cluster analysis and Canonical correspondence analysis (CCA) with R software were used to identify plant community types and analyze the relationship between plant community types and environmental variables, respectively. The Shannon Wiener diversity index was used to compute species diversity among community types. Five significantly different (p ≤ 0.001) plant community types were identified. The CCA results showed that species diversity and community composition among different community types were significantly influenced by altitude, disturbance, soil organic carbon, slope, soil available phosphorus, and pH, which revealed the compounded effect of various environmental factors on species richness, diversity, and evenness among plant community types. The study also identified a significant level of anthropogenic disturbance and a strong reliance of the local community on the forest in the research area. Therefore, it is recommended that sustainable forest conservation interventions be implemented through awareness creation and the promotion of community-based approaches.</div

Pairwise comparison of clusters using Dunn’s test.

Pairwise comparison of clusters using Dunn’s test.</p

Biplot scores for the constraining variables, eigenvalues and proportion of variances explained by the first six axes.

Biplot scores for the constraining variables, eigenvalues and proportion of variances explained by the first six axes.</p

Synoptic cover abundance value of species in each community type.

Synoptic cover abundance value of species in each community type.</p

Dendrogram showing the five plant community types.

1 (Community type 1) = Dichrostachys cinerea-Balanites aegyptiaca-Commiphora africana community type, 2 (Community type 2) = Terminalia brownii—Hyparrhenia filipendula—Rhus natalensis community type, 3 (Community type 3) = Vachellia nilotica—Harrisonia abyssinica—Ziziphus mucronata community type, 4 (Community type 4) = Senegalia brevispica—Croton zambesicus—Teclea nobilis community type, 5 (Community type 5) = Combretum collinum—Heteropogon contortus—Grewia velutina Community type.</p

CCA biplot of community types with significant environmental variables (<i>p</i>≤0.05).

CCA biplot of community types with significant environmental variables (p≤0.05).</p

Location map of the study area.

This work does not need to supply a copy right notice for Fig 1 because the shape file of Fig 1 (location map of the study area) is free and open to researchers and downloaded from the Ethiopian Mapping Agency website (https://africaopendata.org/dataset/ethiopia-shapefiles).</p