Comparative Analysis Of Woody Species Composition And Carbon Stock Of Yayu Forest Coffee Biosphere Reserve In Illubabor Zone Ethiopia

Moist Afromontane rainforest plays a significant role in biodiversity conservation, mitigation of carbon dioxide emissions, and other ecosystem services. Application of allometric equations is a crucial step for carbon stock assessment. This study was conducted to determine woody species diversity, structure, and regeneration status of the Afromontane rainforest in southwestern Ethiopia. Additionally, the research was conducted to estimate carbon stock of the forest and formulate allometric equations for selected three tree species. Systematic sampling design was applied for the measurement of vegetation and soil data. A total of 100 main quadrats of 400 m2 were laid to record individuals with a Diameter at Breast Height (DBH) ≥ 5cm. The subquadrats of 25m2 in the main quadrats were laid for seedlings, saplings, and shrubs sampling. A semi-destructive method was applied to generate data for formulation of allometric equations for selected tree species. A total of 90 individuals were measured for allometric equation development. The statistical software packages in R-Environment were used for analysis of all datasets. A total of 78 woody species belonging to 69 genera and 37 families were recorded. The mean Shannon-Wiener index (H’) was 2.04±0.05 for core zone and 1.72±0.06 for buffer zone forest indicating a significant difference. Variation of woody species diversity has shown a relationship with elevation and slope gradients. A total of three community types were identified based on the cluster analysis and highest synoptic value of the species. The community diversity (H’) value of core zone forest differs from 2.74 to 3.41; and from 2.89 to 3.64 for the buffer zone forest. A comparison of woody species composition shows that the most important families for both forest types were different. The density of trees for core and buffer zone forests is 688.46 and 521 stem ha–1 respectively. The mean basal area for the core zone forest is 31.88 m 2 ha–1; while it is rn31.13 m2 ha–1 for buffer zone forest. In core zone forest, the density of tree seedlings and saplings is 1398.08±256.56 and 1052.89±169 individual ha –1 respectively. Conversely, in buffer zone forest individuals of seedlings (2475±399.5 ha–1) and saplings (766.67±192 ha–1) recorded. A total of 22 species of core zone contributed 81.64% of IVI; whereas 19 species of buffer zone contributed 79.62% of IVI. The mean carbon stock density for major pools was 203.80±12.38 t ha–1 (aboveground biomass), 40.76±2.47 t ha–1 (belowground biomass). The soil organic carbon stock was 61.50±1.91 t ha–1 for topsoil (0-15cm depth) and 55.68±2.41 t ha–1 for subsoil (15-30cm depth). The highest proportion of AGCS t ha–1(42.34%) was contributed by tree individuals with DBH > 70cm. Eight allometric equations were developed for three selected tree species. The best fitted allometric equatios were selected based on their coefficient of determination (adj.R2), residual standard error (RSE), and Akaike information criterion (AIC) values. Higher bias was reported when best-fitted species-specific allometric equations were compared with pantropical allometric equation. As a result, the formulated allometric models can be applied as a species-specific in the moist Afromontane forest of southwestern Ethiopia. Overall, the Afromontane rainforest has comprised high woody species diversity and also playing a significant role in mitigating Carbon dioxide emission. Therefore, sound management approach that promotes forest sustainability through conservation of biodiversity and improvement of carbon sequestration potential is needed.

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