Effects of Elevations on Carbon Stocks of Kella Natural Forests in Konso Zone, Southern Ethiopia

Abstract

Different human made and natural factors can affect woody species diversity and carbon stocks, elevation is among them.  This study, thus, was conducted to evaluate the impact of elevation on woody species diversity and carbon stock potential in Kalla forest, Konso zone, Sothern Ethiopia. The study was conducted along three elevation gradients, namely, low (1,605-1,690 m), middle (1,691-1,775 m) and high (1,776-1,860 m) elevations. A total of 60 sample plots (20 m x 20 m) were systematically laid down along the elevation gradients at interval of 200 m between transects and 50 m between sample plots. In each main plot a 5 nested sub plots (four from corners and one at the center) with 4 m x 4 m were used to collect sapling and seedlings. Moreover, 1 m x 1 m subplots were used to collect litter and soil. A total of 120 soil samples for soil chemical analysis and 120 samples for bulk density determination were taken separately. A total of 22 woody species, belonging to 19 genera and 14 families were recorded. Of all woody species 10, 13 and 17 species were recorded in the high elevation (HE), middle elevation (ME) and low elevation (LE), respectively. Abundance, species richness, Shannon diversity index, Simpson diversity index, basal area and stem density were significantly higher in the LE than ME and HE. The average stem density and basal area of LE were 1.5 and 1.7, 1.2 and 1.4 times higher than that of the HE and ME, respectively. The Shannon and Simpson diversity indices were 1.62±0.2 and 0.76±0.06 in LE, 1.29±0.4 and 0.6±0.16 in ME whereas in HE 1.55±0.2and 0.73±0.11, respectively. The total ecosystem carbon stocks (biomass plus soil, 0-60 cm) were significantly different (p < 0.05) across the three studied elevations. The LE showed higher ecosystem carbon stock (301.8 ± 171.6 t C ha^-1) than ME (255.6±88.2) and HE (190.8± 58.2). The SOC stock (0 - 60 cm depth), standing biomass and litter accounted 90.8 %, 6.6 % and 2.6% in the LE whereas 93.0 %, 5.1 % and 1.9 % in the ME and. 92.1%, 6.3% and 1.6% in the HE. Juniperes procera and Euphorbia tirucalli in the LE contributed altogether 81 % of the total biomass carbon stocks. , Euphorbia tirucalli and Juniperes procera altogether contributed 60 % in the ME whereas  Euclea racemosa and  Juniperes procera shared 48% of the total biomass carbon stock in and HE.. The total above ground biomass carbon stocks were significantly correlated with the species diversity. Finally, this study indicated that LE and ME have better contribution to improve woody species diversity and total carbon stocks in Kalla forest, Sothern Ethiopia.

Key words:  , Biomass, carbon stock, Elevation range, woody species diversity