Woody Species Diversity and Carbon Stock along Altitudinal Gradient in Jallo Muktar Dry Evergreen Afromontane Forest, West Hararghe Zone, Ethiopia

This study was conducted in Jallo Muktar forest, Western Hararghe Zone, Ethiopia. Data were collected from December 2018 to January 2019 with the aim of woody species diversity and carbon stock estimation along altitudinal gradients. Transects were laid out on three altitudinal gradients namely lower altitude (LA:2060 – 2410 m.a.s.l.), middle altitude (MA: 2411– 2760 m.a.s.l.) and upper altitude (UA: 2761 -3017 m.a.s.l). A total of 60 sample plots of 20m×20m (400 m2) in each altitudinal gradient were established with a distance of 100m between plots. Tree and deadwood were measured in the 400m2 main plot, shrubs, saplings and seedling were collected from 5m×5m subplot while soil and herbaceous plant data were collected inside 1m2 subplots. Biomass and carbon estimation were computed by using allometric equation. Soil organic carbon (SOC) was analyzed following Walkely-Black procedure. To analyze mean of carbon pools and species diversity, ANOVA was used at α=0.05 and the Tukey test was used to compare the mean difference among altitudinal gradients. Fifty-three species belonging to 35 families and 42 genera were identified. Rosaceae and Fabaceae were the most dominant families consisting of 5 species each. Both DBH and height class distribution of the population in the three altitudinal gradient exhibited inverted J-shape. The Jaccard’s similarities index indicated highest species similarity between MA and UA and lowest similarity between LA and UA. Middle altitude had significantly (P < 0.05) higher Shannon’s diversity index value (2.8) than the others. The mean aboveground carbon (AGC), belowground carbon (BGC), deadwood carbon (DWC) and grass, herb and litter carbon (GHL) stock of the forest were 171 t C ha− 1, 46.6 t C ha−1, 0.3 t C ha−1 and 1.6 t C ha−1 respectively. The mean soil organic carbon (SOC) up to 40cm depth was 273 t C ha− 1. AGC, BGC, DWC and GHL had a positive correlation with altitude and were significantly higher in the UA. However, SOC had a negative correlation with altitude and it was significantly higher in the LA. It can be concluded that Jallo Muktar forest possess ecologically important and diversified woody plant species. Also, the forest is a reservoir of high carbon in different carbon pools, which may greatly contribute to the climate change mitigation. Though the study forest holds a high potential of carbon storage for climate resilience green economy, human disturbance on stand density and species diversity of forests in the lower altitudinal gradient which inhibits additional accumulations of carbon stocks so their conservation should be promoted especially the study highlights the need to conserve lower altitude forest to maintain diversity and improve forest structure.