WOODY SPECIES DIVERSITY AND CARBON SEQUESTRATION POTENTIALS OF YEGOF MOUNTAIN NATURAL VEGETATION IN SOUTH WOLLO ZONE OF ETHIOPIA

Abstract

This MSc thesis was conducted in Yegof Mountain in South Wollo zone of Amhara Regional State of Ethiopia from October-December, 2017 with the objective of analysing the contribution of natural vegetation to climate mitigation through assessing the carbon sequestration and biodiversity restoration potentials under three altitudinal gradients [i.e. Lower altitude (LA: 2050 – 2400 m.a.s.l.); Middle altitude (MA: 2401 – 2750 m.a.s.l.) and upper altitude (UA: 2751 – 3014 m.a.s.l.)]. A total of 57 quadrats of 20m x 20 m, 5m x 5m and 1m x 1m with 9 horizontal transect lines were used for collecting the data on tree, shrub, and herbaceous and soil respectively in the three altitudinal gradients. Soil parameters were collected from three soil profiles (i.e., 0-10 cm, 10-20cm and 20-30 cm) and data on soil bulk density and organic carbon percentage were analysed at Sirinka Agriculture Research Centre in Amhara Agricultural Research Institute of Ethiopia. Non-destructive method was employed using locally developed allometric equations for estimation of aboveground and belowground biomass and carbon. The vegetation and soil data were analysed stastically in one-way ANOVA using SPSS software pakage (version 24). A total of 57 woody species were identified in the study area that fall within 37 families and 49 generas of which 45 % were shrub, 33% were tree, 9% were tree/shrub and the rest 14% were climbers. Fabaceae was the dominant family identified in the area occupying 5 species. Both diameter and height class distribution of the population in the three altitudinal gradients exhibited inverted J-shape which indicate that most of the species were in healthy conditions. The Jaccard’s similarities index indicated that the highest species similarity was observed between MA and UA (49%) followed by LA and MA (42%). However, there was very low similarity (34%) between LA and UA as a result of higher variation in environmental and biological atributes between these two. A significant difference (P<0.05) was observed among the three altitudinal gradients for woody species density ha-1, as UA had significantly higher woody plant density (1251 ha-1) than MA (1038 ha-1) and LA (903 ha-1). Middle altitude had significantly (P<0.05) higher Shannon’s diversity index value (3.03) than the other two altitudinal gradients. However, there were no significant difference (P>0.05) for evenness value among the three altitudinal classes, this might indicate there is no need for site or species specific conservation and rehabilitation activity as the distribution of species shows no significant variation. So conservation activities that integrated all the biotic and abiotic component of the area drafted in ecological or ecosystem level are possibly the better options. Regeneration stratus on the three altitudinal gradients were identified in good condition as number of regenerating population (seedling and sapling) was higher than matured ones, as seedling > sapling > matured woody plants in MA and UA and sapling generation took the front raw followed by seedling and matured woody plants in LA. Higher number of matured trees in UA made it to posses significantly (P<0.05) higer basal area coverage and dominance with 59.73 m2ha-1 than LA (18.62 m2ha-1) and MA (40.47 m2ha-1). Aboveground and belowground carbon stocks were significantly higher (P<0.05) in UA gradient with 187.3±27 ton ha-1 and 37.5±5.4 ton ha-1, respectively than other gradients. However, LA had the lowest (P<0.05) AGC (84.7±9.2 ton ha-1) and BGC (16.9±1.8 ton ha-1) than others. Dead wood carbon was only found in the upper and middle altitudinal gradients as they had relatively less human intervention for wood collection. However, there was no significant difference in dead wood carbon (DWC) between the two above altitudinal gradients. Similarly, GHL carbon also exhibit non-significant xv difference in the three altitudinal gradients with P>0.05 even if UA had the highest value (1.13±0.73 ton ha-1) than MA (0.99±0.28 ton ha-1) and LA (0.95±0.8 ton ha-1). Lower altitude had significantly higher (P<0.05) SOC value than the other two altitunal gradients with 266.07±51.61ton ha-1, followed by MA with 194.55±26.07 ton ha-1. The UA had lowest SOC value (187.92±17.92 ton ha-1) in the mountain. Similarly, SOC across the three soil profiles follows a reduction trend from top soil depth (0-10cm) to lower soil depth (20-30 cm) with significant variation (P<0.05). However, the overall carbon sock (TC) were higher in MA (415.3 ton ha-1) with slight difference from the UA (414.2 ton ha-1), But the LA had the lowest TC stock of 368.7 ton ha-1). Generally, MA had relativlly better TC and species diversity than the other gradients. However, high level of illegal human and animal intervention in LA with poor security and law enforcement actions beside altitudinal and ecological variation resulted in relatively poor TC and species diversity in it. Therefore, better ecological, policy and socioeconomically concerns should be adopted in the area especially in LA than the other gradients as it possesses the poorest performance of all.