THE ROLE OF AREA ENCLOSURE IN VEGETATION RESTORATION, CARBON STORAGE POTENTIAL, AND LAND USE LAND COVER CHANGE, CENTRAL RIFT VALLEY, ETHIOPIA

Abstract

Loss of biodiversity and the impoverishment of rural communities are potential consequences of land degradation, a widespread environmental issue that affects ecosystem services and ecological functions. Area enclosure is believed to be an effective approach for the restoration of degraded areas and improves vegetation composition and species diversity. In the Bilate Watershed, the present study area, area enclosures were employed to restore natural vegetation in the degraded lands. Yet, the effects of these enclosures on vegetation restoration and carbon storage potential, current vegetation pattern and people's perceptions of area enclosures have not yet been studied. Therefore, the objective of this research to assessed people's perceptions toward area enclosures and identified the dynamic patterns and driving forces that lead to land use and land cover changes in the study area, compared the vegetation composition and structure, soil seed bank, and carbon stock between enclosures and open lands. A household survey was conducted to evaluate respondents' perceptions and attitudes towards the role of enclosures in mitigating land degradation. To investigate the dynamic patterns and driving forces of land use and land cover changes, we utilized GIS and remote sensing tools, specifically Landsat 5 (Thematic Mapper) and Landsat 8 (Operational Land Imager), along with field observations. Systematic sampling techniques were employed to collect data on the composition, diversity, and structure of both aboveground and belowground vegetation, as well as soil and litter from various sampling plots. One hundred sixty quadrats (80 in enclosed areas; 80 in adjacent open lands), each having 20 m × 20 m for trees, 5 m x 5 m for shrubs, and 1 m x 1 m for herbs, grasses and soil sample were laid along six transects to collect data using systematic sampling methods The survey results indicated that respondents had positive attitudes towards existing enclosures and expressed support for further expansion of these areas. The analysis of land use and land cover changes revealed a progressive increase in vegetation cover over the study periods. The survey confirmed that the primary causes of changes in land use and land cover were human-induced factors, such as livestock grazing, grass cutting, and fuel wood collection. Shannon diversity index in area enclosure and open lands were 2.35 and 1.78, respectively. Based on diameter and height class distribution, the population structure of woody species showed an inverted J-shape for area enclosure but an interrupted bell-shaped for open lands. The regeneration status of the enclosures was considered good since seedling > sapling > matures. Besides, the regeneration status of the open lands was considered fair since mature > sapling > seedling. The enhanced floristic composition, diversity, and regeneration status of the enclosures make them a potentiallyeffective practice for restoration and rehabilitation initiatives. Moreover, by utilizing the improved soil moisture, organic matter, and other soil nutrients provided after the removal of human-induced stress by enclosing the area, the majority of soil seed bank species were successfully germinated inside the enclosures. Seed abundance and diversity decreased with increasing soil depth in enclosures and open lands. Moreover, seed densities (m-²) of soil seeds up to 9 cm deep were 0.026 ± 0.003 for the enclosures and 0.022 ± 0.003 for open lands. The highest seed density was recorded in the litter and upper layers of both enclosures and open lands. Our findings indicated that the majority of soil seed bank species germinated successfully in the enclosures. The carbon stock of all carbon pools showed statistically significant differences between the enclosures and open lands. Total mean carbon stock in the enclosure and open land were 87.81±30.63 and 52.95±31.89 tons/ha, respectively. Aboveground plant biomass had a higher proportion of carbon stock in both enclosures and open lands. However, the contribution of plant litter biomass and deadwood carbon pools was insignificant. Our findings also indicated that establishing enclosures on degraded lands with reduced human and livestock interference may encourage the restoration of native vegetation and soil properties. Consequently, this improves the potential for restoring vegetation biomass and carbon stocks and improving soil properties. These results suggested that with improved soil nutrients and enhanced carbon storage potential of the ecosystem and species diversity, it is better to extend enclosures to further open lands with a win-win approach that benefits both the conservation effort and the livelihood of the local community. As this is a short-term study, data from long-term research could enhance the findings of this study for feasible policy formulation