Abstract
Terrestrial carbon stock quantifying is important for the successful implementation of climate change mitigation policies. With the rapid global urbanization rate urban forests are becoming important components of the global forest ecosystem. Urban development strongly associated with a disturbance of habitats such as urban parks. Most of the urban vegetation resources in Addis Ababa were not based on scientific evidence.
The study aims to estimate Carbon stock and woody species diversity along the altitudinal gradient of closed urban public Parks. Seven parks were selected purposively based on altitude range, better woody species composition, and area coverage. The parks were stratified into two altitude ranges: upper strata 2338-2588 masl and lower strata 2088-2338 masl. Then by applying the stratified systematic sampling method and distributing the transect line with a 100m gap using QGIS software version 3.2 a total of 70 sample plots were determined. Sample plots were distributed by optimal allocation and with a circular plot design applied for biomass carbon stock assessment and species identification. Whereas 24 sample plots were selected for soil sampling of five 1m2 sub-plot in each main plot. Parameters of carbon stock and species diversity towards altitudinal gradient were tested by descriptive statistics, correlation test, and one-way ANOVA test analyzed using statistical software R version 3.4.3. According to the study results, 125.33 +40.4-ton ha-1 mean carbon stock was contained in the above-ground biomass and 25.07+8.08-ton ha-1 mean carbon stock was obtained in belowground biomass. Soil organic carbon stock in the selected public parks ranged from 87.071 to 196.281-ton ha-1. Thus, mean carbon stock of 302.3-ton ha-1- And 231.9-ton ha-1 was estimated on upper and lower altitudes respectively. There is a significantly increased amount of carbon stock with increasing elevation (P-value = 0.016). A total of 52 woody species belonging to 28 families were identified with a total number of 2123 trees. Of the total species, 53.8% of the species were indigenous while the remaining were exotic tree species. The study also shows there is higher species diversity on lower strata public parks than upper strata parks 2.81 and 2.64 each. Likewise, the Simpson index and species richness recorded were higher at lower altitude parks. On the other hand, species evenness value implies there is equivalent distribution among each stratum and between selected urban parks. Juniperus procera, Cupressus lustanica, and Grevillea robusta tree species had higher IVI values as compared to others. Based on the study findings forests in public parks altitude has a direct effect on mean carbon stock density, species composition, and diversity. So consideration of topographic elevation factor in green area improvement will have a better contribution to the performance of green infrastructure development planning and implementation.
Keywords: climate change, elevation, green-infrastructure, mitigation, urbanization,