Abstract
Plantation forests can capture and retain carbon in their biomass and soil over time. Carbon stock estimation provides information on the current status of the carbon stock of the forest and important to know the future change by deriving from it. The present study was conducted to estimate the carbon stock and its variation along the elevations gradients in Garabocan state plantation forest found in Amhara Regional State of Ethiopia.
After the reconnaissance survey, the site was stratified based on three elevations ranges including lower, middle and higher. Nested plots of size 20m * 20m as main plots were systematically established and used for tree inventory. Three 1m * 1m sub-sample plots within the main plots were selected for soil and litter sampling. Data of trees whose DBH (≥ 5 cm) and total tree height were measured in the main plot using diameter caliper and hypsometer respectively. The litter was collected from three sub-sample plots 1 m x 1 m laid randomly within the main plots. To analyze the total biomass carbon stock was analyzed using locally developed biomass allometric equation for E.globulus at kofele and degaga was used for determining above ground biomass. In this study the carbon stocks in above ground, below ground, litter and soil of E. globulus plantation assessed. A total of 34 sample plots sized constituting 13 lower, 11 meddle and 10 higher elevation, were inventoried and soil sampled. Soil samples for carbon content determination were collected from three randomly selected sub-sample pots 1m * 1m in the main plots from the soil depth 0 - 20 cm, 20 - 40 cm and 40-60 cm using auger method. Similarly, soil samples were taken from 0 - 60 cm soil depth (0 - 20 cm, 20 - 40 cm and 40 - 60 cm in layers) to determine soil bulk density using core method. The result indicated that the average basal area (m2/ha) in the study site was 48.72 m2/ha. The above ground biomass carbon significantly highest the lower elevation (342.09 ± 43.60 t ha-1), middle elevation (339.03 ± 32.61 t ha-1) and lowest in lower elevation (257.44 ± 18.01 t ha-1). The below ground biomass carbon was also significantly highest in lower elevation (88.94 ± 26.99 t/ha-1) and lowest in upper elevation (66.93 ± 20.19 t/ha-1). The litter biomass carbon stocks in both middle and higher elevations were significantly different from lower elevation. Results showed that bulk density, soil organic carbon concentration (%) varied significantly with elevations (p=0.000) and soil depth (p=0.000). The bulk density value was found to increase when soil depth increased but, soil organic carbon concentration (%) and stock was decreased when soil depth increased for all elevations ranges. The mean soil organic carbon stock was significantly highest in higher elevation (108.9 t/ha-1) and lowest middle elevations (96.89 t/ha-1). It was significantly highest in the top layer of soil (40.19 ± 13.85 t/ha-1) and lowest in sub-surface of soil (29.52 ± 13.74 t/ha-1). With respect to elevations ranges, it was significantly highest in higher elevations and lowest in the middle elevations ranges. The overall, carbon stock (biomass and soil) of the studied plantation was 496.84 t ha-1. The ultimate result entailed that GBPF is a reservoir of high carbon. Thus, GBPF should be given special concern to manage it sustainably, to keep ecosystem services running smoothly and benefit from future carbon financing opportunities.
Key words; Carbon sequestration, Ecosystem, litter, bulk density
