Carbon stocks and patterns in native shrub communities of Senegal's Peanut Basin

Accurate and reliable estimates of carbon (C) storage in landscapes are critical to the development of effective policies and strategies to mitigate atmospheric and climate change. Carbon stocks of two native woody shrub (Guiera senegalensis J.F. Gmel and Piliostigma reticulatum (DC.) Hochst) communities and associated soils within Senegal's Peanut Basin were determined and the spatial structure of soil C quantified. These shrubs are of interest because they dominate semiarid sub-Sahalien Africa and commonly coexist with row crops but have been largely overlooked as a key vegetative component of this landscape. Peak-season shrub biomass C was measured in forty-five 0.81 ha plots at 8 locations using allometric relationships along with soil sampling (0 to 40 cm depth) and analysis for organic C and bulk density. Soil samples to a depth of 20 cm were taken every 2 m in 24 × 20 m grids and every 0.5 m in four nested 3 m × 3 m grids containing at least one shrub or tree canopy, and geostatistical techniques were then used to quantify scale and degree of soil C spatial dependence. Estimates of peak-season biomass C ranged from 0.9 Mg C ha− 1 to 1.4 Mg C ha− 1 with an overall mean of 1.12 Mg C ha− 1 (SEM = 0.079) in the G. senegalensis sites and from 1.3 to 2.0 Mg C ha− 1 (mean = 1.57 Mg C ha− 1; SEM = 0.18) in the P. reticulatum communities. The overall mean of SOC to 40 cm was 17 and 17.2 Mg C ha− 1 respectively, at the G. senegalensis and P. reticulatum sites with 57% of that C residing in the top 20 cm. Semivariograms of soil C showed moderate spatial dependence and spatial autocorrelation at distances of less than 0.56 and 1.34 m at the G. senegalensis and P. reticulatum sites, respectively. Comparison across the different grids showed that the presence of shrub canopies at either site had much closer relationship to soil C levels than trees.