Carbon Stocks in an African Woodland Landscape: Spatial Distributions and Scales of Variation

Abstract

Current knowledge of Africa’s carbon (C) pools is limited despite its importance in the global C budget. To increase the understanding of C stocks in African woodlands, we asked how C stocks in soil and vegetation vary across a miombo woodland landscape and to what degree and at what scales are these stocks linked? We sampled along a 5-km transect using a cyclic sampling scheme to allow geostatistical analyses. Soil C stocks in the top 5 cm (12.1 ± 0.6 Mg C ha−1 (± SE)) and 30 cm depths (40.1 ± 2.5 Mg C ha−1) varied significantly at scales of a few meters (autocorrelation distance 14 m in 0–5-cm and 26 m in 0–30-cm interval), and aboveground (AG) woody C stocks (20.7 ± 1.8 Mg C ha−1) varied significantly at kilometer scales (1,426 m). Soil textural distributions were linked to topography (r2 = 0.54) as were large-tree AG C stocks (r2 = 0.70). AG C stocks were constrained to an upper boundary by soil texture with greater AG C being associated with coarser textured soils. Vegetation and soil C stocks were coupled in the landscape in the top 5 cm of soil (r2 = 0.24) but not with deeper soil C stocks, which were coupled to soil clay content (r2 = 0.38). This study is one of the most complete transect studies in an African miombo woodland, and suggests that C stock distributions are strongly linked to topography and soil texture. To optimize sampling strategies for C stock assessments in miombo, soil C should be sampled at more than 26 m apart, and AG C should be sampled at more than 1,426 m apart in plots larger than 0.5 ha.