Belowground carbon storage and dynamics accompanying woody plant encroachment in a subtropical savanna

This chapter focuses on the Rio Grande Plains of southern Texas, where C₃ subtropical thorn woodlands dominated by highly productive N-fixing tree legumes have largely replaced C₄ grasslands over the past 100 to 150 yr. This vegetation change has increased rates of above- and below-ground productivity in wooded areas relative to remnant grasslands. The chapter assesses the impact of grassland-to-woodland conversion on the soil carbon cycle in the Rio Grande Plains of southern Texas by quantifying rates of soil organic carbon (SOC) sequestration following grassland-to-woodland conversion, and evaluating the role of physical and biochemical mechanisms of SOC stabilization. It also assesses the relative importance of residual grassland-derived C₄-C versus C₃ woodland-derived carbon inputs to total SOC content in bulk soil, and estimates turnover rates of SOC in bulk soil using the natural isotopic difference between C₄ grasses and C₃ woody plants.