Can soil organic carbon isotopes be used to describe grass‐tree dynamics at a savanna‐grassland ecotone and within the savanna?

Abstract. We evaluated the use of soil organic carbon (SOC) isotopes to describe grass‐tree dynamics at locations at the savanna‐C₄ grassland ecotone and within a temperate semiarid Quercus savanna in southeastern Arizona, USA. SOC will not describe grass‐tree dynamics at locations within the savanna because isotope composition near the soil surface does not correspond with the overlying vegetation and recent C₃ carbon has been deposited at deep soil depths with no C₄analog. In contrast, SOC can describe grass‐tree dynamics at the savanna‐grassland ecotone because isotope composition near the soil surface corresponds with overlying vegetation and significant deep soil deposition of C₃ carbon was not apparent. At the ecotone, trees became established in the last 700–1700 years. There is no evidence to suggest an unstable grass‐tree mixture at the ecotone since that time. 1995 IAVS ‐ the International Association of Vegetation Science