Individual- and stand-level stem CO₂ efflux in a subtropical Schima superba plantation

Abstract. Stem respiration is an important, but poorly studied component of total forest ecosystem respiration. Stem CO₂ efflux was investigated with an open gas exchange system while stand microclimate and stem temperature were continuously monitored in a Schima superba plantation in South China for several days in August and December 2010. The temperature response of respiration in the different seasons, the vertical variation in stem CO₂ efflux along the stem, and the stand-level stem CO₂ efflux were examined. Stem volume was identified as the better correlate for stem CO₂ efflux and was used as the scalar for the stand-level estimates of stem CO₂ efflux in this S. superba plantation. Volume-based stem CO₂ efflux was higher at 2 m than at 1.3 m. Mean stem CO₂ efflux was 268.9 and 104.6 μmol m⁻³ s⁻¹ in August and December, respectively, indicating a dramatic seasonal variation of stem CO₂ efflux. The temperature response of stem CO₂ efflux remained constant during our study period with Q₁₀ values of 1.9 and 1.8. In this subtropical S. superba plantation, stem CO₂ efflux per unit ground area averaged 3.36 and 1.26 μmol m⁻² s⁻¹ based on the measurement data at 1.3-m height of the stem in August and December, respectively. Our results suggest that stem CO₂ efflux has a constant temperature response, and the seasonal variation in stem CO₂ efflux is mainly controlled by stem temperature, and the vertical variation in stem CO₂ efflux needs to be considered in the stand-level estimation.