Interannual variation in CO₂ effluxes from soil and snow surfaces in a cool-temperate deciduous broad-leaved forest

We estimated the inter-annual variation in soil CO₂ efflux in a cool-temperate oak-birch forest in central Japan. CO₂ effluxes from the soil surface during the snow-free season and from the snow surface during the snow-covered season were measured using an open-flow infrared gas analyzer method from December 1994 to December 1995. Climatic conditions in 1995 were significantly colder than the 22-year mean; this decreased observed values of daily CO₂ efflux and resulting in different temperature response of CO₂ efflux (estimated on the basis of the annual Q₁₀ function) compared with the Q₁₀ function derived from measured effluxes obtained at the same site and with the same method in normal, warmer years from 1999-2002. This suggests that empirical models such as annual Q ₁₀ function must be parameterized for the target year before they can be used to estimate annual soil CO₂ efflux, especially during periods of abnormal climatic conditions. Estimated annual values of soil CO ₂ efflux from 1994-2002, based on the Q₁₀ functions derived from annual datasets for 1995 (an abnormally cold year) and 1999-2002 (normal warm years), ranged from 597 to 793 g C m^-2 y^-1, with a mean ±SD of 713±71 g C m^-2 y^-1. The annual soil CO₂ efflux in 1995, an abnormally cold year, was 16% lower than the mean for the 1994-2002 period, whereas efflux in a warm El Niño year (1998) was 11% higher than the mean. This suggests the presence of a large inter-annual variability in the annual soil CO₂ efflux in this forest.