This is the first study quantifying total soil CO₂ efflux, heterotrophic and autotrophic respiration in an old-growth kauri forest. Root biomass explained a high proportion of the spatial variation suggesting that soil CO₂ efflux in this forest is not only directly affected by the amount of autotrophic respiration but also by the supply of C through roots and mycorrhiza. Our findings also suggest that biotic factors such as tree structure should be investigated in soil carbon related studies.