An experimental study has been made in the near field of a variable swirl burner under isothermal and reacting conditions in order to quantify the effect of combustion on the isothermal flow field, and to explain the mechanism of flame stabilization due to internal recirculation zones. A two colour Laser-Doppler velocimeter was used to determine turbulence properties in-/and outside of the recirculation zone. Temperature and species concentrations were measured by conventional measuring techniques. Turbulent exchange coefficients for momentum, matter and heat have been obtained by measurements and by calculations from time mean value distributions, respectively. The results show that, with strong swirl, the intensity of recirculation is reduced by the presence of combustion due to a marked decrease of the effective swirl number. Divergent burner nozzles at the burner exit lead to a radial extension of the reverse flow zone, but do not affect the reverse flow density. Reynolds number similarity of the diffusion flame is confirmed as long as reaction kinetic effects are negligible. On the other hand, blow-off occurs as a result of a reduction of local residence time in the ignition zone when increasing burner load. LDA-measurements exhibit high turbulence intensities and strong turbulent fluxes in the region of the stabilization zone. All turbulent fluxes agree with the gradient law, so that no countergradient diffusion exists under the conditions studied. The presence of combusion leads to a damping of turbulent exchange as compared with the isothermal flow of same swirl intensity.