We consider the role of two-dimensional turbulence (generated in a sunspot umbra under the influence of a strong magnetic field) and Alfven oscillations (excited in a sunspot by a relatively weak magnetic field) in the sunspot evolution. Two phases of decaying of sunspot magnetic field are revealed. The initial rapid phase of magnetic dissipation is caused by two-dimensional turbulence. The subsequent slow phase of magnetic dissipation is related to the Alfven oscillations. Our results agree with observed data on two types of temporal evolution of sunspots. A substantial role in the protracted stability of the equilibrium state of vertical magnetic power tubes of sunspots is played by the effect of the macroscopic diamagnetic «expulsing» of magnetic field from the convective zone or photosphere to the sunspots.