  We investigate the locality or nonlocality of the energy transfer and of the
spectral interactions involved in the cascade for decaying magnetohydrodynamic
(MHD) flows in the presence of a uniform magnetic field $\bf B$ at various
intensities. The results are based on a detailed analysis of three-dimensional
numerical flows at moderate Reynold numbers. The energy transfer functions, as
well as the global and partial fluxes, are examined by means of different
geometrical wavenumber shells. On the one hand, the transfer functions of the
two conserved Els\"asser energies $E^+$ and $E^-$ are found local in both the
directions parallel ($k_\|$-direction) and perpendicular ($k_\perp$-direction)
to the magnetic guide-field, whatever the ${\bf B}$-strength. On the other
hand, from the flux analysis, the interactions between the two
counterpropagating Els\"asser waves become nonlocal. Indeed, as the ${\bf
B}$-intensity is increased, local interactions are strongly decreased and the
interactions with small $k_\|$ modes dominate the cascade. Most of the energy
flux in the $k_\perp$-direction is due to modes in the plane at $k_\|=0$, while
the weaker cascade in the $k_\|$-direction is due to the modes with $k_\|=1$.
The stronger magnetized flows tends thus to get closer to the weak turbulence
limit where the three-wave resonant interactions are dominating. Hence, the
transition from the strong to the weak turbulence regime occurs by reducing the
number of effective modes in the energy cascade.
