  Decay in time of undriven weakly collisional kinetic plasma turbulence in
systems large compared to the ion kinetic scales is investigated using fully
electromagnetic particle-in-cell simulations initiated with transverse flow and
magnetic disturbances, constant density, and a strong guide field. The observed
energy decay is consistent with the von K\'arm\'an hypothesis of similarity
decay, in a formulation adapted to magnetohydrodyamics (MHD). Kinetic
dissipation occurs at small scales, but the overall rate is apparently
controlled by large scale dynamics. At small turbulence amplitude the electrons
are preferentially heated. At larger amplitudes proton heating is the dominant
effect. In the solar wind and corona the protons are typically hotter,
suggesting that these natural systems are in large amplitude turbulence regime.
