Dynamics of the photoinduced absorption and holographic-grating recording in photorefractive bismuth silicate crystal has been studied. It has been shown that, with the use of nanosecond laser pulses and at the intensity above 1 МW/cm2, the induced absorption takes place due to population of the short-lived trapping levels having the characteristic relaxation times from milliseconds to a few tens of milliseconds. Recording of dynamic holograms in bismuth silicate has been realized in these conditions. Two mechanisms of holographic grating recording have been established, with the lifetimes differing by three orders of magnitude. Though the intensities are relatively low, below or on the order of 1 MW/cm2, the medium response is determined by a photorefractive nonlinearity mechanism with relaxation times at a level of several seconds. The intensities above 5 MW/cm2 are associated with fast components (ms relaxation times) appearing due to population of short-lived traps. It has been demonstrated that a contribution of each mechanism is dependent on the intensity of laser radiation and that, for the intensities above 10-15 MW/cm2, the decisive part is played by the short-lived traps with lifetimes on the order of milliseconds.