Protected areas form the backbone of global conservation efforts. Vegetation is the primary foundation for achieving conservation goals, and the soil seed bank is a cryptic biodiversity reservoir for recruiting species that may not be represented in aboveground vegetation. Unfortunately, unmanaged grazing by wild herbivores has led to vegetation degradation in semi-arid to arid regions. However, experimental evidence on the long-term impacts of wild herbivores on soil seed banks is largely lacking. Here, with the aim of examining how wild herbivores impact soil seed bank, we investigated the composition of the germinable seed bank in three protected areas along a semi-arid to arid precipitation gradient in southeastern Australia. The density and species richness of the soil seed bank increased with increasing aridity, which indicated that the soil seed bank in arid regions is an important biodiversity reservoir. The effects of wild herbivores on soil seed density were strongly dependent on precipitation. Wild herbivores disrupted the soil seed bank at the most arid site but promoted the accumulation of seeds in the soil at the least arid site. Grazing was linked to an increase in the frequency of the seeds of introduced species and a decrease in the frequency of the seeds of perennials. Disruption of the soil seed bank by the grazing of wild herbivores could lead to the failure of post-rain pulses of vegetation growth and hamper efforts to restore vegetation in protected areas. Therefore, suppressing wild herbivore numbers is a strategy that could enhance soil seed bank reserves and revegetation efforts in arid protected areas.