Impacts of wild herbivores on soil seed banks are explained by precipitation conditions in protected areas across semi-arid to arid regions

Protected areas form the backbone of global conservation efforts. Vegetation is the primary foundation for achieving conservation goals, and soil seed banks is a cryptic biodiversity reservoir for recruiting species that may not be represented in above-ground 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 banks, we investigated the composition of the germinable seed banks in three protected areas (Yathong, Mungo and Boolcoomatta) along a semi-arid to arid precipitation gradient in south-eastern Australia. The density and species richness of the soil seed banks increased with increasing aridity, which indicated that the soil seed banks 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 banks 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 decrease in the frequency of the seeds of perennials. Synthesis and applications: Disruption of the soil seed banks 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.