Vegetation and seed banks of arid ephemeral gilgai wetlands subject to contrasting grazing regimes

Abstract

Ephemeral gilgai wetlands of the stony-plains of arid Australia have a relatively high diversity of native plant species and are extensively utilised for livestock grazing. We sampled the standing vegetation (SV) and germinable soil seed bank (SSB) of 40 gilgais, comparing gilgais near and far from watering points, and continually stocked versus rarely stocked. Despite historically heavy stock grazing, we found no significant differences in native species richness between treatments, indicating the general resilience of gilgai vegetation. One contributing factor is the abundance of Atriplex nummularia ssp. omissa. Cover of this long-lived shrub did not differ significantly between treatments and was positively correlated with “highly palatable” species’ cover, suggesting that it may act as a nurse species. In contrast, two other long-lived species, Atriplex vesicaria and Astrebla pectinata, had significantly reduced cover or were absent near to watering points. These and other long-lived species had a poorly developed SSB and thus limited ability to regenerate from seed if killed by sustained heavy grazing. The absence of fifteen locally rare species (including 12 short-lived species) from water-near gilgais indicates the need for more intensive survey to determine whether the proliferation of watering points poses a threat to such species.