Effects of Grazing by Native and Non-Native Terrestrial Vertebrates on the Growth of Tecticornia arbuscula in Australian Temperate Saltmarshes

Abstract

The effects of grazing and browsing by terrestrial vertebrates are poorly understood for southern hemisphere saltmarshes, many of which are recovering from stock grazing. We investigated whether the native late-successional shrub, Tecticornia arbuscula, regenerating several years after the cessation of stock grazing, was grazed by wild herbivorous mammals to the degree of impeding recovery. We measured T. arbuscula growth parameters in exclosures and adjacent controls for two years and used camera trapping of animals across four consecutive austral seasons to indicate grazing pressure. Height growth was more affected by exclosure from grazing than lateral change. Notably, grazing did not prevent the recovery of the shrubs from stock grazing at either site, suggesting that the growth rate of T. arbuscula relative to total grazing pressure is at sustainable levels and these shrubs are in a trajectory of recovery, with the smaller plants growing the fastest. Also, we found little difference between our two sites in grazing impact, despite one site having twice the number of animals, largely native macropods, as the other site, which was dominated by introduced lagomorphs (rabbits and hares). These findings further the knowledge of native and non-native terrestrial vertebrates in austral saltmarsh ecology and conservation.