Life histories of two arid-zone shrubs change with differences in habitat, grazing and climate

Abstract

Shrubs are an important component of vegetation throughout the world. They are particularly significant in semiarid environments where they can dominate, driving ecosystem structure and functioning, and shaping land use. Lifehistory information was derived for Eremophila sturtii R.Br. and Dodonaea viscosa subsp. angustissima J.G.West, two widespread and common shrubs of semiarid eastern Australia. Plants growing under background climatic conditions took between2and4yearstobecomeestablished,attainedthecapacitytoreproducesexuallyatbetween10and12years,wereina sexually reproductive stage for between 17and28 yearsandlivedanaveragemaximumof33–40years.Underbackground climatic conditions between 70 and 80% of plants that entered the juvenile stage survived to sexual maturity while under severe droughtthis proportion fell to between 40and60%.Juvenileplants,particularly ofE.sturtii, experienced the highest mortality under background conditions while, when exposed to severe drought, older plants, particularly D. viscosa subsp. angustissima in the intermediate stage, experienced the greatest increase in mortality, dying at more than twice the background rate. The high survival rates of E. sturtii and D. viscosa subsp. angustissima shown here, even under extreme drought conditions and in grazed- and ungrazed areas, help to explain why these shrub species have been observed to dominate vegetation in large areas of eastern Australia.