Ephemeral plant indicators of livestock grazing in arid rangelands during wet conditions

Abstract

Vegetation communities in arid rangeland systems are typically dominated by short-lived, ephemeral (annual) plants during periods of high rainfall. These conditions present a rare opportunity to examine herbivore–plant interactions and identify potential indicators of grazing intensity. The influence of cattle grazing on vegetation communities of arid cracking-clay gibber-gilgai systems in Australian rangelands was investigated during La Niña (wet) conditions, including 2010, which was the wettest year on record in the region. Seasonal annual plant diversity was assessed at three grazed and three less-grazed sites. Individual annual species’ responses to grazing intensity were examined among grazed and less-grazed sites (i.e. increasing or decreasing response). Additionally, rare (found at one site only) and restricted (found at grazed or less-grazed sites only) annual and perennial species were identified to elucidate their status as indicators. Prevailing La Niña conditions allowed the study of little-known, short-lived species, which constituted the bulk of species richness. Differences in grazing intensity were more clearly ascertained from examining individual species than plant diversity. Of 31 annual/short-lived species, 21 responded to grazing intensity. Although most species responded to grazing (n = 7 increasers and n = 14 decreasers), these responses did not necessarily reflect published accounts of their so-called palatability. Thirty other species were restricted to certain site types (grazed or less-grazed) and 20 were rare. The indicator species concept should be applied at appropriate scales, and more detailed information is needed on stock preferences for these ephemeral plants in these rangeland systems. Elucidating the effect of grazing on individual plant species’ phenology, and identifying indicators, is important for developing efficacious land management practices.