Evidence for palatability variation between the sex phenotypes of bladder saltbush from small-plot grazing trials

Abstract

Abstract. This paper reports the results of the first intensive grazing trials to study palatability variation between the sex phenotypes of bladder saltbush (Atriplex vesicaria Hew. ex Benth.). The results show that Merino sheep preferentially graze female shrubs over male and bisexual shrubs in South Australia, which supports earlier paddockscale observations made in New South Wales. Male shrubs with higher densities of flower spikes were consumed less than those with lower densities. However, when male flowers were small and/or sparse, the removal of male flowers by clipping did not significantly increase the consumption of male shrubs. Female shrubs with very low or very high densities of fruit tended to be consumed significantly more than those with moderate fruit densities. Other physical aspects such as plant growth habit and foliage density did not have a consistent influence on grazing behaviour. Chemical differences between the sex phenotypes are implicated. The presence of palatability variation between the sex phenotypes suggests that there is potential to refine the existing use of bladder saltbush as an indicator species in southern Australia.

The role of the male flower spike as a cue for selective grazing in bladder saltbush

“…This was confirmed in the first trial, which showed that the female phenotype was preferentially grazed over the male phenotype. This pattern was consistent with all previous findings to date (Williams 1972;Williams et al 1978;Graetz and Wilson 1979;Walsh et al 2005).…”

“…The results of small-plot grazing trials from that study confirmed that female shrubs were preferentially grazed over male shrubs, which was the first confirmation of the phenomenon in the rangelands of South Australia (Walsh et al 2005).…”

“…Walsh et al (2005) found evidence to support the idea that it is the male flower spike that is a deterrent to grazing rather than fruits being an attractant.…”

“…Rather, we believe that sheep use the spike primarily as a visual cue to a chemical deterrent contained in male plants. The nature of this chemical deterrent is not known at this time (see Walsh et al 2005).…”

“…All plant material used in the trials was harvested from shrubs in Little One Mile Paddock, Middleback Station (see Walsh et al 2005). This paddock has rarely been used by sheep (A. W. Nicolson, pers.…”