The Influence of Sheep on Pattern and Process in Atriplex vesicaria Populations From the Riverine Plain of New South Wales

Abstract

The application of multiple pattern analysis (multiscale ordination) to a phase-differentiated sample of perennial saltbush (Atriplex vesicaria) rangeland, along with assessments of the vegetative and reproductive states of individual plants, served to indicate the importance of sheep in determining some scales of distributional pattern in the shrub population. By comparison with conventional pattern analysis, it is shown that multiple pattern analysis can be used to provide an economic description of 'total' pattern in temporally related phases of a monospecific plant population. It is demonstrated that the pattern-determining interaction between sheep and saltbush individuals is dependent on plant size, sex and location with respect of other shrub individuals, in particular due to the trampling of seedling and pioneer phases and the selective grazing of sexually mature shrubs by sheep.

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).…”

“…Both Williams et al (1978) and Graetz (1978) found that the sex ratio of grazed saltbush populations in western New South Wales was strongly biased in favour of the male phenotype and Graetz (1978) reported a 5-fold increase in the ratio of male to female plants with decreasing proximity from water. Subsequently, Graetz and Wilson (1979) found that female shrubs were more likely to be grazed than male shrubs at all distances from water.…”

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

“…Furthermore, it has been found that female shrubs are more likely to be grazed than male shrubs at all distances from water . Williams (1972) and Williams et al (1978) found that male plants in grazed populations were vegetatively and reproductively more vigorous than females of the same lifestage, and noted that this could be explained by selective grazing. Graetz (1978) noted that preferential grazing of females reduced their size in comparison to males.…”

“…Most of the research, however, has focused on the differential acceptability of the sex phenotypes to Merino sheep. In separate studies, Williams et al (1978) and Graetz (1978) found that the sex ratio of grazed saltbush populations was strongly biased in favour of the male phenotype. Graetz (1978) found up to a 5-fold increase in the female to male sex ratio with increasing distance from water.…”

Spatial Distribution Pattern of the Populations of Cephalanthera erecta at Mt. Ahop in Busan

“…Ahop is as a relatively homogeneous area that differs from its surroundings. There is, however, a lot of field data indicating that even-aged population of trees, shrubs and herbs tend to decrease the intensity of aggregation in the course of self-thinning, being initially distributed in clumps [24] or tend to nearly regular distribution [17,18]. When R = 1, it is a random distribution; R < 1, it is an aggregation; R > 1, it is a uniform distribution [15].…”