Grassland dynamics in a degraded disclimax grassland dominated by Danthonia caespitosa Gaudich. are examined using both demographic and multivariate approaches in an experiment designed to determine the effect of grazing intensity and exclosure on pasture dynamics. The experiment ran for 20 years from 1949 to 1968, using permanent quadrats at 3 grazing intensities and within exclosures. Demographic studies of some perennial grass species demonstrated markedly different responses to grazing; Danthonia caespitosa was unaffected by grazing but responsive to seasonal rainfall differences. Enteropogon acicularis survived only o n protected sites. Numerical classification of total species set (121 species) for six observation periods demonstrated that community types were sensitive to differences in winter rainfall, and time since the start of experiment. Principal component analysis of permanent quadrat observations for individual years demonstrates quadrat trajectories which confirm this and indicate progressive divergence of the successional trends of the grazed and ungrazed quadrats. Repeated analysis on grazed quadrats only, shows that three components of pasture dynamics can be recognized; these are trend (succession?) and seasonal differences, each of which account for about 20% of the variance, and differences due to soil heterogeneity in the experimental paddock (8% of variance accounted for). No effect of grazing intensity was detected. Multivariate techniques can provide a clear partitioning of types of dynamic behaviour present in grassland communities. It is concluded that partitioning of environmental heterogeneity prior to demographic studies would increase their sensitivity. Vegetatio 47, 201-211(1981). 0042 3106/81/0471 0201/$2.20.

Substantial recruitment of Callitris glaucophylla in woodland, Sclerolaena birchii in cleared woodland, and Astrebla lappacea in grassland is related to catastrophic events of the past century in the form of interactions between climate, the impact of European land use (sheep, cattle, rabbits) and the rabbit myxoma epizootic. The direct effect of rainfall on the demography of these species and its indirect effect through competition via suites of accompanying plant species are examined. Major long-term changes in plant populations are generated by extreme sequential events rather than by random isolated events. One of the most potent climatic agents for change in eastern Australia is the E1 Nifio/Southern Oscillation phenomenon.

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Seasonal variations in sulphur content and growth rate of wool were measured at intervals of 6 weeks over a period of 1 year on two groups, each of six Merino wethers, which grazed on two semi-arid grasslands. Each group consisted of three high-producers and three low-producers, selected on the basis of wool growth rate. There were substantial seasonal variations in sulphur content, which followed very closely the seasonal pattern of wool growth. Mean sulphur contents on the two grasslands ranged from 3.25 and 3.32% during December–April, to 3.67 and 3.79% respectively during July-October. Seasonal variations in sulphur content and growth rate of wool were related to the amount of edible forage available, and it was concluded that these seasonal variations were due mainly to variable nutrition. The range of sulphur contents was 2.93 to 3.92%, owing to seasonal nutritional variations and differences between sheep; annual mean sulphur contents of wool from individual sheep ranged from 3.22 to 3.84%. The annual mean sulphur content of the wool from high-producers (3.39%) was lower than that of wool from low-producers (3.66%). The seasonal variation in sulphur content also appeared to be greater in wool from high-producers than in wool from low-producers.

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