Measurements on a 1/10-acre sample of brigalow forest indicated a total biomass of 293x 103 kg/ha, 46% of which consisted of dead materiai, either on the ground or standing. The presence of large amounts of dead material is attributed to the semiarid climate, which results in low decomposition rates, hardness of the wood, absence of termite activity above ground, and lack of running fires. Moisture percentages were low, varying from 4-6% for dead material to 65% for living leaves plus twigs. Amounts of elements immobilized in the biomass were 1600, 38, 300, 100, 2230, and 180 kg/ha for nitrogen, phosphorus, potassium, sodium, calcium, and magnesium respectively. Brigalow showed high nitrogen/phosphorus and calcium/potassium ratios compared with lucerne and grasses grown on a similar cleared area. No differences in sodium and calcium concentrations were found in different components of brigalow, but the canopy showed higher levels of nitrogen, phosphorus, potassium, and magnesium than the trunks, with branches and roots intermediate. In addition the canopies of larger trees showed higher concentrations of nitrogen, phosphorus, and potassium than those of smaller trees. The uneven spatial distribution of living trees associated with the gilgai topography resulted in large sampling errors. The dead material and roots, being more uniformly distributed, showed lower errors. Subsampling techniques used for obtaining samples for chemical analyses were adequate, as standard errors for nutrient concentration determinations were generally lower than those for dry matter determinations.

In a study of a brigalow (Acacia harpophylla F. Muell.) ecosystem the underlying soil material (0-90 cm) was intensively sampled in addition to complete harvesting of vegetative material. Microrelief contours were plotted and random sampling of soils within each of three microtopographic classes carried out. There was a tendency for larger trees to be confined to the higher portions of the microrelief. Differences in soil properties in various microtopographic positions appear to be related to canopy interception and leaf drip of these larger trees. Thus the apparent uniformity of soil salinity isopleths in corresponding layers at different topographic positions, in spite of run-off from higher portions of the microrelief, was attributed to the counteracting effect of canopy interception resulting in the concentration of incident rainfall on the higher parts. This effect was also considered to contribute to the higher soil exchangeable potassium values found on the upper portions of the microrelief. The higher values for soil organic carbon and nitrogen in the upper portions of the microrelief were attributed to the greater concentration of roots in these areas. Relationships between the chemical content of the various components of the ecosystem were examined. The relatively low phosphorus content of the soils and of the forest suggests the adaptation of brigalow to soils of low phosphorus status. The high uptake of calcium is of especial interest in view of the acidity and salinity of the soil. It seems probable that the trend of increasing acidity with depth in these soils is associated with the accumulation of calcium by brigalow and its release during litter decomposition, the low buffering capacity of the soil, and the increasing salinity of the soil with depth. The factors involved in the persistence of brigalow and its high dry matter production under the hot, dry climatic and saline soil conditions in this area are worthy of further study.

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Statistical and other numerical methods of analysis were used to examine variation in Acacia harpophylla (brigalow), a species of wide occurrence in north-eastern Australia. Experiment indicated that the species is largely cross-pollinated. From material collected in the field floret counts, seed size, longevity, and imbibition and germination rates all revealed substantial variation, possibly of a clinal type, within the species. In a glasshouse experiment with 255 seedlings measurement of 19 characters revealed wide differences in morphology, growth, and ontogeny. Over the geographic range sampled, much of the variation found would be consistent with selection for adaptation to increasing temperature and aridity. It is suggested that analogous variation may occur in other Australian species of Acacia.

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