During the first half of 1965 an unprecedented drought caused widespread wilting of native trees from southern Queensland to the New South Wales-Victorian border. The reaction of some of the native vegetation in parts of the Australian Capital Territory and Monaro Region has been studied. Rainfall from January 1 to June 30 was less than one-quarter of the normal, and by the end of March signs of water stress were apparent over a wide area. The communities most severely affected were dry sclerophyll forests, especially on shallow, stony soils on northerly and westerly aspects. The ability of Eucalyptus spp. to withstand sustained severe dehydration is shown by the fact that the relative moisture content of living leaves could be reduced to 40-45 %, and maintained at these levels for long periods. The prolonged period of dehydration caused general drying out of the trees, rather than leaf and twig desiccation only. In the most severe cases, shrinkage and fissuring of the bark of E. rossii, with ultimate separation at the cambium, was observed. It is suggested that so-called ineffective summer rain in south-eastern Australia is both effective and essential for the native communities on soils of low water-holding capacity. The role of drought in the distribution of native communities is discussed.
Observations in a number of stands of Eucalyptus macrorhyncha-E. rossii dry sclerophyll forest on the Southern Tablelands of New South wa!es had suggested that differences in botanical composition and structure were associated with differences in aspect. Quantitative studies were made in a relatively undisturbed forest on Black Mountain. For assessment of the forest overstorey, permanent transects 10 ch by 1 ch were established on north- and south-facing slopes parallel to the ridge or valley axis. All stems of 4 in. diam. at breast height or more were identified and measured. Shrub and herbaceous strata were assessed on five north-facing and five south-facing slopes. A list of species, together with an estimate of cover for species occupying more than 1 % of the plot area, was recorded on 100 contiguous milacre plots along the mid-line of the permanent transects. There were no significant differences between north and south slopes in respect of total number of stems or basal area of trees. In terms of both density and basal area, however, E. rossii is the dominant eucalypt on the warmer northerly aspects, while E. macrorhyncha is dominant on the cooler southerly aspects. On the basis of the frequency data, three groups of shrubs can be recognized, viz. (1) species of high frequency on north aspects but relatively low frequency on south aspects; (2) species of similar frequency on both aspects; and (3) species which occur most commonly on south-facing slopes. Of the two common grasses, Danthonia pallida occurs with equal frequency on both aspects, while Poa sp. is virtually absent on north-facing slopes but occurs with the same frequency as D. pallida on south aspects. Though total cover of shrubs plus herbaceous species is similar on both aspects, shrubs characterize the understorey on north aspects, and grasses on south aspects.
The results of an ecological survey of the south-eastern Riverina are presented. The general features of the environment (climate, geology, physio- graphy, and soils) are described. Twenty-three plant associations are recognized and described and these are grouped into seven alliances and two formations. The distribution of the alliances is shown on the vegetation map of the region. The relationships between the vegetation and environmental factors are discussed. There is little correlation between the vegetation and geological formations. The distribution of the communities does not appear to be closely related to climatic factors, chiefly owing to the over-riding effects of soil and topography. Evidence is presented to show that the grasslands in the Narrandera, Urana, Jerilderie area are disclimax corninunities developed from the Acacia pendub-Atriplex nummularia Alliance. The life-form spectra of each alliance and of the whole region are given and briefly discussed. There is a preponderance of henlicryptophytes and therophytes except in the Eucalyptus dealbata-E. sideroxylon Alliance which is strongly nanophanerophytic. The appendix gives a species list for each alliance, together with notes on the occurrence of species rarely found in the region.
Twelve species of Eucalyptus were grown in sand culture to determine their response to nitrate and ammonium nitrogen, and to different proportions of the two ions. Response was measured in terms of plant height, yields of plant parts (stems, branches, leaves, and roots), and number of branches. The results indicate a wide variation in the response of different species to form of nitrogen. A classification of species in terms of their overall response bears no relation to the accepted taxonomic classification. On the basis of the results for the 12 species, it appears that plants of similar ecological habitat tend to have similar responses. Thus, typical woodland species (E. melliodora, E. blakelyi, and E. albens) behave quite differently from typical forest species (E. rossii and E. sideroxylon). Nevertheless, there are differences within such general groupings; e.g. forest species such as E. Agglomerata and E. macrorhyncha form a distinct group, apparently unrelated to the other forest species tested. The response of E. polyanthemos, which occurs in both dry sclerophyll forests and woodlands, is similar to that of the typical forest species. When Eucalyptus species are to be grown in sand culture for nutrition or other trials, a preliminary test is necessary to determine the preferred form of nitrogen for each species. Otherwise the effects of the factor being tested may be so masked as to render the test valueless.
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