Isonome Mapping: Graphic Analysis of Patterns of Species Distribution I. M. Brewer (nee Pidgeon) Brewer, I.M., Isonome mapping: graphic analysis of patterns of species distribution. Proc. Soc. Linn. N.S.W. 115: 259-279 (1995). Fine scale analysis of species distribution and abundance is important in under-standing processes of vegetation change. A novel mapping technique based on simple quadrat-sampling was devised in 1941 for this purpose and used to describe and analyse the structure and patterns of species distribution in two vegetation types on Hawkesbury sand-stone of the Hornsby Plateau. In moist shrubland and in the understorey of adjacent Eucalyptus woodland at two sites, relative densities of shrubby species were calculated from the total numbers of plants of individual species recorded in rectangular (9.1 x 0.9 m) quadrats arranged in a grid. For each species with a sufficiently high density, the variation in its relative density across the grid was mapped as contour lines of equal percentage value called 'isonomes' (from iso, equal, and nome, distribution) . In isonome maps for individual species, mostly complex systems of isonomes with one or more centres of high relative den-sity emerged. By superimposing isonome maps of individual species, the composite pattern of species distribution over the area revealed a complex social structure in which the cen-tres of high relative density formed a mosaic, around the margins of which there was over-lapping of the lower-value isonomes. Graphic analysis by isonome mapping has provided information on sandstone vegetation not previously reported: e.g. sociology of woodland and scrub communities, patterns of occurrence and density of species across sharp eco-tones, and specific patterns have generated an hypothesis of temporal change operating at a small scale. In the application of isonome mapping techniques to other vegetation types, the investigator has to choose the appropriate size and spacing of the rectangular quadrats, so that variation in relative density of species across the grid will generate discernible pat-terns. This paper is of historic interest, not only as the first quantitative method devised to show the pattern of species distribution and abundance in a community, but also as the first quantitative analysis of sandstone vegetation. It is also a record of species composition of pristine communities, devoid of introduced species, in urban fringe, pre-development veg-etation of Sydney. I.M. Brewer, 18 Eastbourne Road, Darling Point, NSW 2027, Australia; manuscript received 15 November 1 994, accepted for publication 15 February 1995. KEYWORDS: isonome mapping, species distribution, Hawkesbury sandstone vegetation. Introduction The twentieth century has seen the evolution of new methods and techniques for the classification, description and quantitative analysis of vegetation. The basis of quantitative investigations in plant sociology is the quadrat method, originally proposed for pastures by Stapledon (1912) . Statistical methods of analysis gave information on the floristic composition of the community, or on density and type of distribution of species (random, over-and under-dispersion). With random dispersion, ecologists and agronomists had a valuable tool for studying changes in plant populations (Blackman, 1935; Ashby, 1935; Clapham, 1936). The arrival of Ashby in 1938, as Professor of Botany at Sydney University, and his fascination with the complexity of sandstone vegetation stimulated studies by Beadle in arid western NSW and that of Pidgeon on the sandstone vegetation. It also led to the collaboration with Pidgeon (now I.M. Brewer) in 1939 in a rigorous statistical analysis (using random-sampling techniques and rectangular strip-quadrats) of the effects of over-grazing on vegetation around Broken Hill (Pidgeon and Ashby, 1940) . Proc. Linn. Soc. N.s.w., 115, 1995
BioStor
