An analysis was made of the floristic composition of 26 cerrado areas in Brazil, encompassing most of the latitudinal and much of the longitudinal extension of this vegetation. A total of 485 species of trees and large shrubs occurred in these areas but those present at only one site were eliminated so that the number analysed was reduced to 255. Numerical classification and ordination, followed by an environmental/geographical interpretation of site patterns, were used in the analysis. The analyses revealed three major gradients of variation associated with latitude, longitude and, most strongly, soil-type (mesotrophic or dystrophic). The study demonstrated that cerrado vegetation is extremely heterogeneous: none of the 485 species recorded occurred at all sites and only 27 were present at 15 or more. Further knowledge of this distributional heterogeneity is essential for the planning of representative conservation areas of this extremely endangered vegetation.Uma analise foi feita da composifao floristica de 26 areas de cerrado no Brasil, alcancando a maioria da extensao latitudinal e uma grande parte da distribuicao longitudinal desta vegetacao. Urn total de 485 especies de arvores e arbustos grandes ocorreu nestas areas mas as registradas em um so local foram eliminadas e por isso o numero analisado se reduziu a 255. Uma classificacao numerica e ordena?ao, seguida por uma interpretacao ambiental/geografica de padroes dos si'tios, foram usadas na analise. As analises mostraram tres gradientes maiores da variacao associadas com latitude, longitude e, mais fortemente, com caracteristicas do solo (meso-ou distrofico). O estudo mostrou que a vegetacao do cerrado e extremamente heterogenea: nenhuma das 485 especies registradas ocorreu em todas as localidades e somente 27 estiveram presentes em 15 ou mais. Um conhedmento mais amplo dessa heterogeneidade da distribuicao e necessario para a delimitacao de areas representativas para a conservacao dessa vegetacao altamente ameacada.

A b s t r a c tThe need for rigorous methods of interpreting indirect site ordinations is discussed and the problem of oblique habitat and phytosociological trends is emphasized. A sequential approach, termed integrated interpretation, is introduced to overcome this problem. It first involves a technique termed rotational correlation, a linear form of trend surface analysis, which locates the best fit between a habitat variable and the coordinates of a pluridimensional ordination. The coordinates at positions of best fit are then used to produce two-way site-species tables (seriation arrays) which summarize floristic variation in relation to each major habitat trend. The seriation arrays can also be used to identify groups of differential species. Integrated interpretation is demonstrated using semi-arid vegetation from Murcia Province, SE Spain. A two-axis site ordination of vegetation data by non-metric multidimensional scaling is shown to have two oblique trends related to aspect-induced topoclimates and types of past anthropogenic disturbance. Rotation of the configuration to maximum linear correlation achieves very high levels of explanation for each factor. Rotated ordination coordinates from the correlation analysis are used to obtain two seriation arrays and floristic noda which relate directly to the two underlying habitat trends. A floristic discontinuity is revealed on the topoclimate continuum and it is hypothesized that temperature conditions are a major determinant of floristic composition, but that moisture partly determines vegetational cover and phytomass. Several patterns of past cultivation are detected and associated with five main kinds of geomorphological unit, together with some evidence that the rate of succession is partly determined by topoclimate. The integrated approach to interpretation is compared with visual methods and other multivariate techniques. A case is made for increased interpretational rigour in site coordinate studies, especially the discontinuation of trend-seeking using individual unrotated ordination axes.

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Abstract. Two contrasting Egyptian desert environments are examined by ordination and integrated inter‐pretationmethods. A crude site moisture index is strongly related to vegetation in both desert regions. Water quality is an additional strong control of floristic variation on the Sinai coastal plain and disturbance (by grazing and woodfuel collection) is important in the Eastern Desert. Useful indicator groupings of species are obtained as part of the analysis and are potential aids in the development and conservation of desert areas. Modern numerical methods offer considerable advances on the traditional descriptions of Egyptian desert ecosystems.

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