J. B. Thornes

Topographic control of soil moisture, vegetation cover and land degradation in a moisture stressed mediterranean environment

Abstract An erosion-vegetation competition model (THORNES 1985) assumes that surface litter, soil organic matter and soil moisture are positively correlated and that these in turn are correlated with topographic conditions on a uniform soil in a moisture-stressed environment. These relationships are tested for an experimental site in Mediterranean Spain. The results show that while these relationships are statistically significant, but rather weak, when all the data are used or when they are grouped according to geomorphic position (interfluve, hollow or slope), the correlations become stronger when considered in relationship to transects and when the data are subject to a low level of spatial smoothing. Even then, the relationships are rather complex, reflecting local features, the stage of vegetal development and, perhaps, the status of competition between erosion and vegetation.

The Hydraulic Geometry of Stream Channels in the Xingu-Araguaia Headwaters

References Askew, G. P., D. J. Moffatt, R. F. Montgomery and P. L. Searl 1970 Soil landscapes in north-eastern Mato Grosso. Geogr. J. 136: 211-27. Bartlett, H. H. 1956, Fire, primitive agriculture, and grazing in the tropics. In W. L. Thomas (editor), Mans role in changing the face of the Earth pp. 692-720. Chicago: University of Chicago Press. Beard, J. S. 1955 The classification of Tropical American vegetation-types. Ecology 36: 89-100. Cole, M. M. 1960 Cerrado, caatinga and pantanal: the distribution and origin of the savanna vegetation of Brazil. Geogr. J. 126: 168-79. Hills, T. L. 1965 Savannas: a review of a major research problem in tropical geography. Canad. Geogr. 9: 216-28. Lemos, R. C. de 1968 The main tropical soils of Brazil. World Soil Resources Reports 32: 95-106. Rome: FAO/UNESCO. Metson, A. J. 1961 Methods of chemical analysis for soil survey samples. Soil Bur. Bull. 12. Wellington: DSIR. Nye, P. H. 1961 Some effects of natural vegetation on the soils of West Africa and on their development under cultivation. Tropical Soils and Vegetation. Proc. Abidjan Symp.: 59-63. Paris: UNESCO. -and M. H. Bertheux 1957 The distribution of phosphorus in forest and savanna soils ofthe Gold Coast and its agricultural significance. J. Agric. Sci. 49: 141-59Ratter, J. A. 1970 Unpublished notes. Richards, P. W. 1969 Unpublished report to RS/RGS Brazil Expedition Committee. Rizzini, C. T. and E. P. Heringer 1962 Preliminares Acerca das Formacoes Vegetais e do Reflorestamento no Brasil Central. Rio de Janeiro: Ministerio da Agricultura, Servico de Informacao Agricola. Saunder, D. H. 1956 Determination of available phosphorus in tropical soils by extraction with sodium hydroxide. Soil Sci. 82: 457-63. Soil Survey Staff 1960 Soil Classification. A comprehensive system. Jth Approximation. Washington: US Dept. Agric. 1967 Supplement to Soil Classification System. Washington: US Dept. Agric. Waibel, L. 1948 Vegetation and land use in the Planalto Central of Brazil. Geogr. Rev. 38: