THE TROPICS: ENVIRONMENTS AND HUMAN IMPACTS UNDERSTOOD AND REINTERPRETED

In the 1950s, few people had travelled widely through different parts of the tropics and interpretations on tropical landforms, soils, vegetation and climate largely rested on impressions gained from residence or long sojourns in particular tropical countries. Most academic geography on the tropics was then written by expatriates and lacked the perspective gained from long experience of tropical regions. Particular problems of understanding arose as people attempted to extrapolate from one part of the tropics to another. Since then, understanding has advanced enormously, largely through the efforts of tropical scientists working in their own institutions and through the greater technological ability to study tropical lands both remotely and through easier field access. The establishment of a number of field stations, aimed primarily at the biological sciences, but also facilitating the work of geographers, has been a major stimulus to this effort. Concerns over practical issues, particularly local development and global climatic change have prompted new avenues of research, many of which have been assisted by the great increase in data collection in tropical countries. For the future, South-South dialogue between tropical physical geographers is needed to improve their ability to ask meaningful questions so that they can contribute to teach the rest of their discipline more about serious applied and applicable geography.     

Farming ‘practice’ as temporally and spatially situated intersections of biography,culture and social structure

This paper brings anthropological, sociological and geographical perspectives to bear on the problem of farm sustainability and, in particular, the legitimation of sustainable farm practices. It attempts to lay some theoretical foundations for explanation of the adoption of farming practices which may, or may not, promote sustainability. A brief survey of the literature surrounding these issues finds many of the current theoretical perspectives incapable of fully accounting for the complexity of farming practice. Reductionist decision/rational‐action models, in particular, are found wanting for their lack of both cultural consistency and social/spatial specificity. Instead, this paper promotes a generative structuralist approach directed towards an analysis of social and economic practice in lived space; that is, firmly anchored in long‐term ethnographic research.     

A climatology of Southern Hemisphere extratropical cyclones

A climatology of extratropical cyclones determined by an objective automatic scheme applied to 15 years (1975–89) of once-daily Australian Bureau of Meteorology hemispheric analyses is presented. Contour maps of the positions of formation (cyclogenesis), dissipation (cyclolysis) together with other cyclone statistics are presented. The distribution of cyclones through the hemisphere was found to be dominated by a permanent high latitude core coincident with the circumpolar trough. During the winter and intermediate seasons, two mid latitude branches are evident in the cyclone density originating in the Tasman Sea and South American sectors, both spiraling poleward and merging with the circumpolar core in the Southern Oceans. Systems were observed to move in an castsouth-east direction, away from their location of formation, exhibiting peak speeds of migration in the mid latitudes. Little seasonality was evident in the densitiy distribution of cyclones through the Southern Oceans, but a considerable amount was found in their central pressure. Correspondence to: I Simmonds     

A simple method of estimating rock mass porosity and permeability

Conclusion A simple method of estimating fracture porosity and permeability based on empirical relations between fracture aperture andJRC andJCS can be developed. This shows very close correlation with existing data, using simple discontinuity models. There is quite a good correlation between fracture porosity and permeability and depth for larger initial apertures.     

The compressibility of silicate liquids containing Fe2O3 and the effect of composition,temperature, oxygen fugacity and pressure on their redox states

Ultrasonic longitudinal acoustic velocities in oxidized silicate liquids indicate that the pressure derivative of the partial-molar volume of Fe₂O₃ is the same in iron-rich alkali-, alkaline earth- and natural silicate melt compositions at 1 bar. The dV/dP for multicomponent silicate liquids can be expressed as a linear combination of partial-molar constants plus a positive excess term for Na₂O−Al₂O₃ mixing. Partial-molar properties for FeO and Fe₂O₃ components allow extension of the empirical expression of Sack et al. (1980) to permit the calculation of Fe-redox equilibrium in a natural silicate liquid as a function of composition, temperature, fo₂ and pressure; a more formal thermodynamic expression is presented in the Appendix. The predicted equilibrium fo₂ of natural silicate melts, of fixed oxygen content, closely parallels that defined by the metastable assemblage fayalite+magnetite+β-quartz (FMQ), in pressure-temperature space. A silicate melt initially equilibrated at 3 GPa and FMQ, will remain within approximately 0.5 log₁₀ units of FMQ during its closed-system ascent. Thus, for magmas closed to oxygen, iron-redox equilibrium in crystal-poor pristine glassy lavas represents an excellent probe of the relative oxidation state of their source regions.     

Depositional environments of the Hart coal zone (Paleocene), Willow Bunch Coalfield, southern Saskatchewan, Canada from petrographic, palynological, paleobotanical, mineral and trace element studies

Coal petrology, palynology, paleobotany and mineralogy of the Hart coal indicate deposition under wet, warm-temperate to subtropical climatic conditions in low-lying backswamps with fluvial channels and locally ponded areas. The coal is dominated by mixed xylitic/attrital lithotypes and by huminite macerals with secondary inertinite macerals and minor liptinite macerals. Good correlation exists between lithotypes and maceral composition. Local and vertical variations in proportions of huminites and inertinites reflect frequent fluctuations in water levels, periodic flooding, desiccation and burning of the peat. Swamps were dominated by Glyptostrobus-Taxodium forest with Betula-Myrica-Alnus communities and, locally, Laevigatosporites, which are the dominant contributors to the xylite-rich lithotypes. Attrital lithotypes with abundant Pandanus, Typha and Azolla are consistent with wetter areas of a fluvial environment, including ponds and channels. Trace elements Cr, Cu, Mo, Ni, Si, Ti, U, Se, V, W, K and Th, typically associated with synergetic minerals kaolinite, calcite and quartz, may have a volcanic source. High concentrations of Na, Ba and Ca found in organic complexes are of secondary origin and probably originate in deep source brines rather than marine surface waters.