THE BODY TEMPERATURE OF EUROPEANS IN THE TROPICS

The great majority of the forests of the world have been burned over in various return intervals for many thousands of years. Even the perhumid tropical rain forest, where there is limited evidence of recent fires, was certainly affected by fire in the past. Sanford et al. (1985), studying charcoal fragments found in a tropical rain forest soil near San Carlos de Rio Negro, Venezuela, found radiometric ages which ranged from 250 to 6260 years B.P., indicating that fires occurred in that period (see also Saldarriaga and West 1986). Most likely these fires were associated with extremely dry periods or human disturbances.

Land-use change, particularly in the tropics, has a significant impact on the global climate due to biophysical and biogeochemical feedbacks. With a changing climate, an improved understanding of changes in net primary productivity and carbon storage potentials of tropical ecosystems is needed. However, continuous measurements of ecosystem fluxes are sparse in tropical regions and only few localities exist in Central America.

This paper analyses the advantages and limitations in using the Troll, Hargreaves and modified Thornthwaite approaches for the demarcation of the semi-arid tropics. Data from India, Africa, Brazil, Australia and Thailand, were used for the comparison of these three methods. The modified Thornthwaite approach provided the most relevant agriculturally oriented demarcation of the semi-arid tropics. This method is not only simple, but uses input data that are available for a global network of stations, Using this method the semi-arid tropics includes major dryland or rainfed agricultural zones with annual rainfall varying from about 500 to 1,250 mm. Major dryland crops are pearl millet, sorghum, pigeonpea and groundnut. This paper also presents the brief description of climate, soils and farming systems of the semi-and tropics.

Climatic fluctuations are a risk factor in agriculture. They hinder agricultural development in extensive and and semi-arid tropical areas of South America. The main uncertainty factors in the tropics are the amount and distribution of rainfall in dryland-farming areas and, in the subtropics, possible spring frost where temperate and subtropical species coexist. Economic losses, caused by these climatic phenomena, should not be underestimated. In Chile, annual losses in agriculture, due to frost, are estimated from 12 to 20 million US$, and due to droughts from 40 to 120 million US$ (Santibanez 1983). To appreciate the magnitude of this problem at a South American level, these values would have to be multiplied by a factor of at least 8 to 10. Drought also affects irrigated areas, because streams and rivers depend on runoff water and/or the accumulation of snow in the upper Andes. The Brazilian northeastern arid zone, one of the agricultural areas with most variable precipitation in South America, is almost entirely dependent on rain for crop production. However, in the last few years underground water has been tapped for irrigation. Livestock production is especially uncertain in areas with less than 300 mm rainfall per year. In spite of this, there is an important segment of the population who depend on the rain to survive in the Chilean mediterranean climates and and steppes of Tierra del Fuego.

The climates of the semi-arid tropics are characterized by high incidence of solar radiation, high temperatures and very variable rainfall. Droughts and floods are both common occurrences. Deficient rainfall years may be followed by similar years or years with excess rainfall in no predictable pattern.

The semiarid tropics (SAT) is a region of limited, erratic rainfall and nutrient-poor soils. It is populated by more than 700 million people, most of whom live at subsistence levels and depend for their food on the limited production of small farms. Current yields are low and production is unstable because of aberrant weather. Semiarid tropics with 13% of the world’s land and 15% of its people produce only 11% of its food.

This chapter aims to synthesise what is known about areas of rapid loss of forest in the tropics and boreal Eurasia from the 1990s onwards, based on data compiled from expert opinion and Earth observation technology. During the 1990s, forest-cover changes were much more frequent in the tropics than in other parts of the world. In particular, the Amazon basin and Southeast Asia contain a concentration of deforestation hotspots. Forest degradation in Eurasia, related mostly to unsustainable logging activities or increase in fire frequency, has been growing in recent years. The Greenpeace map of the world’s intact forests for the year 2000 depicts the remaining large forest areas, which usually contain high fractions of old-growth forest. Although rates of forest cover changes are now better assessed, uncertainties still exist about the rate of change in intact forest areas.

Abstract Stoops, G., Marcelino, V., Zauyah, S. and Maas, A., 1994. Micromorphology of soils of the humid tropics. In: A.J. Ringrose-Voase and G.S. Humphreys (Editors), Soil Micromorphology: Studies in Management and Genesis. Proc. IX Int. Working Meeting on Soil Micromorphology, Townsville, Australia, July 1992. Developments in Soil Science 22, Elsevier, Amsterdam, pp. 1–15.