THE TROPICS, ITS SOILS AND HORTICULTURE - Tropical Fruits - page 11

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T HE T ROPICS , ITS S OILS AND
H ORTICULTURE

INTRODUCTION

Climate is defi ned as the general temperature and atmospheric conditions of an
area over an extended period of time. Atmospheric conditions include rainfall,
humidity, sunshine, wind and other factors. Climates are subject to modifi cation
by various factors, such as latitude, elevation and whether or not the land
mass is continental, coastal or oceanic, direction of wind and ocean currents,
proximity to large bodies of water and mountain ranges, and cloudiness.
The tropical region is a belt around the earth between the Tropic of
Cancer at 23° 30 ′ latitude north of the equator and the Tropic of Capricorn
23° 30 ′ latitude south of the equator (Fig. 2.1). The term 'tropics' has its
origins in astronomy and comes from the Greek meaning 'a turning'. In
astronomy, it defi nes the farthest southern- and northernmost latitudes where
the sun shines overhead. The Tropics of Cancer and Capricorn are rather rigid
boundaries and do not take into consideration the presence of areas that do
not meet the various climatic characteristics generally established to describe
the tropics. Some climatologists have extended the region to 30° N and S of
the equator, based upon surface temperatures and precipitation, or use the
18°C isotherm of the coolest month (Fig. 2.1). This increases the land mass
in the tropics substantially, from ~40% to ~50%, especially on the continents
of Africa, China, South America and India, and would include approximately
two-thirds of Australia's land mass.

CHARACTERISTICS OF THE TROPICS

The tropical zone is generally described as possessing the following character-
istics:

1. An equable warm temperature throughout the year, having no cold season
at lower elevations. The average annual temperature of the true tropics is