The Geography of Phytochemical Races

Chapter 2
Examples Within Continents
The survey of geographical distribution patterns of secondary plant constituents starts
with examples that come, more or less, from within continents. In many examples,
the patterns of variation involve comparatively small areas, a few counties perhaps,
and could be referred to as local; whereas in others, considerably larger areas are
involved, often several states or provinces, or even large pieces of a country. In most
cases, however, the regions under consideration lie within a single continental landmass.
A few examples come from island systems (e.g., New Zealand) where the existence
of major landmasses separated by a small stretch of water does not appear to
have had an effect upon the distribution reported, or at least none has been reported.
2.1 Africa (Including Madagascar)
2.1.1 A Comparison of Rain Forests
The fi rst example from the African continent represents one of the more wideranging
projects that we will meet. Ninety species were sampled in a study comparing
aspects of the phytochemistry of two African rain forests (Gartlan et al.,
1980). The object of the study was to compare different plant communities from the
perspective of their production of secondary metabolites (presumably) employed
in allelochemical defense. The areas studied are located in the Kibale Forest in
Uganda, East Africa, and the Douala-Edea Forest Reserve in Cameroon, West Africa
(Fig. 2.1). The two areas differ in several respects: rainfall, soil chemistry, terrain,
and vegetation. The Douala-Edea site receives over twice the amount of annual rainfall
(3500–4000 mm over ca. 220 days) than does the Kibale site (ca. 1500 mm over
ca. 166 days). Temperatures in Douala-Edea show comparatively smaller seasonal
variation (23–32°C), whereas average temperatures in Kibale are somewhat lower
and show a greater range (12.7–25.5°C). This is expected in view of the coastal, low
elevation of Douala-Edea compared to the mid-elevation (1300–1500 m) location of
the Kibale site. The soil at the Douala-Edea site is sandy, low in nutrients, and has
an average pH = 3.89. In contrast, the soil in Kibale is dark gray to red sandy loam
of moderate fertility with an average pH = 5.64. The Douala-Edea site vegetation is
B.A. Bohm, The Geography of Phytochemical Races,
© Springer Science+Business Media B.V. 2009
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