Geoscience Reference
In-Depth Information
Figure 2.5 Energy dynamics within a tropical rainforest. Temperatures within the for-
est decrease with nightfall.
(Illustration by Jeff Dixon. Adapted from Lieth et al. 1989.)
The Earth receives 99 percent of its energy from the sun. The tropical zone
between 23
S latitude receives the highest amount of this energy
because of the Earth's revolution, rotation, and axial tilt. A constant input of the
sun's energy, along with the Earth's axial tilt and revolution around the sun, results
in minimal seasonal variation. The maximum day length ranges from 12 hours at
the Equator to 13.5 hours at the Tropics of Cancer and Capricorn when the sun is
directly overhead. Solar radiation is received directly or diffusely depending on
cloud cover. The amount, course, and altitude of tropical clouds influence tempera-
tures, but the growing season is always 365 days per year.
In the Tropical Rainforest, the transfer of energy from the sun to the forest pri-
marily occurs in the forest canopy (see Figure 2.5). Less than 10 percent of the
incoming solar radiation actually reaches the ground due to the density and height
of canopy trees. The forest's own biological regulating mechanisms (photosyn-
thesis, evaporation, transpiration, and so on) regulate energy transfer below the
N and 23
