Light- and shade-demanding trees
There are two types of tree with very different requirements of
light (see Fig. 14.3). The effect of light on tree growth has two
principal energy outcomes. Partly it determines the structure of
the timber and, secondly, it influences the form and character of
the tree itself, depending on whether it is a shade-demanding or
a light-demanding species; and these are also related to latitude
and altitude.
Trees mirror the quality of light in their natural habitat. If the
frequency of green is harmful to them, they will use green leaves as
they will screen out or repel that frequency. In general, if the inci-
dent light has a greater proportion of high-frequency, high-energy,
ultraviolet light, in other words hard light, the wood will be soft.
Conversely, where there is a greater preponderance of low-fre-
quency, low-energy, infrared, soft light, the wood will be hard.^4
Australia's native timbers, notable for their hardness, are a good
example of this. Because of Australias position on the Tropic of
Capricorn in the southern hemisphere, the intensity of infrared
light is greatest when Australia experiences its high summer, and
when the Earth is also at its closest to the Sun at Perihelion in early
January. This is increased by the infrared radiation resulting from
Australia's semi-desert condition. Along with other countries in the
southern hemisphere, Australia is therefore exposed to more
intense infrared light than counties in the north which experience
more moderate conditions.
The new growth of many species of Australian trees presents a
particular mixture of red, violet and blue hues, in order to resist the
potentially harmful penetration of those light frequencies. In Europe
and the temperate latitudes of North America, on the other hand,
with their very different light conditions, most new growth is light
green in colour, with some exceptions (like the copper beech).
To summarize: Softwood species, such as pine, are mostly found
in zones of high-energy, high-frequency 'hard' radiation, at low alti-
tudes in high latitudes, and at high altitudes in low latitudes. Con-
versely hardwood trees, with some exceptions, are generally found
at low altitudes in low latitudes (tropical rainforests) and at low to
middle altitudes at low to middle latitudes — zones of low fre-
quency, 'soft' radiation.
HIDDEN NATURE