absorbs all colours except its particular shade of red. Many meta-
bolic processes are triggered by specific frequencies, and if the
required frequency of light is not available in sufficient quantity,
then the response is blocked.
A tree will absorb most in the ultraviolet or the red to infrared
portion of the spectrum. It is insensitive to green light and, if placed
under green light, appears to be in a state of suspended animation.
The light sensitivity of the human eye on the other hand is exactly
the opposite. It is insensitive to the ultraviolet and infrared frequen-
cies, but very sensitive to the colour green.
Because we cannot observe any green in sunlight itself, without
trees and other vegetation, green would be missing in our experi-
ence. Green is a very soothing, healing colour for humans, sedating
the nervous system and psyche. Its absence in large cities can make
us irritable and even violent. Trees and humans have a symbiotic
relationship with colour.The physical nature of trees
The structure of the tree is a record of its various stages of growth,
and this is mirrored in the movement of sap over the full span of the
tree's existence. As the life energy of the tree recedes with ageing, the
sap sinks lower and lower, progressively drawing back from the
uppermost branches, which die off. In many cases this is accelerated
by human activity and the tree is said to suffer from 'die-back.' Like
an elderly human being, the tree's structure stiffens with age, and
like an elderly human, its consciousness falls back through all the
stages of its previous development, perhaps re-living its earlier
experiences.
It is important in times of climate change to realize that the tree
is probably the organism least adapted to rapid change. The average
lifetime of a tree is the longest after rocks, and therefore many cen-
turies must pass before any real adaptation to changed conditions
can occur. Even minor environmental changes, to which other
shorter-living things can adapt, can cause trees stress and vulnera-
bility to disease, so that they wither and die.
As long as too much heat does not stress them, trees will mod-
erate heat through their absorption of CO 2 and their evapo-tran-
spiration. When the forest cover is substantial the trees distribute
water vapour evenly through the atmosphere, ensuring a balanced
- THE LIFE AND NATURE OF TREES