Tree types are determined to a great extent by: latitude and altitude.(1) LIGHT-DEMANDING timbers — THICK, generally rough bark (e.g. oak, black walnut)
(2) SHADE-DEMANDING timbers — THIN, generally smooth bark (e.g. beech, birch)
(3) HARDWOODS — thick (e.g. oak, jarrah) and thin bark (e.g. walnut, cherry, maple, red alder)
(4) SOFTWOODS — thick (e.g. redwood, pine, spruce) and thin bark e.g. (hemlock, fir, larch)GENERAL DISTRIBUTION*
(5) CONIFEROUS (6) DECIDUOUS (7) RAINFOREST
(evergreen) (intermittent) (evergreen)
(polar latitudes) (median latitudes) (equatorial latitudes)
(high altitudes) (median altitudes) (low altitudes)*These boundaries are not necessarily clearly defined.High altitude trees such as spruce have a relatively short lifes-
pan. Shortwave ultraviolet light, with its higher energy and inten-
sity, has a faster dynamic motion with a smaller radius and shorter
period tend to favour evergreens with soft wood. In contrast, low
latitude or low altitude trees like the beech, where long wavelength,
low-energy, low-frequency, less intense light predominates, has
harder wood and a longer lifespan.
Contemporary forestry practice requires trees to grow rapidly in
girth, putting on a profusion of branches. What this produces is a
great quantity of poor quality timber, full of knots. The disregard by
forestry of the light factor is one of the causes of the deterioration
of forests.
The increase of tree diseases in both logged natural forests and
in plantations is a direct result of the exposure to direct sunlight and
heat of a shade-demanding species. There are two ways to deter-
mine whether a tree is a light- or a shade-demander:
Shade-demanding species have thin smooth bark; growing normally
in the cooler inner forest, they do not need to insulate themselves
from the heating effect of direct sunlight. Light-demanding trees on
the other hand have thick, coarse, thermally insulating bark, which is
Nature's way of protecting them from heat and direct sunlight.
- THE LIFE AND NATURE OF TREES
Fig. 14.3. Tree type distribution.