Geoscience Reference
In-Depth Information
have short-lived rootlets, while on others, particularly evergreens, they survive much
longer, often for several years.
Every year, the root system produces a new crop of white, fleshy roots and a
proportion of them survive, develop woody tissues and form part of the perennial
structure, so that the basic network continues to grow, just as does the branch system
above ground. This network acts as a transport system, collecting water and nutrients
gathered by the absorbing white roots and moving them to the shoots, and also return-
ing sugars made by the leaves to the roots to provide them with energy and materi-
als for growth. Equally, however, it provides the anchorage for the developing crown
above the ground.
The forces acting on a tree can be quite considerable, especially in strong winds,
as can be seen by the devastation caused by hurricane force winds such as those of
October 1987 and February 1990 in southern England. If the force is too great, the
tree may fail either by the trunk snapping or by the roots breaking free from the soil.
Normally the tree survives because the major woody roots radiating out from the base
of the trunk spread the force and dissipate it into the soil. Trees will withstand severe
gales only if the distribution of roots and their integration into the soil matrix is suf-
ficiently strong. In some forestry systems, root growth is restricted, especially where
land has been thrown into ridge and furrow patterns to aid drainage, for the trees are
planted on the ridges and fail to develop roots properly in the furrows. It is now real-
ized that this causes severe windthrow problems in many commercial plantations and
foresters are searching for new cultural techniques which will improve root develop-
ment.
