Civil Engineering Reference
In-Depth Information
Table 10.6:
Use of timber in building -
continued
Timber
Properties
(1)
Areas of use
Common hazel (
Corylus
avallana
)
Grey alder (
Alnus incama
)
Strong and elastic, not particularly
durable
Not particularly durable, light and
brittle, easy to work
Stable, hard wearing
Wattle walling in timber
framework
Internal panelling, veneer
Wild cherry (
Prunnus
avium
)
Plum (
Prunus domestica
)
Holly (
Helix aquifolium
)
Floors
Splits easily when dried
Hard, homogeneous, hard
wearing
Hard, homogeneous, hard
wearing, low resistance to
moisture
Tough, elastic, easy to cleave
Veneer
Veneer
Apple (
Malus pumile
)
Wooden screws, dowels,
thresholds
White willow (
Salix alloa
)
Veneer, wattle cladding on
external walls
Wattle cladding on external
walls
Rowan or mountain ash
(
Sorbus aucuparia
)
Heavy, hard, tough, durable, hard
wearing, easy to work
Note:
(1) Varies according to place of origin and the conditions of growth
These trees induce an acidic soil and reduce the pH level in water and rivers, and
the forests are, ecologically speaking, deserts - local ecological systems do not
function. This form of forestry leads to increased erosion of soil through com-
prehensive drainage systems which quickly channels rainfall into rivers and
streams. In Scandinavia this form of forestry threatens more than 200 different
species of plants and animals with extinction.
Forestry can be run on ecological principles. The secret lies in the natural
regeneration of the forest. This requires sowing seeds of a multitude of local tree
species, including deciduous trees that prevent acidity, and careful harvesting so
that younger trees and other plants are preserved. There is clear evidence that
timber from these mixed forests is of a higher quality than that cultivated in
monocultures (Thörnquist, 1990). The bark from the trees is kept in the forest,
which leaves nutrition on the forest floor, including nitrogen from the needles
which avoids adding nitrogen in the form of artificial fertilizer.
People were once much more careful when choosing trees for felling. They
chose mature trees: conifers more than 80-years-old and deciduous trees
between 30 and 60-years-old. Hardwoods such as beech and oak need to be
well over 100-years-old to be ready for felling. The definition of a mature pine
is that pith and heartwood forms at least half of the cross-section of the trunk.
In both spruce and pine the heartwood begins to form around the age of 30 to
40 years.
