Reaction wood
Encyclopedia
Reaction wood forms when part of a woody plant
is subjected to mechanical stress, and helps to bring parts of the plant into an optimal position. This stress may be the result of gravity, wind
exposure, snow
buildup, soil movement, etc. The reaction wood is not externally visible, although asymmetric growth is a reliable indicator. The cork cambium
in the affected part of the trunk is more active on one side, leading to thicker growth rings. Branches practically always have reaction wood, since they need support to maintain their horizontal or nearly horizontal position. There are two different types of reaction wood, which represent two different approaches to the same problem by these groups of plant
s:
As a rule, reaction wood is undesirable in any commercial application, primarily as its mechanical properties are different: it breaks the uniformity of timber. It also responds differently to changes in moisture.
Woody plant
A woody plant is a plant that uses wood as its structural tissue. These are typically perennial plants whose stems and larger roots are reinforced with wood produced adjacent to the vascular tissues. The main stem, larger branches, and roots of these plants are usually covered by a layer of...
is subjected to mechanical stress, and helps to bring parts of the plant into an optimal position. This stress may be the result of gravity, wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
exposure, snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
buildup, soil movement, etc. The reaction wood is not externally visible, although asymmetric growth is a reliable indicator. The cork cambium
Cork cambium
Cork cambium is a tissue found in many vascular plants as part of the periderm. The cork cambium is a lateral meristem and is responsible for secondary growth that replaces the epidermis in roots and stems...
in the affected part of the trunk is more active on one side, leading to thicker growth rings. Branches practically always have reaction wood, since they need support to maintain their horizontal or nearly horizontal position. There are two different types of reaction wood, which represent two different approaches to the same problem by these groups of plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s:
- In angiosperms reaction wood is called tension wood. Tension wood forms on the side of the affected part of the plant, pulling it towards the affecting force. It is composed almost entirely of celluloseCelluloseCellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
.
- In conifers it is called compression wood. Compression wood forms in the bend on the opposite side of the applied force, thereby lengthening/straightening the bend. Compression wood is rich in ligninLigninLignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
.
As a rule, reaction wood is undesirable in any commercial application, primarily as its mechanical properties are different: it breaks the uniformity of timber. It also responds differently to changes in moisture.