Last Word

13 February 2008

Family tree

Family tree

People often say a child has their mother’s or father’s eyes. Can a similar thing be said for trees? For example, is the pattern of branches related to the position and orientation of its parents’ branches? What, if any, are trees’ visible inherited traits?

• The anatomical, chemical and morphological characteristics found in trees are under varying degrees of genetic and environmental control, just like the traits of other organisms. For a given characteristic, the proportion of total variation that is explained by genetic control is known as its heritability. This can range from 0 to 100 per cent: the higher the value, the more closely progeny resemble their parents and the greater the improvement that can be obtained by selective breeding.

The genetic variation itself includes additive, dominance and epistatic effects, in which one gene modifies the action of another. The proportion of these effects varies between species, populations, environments, plantation management conditions and also between the individual trees. Some pairs of genetically related traits interfere with each other, making it tricky to obtain benefits in both by selective breeding.

“Some pairs of genetically related traits interfere with each other, making selective breeding tricky”


Two major sets of visible traits are under a high degree of genetic control and are of great importance for the end use of the wood. One is “stem form”, which is a measure of sinuosity or deviation from perfect straightness. It is associated with “reaction wood”, which forms in response to mechanical stress, such as exposure to strong wind. Reaction wood is visibly asymmetric and is generally undesirable for end uses such as solid wood and pulping for paper.

The variable characteristics of the tree’s branches are also important to industry and include the thickness, number per unit of stem length, angle of insertion on the stem, and whether branches occur in whorls or are scattered at random along the length of the stem. These variables affect the number and size of undesirable knots.

Other characteristics in which parents and progeny may be similar include flower colour in horticultural species and flower or fruit colour, shape, size, flavour and nutrient content in fruit trees.

Jeffery Burley, Director Emeritus, Oxford Forestry Institute, Abingdon, Oxfordshire, UK