Eucalypts have evolved particularly successful ways of producing shoots which helps to explain their capacity for rapid growth or regeneration. These habits are quite unlike our native trees.
Buds are present in the axil of every Eucalyptus leaf as it unfolds from the parent growing tip. These are called naked buds and are capable of rapid growth as soon as the parent leaf unfolds. The ones nearer the tips continue to produce new growth without limit and in the axil of each new leaf is another naked bud. The number of leaves that can separate from the growing tip is indefinite and the naked buds expand simultaneously.
Also present at the base of the naked buds is an area which, if the naked buds and stem leaves are damaged, can take over growth. They are called accessory buds. These can replace the original buds within a few weeks. Should these be damaged further shoots will develop. They do not require a resting period before they form new shoots. This is a very successful mechanism to ensure growth.
Conversely the buds of our native trees contain the complete annual shoot in embryo form. When these buds open in the spring they unfold and the whole annual shoot reaches its final size in a few weeks. The buds that will make next years shoots are slowly made in the leaf axils and they usually require a resting period before they expand.
Most Eucalypts also develop lignotubers. They start life as swellings in the axils of the cotyledons or first few seedling leaves and tend to fold down the stem and bury themselves beneath the soil. They can produce very many leafy shoots if the crown of the tree is destroyed and will replace the original stem. In Australia they are most important because the lignotubers are usually undamaged by fire or browsing and will allow the tree to regenerate.
Added to this ability to grow indefinitely during the growing season is their relative freedom in the U.K. from native pests and diseases, also their evergreen leaves are available to photosynthesise immediately weather conditions are suitable. |
