Development of Large Plate-Like Lignotubers in Eucalyptus botryoides Sm. In Relation to Environmental Factors

Abstract

Individuals of E. botryoides (nomenclature of eucalypts follows Chippendale 1976) form large lignotubers in a coastal area of high rainfall (c. 1200 mm per year) and relatively infertile siliceous sand. All plants in the area are regularly burnt and those of the seaward edge are exposed to saline winds. A multiple-stemmed (mallee) form of E. botryoides with a large (up to 6 m wide) plate-like lignotuber occurs where the combination of environmental effects is harshest. The lignotuber develops a plate-like form following the death of the upper surface and the consequent progression of decay downwards, so that growth is mainly restricted to its periphery and under surface. The lignotuber gives rise to many generations of stems, mainly from its periphery. New roots are also formed in association with the process of lignotuber extension and hence E. botryoides mallees are an example of vegetative reproduction in the genus Eucalyptus. The probable sequence of events in the development of plate-like lignotubers is outlined diagramatically. Genetical and environmental factors that are probably involved in this development are discussed. It has not been possible to assess satisfactorily the ages of large lignotubers by C14 dating techniques because of sampling difficulties. All decayed wood samples attached to buried parts of such lignotubers so far examined have been aged at less than 200 years.