Temperature and Other Climatic Influences on Shoot Development and Growth of Eucalyptus regnans

Abstract

The growth and development of shoots of Eucalyptus regnans F. Muell. trees up to 8 m tall growing in their natural environment in central Tasmania were studied continuously for 3 years and related to climatic factors. The influences of temperature were further investigated by experiments with seedlings in a phytotron.

Height growth was practically nil in winter and greatest in summer. Throughout the year weekly rates of height growth were closely related to weekly mean maximum air temperatures, increasing from nil or slight at 10°C to peak rates at the highest temperatures experienced (25°). Substantial diameter increments were observed in all seasons and their relation to temperature was relatively weak. There was no positive relation between weekly growth in height or diameter and weekly precipitation.

Bud and shoot growth were characterized by continuity of development of all organs throughout the growing season. The youngest of the leaves and internodes which had emerged before winter from the bud resumed growth in spring, but did not reach the lengths achieved by those leaves and internodes which emerged from the bud after winter. It was only by this morphological feature that the boundaries of the annual shoot were identifiable.

In agreement with the field observations, the growth of seedlings in glasshouses was found to be slow at day/night air temperatures of 10/5°C and to increase steeply with temperatures to 24/19°.

Amongst the notable morphogenic influences associated with increasing temperatures in the glasshouses were poorer root development relative to top growth, thinner and smaller but more numerous leaves, and shorter and more numerous internodes. The elongation of individual leaves and internodes was faster but considerably less prolonged as temperatures increased.

The E. regnans seedlings tested failed to prove thermoperiodically sensitive. It is concluded that the dormancy in shoot development observed in the field during winter is due to quiescence imposed by low temperatures, and that in the Tasmanian environment the pattern of growth and development of the vegetative shoots of E. regnans is directly and predominantly controlled by air temperatures throughout the year.