Seasonal Shoot Growth of Eucalyptus spp. in the Brisbane Area of Queensland (with Notes on Shoot Growth and Litter Fall in other Areas of Australia)
R. L. Specht and Yvonne M. Brouwer
Botany Department, University of Queensland, St. Lucia, Qld. 4067.
Field data, collected at fortnightly intervals over a period of three years, show a distinctly bimodal rhythm in the shoot growth of Eucalyptus species in the Brisbane area of Queensland. Maximum growth occurs in autumn and spring; growth is reduced during summer and, apart from periods of warmer weather, virtually ceases during winter.
The bimodal growth rhythm is due to the interacting influence of unimodal curves relating monthly values for dry matter production of the leaf canopy to the respective effects of mean daily temperature, intensity of solar radiation, and available water. When the mean monthly temperature falls below 16-1SºC, most photosynthates are translocated to stems and roots: little canopy growth then occurs, thus accentuating the winter depression in shoot growth.
Shoot growth in the Brisbane region is compared with that observed in other areas of Australia. Shoot growth is minimal in plant communities dominated by: (a) arid to subhumid species of Acacia when the mean monthly temperature falls below 24-26°C; (b) Eucalyptus spp., Myoporum sp., Heterodendvum sp. and dominant heath species when the mean monthly temperature falls below 16-18°;(c) Acmena smithii (at least at Wilson's Promontory) and Leptospermum myrsinoides when the temperature falls below 13-14°;(d) Pinus radiata when the temperature falls below 10". In contrast, Nothofagus cunninghamii shows little shoot growth when the temperature rises above 16°.