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The Monitor - Issue 5 - Considering canopy dynamics from more than one angle

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Raised litter traps underneath 7-year-old E. gunni plantation­, south-east Queensland

Leaf fall and total monthly rainfall in 7-year-old subtropical eucalypt plantations, south-east Queensland. Error bars show variation between species. (March rainfall is incomplete: only for week three onwards)

HemiView image of E. gunni plantation (stand has been pruned and thinned)

In forests, the exchange of carbon and water between the atmosphere and the soil is driven by canopy leaf area, its turnover and its distribution in space and time.  Mila Bristow, a postdoctoral research scientist, and her Queensland colleagues have been investigating these factors and related forest processes such as crown architecture and decomposition in subtropical plantations near Gympie in Queensland.

An important part of transferring our understanding of temperate and Mediterranean forest systems to the tropics and subtropics is to understand the processes that allow us to establish parameters and apply predictive models like CABALA and 3PG. There are differences in absolute values, as well as seasonality, of temperature and rainfall in these northern environments compared with the better understood southern environments. This means that plant architectural characteristics as well as processes such as foliage turnover and decomposition are likely to be quite different.

We have been tracking monthly litter fall and decomposition and comparing this to climatic conditions in Eucalyptus dunnii, E. cloeziana and Corymbia citriodora subsp. variegata plantations near Gympie in southern Queensland.  Analyses from the initial six months of this study indicate that monthly rainfall is driving canopy dynamics as less leaf litter falls in the months in which there is greater total rainfall.

To complement our measures of leaf litter fall, we are examining hemispherical canopy photos with Greg Unwin from the University of Tasmania. Greg’s photos allow us to describe the light environment in these eucalypt plantations with digital estimation and modelling of leaf area index (LAI), radiation load, canopy and subcanopy light description. In March 2008 HemiView data confirmed that C. citriodora subsp. variegata has an LAI less than half that of E. dunnii. Measurements were repeated in December, and will be taken again in March 2009. The results will help us to address questions about efficiency of resource capture and allocation for these species.

Dr Mila Bristow

Postdoctoral Research Fellow, Project 1.4
Tel: 07 5482 0865
Mila.Bristow@dpi.qld.gov.au

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