Unlocking century-scale climate signals using daily stem growth and wood property responses in native Tasmanian rainforests

A project undertaken by the CSIRO Sustainable Agriculture Flagship and managed by Dr Geoff Downes

Summary

This project generated unique data describing the growth of huon pine (Lagarostrobos franklinii) and celery-top pine (Phyllocladus aspleniifolius) at two contrasting Tasmanian sites.  Growth was monitored at 15 min intervals across a range of trees for 2-3 years.  Wood property variation was measured at 25 micron intervals over the past 150+ years.
Despite high rainfall, tree ring width measurements showed that huon pine was surprisingly sensitive to water deficits. Wood properties were found to reveal a better, more robust climate signal than ring width.  Dendrometer measurements of short-term growth responses supported these findings and are the subject of ongoing studies. 
The findings of this project have been expanded in an ARC project led by Dr Patrick Baker, University of Melbourne, and has allowed us (Dr David Drew, CSIRO) to continue the dendrometer monitoring of these sites while establishing others in New Zealand and Argentina.  The results suggest that useful climate data may be available from a much wider range of sites across Tasmania, if wood property variation is used rather than annual ring width.

Project description.

Tree ring records are an important climate proxy, used to interpret current climate trends in terms of past climate variation. These records are based on measurements of the width of annual tree growth rings. Typically, these tree rings are produced during a relatively small portion of the year and annual width can be affected by interactions between many factors including temperature, rainfall, radiation, CO2 concentration and soil type.
Tasmania contains a unique set of long-lived tree species; unique in terms of life-span as well as global location.  Huon pine is well known as a species that can live for several millennia.  Lesser known species such as celery top pine and king billy pine can live for many centuries.  Their science value has been under-utilised. 
In a collaboration between the CSIRO Sustainable Agricultural Flagship, Monash University and the University of Tasmania, this project sought to understand the biology that under-pins the annual growth of these trees by measuring changes in stem radius and important weather variables at 15 minute intervals over the last 3 ½ years to better inform the relationship between climate and tree growth.  This work is ongoing. Research on other forest species has shown that annual growth is affected by both the daily rate at which trees grow and the number of growing days per year.  Two sites were instrumented; a low elevation “control” site near Queenstown, Tasmania and a high-elevation (975m ASL) site at Mt Read.  Mt Read contains some of the oldest known living Huon pine in Tasmania and is known to be useful in dendroclimatological applications.  As an additional comparison, open and grove trees of Callitris intratropica were also studied in similar fashion at a site near Darwin in the Northern Territory.

In addition to understanding patterns of growth, the study aimed to determine the extent to which annual or decadal variation in wood properties can be used to infer past-climate variation.  Wood physical/chemical properties may contain a clearer or different signal than ring width alone, but this has been little studied, largely owing to the difficulty of obtaining suitable measurements.  Over the past two decades CSIRO has developed the state-of-the-art SilviScan technology that can measure, at high-spatial resolution, the variability in a range of wood properties.  In addition to wood density, changes in the size of wood cells, thickness of their walls and the orientation of cell wall crystalline cellulose (MFA) can now be determined.  These have been shown in plantation species to be sensitive to changes in growth rate and patterns of growth.  This project harnessed these technologies to explore this little-studied area of science. 
The work yielded large amounts of detailed information describing tree growth and wood variation in these slow-growing trees.   In summary, this project provided a better understanding of the nature of historic climate information contained in tree rings by improving our understanding of tree growth and physiological responses to varying environmental conditions.  It demonstrated the potential of wood property variation as a better climate proxy (Figure 2) than the more commonly used annual ring width.

The two sites involved in this study will continue to be monitored as part of a broader study led by Dr Patrick Baker, University of Melbourne.  As a consequence of the success of this project, the study has been broadened with the support of ARC funding to address more years and more sites.  Additional sites have been instrumented in New Zealand and Argentina.

Manuscripts published or in preparation
  • Drew D., Richards A., Downes G.M., Baker P. and Cook E.R. (2011) The development of seasonal tree water deficit in Callitris intratropica. Tree Physiology 31(9), 953-964 doi: 10.1093/treephys/tpr031
  • Allen K., Baker P., Drew D.M., Downes G.M. and Evans R. (2012) Investigating relationships between ring width, density and cell properties for two long-lived Southern Hemisphere conifers. Dendrochronologia 30, 161177
  • Drew D.M., Allen K., Evans R., Downes G.M., Evans R., Baker P.J. and Battaglia M. (2013) Wood properties in a long-lived conifer reveal strong climate signals where ring-width series do not. Tree Physiology 33, 37–47 doi:10.1093/treephys/tps111
  • Allen, K.J., Drew, D.M., Downes, G.M., Evans, R., Cook, E.R., Battaglia, M., Baker, P.J. (2013) A strong regional temperature signal in low elevation Huon pine. J. Quat. Sci. (in press)
  • Drew DM, Richards AE, Cook GD Downes GM, Gill W, Baker P. (2012) Tree ring formation in young Callitris intratropica is insensitive to wet years (in preparation)


Figure 1. Huon pine site at Lake Johnston, Mt Read, Tasmania.  Inset show scientist David Drew mounting a high-precision dendrometer on a moss-covered tree at the site.

Figure 2. Chronologies based on wood properties from the Queenstown site gave good  spatial correlations with temperature across South-eastern Australia.  Top row: Tree-ring width (RW); second row microfibril angle (MFA); third row tracheid radial diameter (TRD); bottom: Mt Read. Left column is 1901 - 2009, middle column is1901 - 1954 and right column is 1955 -2009. Areas outlined in black include those grid points for which the correlation value of the chronology with mean temperature was more extreme than 97.5% of all  correlations between the synthetic series and mean temperature. (Allen et al 2013)

(Click on thumbnail image to enlarge)