David M. Drew

Wood properties in a long-lived conifer reveal strong climate signals where ring-width series do not

Although tree-ring-width chronologies have been widely used for temperature reconstructions, there are many sites around the world at which there is little evidence of a clear climate signal in the ring-width chronologies. This is the case with the long-lived conifer Huon pine (Lagarostrobos franklinii (Hook. F.) Quinn), endemic to Tasmania, Australia, when the species grows at low elevation. In this study, we developed chronologies of several wood properties (e.g., tracheid radial diameter, microfibril angle) from Huon pine growing at a low-elevation site. We found that despite the absence of a climate signal in the ring-width chronologies, there were significant correlations between wood density, tracheid radial diameter and microfibril angle and temperature, stream flow and a drought index, enabling the development of robust chronologies. This novel finding suggests that chronologies based on these wood properties may have important potential for climate reconstructions from sites and species that have not yet been realized. In particular, a relatively extensive resource of ancient, low-elevation Huon pine in western Tasmania, in which climate signals have not been found using ring widths, may now be useful as part of the broader effort to reconstruct Southern Hemisphere climate.

Xylem as the main origin of stem radius changes in Eucalyptus

The state-of-the-art interpretation of stem radius changes (DRTotal) for tree water relations is based on knowledge from mostly slow growing tree species. The ratio between diurnal size fluctuations of the rigid xylem (DRXylem) and the respective fluctuations of the elastic bark (DRBark) is known to be small (<0.4) and is of importance for the localisation of water storage dynamics in stems. In this study, fast growing Eucalyptus globulus Labill. in Tasmania were investigated by point dendrometers in order to investigate tree water relations. Unexpectedly, DRXylem was found to be the main driver of DRTotal with the bark acting as a passive layer on top of the fluctuating xylem under most conditions. Accordingly, the ratio between the diurnal fluctuations of the two tissues was found to be much higher (0.6-1.6) than everything reported before. Based on simulations using a hydraulic plant model, the high tissue-specific elasticity of the Eucalyptus xylem was found to explain this atypical response and not osmotically-driven processes or species-specific flow resistances. The wide zone of secondary thickening xylem in various stages of lignification is proposed to be an important component of the high wood elasticity. The tissue acts as additional water storage like the bark and may positively affect the water transport efficiency.

Future wood properties in Australian forests: effects of temperature, rainfall and elevated CO2

ABSTRACT While focus is often placed on possible reductions in forest growth and timber volume yield under different future climates, less attention is paid to changes in wood properties, such as wood density. In this paper we explore the literature on climate effects on wood properties, with a particular focus on Australian plantations and forests. We also present results from modelling exercises, designed to explore possible growth and wood property changes in two Australian forestry regions under a hotter and wetter future, or a hotter and drier future. While the effects of different climates on tree growth and wood formation are complex and difficult to generalise, some broad tendencies can be identified. Temperature has varied effects on wood properties, but much research has shown that the density of wood is higher when formed under higher temperatures. Similarly, an elevated concentration of atmospheric CO2 (eCO2) has been found to have variable effects, but trees in eCO2 environments can produce higher density wood. The effects of water deficits are clearer: in general, trees produce higher density wood in drier environments, through a combination of narrower rings, higher proportions of latewood, and thicker walled/narrower cells. The extent to which, when other factors such as changes in transport efficiencies are taken into account, losses in wood volume under different future climates may be compensated by increases in wood density, or other changes in wood properties, needs to be clarified.