From desert to rainforest, sapwood width is similar in the widespread conifer Callitris columellaris
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The process that transforms conductive sapwood to non-conductive heartwood in trees is poorly understood. Here, we use natural variation in climate to examine the environmental control of sapwood width in a widespread conifer species. We hypothesised that if sapwood width is linked to transpirational load, there would be a positive association between sapwood width, and continental gradients in mean annual rainfall, whereas age-related conversion to heartwood would be revealed from estimates of the age of the inner-most sapwood ring. Using the widespread Australian conifer Callitris columellaris we took cores from trees at 85 sites spanning a range of 168–2,117 mm in mean annual rainfall, and 14–28 °C in mean annual temperature. We found that sapwood width was remarkably similar throughout the species range, being only slightly lower in the tropics than the arid or temperate zone. There was a weak negative relationship between sapwood width and mean annual rainfall, which is in the opposite direction expected from transpirational control of sapwood width. Sapwood growth rings were wider, but there were fewer of them in the tropics than elsewhere, indicating conversion to heartwood occurred earlier here. Together with an earlier finding that tracheid diameter was largest in the tropics, our results show that differences amongst climate zones more strongly influence the hydraulic properties of sapwood than its amount.
KeywordsClimate Rainfall Temperature Tracheid diameter
We thank Scott Nichols, Marj King, Lachie McCaw, Pauline Grierson, Alison O’Donnell, Kim Whitford, Philip Moser, Diane Prior, Sharyn Yelverton, Herman Mouthaan, Clancy Bowman, Ian Radford, Richard Fairman, Chris Weston, Kathy Allen, Quan Hua, Mick Cotter, Ian Kealley, Rigel Jensen, Mike Lawes, Dave Lindner, Russell Willis and Adrienne Williams for field assistance. We are grateful to the Northern Territory Parks and Wildlife Service, Kakadu National Park, NSW State Forests, NSW Department of Environment and Climate Change, Queensland Department of Environment and Resource Management, SA Department of Environment and Heritage, WA Department of Environment and Conservation, Victorian Department of Sustainability and Environment, Anindilyakwa Land Council, Northern Land Council, Tiwi College, the Arid Recovery Reserve, the Australian Wildlife Conservancy, and many private landholders for help with site selection, and permission to sample on their land. We also thank Grant Williamson for sourcing the potential evapotranspiration data. This project was funded by Commonwealth Environment Research Facilities grant B0016193.
Conflict of interest
The authors declare that they have no conflict of interest.
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