Plastic and adaptive response to weather events: a pilot study in a maritime pine tree ring

This work proposes a novel approach to describing intraring wood density characteristics as functions of annual weather events. This approach was tested using three different maritime pine clonal experiments, in which X-ray microdensitometry has revealed conspicuous within-ring patterns affecting most of the trees in 1996. This pattern has been interpreted as the variation of tree response to weather-controlled changes of water balance during the 1996 growing season. The level of tree response was estimated using an original norm of reaction obtained from the microdensity profiles. A 1996 site drought index profile was synchronized with the 1996 microdensity profile by pairing conspicuous points of abrupt change in both profiles (breakpoints). Regression of density breakpoints on drought breakpoints describes the norm of reaction of radial increment to water availability, and the plasticity of radial increment to changes in soil moisture is described by the slope of the regression. The slope showed moderate levels of genetic control that depended on the site and could potentially be used as criteria for the evaluation of tree adaptation to weather.