Why do we have amber forests? The relationship between resin production and amber deposits

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Plants produce resins which are a complex mixture of chemicals, but generally resins have a volatile and a non-volatile component, and it is this mixture of chemical compounds in the components that is often unique to a species. Plant resins are generally for defensive purposes, such as protection from herbivores or pathogens, or to seal cracks and other damage, although it is not clear why all resinous plants produce these exudates. Amber is fossilised resin, where it is thought that the volatile component is lost, and polymerization and other chemical changes occurred in the non-volatile fraction. Amber is rare throughout the rock record, but there are three instances where numerous, often large deposits occur worldwide, and are called amber bursts. These occur in the Eocene to Miocene (55-17 Million years ago, Mya), Early to mid-Cretaceous (145-80 Mya), and Late Triassic (c. 230 Mya). Why amber should occur at these times in such large quantities and in so many localities worldwide is not understood. Why did the resin producing species produce so much resin that became preserved as amber bursts at these times? There are several explanations, such as the evolution of new wood-boring insects or heightened fire risk but there has been no substantiating of these ideas to date. This project aims to empirically test ideas for resin production in the modern world and evaluates whether these reasons could be the causes of the amber bursts found in the rock record, and to discover whether there are distinctive chemical signatures in the modern resins that point to one particular reason for a resin outpouring in the past. The focus of this project is on the most resinous conifers today; the Araucariaceae of New Zealand and New Caledonia. By combining field observations and replicate tree experimentation it will test if differing chemical signatures in modern resins released in response to different causes can be detected and used to tell such resins apart. Such chemical differences would then be prospected for in older resins and ambers from New Zealand, which are thought to have also been produced by araucarian species. The resins and ambers will be chemically compared through a range of methods including standard pyrolysis-gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy identifying the resin chemistry to the new ToF-SIMS method testing the chemical homogeneity of resins. This is the first study to combine the testing of multiple ecological reasons for resin production in the natural world and through replicate experiments, using a range of techniques and expertise. As a result of this project, our understanding of the ecology of amber forests and why they produced their resins will be significantly improved.