Scaling tropical giants: Understanding how tree height influences the function of the world tallest tropical rainforest species

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Project Background:The immense quantities of carbon stored in tropical forests is strongly influenced by a relatively small number of very large trees.On average trees with a diameter >70cm contain between 25-45% of the stored carbon, but represent <4% of the number of trees in tropical forests. 2019 saw a ground-breaking discovery of trees in the Amazon exceeding 80m tall, ~30m taller than other trees previously recorded in Amazonia and more similar in size to the dipterocarp trees found in Borneo, the family containing the largest known angiosperm tree in the world, standing at >100m tall. However, the persistence of these tropical giants under future hotter, drier tropical climates remains uncertain.The impact of the higher resistances associated with getting water to the top of tall trees, which is generated by longer paths from root-to-leaf and greater impacts of gravity, results in taller trees being likely to be disproportionately more vulnerable to climate change, than smaller trees. Currently however, we lack a fundamental understanding of how tall trees adapt their water-transport systems to enable the transport of water over such large distances and whether they can indeed adapt their water transport systems to fully compensate for the increased hydraulic stresses associated with being so tall. Improved understanding will allow us to better predict the climatic tolerance thresholds of large tropical trees.Project Aims and Methods:Aim: Address a critical science gap regarding how the water transport systems of tall tropical trees adapt to allow themselves to reach heights in excess of 80 meters.Specific Objective:Evaluate how key plant traits change with height in the world's largest tropical speciesEvaluate if the changes in structure and function make larger trees more vulnerable to changes in climateThese objectives will be met through extensive field campaigns in Bornean tropical rainforest, with the option to also sites go to sites in the Brazilian Amazon, housing the recently discovered giant Amazonian tropical tree species Dinizia excelsa.These objectives are however broad and specifics of how they can be addressed will be determined through the candidate co-designing a cutting-edge field research programme with the supervisory team, to specify focal research questions, what to measure and how to measure it. As this studentship will compliment an existing NERC-funded research project, it involves joining a team of 15 world-renowned scientists, with specialisms ranging from plant hydraulics, plant anatomy, tree architecture, tropical forest dynamics and vegetation modelling. This provides the candidate with a breath of research specialism to draw upon, when designing their research.