PS PhD Exit Seminar: Tree structure and carbon cycling in a tropical rainforest under long-term drought

Abstract: Tropical forests are highly productive and biodiverse, exchanging more carbon with the atmosphere than any other terrestrial ecosystem and representing the apex of taxonomic and structural diversity on land. However, their high productivity is sensitive to climate, which for many tropical regions, and especially the Amazon, is predicted to become more extreme this century, with stronger and more frequent drought events likely to occur. Extreme drought has been shown to alter net carbon gain in Amazon forests, causing a decline or sometimes a reversal in the natural carbon sink. The long-term effects of increasing drought exposure are poorly understood, but are thought likely to substantially weaken or reverse the future Amazon carbon sink, with impacts at the scale of the global carbon cycle. Our understanding of the response by any forest to drought is hampered by observational opportunity. One way to resolve this is to manipulate water availability experimentally at large scale. I use one such 'ecosystem-scale' (1 ha) rainfall manipulation experiment in Amazon rainforest, combining new structural, ecological and ecophysiological measurements on a forest that has experienced long-term experimental drought, over twenty years. For my PhD, I analysed new structural measurements of the forest, obtained using terrestrial laser scanning (TLS) to quantify detailed tree and forest structural metrics. I complemented this analysis with a suite of new physiological measurements focused on using these novel structural datasets to estimate and scale woody tissue carbon dioxide effluxes from twig to forest. Finally, I used these structural data to help me analyse tree growth and changes in biomass over the twenty-year period of experimentally-imposed drought.

Biography: Ingrid is from southern California, and did her undergraduate degree in Biochemistry at the University of California, Los Angeles. In her final year as an undergraduate she took an elective course in terrestrial biogeochemistry given by Prof. Ulli Seibt, which inspired her to begin her journey into research. She did her Masters at the University of São Paulo, Ribeirão Preto, looking at leaf anatomical changes in response to drought. For her PhD, she shifted her focus from leaf to woody tissue, aiming to better understand the woody structure of tropical rainforests during drought, focusing on the efflux of CO2 from woody tissue, tree growth and biomass. She began her PhD with Dr. Patrick Meir at ANU in 2018.