UC Berkeley

The carbon and water cycles in global terrestrial ecosystems hold significant importance due to their unique influence on biosphere-climate interactions. In my dissertation, I adopted a data-driven method to deepen our understanding of these global cycles. In the first chapter, I enhanced the AmeriFlux data product, resulting in the creation of a publicly accessible dataset named ONEFlux BETA. This process entailed the downscaling, gap-filling, and partitioning of flux observations from 63 distinct flux tower sites. Subsequent chapters employed this dataset, paired with other global data such as FLUXNET 2015, MODIS observations of phenology, and remote sensing observations of vegetation indices, to examine ecosystem autumn phenology and water use efficiency. Specifically, in the second chapter, I investigated the connection between photosynthesis during the growth season and end-of-season (EOS) senescence across various ecosystems, using data from 40 flux tower sites. This analysis challenged existing theories by revealing no significant negative correlation between growing season photosynthesis and EOS. On the contrary, more productive growth seasons are often associated with a delayed EOS in diverse ecosystems. The third chapter shifted the focus to water use efficiency (WUE) and its responses to water stress, factoring in variables such as vapor pressure deficit (VPD) and soil moisture. The results indicated a more consistent response to VPD across most sites. My dissertation showcases a data-driven approach to understanding ecosystem dynamics, with a particular emphasis on the carbon and water cycles of terrestrial ecosystems, harnessing data from global flux tower sites.