Named in honor of one of the founders of our department, the Melnick Award recognizes outstanding dissertation work and other departmental activities. Using an uncommonly wide array of techniques, Sian’s thesis overturned a long-held belief. Prior to her work, nitrogen-fixing trees were thought to be a boon to climate mitigation. The idea was that their rapid growth and ability to fertilize the surrounding soil led to greater carbon storage in plants. In her first chapter, an elegant bit of mathematical theory, Sian showed that another consequence of nitrogen fixation – emissions of nitrous oxide (a powerful greenhouse gas) from the soil – could counteract the carbon storage effect. Her theory predicted that nitrogen-fixing trees could actually be worse for climate (compared to non-fixing trees), and under what conditions. Sian’s second chapter used a meta-analysis to show that the nitrous oxide effect predicted by her theory was borne out across a wide range of sites. Her third chapter combined painstaking, rigorous experimental fieldwork, lab work, statistical modeling, and an extended theoretical model to show that her theoretical predictions were correct in Black Rock Forest. These three chapters have changed the way we think about nitrogen-fixing trees and climate. Sian’s fourth chapter developed, tested, and validated a new version of the nitrogen cycle in the land model of NOAA’s earth system/climate model. This herculean effort will pay off for decades, given the centrality of NOAA’s model for climate science and policy.

In addition to her outstanding research, Sian was a phenomenal teacher, an excellent departmental citizen, and a strong voice for diversity. She is now revamping the nitrogen cycle in another earth system model as a postdoc at the Canadian Centre for Climate Modeling and Analysis.

Congratulations Sian!