Julie Messier studies the causes and consequences of trait variation and integration across biological scales, from within individuals to among communities. As an empiricist, she uses observational and experimental studies (field and lab) to uncover general principles governing patterns of phenotypic diversity. Her research falls along two main axes:

1. Understanding variation and covariation in plant traits across scales.
2. Linking plant traits to performance across environments.

Her work with DIVERSE, which examines trait variation in Canadian tree species, aligns with the first research axis. It contributes to filling an important knowledge gap in Canadian ecology: the understanding of the standing biodiversity of forests. We first need to know what diversity occurs in our Canadian forests in order to track how it changes over time with both natural and human-caused drivers change, to conserve it and to manage it adequately.