His research focuses on quantitative ecology and ecophysiology, and in particular on modelling the complex responses of plants to multiple environmental factors and predicting the phenological adaptation of trees to climate changes. Investigations include long-lasting observations in permanent plots across wide alti-latitudinal ranges, manipulated experiments in nature and remote areas, assisted migration of ecotypes, and experimental designs under strictly-controlled environments. His actual projects are related to the dynamics of tree growth and reproduction at local to global scale and how the effects of climate change on forest productivity can be taken into account by the new strategies of forest management. Dr. Rossi is considered a pioneer of the intra-annual studies on wood formation in temperate and cold ecosystems and treeline ecotones, and has successfully realized several meta-analyses on the recurrent timings of tree growth across the northern hemisphere.