Plants, rooted in sedentary lifestyles, have evolved remarkable abilities to adapt to environmental changes. Yet, the molecular basis of these adaptive processes remains largely unknown. My research employs systems genetics approaches to understand the flow of biological information that underlies complex traits in trees. By utilizing a broad array of experimental and statistical methods, I integrate genetic, epigenetic, transcriptomic and metabolomic data in a natural population of Populus nigra which exhibits variation in adaptive traits such as biomass, phenology, leaf morphology, disease resistance, and the production of specialized metabolites. This work offers valuable insights into how natural tree populations adapt, a key to their survival in an ever-changing landscape, especially in the context of global climate change.