Understanding the traits mediating species' responses to climate change is a cornerstone for predicting future community composition and ecosystem function. Although species' eco-physiological properties determine their response to environmental change, most trait-based studies focus on a small subset of easily-measured morphological traits as proxies for physiology. This choice may limit our ability to predict the impacts of climate change on species' demography, and obscure the underlying mechanisms. We conducted a transplantation experiment along a 1000 m Alpine elevation gradient to quantify the degree to which plant demographic responses to climate were predicted by eco-physiological performance versus common morphological traits. Although physiological measurements revealed that warming favored species with a conservative water use strategy, the predictive power of physiological traits did not exceed that of morphological traits. Our results show that while easily-measured morphological traits can successfully predict demographic responses to climate, eco-physiological approaches are needed to understand mechanism.