<p>Forest communities are experiencing an increasing rate of disturbance that affects their long-term stability. Functional trait composition and diversity play a crucial role in forest functioning, and hence can influence temporal stability, with consequences on resilience. In this study, we examined the role of functional trait composition and diversity, along with climate and vegetation structure variables, in determining the stability of forests in Catalonia (Northeastern Spain). We used functional trait and vegetation structure data from the ecological forest inventory of Catalonia, and calculated the temporal stability of tree productivity across 548 plots over a 20-year period (2000–2019) using NDVI data from the MODIS sensor on the TERRA satellite. Results showed that water availability and thermal amplitude had the strongest effects on stability. The community-weighted mean (CWM) of wood density (WD) positively influenced forest stability, whereas the CWM of leaf mass per area (LMA) and leaf biomass-to-sapwood area ratio (B_L:A_S) had a negative effect. Additionally, functional richness and dispersion, calculated using all studied traits, positively influenced stability. These findings suggest that the presence of both stress-tolerant (conservative) species and stress-intolerant (acquisitive) species enhances long-term forest stability, and, more generally, that functionally diverse forests are more stable.</p>