Aim Climatic equilibrium is a foundational principle in ecological theory and models used in conservation, but has been challenged by growing evidence of disequilibrium, particularly for long‐lived, sessile organisms like trees. Here, we calculated range filling for North American trees to detect the degree to which trees are filling their potential climatic niches, and to assess climatic and non‐climatic drivers of underfilling. Location North America (22°N–72°N). Taxon Trees and shrubs. Methods We modelled the potential ranges of 447 North American tree and shrub species with species distribution models using bioclimatic variables, and calculated the occupied proportion of each potential range. Results were compared to a null model using simulated ranges generated by a spreading‐dye algorithm. We further used range shape ratios (latitude/longitude) to detect the drivers of disequilibrium. Results The potential ranges of North American trees and shrubs are broadly underfilled (mean = 48%). Furthermore, range filling is positively correlated with geographic range size. Large‐ranged species have higher range filling than the null model, and shape ratios indicative of climatic restrictions. Small‐ranged species showed a stronger influence of dispersal limitation. Main conclusions Climate explains only about half of tree species' ranges, and the signal of climatic equilibrium increases with range size. Small‐range species show high levels of climatic disequilibrium, which is likely be driven by combinations of dispersal lags, and undetected environmental factors or biotic interactions. These results highlight the importance of conserving small‐ranged species and the difficulty of forecasting how their distributions will shift in the coming centuries.

Models that are both spatially and temporally dynamic are needed to forecast where and when non-native pests and pathogens are likely to spread, to provide advance information for natural resource managers. The potential US range of the invasive spotted lanternfly (SLF, Lycorma delicatula) has been modeled, but until now, when it could reach the West Coast’s multi-billion-dollar fruit industry has been unknown. We used process-based modeling to forecast the spread of SLF assuming no treatments to control populations occur. We found that SLF has a low probability of first reaching the grape-producing counties of California by 2027 and a high probability by 2033. Our study demonstrates the importance of spatio-temporal modeling for predicting the spread of invasive species to serve as an early alert for growers and other decision makers to prepare for impending risks of SLF invasion. It also provides a baseline for comparing future control options.