Abstract : Despite the high quality reached by today's CG tree generators, there exists no realistic model for generating the appearance of bark: simple texture maps are generally used, showing obvious flaws if the tree is not entirely painted by an artist. Beyond modeling the appearance of bark, difficulty lies in adapting the bark features to the age of each branch, ensuring continuity between adjacent parts of the tree, and possibly ensuring continuity through time. We propose a model of bark generation which produces either geometry or texture, and is dedicated to the widespread family of fracture-based bark. Given that the tree growth is mostly on its circumference, we consider circular strips of bark on which fractures can appear, propagate these fractures to the other strips, and enlarge them with time. Our semi-empirical model runs in interactive time, and allows automatic or influenced bark generation with parameters that are intuitive for the artist. Moreover we can simulate many different instances of the same bark family. In the paper, our generated bark is compared (favourably) to real bark.