Successional ecology requires general theories for synthesis and forecasting. While site-specific idiosyncrasies have been demonstrated in many recent studies and across-site variation is increasingly being appreciated, we still need to find characteristics of succession that are invariant across sites or that vary predictably along major environmental or anthropogenic gradients (e.g., rainfall and land use history). The metabolic scaling theory, though based on a few assumptions, provides a simple and elegant model that can be used to examine shifts in the size frequency distribution of tree communities after disturbance and compare scaling parameters across multiple sites. The process of competitive (a)symmetry is expected to drive similar successional patterns of tree size variation across a wide range of tropical forests, but the rate at which size distributions become more unequal may depend on the nature of the most limiting resource(s). Using datasets from multiple 2ndFor sites and modifying a modelling framework developed by Niklas et al. (2003), we quantify successional trajectories in term of tree-size structure and show how these trajectories change along a wide rainfall gradient. We also outline key statistical challenges and potential ways forward in terms of data collection and modelling.