We are a research group studying what controls the distributions of species and composition of communities in forest and rangeland ecosystems. This work has become more challenging and more urgent in this era of rapid global changes. Climate change and unprecedented rates of species’ movement around the globe (biological invasions) are creating many “novel ecosystems”. We use these changes as natural experiments to understand communities, while also building capacity to predict changes in the coming decades. We use field experiments, greenhouse experiments, theory, and demographic and statistical modeling that can test hypotheses and quantify processes at different spatial and temporal scales.