This book presents a systematic study of driving forces of plant community assembly in variable environment, using mathematical modelling tools and dynamical systems theory. Understanding plant community assemble in variable environment is a central tenet in ecological theory and underpinning the study of plant-climate interactions. Plant community in variable environment is basically regulated by two opposing forces: competition and facilitation. Main topic of the book includes quantification and quantitative analyses of these forces. It demonstrates and quantifies how these two forces interact in variable environment for shaping plant community diversity. It also discusses the roles of potential process-controlling factors and its potential consequences.