Community assembly is a branch of ecology that looks at how communities are assembled as they follow trajectories through time. A trajectory is controlled by biotic and abiotic constraints (filters) that act at multiple scales. From a total species pool, environmental and dispersal constraints control which species enter an ecological species pool. Within this pool, internal dynamics determine which of these species becomes part of the extant community. Environmental filters act by removing species that lack specific traits. Thus, traits are filtered, and with them, species. In this paper, we present the basic ecological theory of community assembly and address how it can be used in conjunction with a trait-based approach to understand and possibly predict how weed community structure changes in response to imposed filters such as tillage or crop rotation. Weed ecologists have struggled with the need to place our practical knowledge of agriculture and weeds into a broader theory, and there have been many calls to integrate ecology with agronomy and weed science. Community assembly might be one way to do so.
