Abstract: WK-recursive networks constitute a class of interconnection network topologies for massively parallel systems, purposely devised by the authors. These networks are constructed in a recursive fashion to achieve a fully scalable structure. Starting from the peculiar structure of these networks, this paper describes a tree-based communication model, which allows one to handle, in a very simple and efficient way, several forms of collective communications, such as multicasting and broadcasting. Because efficient collective communications are closely associated with the structure of the multiple paths concurrently engaged in the network, this communication model, directly tied to the WK interconnection network topologies, represents a good solution for designing collective communication mechanisms.