The aim of the present work is to offer new data for discussion on the structural characters induced by the tree covering in grassland communities. Particular emphasis is given to the heterogeneity caused by the location (canopy understory, canopy edge and open grassland) and orientation of the plots; the set of both these parameters indicates the global degree of heterogeneity. The overall development of the work is based on a hierarchical perspective, integrating small units into others of higher rank. Reference is also made to distribution models as a function of diversity, which is obligatory since such models point to the peculiarities masked by the commonest norm.