The vast grass-covered region of the Rio de la Plata has not been the exclusive territory of cattle and "gauchos", those mythic cowboys of the Pampas. This article tries to enlighten an unknown aspect of the Uruguayan society between the 18 ^th and the 19 ^th century, the existence of human groups living on the exploitation of the very scarce wood-resources of the Montevideo region. The analysis of the conflicts about those resources, in a historical bio geographic perspective, enables to set out some assumptions about the social and spatial place of forest galleries of this region around 1800. These marginal vegetal formations show peculiar territorial dynamics: being fundamental resources for the breeders and farmers of the prairie, their conflicting use would have led to an alteration of the spatial organization of rural activities.