Large scale plantations of exotic trees (mostly Pinus and Eucalyptus) are replacing vast areas of native environments in South America, with still poorly known consequences on local communities. This is particularly worrisome in endangered ecoregions of high biodiversity that contain endemic and endangered species. This study was aimed at assessing the effects of pine plantations on the mammal assemblages of NE Argentina, in areas where plantations are rapidly increasing. We evaluated the effects of the native forest replacement by non-native pine (Pinus sp.) plantations on the composition of the assemblages of terrestrial mammals in two forest productive landscapes. In the first study area, of approximately 5,000 km2 and located in the endangered Atlantic Forest of N Misiones province, we deployed 184 camera-trap stations in three different "treatments": 53 in continuous forest, 69 in forest fragments and 62 in tree plantations. In the second, of approximately 20,000 km2 and located in the vulnerable Southern Cone Mesopotamian Savanna ecoregion of NE Corrientes province and S Misiones, we deployed 234 camera-trap stations: 35 in grasslands without cattle, 54 in grasslands with cattle, 35 in forests without cattle, 19 in forests with cattle, 54 in pine plantations without cattle and 37 in plantations with cattle. We used NMDS and PERMANOVA to assess the effect of the treatment, the structural complexity of the vegetation, the presence of cattle (in Corrientes) and several landscape variables (cost-distance to the continuous forest in Misiones, the percentage of different environments within different radiuses, and the cost of human access as a proxy for hunting pressure) on species composition. We recorded 34 species (4735 records) in Misiones and the same number of species (4460 records) in Corrientes. Mean recording rate (a proxy of relative abundance or activity) and richness were much lower in pine plantations than in natural environments in both landscapes (e.g., mean mammal richness per station in Misiones was (X±SD) 7.54±2.65 species in continuous forest, 5.97±2.46 in fragments and 3.39±1.90 in plantations). In both landscapes mammal composition was affected by treatment, the proportion of native environments in the landscape, and human access. In Misiones, the distance to the continuous forest also had a strong effect on the compositions of the assemblage. Different management practices (e.g. pruning and thinning), the presence-absence of cattle and landscape features can partially mitigate the negative effect of tree plantations on mammal assemblages. Large areas of native environments that function as population sources and forest fragments immersed in the matrix of plantations (in Misiones) are necessary to preserve the original native mammal assemblage at the landscape level. Promoting connectivity of the native environments and improving hunting controls will also mitigate negative impacts.