These data were collected to explore the capacity of <i>Alnus alnobetula</i> (green alder) shrub patches to modify the habitat and composition of the local plant community at the taiga-tundra ecotone near Trail Valley Creek Research Station in the Northwest Territories. To do this we selected ten sites on south facing slopes with both alder shrub patches and adjacent shrub-free tundra and established quadrats in each habitat and across topographic positions. Within each of these quadrats we selected two sub-quadrats for vegetation community composition and birch height observations. We also measured a suite of environmental variables within 50 cm of each larger quadrat. For detailed description of methods see Wallace and Baltzer (2019), https://doi.org/10.1007/s10021-019-00435-0.