Woody plant encroachment (WPE) into grass- and dry-lands is resulting in type conversions of ecoregions that are of unique ecologic, cultural, and economic importance. In North America rates of WPE varies by ecoregion but ranges from 0.1% to 2.3% changes in cover per year. WPE provides a system to investigate the degree in which the establishment of new plant species in an environment is driven by the traits of the organisms or if they are passengers of change. The causes of WPE vary between ecoregions but are generally driven by alterations in disturbance regimes (e.g. fire and grazing) or due to anthropogenic driven climate change. Hybridization with native congeners in the area or local adaptation may also play an important role in range expansion of some woody plants. WPE can change the species interactions and the ecosystem functions of the encroached areas and can result in the loss of these important ecosystems. This session gathers researchers studying the different aspects of encroachment, scaling from organismal- to landscape-level questions. Current insights of individual plant physiology, community interactions, and management will be discussed in the light of climate change to ask whether plants are drivers or passengers of WPE.