Trees outside forests constitute a prominent feature of either agricultural lands or built-up areas that was overlooked for a long time. Their benefits and services are numerous and now increasingly acknowledged, but they can also provide disservices, especially in the context of global changes. While the number of paddock trees tended to decrease in long-standing industrialized countries because of mechanisation of agriculture and urban growth, the number of ornamental trees has strongly increased. For instance, French households buy and plant 50 millions of trees and shrubs every year (roughly as many as foresters plant trees). It is well documented that intensification of ornamental plant trade has promoted biological invasions through inter- and intra-continental accidental transport of exotic species. Moreover, cities with their street, park and garden trees constitute a common entry point where urban heat islands can facilitate the establishment. In Europe, in addition to the increase in the number of alien species, there is an increase in spread rates over time, especially for species arrived after 1990. The box tree moth is a good example of the role of intra-continental trade in rapid expansion. Lastly, structural changes in horticultural industry and changes in household demand have also affected landscape connectivity for both alien and native forest pest species, but quantification remains a difficult task. We addressed this issue using the pine processionary moth as a model species. Its larval colonies are readily detectable in the field and it is expanding northward across both forest and non forest lands because of climate warming. We set up a multidisciplinary approach including spatial modelling, flight mill experiments and landscape genetics in order to assess the role of trees outside forests in its range expansion.