Abstract Plant invasions are strongly shaped by cultural histories of introduction and cultivation. However, positive spatial associations between non-native plant occurrences and urban areas or transportation corridors are often interpreted as evidence that cities act as primary invasion foci. Such pattern-based inference risks overlooking historically important propagule sources outside urban environments. The central hypothesis addressed here is that historical non-urban plantings can function as long-term, spatially diffuse invasion foci that substantially shape contemporary distribution patterns. Using Ailanthus altissima (tree of heaven) as a global case study, this study aims to reconstruct the purposes, habitat types, spatial distribution, and temporal dynamics of rural plantings based on nineteenth- and twentieth-century sources. Since 1804, Ailanthus was widely planted outside settlements for timber and firewood supply, erosion control, silk production, land reclamation, and other purposes. Plantings occurred across diverse habitat types, including agricultural land, deforested areas, dry grasslands, rocky slopes, and transportation corridors—many of which are now recognized as conservation priorities. Vigorous clonal growth and seed production, combined with subsequent land-use change and disturbance regimes, likely enabled many rural plantings to persist and function as long-term propagule sources. As a result, present-day distribution patterns may resemble outward spread from cities, leading to overestimation of dispersal distances, invasion rates, and the relative importance of urban areas as invasion sources. Accounting explicitly for historical planting legacies is therefore essential for accurately identifying invasion foci and interpreting urban–rural gradients of widely cultivated non-native species, thereby improving the evidence base for proportionate and spatially targeted management decisions.
Ingo Kowarik (Wed,) studied this question.