Tree-length gap-cuttings facilitate the invasion of the Tree of Heaven (Ailanthus altissima) in oak–hornbeam and submontane beech forests in South Börzsöny Mts., Hungary

The Tree of Heaven ( Ailanthus altissima ) is among the most notorious invasive tree species globally, including in Hungary. While it became widespread in ruderal habitats and lowland to hilly forests by the millenium, its expansion into oak–hornbeam and submontane forests has only begun within the last two decades. This spread has now reached converter systems, where management incorporates conservation goals, but economic objectives still prevail. The aim of this case study was to characterize the invasion of A. altissima in artificial canopy gaps of such forests in South Börzsöny Mts. (North Hungary), and to identify the key environmental and structural factors impacting its spread. The results revealed a non-monotonic invasion, suggesting that tree-length gap cuttings may have facilitated its local expansion. Remarkably, only a few seed-bearing individuals were sufficient to initiate widespread establishment across the 134-hectare study area. A. altissima was closely followed light availability, with higher abundances observed toward the center and northern parts of the gaps. Native woody recruitment emerged as an important limiting factor, indicating a competitive resistance. Additionally, Rubus fruticosus agg. played a significant role in the abundance patterns, partly by reducing browsing pressure. The species performed better in oak–hornbeam forests than in submontane beech forests, and showed higher abundance on lithomorphic soils compared to luvisols. These findings underscore the need to reassess such kind of silvicultural interventions. Our management recommendations include establishing a dense native understory prior to gap creation, preserving the shrub layer, further reducing canopy gap sizes, and implementing prevention measures before A. altissima becomes unmanageable.