Seed longevity and dormancy state in an invasive tree species: Ailanthus altissima (Simaroubaceae)1

Abstract

Successional tree species often form soil seedbanks, suggesting that extended seed dormancy may also facilitate regeneration in nonnative species. We examined seed dormancy in Ailanthus altissima, which is currently spreading into long-established forests of Europe and eastern North America. Ailanthus seeds were sewn into replicated nylon mesh bags and buried in 10 second-growth stands in southeast Ohio, USA. North- and south-facing slopes were included as a coarse-grained test for environmental control. Bags were recovered at 2-mo intervals and seeds were tested for viability and germination. Fifty percent of Ailanthus seeds survived the full length of the study (24 mo) after an initial phase of partial germination (51–79% of viable seeds). Remaining seeds returned to a state of induced dormancy, allowing a second flush of germination (3–28%) after 18 mo. After the first 5 mo no further decline in seed number was observed, suggesting persistence in the soil well beyond the 2-yr length of this study. No slope-aspect effect was observed. Long-term seed dormancy potentially facilitates Ailanthus invasion by buffering against extended canopy closure or allowing passive dispersal with movement of soil. Complete eradication of a population will depend on elimination of the soil seed bank, which may require many years. Management should avoid creating canopy openings near existing populations with the goal of suppressing sexual reproduction and seedling establishment.