Native perennials’ germination and growth response to decomposing tree of heaven ( <i>Ailanthus altissima</i> ) stems

Abstract Tree of heaven [ Ailanthus altissima (Mill.) Swingle] is an invasive tree that inhibits regeneration of forests. Management of forests invaded by A. altissima often includes chemically treating it and leaving dead boles behind. Verticillium wilt ( Verticillium nonalfalfae ) infects some populations of A. altissima , leading to localized mortality. Areas with population-wide A. altissima mortality may increase as this disease spreads or is used as a biocontrol agent. Ailanthus altissima has documented allelopathic compounds; stems left to decompose may result in soil legacy effects that negatively impact native plant restoration. The goal of this study was to determine whether soil under decomposing A. altissima wood has negative impacts on native perennial plant germination and growth. Ailanthus altissima was grown in a garden for 4 yr, basally cut, and treated with herbicide. The stems were sectioned and stacked into piles to decompose for 18 mo on grass and garden fabric, after which the wood was mulched. Soil from cores taken under each woodpile was added over potting media in pots in which seeds of three native perennials (purple coneflower [ Echinacea purpurea (L.) Moench], dogbane ( Apocynum cannabinum L.), and false nettle [ Boehmeria cylindrica (L.) Sw.]) were planted. Seeds for half the pots were covered with potting media or mulch, respectively. The plants were grown under high- and low-light conditions in a greenhouse for 3 mo. Germinations were tallied, and dry shoot biomass was determined. Pots with woodpile soil had lower germination and biomass production for two of the native species, but mulch reduced the impact. Biomass was greater for all soil treatments with mulch added compared with treatments with no mulch. Plants growing in soil under garden fabric had germination values similar to plants in woodpile soil. This study reveals that soil under decomposing A. altissima wood is likely to negatively impact germination and growth of some newly seeded species for at least 18 mo.