Effects of prescribed fire and stem-injection herbicide on Ailanthus altissima demographics and survival

Abstract

Ailanthus altissima ((Mill.) Swingle, tree-of-heaven, Chinese sumac, stink tree) is a nonnative invasive tree that is common throughout much of the eastern United States. It can invade and expand dramatically when forests are disturbed. Anecdotal evidence suggests that fire might facilitate its spread, but the relationship between fire and this prolific invasive tree is poorly understood. To better understand the impacts of fire on Ailanthus, we conducted a study at Tar Hollow State Forest in southeastern Ohio, USA where Ailanthus is widely distributed. Our objective was to quantify the direct effects of prescribed fire on the demography of Ailanthus populations, with and without the pre-burn application of the stem-injected herbicide, imazapyr. We quantified demographic attributes (survival, density, and sprouting) of Ailanthus germinants, seedlings, saplings, and trees in a field experiment with four treatment combinations: (1) no fire and no herbicide, (2) herbicide, (3) fire, and (4) herbicide plus fire. Ailanthus stems >3 cm dbh were stem-injected with the herbicide, imazapyr in late summer to early fall followed by prescribed fire in April. We determined that herbicide plus prescribed burn treatment was highly effective in killing large saplings and trees, with no resprouting evident after four growing seasons. In the season immediately after the burn with and without herbicide treatment, small Ailanthus sapling and seedling abundance increased, but did not persist. Over time, Ailanthus germinants and sprouts from top-killed stems were poor competitors with faster-growing post-fire woody regeneration as forest floor shading increased. In addition, the late growing season application of imazapyr was highly effective in killing Ailanthus and subsequent sprouts. This study, the first to quantify the direct effects of fire on Ailanthus, demonstrates that prescribed fire alone does not appear to facilitate the spread of Ailanthus.