CASE STUDY: Restoring Remnant Hardwood Forest Impacted by Invasive Tree-of-Heaven (Ailanthus altissima)

Tree-of-heaven (Ailanthus altissima) is a fast growing tree native to China. Introduced as an ornamental plant, A. altissima has spread throughout North American landscapes, imposing a threat to the biodiversity of native ecosystems. Recommended control methods include basal bark treatments using herbicide with an oil-based carrier around the base of Ailanthus stems. Land managers value application methods that maximize efficiency while also reducing environmental impacts when applied over landscape scales. The focus of this study was to assess the efficiency of herbicide concentrations and carriers on the mortality of A. altissima. This study was conducted in a 105 ha hardwood forest at the Wilds Conservation Center in Cumberland, OH. The forest is directly adjacent to areas mined for coal and reclaimed in the 1980s. Twenty-five plots were established consisting of 732 target trees. Two carriers (AX-IT basal oil and diesel fuel) mixed with Garlon 4 Ultra herbicide were tested at two different concentrations: 1) 10% Garlon in 90% diesel fuel carrier, 2) 20% Garlon with 80% diesel carrier, 3) 10% Garlon with 90% AX-IT carrier, and 4) 20% Garlon with 80% AX-IT carrier. Basal bark treatments were applied using a backpack sprayer. After one year, treatments were similar (89-100% mortality) with one exception, the 10% Garlon in 90% diesel treatment was least effective (69% mortality; P< 0.0001). This was more apparent as the diameter at breast height (DBH) increased (P < 0.0001). When canopy dieback was compared across treatments, AX-IT basal oil remained more effective regardless of the DBH or concentration. Cost comparisons show 10% Garlon solution in AX-IT oil base can be the most economically and ecologically beneficial treatment when applied on a large scale. Long-term monitoring will determine the occurrence of re-sprouts (via seed and root sprouting) and the impact each treatment has on the plant communities within this forest system. Additional