Management of the Invasive Shrub Amur Honeysuckle (Lonicera maackii) for the Endangered Perennial Wild Dill (Perideridia americana)

Radnor Lake State Natural Area in Nashville, TN, has cedar glades that contain the endangered perennial herb wild dill [Perideridia americana (Nutt. ex DC.) Rchb.] and the invasive shrub Amur honeysuckle [Lonicera maackii (Rupr.) Herder]. This research examined whether L. maackii treatment in the Radnor Lake State Natural Area cedar glades is followed by an increase in P. americana plants. A grid of 60 adjacent 2 m by 4 m plots was placed in five cedar glades to encompass the P. americana population. With great care to protect P. americana, the annual treatment for L. maackii was to pull plants ≤1-m tall from the ground; and to cut stems >1-m tall and then treat the stumps with glyphosate. The t-tests of means for the log natural of the number of plants in the 60 plots (significance level of P-value = 0.05) were used to compare pretreatment L. maackii and P. americana counts with posttreatment counts in 2018 and P. americana counts at leaf out and flowering in 2018. The L. maackii population was significantly smaller (P-value < 0.001) in 2018 than pretreatment at all five sites. When pretreatment in 2014 and 2015 was compared with posttreatment in 2018 for the P. americana populations, the increases were significant at the Cheek, Harris 2, Hideaway, and Norfleet sites, but the increase at East Hall Farm was not significant. White-tailed deer (Odocoileus virginianus Zimmermann) trampling was the explanation given for the decreases in P. americana from leaf out to flowering at all five sites in 2018. Browsing was evident only at Hideaway, which had a greater loss for P. americana from leaf out to flowering in 2018 than the combined losses for the Cheek, East Hall Farm, Harris 2, and Norfleet sites. The research informed the creation of adaptive management decisions regarding monitoring and treatment of the invasive species L. maackii for an endangered species.