Leaf phenology and freeze tolerance of the invasive shrub amur honeysuckle and potential native competitors

The non-native invasive deciduous shrub Lonicera ,naackii causes a reduction in plant growth and species diversity under its canopy. The mechanisms of these effects are not fully understood, but an apparent difference between L. ,naackii and native shrub species is its extended leaf duration. We tested the hypothesis that L. inaackii has a longer leaf duration than native shrub species found in the same habitats. Leaf phenology of L. ,naackii and the native deciduous shrubs Asimina triloba and Lindera benzoin was observed at four sites in central Kentucky (USA) from March until December, 2007. Additionally, a late spring freeze allowed for examination of freeze tolerance among the three test species. Lonicera ,naackii leaf development was two to three weeks earlier than the natives in March and early April. A hard freeze in early April caused significant (P < 0.05) leaf mortality to both of the native species (60- 100% leaf mortality at 3 of 4 sites) while L. ,naackii showed no observable damage. L. ,naackii had a later transition to fall color and leaf abscission than the native species, which were at a significantly later stage of development (closer to leaf abscission) for a period of four to six weeks. These data suggest two advantages for L. ,naackii over potential native competitors: 1) greater access to carbon via a longer leaf duration, and 2) a greater capacity to withstand freezing temperatures.