Effects of Chinese privet on bees and their vertical distribution in riparian forests.
Chinese privet (Ligustrum sinense Lour.), is known to negatively affect biodiversity near the ground in invaded forests by forming thick layers of non-native vegetation in the midstory. Whether these effects extend above the shrub layer into the canopy remains unclear. We sought to test this question by using flight-intercept traps (clear plastic panels attached to a white bucket) to sample bees at three heights (0.5, 5, and 15 m) in plots in which L. sinense had or had not been experimentally eliminated. Privet removal (i.e., restoration) resulted in significantly higher bee abundance, richness, and diversity than in invaded sites, but this effect was only observed at 0.5 m. In restored plots, bee diversity was generally higher at 5 and 15 m than near the forest floor, but there were no differences between traps at 5 and 15 m. Our findings show that bees will benefit from the removal of invasive shrubs near the forest floor but not in the canopy. Why bee diversity is higher in the canopy than near the ground in temperate deciduous forests remains unknown.