Invertebrate Abundance, Biomass, and Richness Associated with an Exotic Invasive Shrub (Lonicera morrowii A. Gray)

Abstract

Exotic bush honeysuckles ( Lonicera spp.) are becoming increasingly common in the eastern and mid-western United States, but little is known about their impacts on invertebrates. We used a modified leaf vacuum to sample invertebrates in the shrub strata and understory of three shrub types (and open plots in the understory): single Morrow’s honeysuckle ( L . morrowii A. Gray) shrubs, single native southern arrowwood ( Viburnum recognitum Fernald) shrubs, and dense thickets of Morrow’s honeysuckle, in southwestern PA, USA during 2004 and 2005. We also assessed the degree of herbivory on the two species of shrubs. Within the shrub strata, invertebrate biomass was lower in southern arrowwood shrubs, but there was no difference in invertebrate abundance or family richness. Invertebrate abundance and richness were lowest in August, but there was no difference in biomass among the months. Invertebrate abundance, biomass, and family richness were lowest in the understory below dense thickets of Morrow’s honeysuckle. Overall, the percent cover of herbs was the proximate factor responsible for driving patterns of invertebrate abundance, though ultimately these patterns were being driven by shrub type. Abundance and biomass of larval leaf chewers were highest in the native shrub; Morrow’s honeysuckle had a mean of 29.7 cm 2 of leaf area consumed per 1 m 2 of leaf area, while the native shrub had a mean of 284.3 cm 2 of leaf area consumed. Our results suggest that areas dominated by the exotic shrub negatively impact invertebrate biomass, which may in turn affect organisms at higher trophic levels.