Comparative Analyses of Herbivory Rates and Leaf Phenology in Invasive and Native Shrubs in an East-Central Indiana Forest1

Abstract

Exotic species that become invasive can have a strong impact on the success of native species because of traits that enhance their competitive abilities. This study investigates three potential trait differences between common invasive and native shrubs that could enhance the competitive success of invasives: resistance to herbivory, length of autumn leaf retention, and timing of spring leaf emergence. We measured herbivory per plant by leaf-chewing insects, autumn leaf color change and retention, and spring leaf-out in five native and five invasive shrub species in Wildman Woods near Richmond, Indiana, during the fall of 2014 and the spring of 2015. Although we found variation among species, native plants as a group had significantly greater percent leaf herbivory per plant compared to invasive plants, while invasive plants kept chlorophyll significantly later in autumn and had longer leaf retention. Invasive plants also leaf out slightly earlier than native species. Our findings in 2014 were very similar to previous unpublished work in the same area on several of the same species in 2002, 2004, and 2007, suggesting that these patterns are consistent between years. Overall, we found evidence that lower herbivory rates, longer leaf retention in fall, and perhaps earlier leaf-out in spring could improve the competitive abilities of invasive shrub species through increased season-long photosynthesis.