Trees provide essential habitat for insects in urban areas. Due to a combination of top-down and bottom-up effects, insect abundance and community composition are often vastly different on urban trees than in forests outside the city. Within cities, heterogeneous mosaics of impervious surface, ornamental plants, and fragmented habitat drive further differences in insect communities. Here, we study how the density and structure of trees in urban forests affect insects on Acer (maple) and Quercus (oak) trees, two of the most common genera in urban forests of the eastern U.S. We use a field study of mature trees in Raleigh, North Carolina, to compare the relative importance of tree species and surrounding vegetation on insect abundance and diversity.
Results/Conclusions
The relative abundance and diversity of insects on maples and oaks was dependent on surrounding vegetation. For example, Acer x freemanii supported more insect diversity than other maple species in areas with high surrounding vegetation cover but not in areas with low vegetation cover. Scale insect density was higher on Q. alba than on other oak species, but only when local vegetation complexity was high. These patterns highlight the role of urban vegetation such as forest fragments and street trees in shaping insect communities in cities. We conclude with a discussion about how interdisciplinary study of urban forests could improve understanding of temperate deciduous forests in general, now and in the future.