LB 41-349 - The effect of non-native urban street trees on native insect biodiversity

Trees are essential for responding to the biodiversity and climate emergency. In urban environments in particular, trees filter and cool the air, absorb storm water, and provide cultural benefits. Despite this knowledge of the benefits of urban trees to people, how the selection and planting of urban trees has affected insect communities is unknown. Previous research has shown that in many cases, native plants support greater native insect diversity and abundance, compared to non-native plants. The replacement of native trees by non-native trees in urban environments is expected to result in decreases in native insect species and may be contributing to global insect declines. Here we test this idea by examining the diversity of native Lepidoptera associated with 132,854 native and non-native street trees in Vancouver, British Columbia. Our dataset included 96 tree species (11 native, 85 non-native), and represents 88.6% of the total Vancouver Street Tree database. We used published literature and online databases to compile all available information on tree-Lepidoptera associations, and filtered this data to include only Lepidoptera found in British Columbia. Overall there were 546 lepidopteran species associated with Vancouver street trees. There was a significant effect of tree origin on Lepidopteran richness, with native trees associated with 57.8 Lepidoptera species per tree species, and non-native trees associated with 13.7 Lepidoptera species. We further investigated potential relationships between exotic insects and tree origin, and found that exotic insects were found on 57% of non-native trees but only 45% of native trees. Overall these findings suggest that non-native street trees are less likely to support native insect species, and more likely to support exotic and potentially damaging insect species. We encourage increased dialogue between ecologists and municipal arborists to facilitate the planting of trees that can both mitigate effects of climate change in urban environments and support native insect biodiversity.