TREE GENETICS AND GREENSPACE MANAGEMENT INTENSITY INFLUENCE URBAN TREE INSECT COMMUNITIES, DAMAGE, AND FOLIAR TRAITS

Abstract

Trees are essential to well-functioning urban systems, providing services that benefit humans and wildlife. For example, arthropods that use trees in cities perform key roles in the urban food web as both prey and predators, but they can also be vulnerable to environmental stressors associated with cities. Previous work documents broad patterns in arthropod communities associated with management practice gradients in urban areas. How these patterns relate to changes in tree genetic background across management types remains a largely unexplored topic. To disentangle the genetic and management associated effects on arboreal insect abundance, communities, and foliar damage, I repeatedly sampled trees of known genetic relatedness for two commonly planted tree species: Acer rubrum (n = 65), and its non-native congener Acer platanoides (n = 71), in June and August of 2023 and 2024. I systematically selected about 3 individual trees growing in four human management intensity categories (street trees, parks and residential yards, urban forest patches, or rural forests) for each of 5 genetic lineages per tree species. I used vacuum sampling to collect mobile arthropods from the lower canopy of each focal tree in June and August of 2023 and 2024, and identified samples to order. I also assessed insect and systemic foliar damage, gall abundance, and select physiological traits in August 2024. I found the general trend of increasing total arthropod abundance with increasing management intensity. However, management effects differed across genetic background with almost ubiquitous interactions between management type and genetic lineage. The most dominant group of insects found on study trees belonged to the order Hemiptera. This group of primarily herbivorous piercing/sucking insects were the primary drivers of these overarching abundance patterns. Spiders, which were the most abundant primarily predatory arthropod order, exhibited the opposite pattern, increasing in overall abundance in the later season, decreasing with increasing management intensity, and generally not responding to tree genetic lineage. In 2024, increasing management intensity negatively affected cumulative insect herbivore damage and gall abundance, and did not vary by genetic lineage. Gall formers were found only on native Acer rubrum, with no galls sampled from the non-native A. platanoides. In contrast, systemic foliar damage did not change with management, and only varied by tree genetic lineage for Acer platanoides. Foliar photosynthetic traits’ variance by management intensity or tree genetic lineage was species dependent; A. rubrum traits varied by tree genetic lineage, while A. platanoides traits varied by management intensity. Overall, my results suggest that tree genetic background plays an important role in mediating management effects on insect populations, particularly for piercing-sucking herbivorous species, but genetic background’s effect on other metrics such as foliar damage and traits may be species-specific. Further studies should be sure to consider the structure of genetic populations when describing patterns of insect use. Results of this thesis will serve to inform best practices for urban tree management and pest mitigation, as cities work to maintain and increase urban canopy cover.