HUFBAUER Ruth Arabelle
- Department of Agricultural Biology, Colorado State University, Fort Collins, United States of America
- Agroecology, Biological control, Biological invasions, Colonization, Dispersal & Migration, Eco-evolutionary dynamics, Evolutionary ecology, Experimental ecology, Herbivory, Phenotypic plasticity, Population ecology
Insect herbivory on urban trees: Complementary effects of tree neighbours and predation
Tree diversity is associated with reduced herbivory in urban forestRecommended by Ruth Arabelle Hufbauer and Ian Pearse based on reviews by Freerk Molleman and Ian Pearse
Urban ecology, the study of ecological systems in our increasingly urbanized world, is crucial to planning and redesigning cities to enhance ecosystem services (Kremer et al. 2016), human health and well-being and further conservation goals (Dallimer et al. 2012). Urban trees are a crucial component of urban streets and parks that provide shade and cooling through evapotranspiration (Fung and Jim 2019), improve air quality (Lai and Kontokosta 2019), help control storm water (Johnson and Handel 2016), and conserve wildlife (Herrmann et al. 2012; de Andrade et al. 2020).
Ideally, management of urban forests strikes a balance between maintaining the health of urban trees while retaining those organisms, such as herbivores, that connect a tree to the urban ecosystem. Herbivory by arthropods can substantially affect tree growth and reproduction (Whittaker and Warrington 1985), and so understanding factors that influence herbivory in urban forests is important to effective management. At the same time, herbivorous arthropods are important as key components of urban bird diets (Airola and Greco 2019) and provide a backyard glimpse at forest ecosystems in an increasingly built environment (Pearse 2019). Maintenance of arthropod predators may be one way to retain arthropods in urban forests while keeping detrimental outbreaks of herbivores in check. In “Insect herbivory on urban trees: Complementary effects of tree neighbors and predation” Stemmelen and colleagues (Stemmelen et al. 2020) use a clever sampling design to show that insect herbivory decreases as the diversity of neighboring trees increased. By placing artificial larvae out on trees, they provide evidence that increased predation in higher diversity urban forest patches might drive patterns in herbivory. The paper also demonstrates the importance of tree species identity in determining leaf herbivory.
The implications of this research for urban foresters is that deliberately planting diverse urban forests will help manage insect herbivores and should thus improve tree health. Potential knock-on effects could be seen for the ecosystem services provided by urban forests. While it might be tempting to simply plant more of the species that are subject to low current rates of herbivory, other research on the long-term vulnerability of monocultures to attack by specialist pathogens and herbivores (Tooker and Frank 2012) cautions against such an approach. Furthermore, the importance of urban forest insects to birds, including migrating birds, argues for managing urban forests more holistically (Greco and Airola 2018).
Stemmelen et al. (2020) used an observational approach focused on urban forests in Montreal, Canada in their research. Their findings suggest follow-up research focused on a broader cross-section of urban forests across latitudes, as well as experimental research. Experiments could, for example, exclude avian predators with netting (e.g. (Marquis and Whelan 1994)) to evaluate the relative importance of birds to managing urban insects on trees, as well as the flip side of that equation, the important to birds of insects on urban trees.
In summary, Stemmelen and colleague’s manuscript illustrates clever sampling and use of observational data to infer broader ecological patterns. It is worth reading to better understand the role of diversity in driving plant-insect community interactions and given the implications of the findings for sustainable long-term management of urban forests.
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