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.
Airola, D. and Greco, S. (2019). Birds and oaks in California’s urban forest. Int. Oaks, 30, 109–116.
de Andrade, A.C., Medeiros, S. and Chiarello, A.G. (2020). City sloths and marmosets in Atlantic forest fragments with contrasting levels of anthropogenic disturbance. Mammal Res., 65, 481–491. doi: https://doi.org/10.1007/s13364-020-00492-0
Dallimer, M., Irvine, K.N., Skinner, A.M.J., Davies, Z.G., Rouquette, J.R., Maltby, L.L., et al. (2012). Biodiversity and the Feel-Good Factor: Understanding Associations between Self-Reported Human Well-being and Species Richness. Bioscience, 62, 47–55. doi: https://doi.org/10.1525/bio.2012.62.1.9
Fung, C.K.W. and Jim, C.Y. (2019). Microclimatic resilience of subtropical woodlands and urban-forest benefits. Urban For. Urban Green., 42, 100–112. doi: https://doi.org/10.1016/j.ufug.2019.05.014
Greco, S.E. and Airola, D.A. (2018). The importance of native valley oaks (Quercus lobata) as stopover habitat for migratory songbirds in urban Sacramento, California, USA. Urban For. Urban Green., 29, 303–311. doi: https://doi.org/10.1016/j.ufug.2018.01.005
Herrmann, D.L., Pearse, I.S. and Baty, J.H. (2012). Drivers of specialist herbivore diversity across 10 cities. Landsc. Urban Plan., 108, 123–130. doi: https://doi.org/10.1016/j.landurbplan.2012.08.007
Johnson, L.R. and Handel, S.N. (2016). Restoration treatments in urban park forests drive long-term changes in vegetation trajectories. Ecol. Appl., 26, 940–956. doi: https://doi.org/10.1890/14-2063
Kremer, P., Hamstead, Z., Haase, D., McPhearson, T., Frantzeskaki, N., Andersson, E., et al. (2016). Key insights for the future of urban ecosystem services research. Ecol. Soc., 21: 29. doi: http://doi.org/10.5751/ES-08445-210229
Lai, Y. and Kontokosta, C.E. (2019). The impact of urban street tree species on air quality and respiratory illness: A spatial analysis of large-scale, high-resolution urban data. Heal. Place, 56, 80–87. doi: https://doi.org/10.1016/j.healthplace.2019.01.016
Marquis, R.J. and Whelan, C.J. (1994). Insectivorous birds increase growth of white oak through consumption of leaf-chewing insects. Ecology, 75, 2007–2014. doi: https://doi.org/10.2307/1941605
Pearse, I.S. (2019). Insect herbivores on urban native oak trees. Int. Oaks, 30, 101–108.
Stemmelen, A., Paquette, A., Benot, M.-L., Kadiri, Y., Jactel, H. and Castagneyrol, B. (2020) Insect herbivory on urban trees: Complementary effects of tree neighbours and predation. bioRxiv, 2020.04.15.042317, ver. 5 peer-reviewed and recommended by PCI Ecology. doi: https://doi.org/10.1101/2020.04.15.042317
Tooker, J. F., and Frank, S. D. (2012). Genotypically diverse cultivar mixtures for insect pest management and increased crop yields. J. Appl. Ecol., 49(5), 974-985. doi: https://doi.org/10.1111/j.1365-2664.2012.02173.x
Whittaker, J.B. and Warrington, S. (1985). An experimental field study of different levels of insect herbivory induced By Formica rufa predation on Sycamore (Acer pseudoplatanus) III. Effects on Tree Growth. J. Appl. Ecol., 22, 797. doi: https://doi.org/10.2307/2403230
DOI or URL of the preprint: https://doi.org/10.1101/2020.04.15.042317
Dear Drs. Castagneyrol and Paquette,
Thank you for carefully addressing the reviewers comments. I find your manuscript much improved. I have read the manuscript in MS word, and took the liberty of making suggested edits using track changes, and commenting using the comment tool.
My suggestions are quite minor and I hope you will find them helpful and will submit a finalized pre-print at your convenience. I would like to write a recommendation focused on how much can be revealed from this kind of work, what it suggests would be a next step, and the implications for urban forest management.
Hmm. I'm getting an error message when I attaching the file. I'm going to remove it from this email going through PCI Ecology, and will send a separate email outside the system with the file attached.
With my best wishes, RuthDownload recommender's annotations
DOI or URL of the preprint: https://doi.org/10.1101/2020.04.15.042317
The reviewers and I appreciate the work you present. However, to warrant recommendation by PCI Ecology a fairly major revision should be implemented, following the suggestions of the reviewers, including exploring new analyses as suggested by the reviewers, and making sure that the title appropriately describes the results.
As with a traditional journal, a detailed response to reviews would be appreciated upon resubmission.
Ruth Hufbauer, Professor
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