Urbanization affects oak–pathogen interactions across spatial scales

Laura J A Van Dijk,Ayco J M Tack,Luis Abdala‐Roberts,Ricardo Matheus Pires,Bart G H Timmermans,Dmitry S Schigel,Raúl De La Mata,Bastien Castagneyrol,Bess Hardwick,Maria Faticov,Tomas Roslin,Anna E Barr,Jan P J G Ten Hoopen,Xoaquín Moreira

doi:10.1111/ecog.06091

Abstract

The world is rapidly urbanizing, thereby transforming natural landscapes and changing the abundance and distribution of organisms. However, insights into the effects of urbanization on species interactions, and plant–pathogen interactions in particular, are lacking. We investigated the effects of urbanization on powdery mildew infection on Quercus robur at continental and within‐city scales. At the continental scale, we compared infection levels between urban and rural areas of different‐sized cities in Europe, and investigated whether plant traits, climatic variables and CO2 emissions mediated the effect of urbanization on infection levels. Within one large city (Stockholm, Sweden), we further explored whether local habitat features and spatial connectivity influenced infection levels during multiple years. At the continental scale, infection severity was consistently higher on trees in urban than rural areas, with some indication that temperature mediated this effect. Within Stockholm city, temperature had no effect, while local accumulation of leaf litter negatively affected powdery mildew incidence in one out of three years, and more connected trees had lower infection levels. This study is the first to describe the effects of urbanization on plant–pathogen interactions both within and among cities, and to uncover the potential mechanisms behind the observed patterns at each scale.

Highlights

The world keeps urbanizing at an unprecedented speed, with over half of the human population currently residing in cities (Richie 2018)
We investigated the effects of urbanization on powdery mildew infection on Quercus robur at continental and within-city scales
The impact of urbanization on pathogen infection levels at the continental scale To analyse the effect of urbanization on powdery mildew incidence, we modelled the proportion of leaves infected by powdery mildew on each tree as a function of urbanization and city size, as well as their interaction

Summary

Introduction

The world keeps urbanizing at an unprecedented speed, with over half of the human population currently residing in cities (Richie 2018). This human-driven transformative process leads to dramatic changes in the physical environment and ecological communities, as well as marked and frequently abrupt environmental shifts along urban–rural interfaces (Kareiva et al 2007, Johnson and Munshi-South 2017). Host–pathogen interactions have been largely neglected despite the importance of pathogens in shaping plant and animal abundance and diversity, as well as host-associated food webs (Knapp et al 2020). Studying host–pathogen interactions within an urban setting is important for preventing biodiversity loss due to disease outbreaks (Potter et al 2011) and for the protection of pathogens as an intrinsic and functionally valuable part of biodiversity (Dougherty et al 2016)

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Conclusion