Urbanization affects oak–pathogen interactions across spatial scales

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 CO 2 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.

Phenology of plant reproduction, foliar infection, and herbivory change along an urbanization gradient

“…1b ). Thus, as for powdery mildew on oaks (van Dijk et al, 2022), warmer temperatures may have contributed to the increased infection prevalence of P. rugelii in suburban and urban populations.…”

“…In regions where baseline climate is cooler than optimal for a pathogen, urban heating may promote disease. Indeed, urban heat is linked to increased severity of powdery mildew on English oak in Europe (van Dijk et al, 2022). However, in regions that are already warmer than optimal for a pathogen, additional heat in cities may inhibit pathogen growth.…”

“…However, effects of urbanization on plant fitness are poorly understood (Johnson & Munshi-South, 2017; Rivkin et al, 2019). Notably, only a single study has tested effects of urbanization on tree diseases (van Dijk et al, 2022), and none have tested effects of urbanization on diseases of wild herbs. Moreover, no studies have simultaneously quantified effects of urbanization on timing of plant reproduction and damage from pathogens, herbivores, and human activities.…”

The co‐existence of multiple oak leaf flushes contributes to the large within‐tree variation in chemistry, insect attack and pathogen infection

“…While E. alphitoides and E. quercicola are more likely to infect the upper leaf side, E. hypophylla only infests the lower leaf side (Desprez-Loustau et al, 2018). Thus, we visually estimated the percentage of the leaf covered by oak powdery mildew, separately for the upper and lower leaf surface (Faticov et al, 2021;McClory et al, 2021;van Dijk et al, 2022). To avoid biases, a single person (AG) measured all 8167 leaves.…”

Latitudinal gradients in predation persist in urban environments

“…As urbanization intensifies, most species decline in abundance or disappear altogether (16,17) though a few experience population booms (18,19). This biotic reshuffling can alter the nature and intensity of local trophic interactions (20)(21)(22), impacting ecosystem services, ecological functioning, and evolution in cities and their suburbs (23)(24)(25). But urbanization is more than a patchwork of local effects; it has created a novel biome in which urbanized areas often resemble other, distant urbanized areas more than adjacent natural areas (26,27).…”