Human and biophysical legacies shape contemporary urban forests: A literature synthesis

Citation: Egerer, M., H. Liere, A. Lucatero, and S. M. Philpott. 2020. Plant damage in urban agroecosystems varies with local and landscape factors. Ecosphere 11(3):Abstract. Biotic and abiotic factors at local to landscape scales influence insect pest and disease dynamics in agricultural systems. However, relative to studies focused on the importance of these drivers of crop plant damage in rural agricultural systems, few studies investigate plant damage from herbivore insects and plant diseases in urban agroecosystems, and consequently, most urban farmers lack knowledge on crop protection tactics. Here we use three common crop species within urban agroecosystems (community gardens) distributed across an urban landscape as a model system to ask how local, landscape, and microclimate factors relate to herbivore and disease plant damage. We hypothesized that plant damage would be lower in gardens with greater local vegetation complexity, landscape-scale complexity, and less variable temperatures, but that the importance of factors is species-and damage-specific. By measuring Brassica, cucurbit, and tomato insect pest and disease damage across the growing season, we confirmed that the importance of factors varies with crop species and by damage type. Both local complexity factors (e.g., number of trees and shrubs) and landscape complexity (percent natural cover in the landscape) relate to lower incidence of herbivore and disease damage on some crops, supporting our prediction that habitat heterogeneity at both local and landscape scales lowers plant damage. Greater temperature variability related to higher disease damage on tomatoes linking microclimate factors to disease prevalence. Yet, local complexity factors also related to higher incidence of plant damage for other crop species, indicating variable species-level impacts of local management factors on plant damage. By measuring the abundance of fungus-feeding lady beetles (Psyllobora) on cucurbits, we confirmed a strong association between natural enemies and powdery mildew. We provide a case study on how changes in local to landscape-scale factors relate to plant damage in urban agroecosystems and suggest how urban farmers and gardeners can apply this ecological knowledge to improve sustainable urban food production.

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“…, Roman et al. ), or novel insect pests associated with fungal pathogens that burgeon in urban areas (Ploetz et al. , O'Donnell et al.…”

Section: Discussionmentioning

confidence: 99%

Plant damage in urban agroecosystems varies with local and landscape factors

et al. 2020

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“…Legacy effects are 'impacts that previous events, processes, and phenomena have on current properties or processes' (Roman et al 2018, p. 159) and being aware of these historical influences matters because they help our understanding of current processes and patterns (Szabó 2010). The importance of history in ecology has been recognised Roman et al (2018) and include e.g. ecological disturbances like extreme weather events and disease outbreaks or aspects related to national and regional identity.…”

Section: Resultsmentioning

confidence: 99%

“…Simply establishing that Accra is yet another city where tree cover varies between areas is insufficient, however, if we want to avoid further deepening the divide. Instead, we must discuss historical legacy effects, i.e., the events and processes that have produced the current structure (Roman et al 2018). While intra-city inequalities might also be reflected by the distribution of other types of green spaces, like urban agricultural lands or lawns (Stow et al 2013), this research focused on trees and their particular services like shading or air pollution removal which are provided at a smaller amount or not at all by other types of vegetation.…”

Section: Introductionmentioning

confidence: 99%

Tree Cover of Accra’s Neighbourhoods—a Green Divide

Hosek

2019

Urban Forum

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Intra-city differences in tree cover are one way in which the urban divide physically manifests itself, adding a green component to the discussion of urban inequalities. I determined the canopy cover of Accra and its 76 neighbourhoods using the 'dot method' approach where random points are displayed on aerial photographs and categorised as located either on a tree or not, obtaining neighbourhood values between 0.2 and 53.6%. The average crown cover of non-poor neighbourhoods is 23.1%, continuously declining to 3.5% in areas of highest poverty. Examining historical events and processes, it can be seen that this canopy cover distribution originates from colonial tree planting patterns. Analysing these legacy effects not only aids our understanding of the present but also can help increase precision when assessing the possible impacts current laws and policies or management systems might have on our urban forest.

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“…The policy suggestion is to ensure that the urban forest is made up of no more than 10 percent of a single species, 20 percent of a single genus, and 30 percent of a single family (Santamour ). Although the feasibility of enacting such a plan has been called into question, researchers and managers believe that such a population structure could prevent catastrophic tree loss in the event of a new introduced pest or pathogen (Roman and others ). However, in studies looking specifically at diversification of urban forests after Dutch elm disease, researchers have focused on either street trees or privately owned trees (Raupp, Cumming, and Raupp ; Berland and Elliott ).…”

Section: Discussion: Urban Forests Through the Lens Of The Commonsmentioning

confidence: 99%

Using the commons to understand the Dutch elm disease epidemic in Syracuse, NY

Bukowski

2019

Geographical Review

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Prior to the arrival of Dutch elm disease to the United States in 1930, American elm (Ulmus americana) had become one of the most beloved and commonly planted urban trees throughout the country, especially in the Northeastern United States. The trees were revered for their beauty, hardiness, and the corridor‐like shade provided to city streets. Syracuse, NY stands as an example of this popularity: in 1951, when the disease first arrived in the city, over 50,000 elms grew in the city. But over the course of twenty years, nearly all elms in the city had become infected and succumbed to the disease. Although efforts to control the fungus in Syracuse ultimately failed to stop elm loss, the case study can be used to better inform contemporary urban forest management practices today by highlighting the effects of mixed property ownership in cities and its effects on pest management.

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Human and biophysical legacies shape contemporary urban forests: A literature synthesis

Cited by 160 publications

References 94 publications

Plant damage in urban agroecosystems varies with local and landscape factors

Plant damage in urban agroecosystems varies with local and landscape factors

Tree Cover of Accra’s Neighbourhoods—a Green Divide

Using the commons to understand the Dutch elm disease epidemic in Syracuse, NY

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