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Urban tree canopy cover is often unequally distributed across cities such that more socially vulnerable neighborhoods often have lower tree canopy cover than less socially vulnerable neighborhoods. However, how the diversity and composition of the urban canopy affect the nature of social‐ecological benefits (and burdens), including the urban forest's vulnerability to climate change, remains underexamined. Here, we synthesize tree inventories developed by multiple organizations and present a species‐specific, geolocated database of more than 600,000 urban trees across the 7‐county Minneapolis‐St. Paul (MSP) metropolitan area in the Upper Midwest of the United States. We find that tree diversity across the MSP is variable yet dominated by a few species (e.g.,Fraxinus pennsylvanica,Acer platanoides, andGleditsia triacanthos), contributing to the vulnerability of the MSP urban forest to future climate change and disturbances. In contrast to tree canopy cover, tree diversity was not well predicted by socioeconomic or demographic factors. However, our analysis identified areas where both climate and social vulnerability are high. Our results add to a growing body of literature emphasizing the importance of considering how complex and interacting social and ecological factors drive urban forest diversity and composition when pursuing management objectives.

 

Terrestrial water fluxes are substantially mediated by vegetation, while the distribution, growth, health, and mortality of plants are strongly influenced by the availability of water. These interactions, playing out across multiple spatial and temporal scales, link the disciplines of plant ecophysiology and ecohydrology. Despite this connection, the disciplines have provided complementary, but largely independent, perspectives on the soil‐plant‐atmosphere continuum since their crystallization as modern scientific disciplines in the late 20th century. This review traces the development of the two disciplines, from their respective origins in engineering and ecology, their largely independent growth and maturation, and the eventual development of common conceptual and quantitative frameworks. This common ground has allowed explicit coupling of the disciplines to better understand plant function. Case studies both illuminate the limitations of the disciplines working in isolation, and reveal the exciting possibilities created by consilience between the disciplines. The histories of the two disciplines suggest opportunities for new advances will arise from sharing methodologies, working across multiple levels of complexity, and leveraging new observational technologies. Practically, these exchanges can be supported by creating shared scientific spaces. This review argues that consilience and collaboration are essential for robust and evidence‐based predictions and policy responses under global change.

 

Scholars have spent decades arguing that policy entrepreneurs, change agents who work individually and in groups to influence the policy process, can be crucial in introducing policy innovation and spurring policy change. How to identify policy entrepreneurs empirically has received less attention. This oversight is consequential because scholars trying to understand when policy entrepreneurs emerge, and why, and what makes them more or less successful, need to be able to identify these change agents reliably and accurately. This paper explores the ways policy entrepreneurs are currently identified and highlights issues with current approaches. We introduce a new technique for eliciting and distinguishing policy entrepreneurs, coupling automated and manual analysis of local news media and a survey of policy entrepreneur candidates. We apply this technique to the empirical case of unconventional oil and gas drilling in Pennsylvania and derive some tentative results concerning factors which increase entrepreneurial efficacy.

 

Green infrastructure (GI) practices improve stormwater quality and reduce urban flooding, but as urban hydrology is highly controlled by its associated gray infrastructure (e.g., stormwater pipe network), GI's watershed‐scale performance depends on its siting within its associated watershed. Although many stormwater practitioners have begun considering GI's spatial configuration within a larger watershed, few approaches allow for flexible scenario exploration, which can untangle GI's interaction with gray infrastructure network and assess its effects on watershed hydrology. To address the gap in integrated gray‐green infrastructure planning, we used an exploratory model to examine gray‐green infrastructure performance using synthetic stormwater networks with varying degrees of flow path meandering, informed by analysis on stormwater networks from the Minneapolis‐St. Paul Metropolitan Area, MN, USA. Superimposed with different coverage and placements of GI (e.g., bioretention cells), these gray‐green stormwater networks are then subjected to different rainfall intensities within Environmental Protection Agency's Storm Water Management Model to simulate their hydrological benefits (e.g., peak flow reduction, flood reduction). Although only limited choices of green and gray infrastructure were explored, the results show that the gray infrastructure's spatial configuration can introduce tradeoffs between increased peak flow and increased flooding, and further interacts with GI coverage and placement to reduce peak flow and flooding at low rainfall intensity. However, as rainfall intensifies, GI ceases to reduce peak flow. For integrated gray‐green infrastructure planning, our results suggest that physical constraints of the stormwater networks and the range of rainfall intensities must be considered when implementing GI.

 

Roadsides are targeted for restoration of pollinator‐friendly plants. Yet, roads are sources of macronutrient, micronutrient and heavy metal pollution that may contaminate roadside plants. Adjacent landscape features such as railroads and agriculture provide additional macronutrient and heavy metal pollution that may exacerbate traffic effects. However, we lack perspective on how roads combine with rural landscape features to influence nutrition of roadside plants, which could have implications for pollinator health.

We surveyed roadsides across Minnesota, USA and measured foliar levels of dietary macronutrients (nitrogen, phosphorous and potassium), a micronutrient (sodium) and metals (iron, zinc, copper, chromium, nickel, lead, aluminium and cadmium) in six abundant roadside forb species used by insect pollinators:Asclepias syriaca,Dalea purpurea,Monarda fistulosa,Ratibida pinnata,Solidagospp. andTrifolium pratense. We aimed to determine (1) how road variables (traffic volume and distance from road) combine with adjacent land use (railroad and agriculture) to influence element content of roadside forbs and (2) whether some forb species show consistent differences in their accumulation of potentially toxic heavy metals, which could inform selection of species to plant along roadsides.

We found that foliar concentrations of nine elements increased with greater traffic volume (nitrogen, phosphorous, iron, zinc, copper, chromium, nickel, lead and aluminium), and concentrations of six elements declined with distance from the road (nitrogen, phosphorous, potassium, iron, zinc and copper). Leaves collected adjacent to railroad had less phosphorous, potassium, iron, nickel and aluminium than leaves collected from sites not adjacent to railroad. Additionally, leaves collected from sites adjacent to agriculture had lower copper levels than leaves from sites without adjacent agriculture. We found no evidence that particular ford species along roadsides consistently rank higher than other species in their accumulation of heavy metals.

Our results show that traffic alters more elements in roadside plants than does adjacent landscape context, alleviating concerns that landscape features exacerbate pollutant levels in roadside pollinator habitat. However, nutrient contamination of most roadside plants is unlikely to reach toxic levels for insect pollinators. This work is consistent with the positive conservation potential of low to moderate traffic roadsides for pollinators.

 

Formal rules define urban governance, yet in democratic systems like the United States, institutions governing public input shape decision-making. Governance literature needs more breadth on how civic engagement varies across types of nature and its implications for urban social-ecological systems. We analyzed five cities’ ordinances within the Minneapolis-St. Paul metropolitan region, identifying nature-based rules and civic engagement mechanisms. We found ten engagement mechanisms across six nature types, primarily discussed within zoning ordinances—farm animals being the exception. Public hearings were the most frequently mentioned engagement mechanism, yet they have documented biases toward elite perspectives. Despite codification of engagement opportunities, it remains unclear whether utilized mechanisms support substantive input and influence into urban nature governance. Our study not only lays groundwork for research on how to address the inequitable distribution of nature-related benefits and burdens felt by some urban communities, but also inspires further exploration into this crucial area of study. 

Studies drawing correlations between Home Owners Loan Corporation “redlining” maps and present-day environmental outcomes have raised public attention about the role of systemic racial discrimination in producing uneven outcomes in the urban environment. In this analysis, we draw on a novel data source—narrative descriptions of neighborhood characteristics included in the area descriptions that accompanied City Survey maps—to explore the mechanisms that historically link HOLC maps and disparate environmental quality. Focusing on nine mid-sized cities in the Midwest, we draw on a combined inductive and deductive coding approach to consider how perceived urban environmental quality and neighborhood racial demographics shaped assessments of neighborhood value and risk. In doing so, we illustrate the ways in which nature, class, and race were already coupled at the time of the HOLC City Survey. The area descriptions in the HOLC City Survey illustrate the ways in which this coupling became codified and reinforced over time through housing and environmental policies, the impacts of which we still struggle to disrupt today.

 

Research has demonstrated the impact of historic discriminatory mortgage lending (i.e., “redlining”) on the distribution of environmental benefits and burdens, while the environmental legacies of other racially discriminatory housing policies remain unexplored. Using a novel dataset of racial covenants in Minneapolis and its suburbs, the first complete map for any U.S. city, we find a significant positive association between historic racial covenant presence and cooler temperatures, increased tree canopy, and reduced impervious surface today. When compared to redlining, we find that covenants have an environmental impact comparable to the two highest HOLC designations (A or B). Further, within each HOLC grade, covenant presence is associated with additional environmental benefits that mitigate the negative environmental impact associated with redlining. This analysis reveals that the positive environmental benefits associated with covenants are not simply driven by an urban-suburban land-use gradient but, rather, are related to the privilege afforded to the legal guarantees of whiteness embedded in the covenant itself. 

The global uptake of green infrastructure in urban settings holds considerable promise for fostering both social and ecological benefits. Recognizing the imperative to ensure equitable distribution of these advantages, this paper draws on the rich traditions of justice considerations within urban studies to inform research on urban greening. Focusing on three key trends - reconceptualizing the 'urban' category, acknowledging the role of historical processes in shaping contemporary uneven and unjust geographies, and considering power dynamics in infrastructure development - we propose five tenets for advancing justice-focused urban greening research. These tenets encourage researchers to act as knowledge brokers, practice reflexivity, recognise the complex dimensions of justice which diversity of scale might reveal, embrace uncertainty, and cultivate a “modest imaginary” concerning infrastructure projects.