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Managing and adapting to climate change in urban areas will become increasingly important as urban populations grow, especially because unique features of cities amplify climate change impacts. High impervious cover exacerbates impacts of climate warming through urban heat island effects and of heavy rainfall by magnifying runoff and flooding. Concentration of human settlements along rivers and coastal zones increases exposure of people and infrastructure to climate change hazards, often disproportionately affecting those who are least prepared. Nature-based strategies (NBS), which use living organisms, soils and sediments, and/or landscape features to reduce climate change hazards, hold promise as being more flexible, multi-functional and adaptable to an uncertain and non-stationary climate future than traditional approaches. Nevertheless, future research should address the effectiveness of NBS for reducing climate change impacts and whether they can be implemented at scales appropriate to climate change hazards and impacts. Further, there is a need for accurate and comprehensive cost–benefit analyses that consider disservices and co-benefits, relative to grey alternatives, and how costs and benefits are distributed across different communities. NBS are most likely to be effective and fair when they match the scale of the challenge, are implemented with input from diverse voices and are appropriate to specific social, cultural, ecological and technological contexts. This article is part of the theme issue ‘Climate change and ecosystems: threats, opportunities and solutions’.

Urban ecology is a field encompassing multiple disciplines and practical applications and has grown rapidly. However, the field is heterogeneous as a global inquiry with multiple theoretical and conceptual frameworks, variable research approaches, and a lack of coordination among multiple schools of thought and research foci. Here, we present an international consensus on how urban ecology can advance along multiple research directions. There is potential for the field to mature as a holistic, integrated science of urban systems. Such an integrated science could better inform decisionmakers who need increased understanding of complex relationships among social, ecological, economic, and built infrastructure systems. To advance the field requires conceptual synthesis, knowledge and data sharing, cross-city comparative research, new intellectual networks, and engagement with additional disciplines. We consider challenges and opportunities for understanding dynamics of urban systems. We suggest pathways for advancing urban ecology research to support the goals of improving urban sustainability and resilience, conserving urban biodiversity, and promoting human well-being on an urbanizing planet.

Urban areas are hot spots that drive environmental change at multiple scales. Material demands of production and human consumption alter land use and cover, biodiversity, and hydrosystems locally to regionally, and urban waste discharge affects local to global biogeochemical cycles and climate. For urbanites, however, global environmental changes are swamped by dramatic changes in the local environment. Urban ecology integrates natural and social sciences to study these radically altered local environments and their regional and global effects. Cities themselves present both the problems and solutions to sustainability challenges of an increasingly urbanized world.

Urbanization is changing Earth’s ecosystems by altering the interactions and feedbacks between the fundamental ecological and evolutionary processes that maintain life. Humans in cities alter the eco-evolutionary play by simultaneously changing both the actors and the stage on which the eco-evolutionary play takes place. Urbanization modifies land surfaces, microclimates, habitat connectivity, ecological networks, food webs, species diversity, and species composition. These environmental changes can lead to changes in phenotypic, genetic, and cultural makeup of wild populations that have important consequences for ecosystem function and the essential services that nature provides to human society, such as nutrient cycling, pollination, seed dispersal, food production, and water and air purification. Understanding and monitoring urbanization-induced evolutionary changes is important to inform strategies to achieve sustainability. In the present article, we propose that understanding these dynamics requires rigorous characterization of urbanizing regions as rapidly evolving, tightly coupled human–natural systems. We explore how the emergent properties of urbanization affect eco-evolutionary dynamics across space and time. We identify five key urban drivers of change—habitat modification, connectivity, heterogeneity, novel disturbances, and biotic interactions—and highlight the direct consequences of urbanization-driven eco-evolutionary change for nature’s contributions to people. Then, we explore five emerging complexities—landscape complexity, urban discontinuities, socio-ecological heterogeneity, cross-scale interactions, legacies and time lags—that need to be tackled in future research. We propose that the evolving metacommunity concept provides a powerful framework to study urban eco-evolutionary dynamics.

Recent climate-change research largely confirms the impacts on US ecosystems identified in the 2009 National Climate Assessment and provides greater mechanistic understanding and geographic specificity for those impacts. Pervasive climate-change impacts on ecosystems are those that affect productivity of ecosystems or their ability to process chemical elements. Loss of sea ice, rapid warming, and higher organic inputs affect marine and lake productivity, while combined impacts of wildfire and insect outbreaks decrease forest productivity, mostly in the arid and semi-arid West. Forests in wetter regions are more productive owing to warming. Shifts in species ranges are so extensive that by 2100 they may alter biome composition across 5-20% of US land area. Accelerated losses of nutrients from terrestrial ecosystems to receiving waters are caused by both winter warming and intensification of the hydrologic cycle. Ecosystem feedbacks, especially those associated with release of carbon dioxide and methane release from wetlands and thawing permafrost soils, magnify the rate of climate change.

Cities are uniquely complex systems regulated by interactions and feedbacks between nature and human society. Characteristics of human society—including culture, economics, technology and politics—underlie social patterns and activity, creating a heterogeneous environment that can influence and be influenced by both ecological and evolutionary processes. Increasing research on urban ecology and evolutionary biology has coincided with growing interest in eco‐evolutionary dynamics, which encompasses the interactions and reciprocal feedbacks between evolution and ecology. Research on both urban evolutionary biology and eco‐evolutionary dynamics frequently focuses on contemporary evolution of species that have potentially substantial ecological—and even social—significance. Still, little work fully integrates urban evolutionary biology and eco‐evolutionary dynamics, and rarely do researchers in either of these fields fully consider the role of human social patterns and processes. Because cities are fundamentally regulated by human activities, are inherently interconnected and are frequently undergoing social and economic transformation, they represent an opportunity for ecologists and evolutionary biologists to study urban “socio‐eco‐evolutionary dynamics.” Through this new framework, we encourage researchers of urban ecology and evolution to fully integrate human social drivers and feedbacks to increase understanding and conservation of ecosystems, their functions and their contributions to people within and outside cities.

Cities need to understand and manage their carbon footprint at the level of streets, buildings and communities, urge Kevin Robert Gurney and colleagues.

Urbanization alters watershed ecosystem functioning, including nutrient budgets and processes of nutrient retention. It is unknown, however, how variation in stormwater infrastructure design affects the delivery of water and materials from urban watersheds. In this study, we asked: (1) How does stormwater infrastructure design vary over time and space in an arid city (Phoenix, Arizona, USA)?, and (2) How does variation in infrastructure design affect fluxes of dissolved nitrogen (N), phosphorus (P), and organic carbon (DOC) from urban watershed ecosystems? From 1955 to 2010, stormwater infrastructure designs shifted from pipes, to engineered channels and retention basins, to natural washes. We monitored 10 nested watersheds, where small (5–141 ha) watersheds had medium-density residential land use but differed in stormwater infrastructure, whereas larger watersheds (1,662–20,247 ha) had a variety of land uses and infrastructures. We measured rainfall in each watershed and discharge and dissolved N, P, and DOC concentrations in flow at each watershed outlet for runoff-generating rainfall events between 2010 and 2012. We used path analysis to test hypotheses about the relationships among infrastructure characteristics, land cover, storm characteristics (including antecedent conditions), and nutrient and DOC loads. We found that retention-basin density decreased and imperviousness increased runoff, which in turn increased nutrient and DOC delivery. Concentrations varied with antecedent conditions and rainfall but did not vary with watershed characteristics. We show that stormwater infrastructure creates heterogeneity in the hydrologic and biogeochemical function of urban watersheds and that stormwater management may represent a major source of ecosystem heterogeneity within and across cities.

The global reach of human activities affects all natural ecosystems, so that the environment is best viewed as a social-–ecological system. Consequently, a more integrative approach to environmental science, one that bridges the biophysical and social domains, is sorely needed. Although models and frameworks for social-–ecological systems exist, few are explicitly designed to guide a long-term interdisciplinary research program. Here, we present an iterative framework, \"“Press-–Pulse Dynamics\"” (PPD), that integrates the biophysical and social sciences through an understanding of how human behaviors affect \"“press\"” and \"“pulse\"” dynamics and ecosystem processes. Such dynamics and processes, in turn, influence ecosystem services -–thereby altering human behaviors and initiating feedbacks that impact the original dynamics and processes. We believe that research guided by the PPD framework will lead to a more thorough understanding of social-–ecological systems and generate the knowledge needed to address pervasive environmental problems.

Urbanization, an important driver of climate change and pollution, alters both biotic and abiotic ecosystem properties within, surrounding, and even at great distances from urban areas. As a result, research challenges and environmental problems must be tackled at local, regional, and global scales. Ecosystem responses to land change are complex and interacting, occurring on all spatial and temporal scales as a consequence of connectivity of resources, energy, and information among social, physical, and biological systems. We propose six hypotheses about local to continental effects of urbanization and pollution, and an operational research approach to test them. This approach focuses on analysis of \"megapolitan\" areas that have emerged across North America, but also includes diverse wildland-to-urban gradients and spatially continuous coverage of land change. Concerted and coordinated monitoring of land change and accompanying ecosystem responses, coupled with simulation models, will permit robust forecasts of how land change and human settlement patterns will alter ecosystem services and resource utilization across the North American continent. This, in turn, can be applied globally.