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Cities are sometimes characterized as homogenous with species assemblages composed of abundant, generalist species having similar ecological functions. Under this assumption, rare species, or species observed infrequently, would have especially high conservation value in cities for their potential to increase functional diversity. Management to increase the number of rare species in cities could be an important conservation strategy in a rapidly urbanizing world. However, most studies of species rarity define rarity in relatively pristine environments where human management and disturbance is minimized. We know little about what species are rare, how many species are rare, and what management practices promote rare species in urban environments. Here, we identified which plants and species of birds and bees that control pests and pollinate crops are rare in urban gardens and assessed how social, biophysical factors, and cross-taxonomic comparisons influence rare species richness. We found overwhelming numbers of rare species, with more than 50% of plants observed classified as rare. Our results highlight the importance of women, older individuals, and gardeners who live closer to garden sites in increasing the number of rare plants within urban areas. Fewer rare plants were found in older gardens and gardens with more bare soil. There were more rare bird species in larger gardens and more rare bee species for which canopy cover was higher. We also found that in some cases, rarity begets rarity, with positive correlations found between the number of rare plants and bee species and between bee and bird species. Overall, our results suggest that urban gardens include a high number of species existing at low frequency and that social and biophysical factors promoting rare, planned biodiversity can cascade down to promote rare, associated biodiversity.

Green infrastructure (GI) is a vital asset for sustainable cities, but an interdisciplinary approach must be taken if multifunctional and socially acceptable GI is to be developed. Here, we present the results of a workshop process to connect researchers and practitioners across academia, industry, and government and to enable a multidisciplinary group of participants to coalesce on a set of cross-cutting issues and prioritise a research agenda to address and advance GI research and uptake in Australia. We found that many of the challenges were ubiquitous across regions and scales, but research in a few key priority areas could advance GI across multiple cities. The key research areas were: Attitudes & Perceptions of GI; Increasing Biodiversity through GI; Optimising Spatial Configuration and Composition for Multiple Benefits; Economic Valuation of GI; Metrics, Models and Tools for Benchmarking Assessments; and Turning Research into Policy and Implementation. Although participants saw that there were many synergies across the research topics, there were challenges of translating the science for decision making and of establishing long-term institutional collaborations. However, urgency for sound evidence to support policy development and planning will require an interdisciplinary process to be maintained so that clear communication can be established across sectors. [ABSTRACT FROM AUTHOR]

Soils are the foundation for cultivating ecosystem services in urban agriculture. Yet, variations in socio-environment characteristics of urbanization leads to variable soil properties and unequal distribution of ecosystem services like soil fertility. Thus, examining relationships among biophysical features and social dimensions of urban agricultural systems is necessary to understand soil functioning variation and to develop urban agricultural systems that promote equitable ecosystem service provisioning. In 25 urban community gardens in California, we examined two links between soil properties and neighborhood socio-demographics: (1) how groundcover management affects soil properties; and (2) how socio-demographics (and in particular, social advantage) can affect groundcover management and soil properties. We found that mulch groundcover improves soil fertility and water holding capacity in gardens, and that socio-demographic factors may affect people’s access to mulch to affect soil properties: neighborhoods with measures of higher mobility (e.g., greater vehicle availability), but measures of poorer public/environmental health (e.g., poorer health care access) had more soil organic matter, higher soil nutrient content, and greater water holding capacity. However, we found indicators of high functioning soils in the absence of mulch, indicating that other factors like social networks and organizational support may be important for urban agricultural ecosystem services. Edited by Graciela Rusch [ABSTRACT FROM AUTHOR]

The international carbon market provides a unique opportunity to increase ecosystem services and biodiversity through the revegetation of agricultural landscapes. Although the primary motivation for revegetation is to increase carbon sequestration, revegetated areas can provide additional financial, social, and environmental cobenefits that provide different levels of private and public net benefit. Conversely, carbon farming, if it is not implemented carefully, can create disbenefits, such as increased land clearing, monoculture plantations replacing diverse remnants, and unintended impacts across national borders. Economic models of carbon revegetation show that policies aimed at maximizing carbon sequestration alone will not necessarily lead to high uptake or maximize cobenefits. Careful consideration of policy incentives that encourage carbon plantings to deliver both public and private cobenefits is required, and solutions will need to balance both objectives in order to incentivize the sustainable, long-term management of carbon plantings across the landscape. [ABSTRACT FROM AUTHOR]

There has long been a debate amongst conservation biologists about how agricultural land use should be distributed spatially. Advocates of land sparing argue that high-intensity food production on small units of land will conserve more natural habitat than low-intensity farming spread across larger areas. Others argue that less intensive production over a greater area of land will reduce the overall load of human stressors upon ecosystems., Although agricultural and urban systems have traditionally been considered as different fields of research, there are strong parallels between the two landscapes in the patterns of their spatial configuration and the trade-offs associated with their development. Continued and rapid urbanization, with associated losses in vegetation, highlights the need for a uniting spatial framework to assess the ecological impacts of urbanization. Here, we apply some of the thinking emerging from the agricultural land-sparing debate to urbanization, review the similarities and differences between the two systems and set out a research agenda., Intensification of urban systems to increase housing density leads to buildings being interspersed with small tracts of natural or semi-natural habitat patches (e.g. forest patches, parks). Urban extensification, on the other hand, is characterized by sprawling suburbanization with less concentrated, more distributed green space, often predominantly in the form of backyard or streetscape vegetation. We argue that regional scale analyses are urgently needed to determine which of these patterns of urban growth has a lower overall impact on biodiversity and to explore the geographical and taxonomic variation in the most ecologically appropriate city layout., Synthesis and applications. The spatial pattern of urban development will affect biodiversity conservation within and beyond a city's borders. We chart the early progress of empirical work on the land-sparing debate in an urban context and suggest that to yield development patterns that minimize overall ecological impact, urban planners must work at the scale of at least the entire city rather than on a case-by-case basis. [ABSTRACT FROM AUTHOR]

• We synthesize three years of research in urban community gardens in Central Coast, California. • Global social and environmental change factors impact management and delivery of ecosystem services. • Garden regulations and management decisions by gardeners determine the ecological complexity of gardens. • Ecological complexity can affect the ecosystem service, such as food provision, coming from gardens. • Active management can increase social-ecological outcomes that feedback to the larger system. Urban community gardens are vital green spaces threatened by global social and environmental change factors. Population growth has reduced the amount of space available in cities, and climate change challenges plant growth thresholds. Urban community gardens provide dynamic socio-ecological systems to study how such social and environmental change factors affect the management and delivery of ecosystem services. They provide spaces where urban citizens purposefully interact with nature and receive multiple benefits. In this paper, we synthesize the results of three years of research in a case study of urban community gardens across the Central Coast of California and present a framework showing how both social and environmental change factors at the regional scale affect the ecological make-up of urban community gardens, which in turn affect the ecosystem services coming from such systems. Our study reveals that global environmental change felt at the regional level (e.g., increased built environment, climate change) interact with social change and policy (e.g., population growth, urbanization, water use policy), thus affecting regulations over garden resources (e.g., water availability) and management decisions by gardeners (e.g., soil management, crop planting decisions). These management decisions at the plot-scale, determine the ecological complexity and quality of the gardens and affect the resulting ecosystem services that come from these systems, such as food provision for both humans and urban animals. A greater understanding of how environmental and social change factors drive the management processes of urban community gardens is necessary to design policy support systems that encourage the continued use and benefits arising from such green spaces. Policies that can support urban community gardens to maintain ecological complexity and increase biodiversity through active management of soil quality and plant diversity have the potential to increase social and environmental outcomes that feedback to the larger environmental and social system. [ABSTRACT FROM AUTHOR]