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BRINGING URBAN BIODIVERSITY RESEARCH INTO PRACTICE
Alessandro Ossola, Ulrike M. Irlich and Jari Niemelä
Cities and towns are the largest construct ever made on earth by a single species, Homo sapiens. Since humans abandoned their nomadic lifestyle, they started to build villages and towns, organising their communities and societies within and around them. Over time, urban expansion has caused numerous species, habitats and even whole ecosystems to be destroyed and altered. Peri-urban areas have been progressively cleared to make space for new developments and agricultural fields to feed an increasingly large human population. For the first time in biological history, novel urban habitats and ecosystems with no counterpart in the natural world have been created by human intervention, creativity and power (Gilbert 1989). Overall, this complex and rich variety of urban species, habitats and ecosystems is what we now commonly define as urban biodiversity (i.e. urban biological diversity).
Urban biodiversity is an ecological term frequently confused and interchangeably used with urban green space and urban green infrastructure, which principally derive from disciplines such as urban planning, landscape architecture and environmental management. By definition, urban biodiversity is a more general term that comprises the two other terms. For example, an urban stream is an aquatic ecosystem but not an urban green space, while an urban park is both an urban green space and an ecosystem. In writing this book, we have therefore privileged the more general term urban biodiversity, though the terms urban green space and green infrastructure are also used in numerous instances.
A brief historical overview of urban biodiversity research
Humans have examined urban biodiversity since the foundation of their early settlements. Much of the knowledge on biodiversity was pivotal for human livelihood, such as the provision of food and natural resources or the control of urban pests and diseases. Knowledge was mostly transmitted orally, though various manuscripts on urban animals and plants have been written from different civilisations over the centuries (Sukopp 2008). It was not until the onset of the twentieth century that a formal and more structured interest in urban biodiversity sparkled among researchers. Paradoxically, humans were the first species studied in an extensive urban research program. In fact, by applying early ecological principles, researchers at the Chicago School conducted numerous studies looking at relationships between human behaviour, social structures and urban environment during the 1920s and 1930s (Weiland and Richter 2012).
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A further impulse to the research on urban biodiversity literarily germinated from the rubbles of World War II. Plant communities in degraded urban areas were in fact extensively studied by researchers of the Berlin School of Urban Ecology during the 1970s. Since then, numerous other studies, mostly focusing on landscape pattern and distribution of urban plants and animals, have been published (Figure 1.1). Researchers have found that the diversity of urban species is often comparable to that of peri-urban landscapes (Pickett et al. 2008), with numerous rare and threatened species still being discovered in urban areas nowadays (Ives et al. 2016). Even urban soils and waters, commonly believed to be biologically depleted, can host bountiful species (Szlavecz et al., Chapter 2). In addition to the native species surviving in cities (i.e. original of that area), countless new species (i.e. introduced or exotic species) have been involuntarily and voluntarily introduced due to their economic and aesthetic value (Aronson et al., Chapter 7). Over time, introductions have increased the species pool in various cities and towns worldwide. However, researchers found that introduced species can often be a significant threat to native species, particularly when these become invasive or pests (Wauters and Martinoli, Chapter 6; Hochuli and Threlfall, Chapter 4), potentially leading to the homogenisation of urban biological communities worldwide (McKinney 2006; Kowarik 2011).
It is not until after the first Convention on Biological Diversity (CBD) held in Rio de Janeiro, Brazil in 1992 (www.cbd.int/) that the term urban biodiversity appeared in the academic literature for the first time. Since then, the number of publications on urban biodiversity has experienced an exponential growth, particularly from the late 1990s (Figure 1.1).
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In 1997, the establishment of two urban Long-Term Ecological Research (LTER) projects in Baltimore and Phoenix (USA) signed the beginning of the modern high-tech investigation of urban ecosystems that is still well underway today. Recent publications are starting to shed light on the important role of urban species and ecosystems in regulating key ecological processes and functions, such as soil nutrient cycling, urban heat island reduction and pollution mitigation (Pickett et al. 2008; Ossola et al. 2016). Almost a century since the Chicago School, humans also returned at the centre of the research agenda in the 2000s, recognised as critical components of urban socio-ecological systems. Researchers discovered that humans can not only affect urban species and ecosystems, but also receive numerous benefits from them as ecosystem services (Langemeyer and Gómez-Baggethun, Chapter 3). For example, it has been shown that the vicinity to green spaces is positively reflected in real estate prices in numerous cities worldwide (e.g. Tyrväinen and Miettinen 2000). Urban green spaces are important for human cultural and recreational activities (e.g. festivals, sports), as well as for local food production (Lin and Egerer, Chapter 5). This can enhance the overall well-being of communities, but also offer new employment opportunities, besides those traditionally related to the management and maintenance of urban green spaces (e.g. gardeners, horticulturalists, arborists, etc.). Research suggests that it is ecologically and economically sound for cities to maintain and further develop their green space networks and green infrastructures (Minor et al., Chapter 12) while planning for (Borgström, Chapter 10) and managing the overall urban biodiversity (Cilliers et al., Chapter 11). The incorporation of people preferences, perceptions and values into biodiversity-sensitive urban designs can further facilitate the conservation of urban biodiversity (Lee and Kendal, Chapter 8; Ignatieva, Chapter 14). Importantly, researchers have found numerous links between urban biodiversity, and human physical and mental health in cities (Korpela et al., Chapter 9). For instance, visiting and spending time in green spaces has been shown to significantly reduce blood pressure. Even seeing green spaces from a window can significantly lower recovery time of hospitalised patients. Recent research confirmed that biodiversity in the surrounding landscape increases the diversity of bacteria on human skin, consequently lowering the incidence of allergies (Hanski et al. 2012). In addition to the direct human health benefits, enhancing green infrastructure of cities can indirectly facilitate innovative nature-based health solutions, such as green care (i.e. care of people using green infrastructure), and preventative medicine. A further recent avenue of research is exploring the interlinkages between urban biodiversity and cultural diversity, following the so-called biocultural diversity concept (e.g. Pretty et al. 2009; Maffi and Woodley 2010). Urban green spaces have a key role in maintaining not only urban biodiversity, but also the socio-ecological memory of urban systems (Barthel et al. 2010), thus sustaining important socio-ecological functions, resilience and adaptive capacity.
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The beginning of the twenty-first century has seen the number of humans living in urban areas surpassing those living in rural areas (United Nations 2015), an unprecedented event in our evolutionary journey. We are approaching apace what researchers have defined the Anthropocene, a new geological epoch where human impacts have been manifested into the earth’s skin – the layers of soil, sediment and ice across the globe (Waters et al. 2016). Much of the environmental and climatic change leading to this new epoch has been directly or indirectly generated from urban areas, anticipating unparalleled threats coming from rampant and seemingly unstoppable urban futures. Many cities have been built near natural biodiversity hot-spots, and future urban expansion poses new, challenging scenarios not only for urban species, habitat and ecosystems, but also for those that persist beyond urban fringes (Seto et al. 2012). Despite the proximity of many cities and towns to pristine ecosystems, humans are becoming progressively detached from nature, spending more time in digital rather than outdoor worlds, with potential deleterious effects for biological conservation (Shwartz, Chapter 13).
This represents an important and stimulating time for urban socio-ecological research and the thousands of researchers that will continue to tackle these numerous issues on urban biodiversity in the coming years (McDonnell and MacGregor-Fors 2016).
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BOX 1.1
Since the early 1990s, more than 3500 publications specifically related to urban biodiversity have been published in the academic literature (based on the Scopus database (Elsevier), 7 June 2016). However, this represents only a small fraction of all the publications related to urban biodiversity. Many others, for example on urban animals and plants, do not explicitly mention the term urban biodiversity in their texts (Figure 1.1). Most publications on urban biodiversity (88 per cent) are represented by articles published in academic journals, followed by conference papers (6 per cent), books and chapters (5 per cent) and other types of documents (1 per cent). In particular, articles have been published in more than 150 different academic journals that cover a vast range of disciplines such as ecology, planning, environmental management, engineering, sociology, policy, conservation, horticulture, toxicology, sustainability, hydrology, forestry and economics. This demonstrates that, particularly in the last 25 years, urban biodiversity has become a vast research topic able to transcend environmental disciplines and stimulate the interest of researchers from numerous other disciplines. The latest research on urban biodiversity has also become more geographically widespread, with researchers from 131 countries having published at least one contribution on the topic to date. Overall, most of the research on urban biodiversity has focused on cities across Europe, Northern America and Australia (Figure 1.2). Urban biodiversity in many countries in Central and Southern America, Africa and Asia has been proportionally less studied (Figure 1.2). This represents a clear gap in the academic literature that future research should timely address, some of these developing countries being located in biodiversity hot-spots ...
