Values and benefits

More than half the world’s population now lives in cities, compared with about 14% a century ago. This increasing urbanisation radically modifies the ecology of landscapes. The effects on urban biodiversity include changes such as:

• loss and fragmentation of natural vegetation, and the creation of novel habitats;

• alteration of resource flows into local human habitats, including reduction in net primary production, so we survive on trucked in foods;

• increase in regional temperature, and degradation of air and water quality;

• disturbance regimes, with many habitats experiencing more frequent disruption;

• change in species composition, species diversity, and proportions of alien species. 

Conservation planners thus face a dilemma: how much of a fixed budget should be spent on conservation in urban versus non-urban landscapes? The answer to this question should depend on the motivations and goals that drive conservation actions because different goals may require very different approaches.

It is difficult to define and assign value to biodiversity in an urban context. In rural ecosystems, definitions of biodiversity are complex and depend on size of habitat, but are relatively straightforward in urban systems.  However, the definition of biodiversity can be controversial, especially with regard to alien species, which often dominate open spaces of urban environments.  Even if these exotic species are excluded from measures of diversity, suburban and peri-urban ecosystems sometimes have higher species richness than the native systems they replaced. This may result from an addition of native species that have adapted to the urbanized areas, or from an increase in resources, such as human waste, and habitat heterogeneity. This increased wildlife richness in such areas may be valuable if the goal is to maximize human residents’ exposure to different species, but may be less valuable if the goal is to maintain functional, sustainable neighbourhood parcels of the native landscape. Thus, the particular reason for biological conservation in an urban area dictates how biodiversity is viewed, defined, measured, and valued by residents.

Some reasons, such as ethical and religious motivations, highlight benefits of biodiversity for both humans and nature. Although many conservation biologists will see human welfare as inextricably linked with conservation of nature, members of the general public often better understand explicit arguments that directly connect human welfare and biodiversity conservation.  This results in a sliding scale of motivation according to whether the emphasis is placed on benefits to nature or benefits to humans (Fig. 1).

Fig 1 Importance of urban biodiversity

For many people, garden or house plants may be their only point of conact with nature apart from feeling the effects of weather.  Private gardens now furnish the human ecological niche and offer the urban citizen the opportunity of dwelling with nature by making personal choices about what plants to grow and how to manage them.  Since the 1992 Rio Environmental Summit, there has been an additional agenda for gardeners, which is to become involved with sustaining their ecosystem services and supporting the biodiversity of their neighbourhood.  This means minimising irreplaceable inputs to gardening and reduce its harmful outputs.  The support of biodiversity brings a demand for wildlife-friendly planting practices, such as reducing the amount of regularly mown lawn and the unnecessary trimming of woody plants for unclear motives.  Gardening with long-lived perennials can create a rich garden habitat that offers natural beauty close at hand, provides resources and homes for wildlife and improves the sustainability of household management.