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No. 90: Suburban gardens - part of the city's natural

Petersen, L.K., Levin, G., Ejrnæs, R., Zandersen, M. Jensen, A. & Brunbjerg, A.K. 2014. Parcelhushaven - en del af byens natur. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 88 s. - Videnskabelig rapport fra DCE - Nationalt Center for Miljø og Energi nr. 90. http://dce2.dk/pub/SR90.pdf

Summary

This report presents the results from a cross disciplinary research project about ecosystem services, nature quality and climate change adaptation in suburban landscapes, focusing on the greater Copenhagen area. The aim was to determine the potential for advancing biodiversity and ecosystem services on private properties in suburban areas and thereby to advance a coherent urban green structure with high nature quality, robust adaptation to climate change and diverse recreational and cultural values.

The project was completed in 2013 through five separate sub-studies concerning (1) land use and green structure in the greater Copenhagen area, (2) garden habitats and their ecology, (3) garden owners’ perception, design and use of their gardens, (4) garden owners’ attitudes towards different initiatives to advance biodiversity and sustainable management of rainwater, and (5) local authorities’ perception and planning of urban green structure, biodiversity and the role of private gardens.

Together the five sub-studies show that there is a potential for advancing biodiversity and retain rainwater in suburban gardens. Gardens cover enough land to make a difference and can easily provide a variety of habitats. Initiatives to advance biodiversity and rainwater retention do, however, not match common practices and perceptions of garden owners and users, but there is a potential for designing gardens in ways that provide more habitats while at the same time accommodating gardens owners’ aesthetics for and uses of their gardens.

Undeveloped areas in connection with buildings, i.e. primarily gardens around single family houses, are usually not included as green areas in land use assessments. However, this report shows that private gardens do in fact cover a significant part of the greater Copenhagen area; around 6 % of the entire area and 10 % the total green structure. A certain share of private gardens consists of sealed surfaces such as asphalt, cement, tiles, or the like and can therefore not be classified as green. The project estimates that sealed surfaces make up app. 22 % of the total garden area. Nevertheless private gardens do cover a sufficiently large area to make a difference for urban drainage systems and to potentially make a difference for biodiversity.

The typical suburban garden already contains habitats that have become rare in the cultivated landscape – e.g. nesting places and sources of nectar for wild bees and scrubs for fungi and small birds – and gardens can potentially be designed in ways that provide more habitats and hence higher biodiversity; for instance by laying out a part of the lawn to dry meadow, or preserving old trees and dead wood (such as a high tree stump). Similarly rainwater can potentially be retained by a green roof or a rain bed, both of which also provide habitats for a larger variety of species.

The project has developed an index by which the biodiversity of private gardens can be assessed. The index can serve as inspiration for all that work with gardens and are interested in promoting biodiversity.

Even though private gardens potentially can contribute to advancing biodiversity and rainwater retention other concerns are at the core of people’s design and use of their gardens. The garden is perceived as an outdoor part of the home, and spaces for relaxation, on your own or with family and friends, is among the key benefits of the garden and crucial in its design and usage. Enjoyment of the garden does, however, also come from the access to nature that it to some extent provides including the experience of living plants and trees, of greenness and changing seasons, of birds and butterflies and other animals. But nature in gardens must be tamed to provide this enjoyment. The garden must be tidy and there must be clear borders between its elements. For some the pleasures of the garden, it’s almost therapeutic qualities, even consist in the garden work itself, the work of trimming, nursing, and tidying.

Attitudes towards biodiversity and sustainable water management in the garden are somewhat ambivalent. On the one hand a surprisingly large majority of respondents agree that property owners have co-responsibility to protect and advance biodiversity as well as to prevent flooding from cloudbursts. On the other hand, people are cautious towards concrete garden elements that can advance biodiversity or retain rainwater. Some of these even seem contrary to common garden designs and aesthetics. Old trees cast shadow and can be dangerous; multiple species in a hedge appear untidy and are more difficult to keep, and a heap of brushwood disturbs the eye.

Within the common aesthetic, practical and social frames for garden design there may, however, be room for additional landscape elements that provide more habitats and hence a larger variety of species. Some of these, like making sure that there are blooming trees and plants throughout the summer half, match existing aesthetic preferences. Other landscape elements such as a heap of brushwood, preservation of old trees or a rain bed, mainly seem relevant in larger gardens or only become pertinent if you have experienced flooding at the property. And some require a nudge in the shape of information and demonstration or in the shape of public subsidies. Thus, the prospect of converting a section of the lawn to a low maintenance meadow was met with positive interest by respondents; they just needed to learn about the possibility. The prospect of refitting a garage or an outhouse with a green roof was met with similar interest, but would more likely require subsidies.

Green structure has in recent years become increasingly important in urban planning, but private gardens have not yet been included in this development, and biodiversity has only recently become a topic in local governments’ perception of green structure. Private gardens are to some extent included in local efforts to adapt to climate change, particularly with respect to water retention, but city planners focus predominantly on public green areas. Hence, biodiversity in gardens and suburban landscapes may best be promoted through a concerted effort involving different actors like garden centres, homeowner’s associations, allotment societies, and other civil society organisations in collaboration with municipalities and government agencies.