A garden full of life: biodiversity
Gardens can contribute to urban biodiversity (ecosystem service ‘natural heritage'), as is exemplified by the counting's of garden birds and butterflies by voluntary observers. The edges of a city often contain remainders of the old landscape and provide better chances for nature in gardens than in more hardened old parts of a city. Especially gardens that are home to native Dutch trees, bushes and florid vegetation are attractive for animals such as pollinating insects, spiders, soil biota, and herewith also for birds and small mammals like mice and hedgehogs.
If the physical planning of a garden encompasses nest- and shelter areas, (by variation of structure and materials) and the garden produces food for animals, then the liveliness of the garden will increase even more. Not only large gardens count, also smaller gardens such as green roofs, yards and patios can be full of life.
It is important to choose plants that can provide nectar and pollen for insects; this is often not the case with cultivated plants. Also almost all the available trees and shrubs are cultivars. Fortunately, garden centers are starting to pay more attention to the functionality of plants as valued-and food plant. (The Dutch national forest organization 'Staatsbosbeheer' owns a public plantation nearby Dronten (Roggebotzand) – a ‘living gene bank' – with trees and shrubs originating from Dutch populations.
Private-owned gardens are getting smaller and contain less greenery
Private-property owners are responsible for about 40% of the urban area; however, the contribution of gardens to a green living environment in the city is declining. Partly because of this, even ordinary species such as sparrows and starlings are facing difficulties today.
The surface reserved for gardens in new neighborhoods has decreased in the last decennia. Moreover, urbanization has been subject to the process that more inhabitants are tiling up their gardens, partly because of the idea that ‘green' costs time and energy.
In addition, gardens function more and more as extension of the living room, with adjacent ‘flooring' i.e. tiles. More than in the past, gardens are altered; a stable ‘garden environment' such as a row of green backyards with old trees and shrubs, is becoming a rarity. In the common small and tiled up gardens of present times, the chances to find a young bird or hedgehog nest are small.
Taken over a whole neighborhood, gardens can provide a relatively large share of greenery and by this assist with delivering the desired ecosystem services. Next to ‘cultural heritage', it also provides recreation (relaxation/health), cooling (climate regulation), pollination, pest resistance and it prevents water disturbances. Sometimes old trees and shrubs fulfill a special ecological function (shelter and nesting spot) and, together with the public greenery and waterways render character to a neighborhood.
How many gardens do we have?
Although knowledge about public greenery, even at national scale, is well known, the data on private gardens is still fragmented. Countrywide information about the size of parcels in relation to garden surface throughout the years is not available. There is some data showing that the level of construction works, paving of surfaces, public green, surface water and gardens has a great degree of variety. The most detailed research took place in three neighborhoods in Groningen. From 1998 until 2013, paved surface in gardens had increased from 3% to 14%, while the average stayed below 5%. Research that followed the developments of a suburban area in Leeds (England) from 1971 to 2004, showed an increase in paved surface from 31% to 44%. Three quarters of this increase was due to the paving of gardens.
Overall, not much attention has been given to a variation of plants and animals in gardens. So far, no national data exists about biodiversity in gardens, nor data about biodiversity in public greenery or urban greenery as a whole.
Influence on water regulation
Water that does not infiltrate in the soil can either evaporate, flow towards waterways or drain into the sewage system. This means that an increase in paved surfaces can aggravate the load on the sewage system. However, opposite effects can also be steered at by smart planning of a neighborhood and by choosing soil type and height differences in the area.
The research in Groningen showed that the neighborhood with the smallest capacity for treating sewage had no problems with water at all. This neighborhood (Helpman), is located on the edge of the city, and its excess of water automatically flows into lower situated meadows.
In the English town of Leeds, the paving of gardens most likely plays a role in their substantial problems with water, according to research done in the suburban neighborhood
Cities are warmer than the countryside. Stones, asphalt and roof tiles hold warmth much better than vegetation does. One of the ‘sources' of cooling in the city is the direct evaporation of water when it is raining, which does not function well when rainwater is quickly drained through the sewage system. In addition, the evaporation by plants, ‘open soils' in which water can infiltrate and the shadow of trees all add up to cooling the city. In principal, the increase in pavement does have consequences for the temperature in an area. A lot depends on neighborhood planning, which includes; water regulation, the total percentage of open soil and the type of soil. In the few investigated cases, the contribution of tiled private gardens to warmth in the city is rather small compared to the influence of buildings and hardened surfaces.
Local circumstances in a neighborhood such as; soil conditions, height differences, water management, the type of sewage system (mixed or separated) and the percentage of open soil (all types of (semi) public green, surface water, presence of trees next to roads etc.) all determine whether the increasing amount of hardened surfaces in private gardens poses a problem.
That is why it is important to map out the conditions of a city including the inter-neighborhood variation, and to connect this information to data about problems with water, urban biodiversity and the quality of the living environment. Knowledge about the water and nature situation in the city, can give inhabitants a different perspective on their garden.
Giving the good example
Besides the duty of caring for rainwater, it is up to the inhabitants what they decide to do with their parcel. A municipality that aims to encourage green gardens, has only one way to go: Providing information, raising awareness, campaigning and triggering (courses, possibly subsidies).
Therewithal, a municipality should of course show how it's done by setting up and maintaining their own ‘garden', the public greenery. Only then, suggestions can be made for gaining beautiful private garden additions to the public green, also taken into consideration the aspect of biodiversity.
Joining initiatives /working together with business
If a municipality wants to work on the greening of gardens, it is advisable to join active inhabitants and /or cooperate with businesses. Also, departments of for example the IVN (institute for nature education and sustainability), the KNNV (institution for field biology), the institution for mammals (also for bats) or the bird protection agency can play a role; The Dutch bird protection agency even has special ‘city-bird advisors'. Projects like the building of a new neighborhood, renewal of the sewage system or redevelopment plans of a business area provide good chances for gaining more nature in the city. Reoccurring problems with water can also be a trigger. It is important that local governments take the chance and provide optimal cooperation and facilitation. This will raise the potential for creating a neighborhood garden, a water playground, having public-managed maintenance of natural green or a project on private gardens.
From tiled to green gardens: municipalities can encourage
When a municipality takes urban biodiversity serious, and wants to encourage green and natural gardens, they should not have too many flaws in their own management of green. The ideal green policy would be that a municipality combines culture-historical and natural values, have a transparent policy that is visible and livable, fits with the neighborhood and a certain ease for civilians to join in with their garden. A municipality can give information, provide seedlings, have inhabitants maintain certain parts of public green or help to make a neighborhood garden possible.
They can also stimulate the fostering of native Dutch shrubs and trees. When inhabitants or businesses are participating in joint maintenance of green and/or nature, it can soon lead to real projects in which sometimes multiple government institutions are involved (municipality, water management bodies). Such projects are a perfect window of opportunity for a municipality to engage in natural green. It can be about a courtyard, a business area or an empty plot of land (‘temporary nature')
Water law: Duty of care for rainwater
In both neighborhoods as well as in business areas, owners, inhabitants and/or users are free to do with their parcel or garden as they please. However, they are responsible for the processing of rainwater on their own parcel by means of infiltration or drainage to surface water (Water law 2009 – under the condition that the water is clean, if not then treatment is compelled). If the rainwater drainage is not possible under the circumstances that is it not someone's own fault, then the municipality is responsible to offer the necessary facilities. If infiltration is impossible because the entire parcel has been paved, then it does not fall within the duty of the municipality
Nature on business areas
Also companies have gardens. Such gardens, possibly together with the collectively maintained greenery on business areas, provide an excellent chance for cooperation between municipality and companies.
Arnhem: A stream through the front yard
The street ‘Julianalaan'' in Arnhem has been created just before the Second World war on country estate ‘Angerenstein'. Situated on a lateral moraine, it was discovered after some time that close by the road in the remnants of the country estate, which now is a park, there exists a natural spring. Around the year 2000, this caused zinc holes in the street ‘Julianalaan'. The designation of the new sewage system was a reason for some inhabitants to solve the water problem in an original way. It became a multi-annual project, with many involved governmental agencies and the necessary (voluntary) digging. Now the water flows from the park across the road, through 16 front yards and again over the road into a ditch. Each yard has their own piece of stream.
Operation ‘Steenbreek' (Stonebreakage)
Operation ‘Steenbreek' is a project of i.e. the gardening sector, the institution for field biology (KNNV) and various (knowledge) institutes, and aims at encouraging civilians to make their tiled-up gardens greener. In eight cities (i.e. Leeuwarden, Groningen, Maastricht and Den Haag) municipalities sometimes together with a garden center, raise awareness for example by offering courses, provide help with development of yards and give help and advice with ‘de-tiling' the garden.
Eindhoven: the forgotten garden
For twenty years there were company buildings standing in the courtyard of a block of small working-class houses in Eindhoven (Palingstraat). After the company left, the terrain turned into set-aside area. Slowly a wild garden started to evolve. In 2002, the garden was transformed in a city-nature-garden, based on a crafty design. The terrain gained the official status of ‘green destination' in 2007. The organization ‘Veldwerk', mainly composed of neighborhood inhabitants maintain the area.
Eindhoven: High Tech Campus
The High Tech Campus in Eindhoven, the former terrain of Natlab (about 100 hectares), is set up as a sustainable business area and a high quality of the working environment is aspired. With the re-development plans at the end of the 90ties, a landscape set-up was chosen that takes into account the soil, the typical stream-valley landscape of Brabant and chances for nature (de Dommel flows next to the terrain).
Zoetermeer: Business area Heineken
Heineken is working with nature on its own business area in Zoetermeer. Within the program ‘Green cirkels', Heineken has started with the development of bee landscapes. The terrain is set up and maintained in such a way that pollinating insects have more chances to collect food and to hibernate in winter. Read the interview with Jan kempers.
- Potential removal of particulates (PM10) by vegetation
- Water purification by the subsoil
- Self-cleaning capacity of the toplayer of the soil
- Soil's moisterizing capacity
- Contribution of the soil to climate regulation