Using green infrastructure to reimagine urban ecosystems

Green transition 2 June 2021 Laura Sanderson

There are many opportunities to reimagine urban ecosystems and introduce species-rich, beautiful areas within towns and cities that also help manage climate change. This article describes best practice with examples from recent projects in London.

8-10 min

What is green infrastructure?

Green infrastructure is described in England’s Planning Policy Statement 12 as “a network of multi-functional green space, both new and existing, both rural and urban, which supports the natural and ecological processes and is integral to the health and quality of life of sustainable communities”. 

It includes a wide range of features, usually but not exclusively urban:

  • Parks and gardens: urban parks, country and regional parks, formal gardens
  • Amenity greenspace: informal recreation spaces, housing green spaces, domestic gardens, village greens, urban commons, other incidental space, green roofs
  • Natural and semi-natural urban greenspaces: woodland and scrub, grassland (eg downland and meadow), heath or moor, wetlands, open and running water, wastelands and disturbed ground), bare rock habitats (eg cliffs and quarries)
  • Green corridors: rivers and canals including their banks, road and rail corridors, cycling routes, pedestrian paths, rights of way
  • Other: allotments, community gardens, city farms, cemeteries and churchyards

Introducing green infrastructure to new developments can provide numerous benefits – improving human health, wellbeing and the look of a neighbourhood, providing opportunities for recreation, increasing sustainability and ecosystem services, reducing urban heat, improving water and air quality, preventing flooding, improving the local economy – before we even get to providing biodiversity benefits.

Green infrastructure can be used as a nature-based solution to address issues such as climate change, for the benefit of people and nature.

Green infrastructure includes landscape planting, biodiverse roofs, green walls, rain gardens, sustainable drainage systems (SuDS)/swales, intertidal terraces and floating islands. This article addresses each of these.

Landscape planting

One of the simplest forms of adding green infrastructure to new developments is landscape planting. This can provide species and features beneficial to wildlife, while also looking attractive and being space-setting. Planted species do not need to be native to be of value, but where possible they should be of known wildlife importance and provide additional benefits such as nectar, pollen or fruit, or add shelter or nesting opportunities. Night-flowering species are beneficial as they attract evening flying insects such as moths, which provide food for bats.

A further consideration in the choice of species is climate change adaptability. Heat tolerant and low-maintenance plants may be important to choose. Creating a variety of habitat types, with taller trees and shrubs and low flowering areas and diverse grasses, creates a mosaic of habitat maximising opportunities for biodiversity.

Green/brown biodiverse roofs

A range of names are used for biodiverse roofs, all with slightly different meanings, including green, brown, intensive and extensive. At Ramboll we prefer to use the term ‘biodiverse roof’ where features for biodiversity are specifically included. Green roofs tend to be sedum dominated, which although they perform well in terms of establishing quickly, forming a colourful roof and being drought tolerant, they do not provide a range of species suitable to support a wider number of invertebrates. Intensive and extensive refer to the depths of substrate and the amount of management and watering they may need. For sustainability purposes, less management is preferable, although deeper substrates (or a range of substrate depths with mounded earth) can allow a greater diversity of plant types to be supported.

The aim in creating biodiverse roofs is often to recreate priority habitat type 'open mosaic habitat on previously developed land'. To maximise biodiversity benefits, features providing a range of niches for invertebrate species should be included, with a varied topography to provide south facing slopes, piles of stone, boulders, sand, earth and logs to provide basking, burrowing and foraging opportunities for invertebrates and birds, and even water holding devices, which can be as simple as shallow trays to collect rain water. A diversity of wildflower plant species should be incorporated appropriate to the site conditions and targeting locally important habitat types where relevant, such as chalk downland species in the south or woodland understorey species on more shaded roofs.

Brown roofs were devised as a move away from sedum green roofs. It was originally intended that these should reuse site-derived aggregate for sustainability purposes. Self-colonisation of plants could also occur, including from the seedbank with site material used, and with seeds blown in naturally from adjacent areas, to ensure locally abundant plant species of local genetic provenance thrive. However, there has been a move away from this approach as there are often problems with contamination of site-derived material, and the quality of it cannot be controlled to ensure a successful growing medium that drains correctly. Furthermore, self-colonisation of planting rarely works sufficiently. Brown biodiverse roofs can still be achieved but using specially prepared substrate (often made from recycled material) and pre-prepared planting with targeted species used.

Wildflower blanket turf is increasingly being used in place of seeding, as this often establishes faster and more successfully. Additional target plant species can still be added, either in advance within the turf planting or added later as plug plants and seeds. Holes can be cut within areas of the turf to allow additional biodiversity features to be included, such as log and sand piles. 

Berkeley Group’s The Green Quarter - Biodiverse roof

Biodiverse roof seen Berkeley Group’s The Green Quarter

Berkeley Group’s The Green Quarter - Biodiverse roof

Biodiverse roof seen Berkeley Group’s The Green Quarter

The addition of piles of sand, pebbles, boulders and logs can improve the biodiversity value of roofs, adding features suitable for insects to burrow in and bask on, and foraging opportunities for birds. Seen here at Berkeley Group’s The Green Quarter.

Biodiverse roofs can work very well with photovoltaic (PV) panels, helping to reduce overheating of the panels and with the panels’ shade reducing drying out of the vegetation. Specific PV biodiverse roofs are available, such as Bauder’s BioSOLAR roofs, which negates any reasoning for not having biodiverse roofs due to the need for PV panels.

The smallest of spaces can be utilised for biodiverse roofs, with bicycle sheds often utilised for this purpose. As well as maximising space, this allows the public at ground level to see and admire the roofs, ensuring they are not all hidden out of sight.

Modular designs of biodiverse roofs are available, to make installation easier. Bird and insect boxes can be incorporated on or near biodiverse roofs to increase their suitability for use by these species and encourage their use of the roofs.

Biodiverse roofs do require some management, particularly initially with watering and replanting of failed planting, until the roofs become established. Ongoing watering in particularly dry years may also be required, as well as annual cuts of vegetation, following the flowering of plants. 

Laban Dance Centre - Biodiverse roof

A biodiverse roof on the Laban Dance Centre in Deptford, one of the first to be built in London

Green walls

Green walls, when done well, look impressive and provide ample opportunity for vertical biodiversity in an urban setting. Successful examples include green walls at Edgware Road Station and Rubens Hotel at Victoria in London. However, being water-intensive, green walls can be costly and fail easily if not well installed and maintained. There are many examples of unsuccessful green walls and their dead vegetation. Ramboll has found that green walls formed from a variety of native climbing species, with appropriate trellis or wiring in place, can work well once established, serving a similar function, and are a lot easier to install and maintain. 

Rain gardens and swales

These green infrastructure features both slow water drainage in a nature-friendly way. They contribute to flood management and provide wetland habitat. Rain gardens can have a variety of planting, with species which are both flood and drought tolerant included. They do not have to be large to serve a useful function. Swales contribute to flood management of larger areas. To be of benefit to biodiversity, they should be planted or have vegetation allowed to develop naturally, and not be managed too intensively. Cutting of vegetation after flowering will encourage wildflowers to develop. 

River and inter-tidal terraces

The Environment Agency is increasingly requesting inter-tidal terraces be provided in previously canalised rivers. These features naturalise hard concrete riverbanks and re-introduce areas for nature to flourish. They can vary significantly in size, from small wood fenders attached to existing river walls, to large stepped terraces replacing hard walls. They are of great benefit to a variety of species, providing space for aquatic planting to develop which in turn provides cover for fish to spawn, niches for aquatic invertebrates and habitat for breeding birds and terrestrial invertebrates. They also look nice and can be linked to riverside walks and recreation, as well as providing flood-risk management and other sustainability benefits. 

Ramboll has worked on several successful examples, including tidal terraces at Fresh Wharf in Barking on behalf of Countryside and Notting Hill and Creekside Village East in Deptford on behalf of Kitewood. 

Tidal terraces at Fresh Wharf © Countryside and Notting Hill

CGI of tidal terraces proposed at Fresh Wharf, Barking, linking aquatic habitats with landscape planting and public access areas

Tidal terraces at Creekside Village East

Tidal terraces at Creekside Village East, Deptford, during high tide, when all but the tallest vegetation is submerged

Floating islands, nesting rafts and micro marshes

Where open water habitats exist within developments, particularly docks, quays, lakes and canals, these features can be used to increase biodiversity. Floating islands can be seen in Canary Wharf and Paddington Basin. Islands can be modular and be pre-planted with aquatic vegetation in coir rolls, with roots extending into the water. This provides both terrestrial and aquatic habitat, with roots providing shelter and foraging opportunities for fish and aquatic invertebrates, and plants above water providing nesting and loafing habitat for birds, shelter for mammals and a foraging resource for pollinating insects. Such features can also contribute to water quality, and by planting with colourful flowers can be very attractive. Modular designs are available, making them easy to install and use. 

Additional features such as brushes and larger spikes (sometimes known as hedgehogs) can be attached to the underside, providing additional shelter for fish. Even miniature versions of these islands (known as micro-marshes) can be beneficial for biodiversity.

Ramboll worked on the design of ecological mitigation features for the newly developed private members club The Quay Club in Canary Wharf, where biodiversity features include two floating rafts from BioHaven attached to the building platform, with pre-planted native aquatic plant species in coir fibre pallets, and additional fish spawning brushes. Biodiverse roofs and bat and bird boxes are also included in the design.

 
Floating islands at Canary Wharf provide habitat for nesting birds, insects and fish

Floating islands at Canary Wharf, providing habitat for nesting birds, insects and fish

Floating islands at Canary Wharf, providing habitat for nesting birds, insects and fish.

Floating islands at Canary Wharf, providing habitat for nesting birds, insects and fish

The green infrastructure types described here can all contribute to Biodiversity Net Gain and Urban Greening Factor assessments, which are often now required within new developments. 

Furthermore, these green infrastructure types do not have to be limited to new developments. New green infrastructure can be retrofitted to existing developments, improving spaces for people and nature. It can even be added to the smallest of spaces. Home-scale urban green infrastructure can include a biodiverse roof on your bin shed, a climbing green wall on your balcony or a rain garden under your down pipe. 

What could you do at home?

A miniature rain garden

A miniature rain garden installed under a down-pipe in the author’s front garden.

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