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.
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.