How to Rewild

Built-up Areas and Gardens

Habitat Management Plan

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Built-up Areas and Gardens
Habitat Guide

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Just over 5% of the UK is urbanised – this includes everything from the local park to an industrial estate, varying a lot in biodiversity value. Some animals piggyback off our existence – bird feeding, compost and waste create artificially-high populations of urban foxes, rats and house sparrows. In wild ecosystems, these animals are found much less often; and even smaller species like headlice, woodlice and house spiders can benefit from our presence.

However, urban habitats are usually degraded in several ways – they are typically treated with pesticides and/or fertilisers. The presence of cats and dogs results in very high predation and disturbance to local animal populations. Artificial and sealed surfaces create a heat island effect, with intensively-mown ground prone to waterlogging in winter and drying out in summer. 

Here and there, pockets of urban green space may escape some or all of these influences, and it is important to identify and protect these refuges. They act as hubs of biodiversity, which connect and replenish the wider landscape.

Sub Habitats

Buildings, roads and other developed surfaces.

Surfaces like concrete and gravel which have little growth of plants.

Typical suburban landscape of gardens, houses and roads, with a mix of green and grey surfaces.

Includes walls, pathways, railways, tracks and other narrow linear developed features of the landscape which cover significant areas of ground.

Value

Residential gardens make up nearly 5% of our land area in England (slightly lower in the UK as a whole). This compares favourably with the 8% of the country that is a designated SSSI – it means that there is huge potential in our gardens to protect and restore the nation’s biodiversity. While individual gardens may only act as a refuge or stepping stone, working collectively across many gardens with a single vision, we can create biodiversity impact on a landscape scale.

But not all of these habitats are of equal value – Built Linear Features generally don’t have the same benefits as a natural linear feature like a river or hedgerow. That is, unless they sit in a strip of uncultivated land (grassland, woodland, scrub), which can act as a valuable wildlife corridor through an urban area. Sparsely-vegetated Urban Land is a ‘seral’ habitat, where a surface like gravel is slowly colonised by pioneer species. This can create a valuable low-nutrient area which is rich in wildflowers and home to specialists like Black Redstart, Linnet and Slow Worm. 

Sparsely-vegetated Urban Land develops from Artificial Unvegetated, Unsealed Surface if this habitat falls out of use over time. However, the earlier habitat is of little value to biodiversity, with no plant life and few patches of bare soil. With even less value in most modern developments is Developed Land; Sealed Surface – here, the surfaces are generally designed to minimise plant growth. However, in older buildings, access to roof and subfloor voids, eaves, and even the inside of buildings can create nesting and foraging opportunities. ‘Green buildings’ featuring swift and bee bricks, bat boxes, green roofs and living walls may also create biodiversity value.

It is worth noting that, what these areas lack in biodiversity, they may make up for in other important resources, like housing, education, jobs and transport. We can integrate biodiversity into these developed areas, but ‘weeds’ will degrade roads, pavements, buildings and infrastructure. Failing to keep them under control will simply result in more emissions down the road, when the area needs to be rebuilt due to root damage. Weed control is an essential part of public infrastructure maintenance, which preserves the economic and cultural productivity of this habitat.

Frog in pond infested with duckweed
Even tiny residential ponds can be valuable for biodiversity, from amphibians to birds, invertebrates and mammals, which will all use the habitat.

Protect

Pesticides (including herbicides) will not only kill a target species, but also destroy valuable soil organisms and pollute nearby watercourses. However, we have been using pesticides to control ‘weeds’ for many decades now and it may be difficult to stop using them in some areas without consequences. As described above, it can result in significant damage to paving, roads, kerbs, bridges and other essential infrastructure. This creates hazards which disproportionately affect those on low income and/or with mobility impairments. Other options for ‘weed’ treatment in sensitive areas of infrastructure include hot foam, white vinegar, steam and flame.

Urban trees are an essential biodiversity component of this habitat, as they allow birds, bats and invertebrates to shelter, forage, breed and disperse from one green space to another. They also intercept rainwater, provide valuable shade, and reduce heat by transpiring, which means trees can be important in reducing human heat-related fatalities. However, we are losing street and garden trees planted by earlier generations, as they are removed rather than being replaced when disease or old age makes them a hazard.

More than a third of a tree is typically hidden below ground, but pavements are too narrow, and roots are sealed-in, in restricted spaces that inevitably lead to cracking and lifting of hard surfaces above. More sensitive urban design with larger, more porous root enclosures and better tree selection can minimise damage to infrastructure while maintaining benefits to humans and wildlife alike. 

Damage to root systems during construction work or garden landscaping is often the cause of tree dieback or death, so it is important to keep a protected zone around tree roots during these operations.

Cats and dogs have vastly different reputations – while most Brits understand the impacts that a cat can have on the local ecosystem, dog-owners are generally much less aware of the effects of their pet. While we have both wildcats and dogs (wolves) which are native to this country, the level of predation and disturbance created by a dense neighbourhood of cats and dogs is unlike anything in nature. Even a fairly sparse population of feral cats or low level dog-walking can significantly reduce the abundance of wildlife in an ecosystem.

The impact of cats is offset somewhat by bird feeding, which supports both birds and rodents at a higher density than in a natural habitat (as we are farming, then importing bird food on a large scale). But both dogs and cats scare away our more timid wildlife; cats can have a devastating impact on less common species, which may be wiped out by a few nest predation events. 

Playing regularly with cats can reduce their drive to hunt; using a bird safe cat collar improves this, and keeping them indoors is even better (though not necessarily for the cat or the owner!). The impact of letting a dog off a lead should not be underestimated, especially in nature reserves, and scrub or hedgerows within urban areas. Dogs can, and do regularly attack and kill wildlife, even up to the size of deer. Dog fouling of urban grassland will increase nutrients over time, so that the habitat may shift towards low value Modified Grassland; binning waste is an important and necessary duty.

Flea collars can cause pesticide contamination in ponds, particularly when dogs are let off the lead in local parks. The level of insecticide treatment which builds up in these water bodies is enough to have an impact on the pond life. Reducing the frequency of flea treatments, using less toxic treatments, or alternatives, is likely to have a beneficial impact on aquatic ecosystems. 

Turning short turf over to wildflower meadow is an obvious win for biodiversity, but in many situations, it may defeat the point of a lawn, which is a functional part of the garden. Artificial turf is extremely toxic – produced from fossil fuels, shedding microplastics, boosting urban heat. In contrast, short turf can be an important asset both at home and in the community, for sports, sunbathing, dog-walking and access to, and across green spaces. It is a better alternative to hard materials like gravel or tarmac, as it reduces urban heat, cushions impact, absorbs rainwater and provides some biodiversity benefits. 

Short turf can be home to more than one species, with a varied community of native and/or non-native wildflowers and grasses that provide a hard-wearing surface with benefits to biodiversity. If grass trimmings are removed rather than left to rot in place, this will maintain a healthier, lower nutrient load. The diversity can initially be improved by planting resilient and vigorous wildflowers on scarified patches (e.g. Birds Foot Trefoil and White/Red Clover). Over time, as nutrients decrease, other species of wildflower may be seeded. Eyebrights and Yellow Rattle may help to reduce the vigour of the grass, but these are annuals, so they need to grow to full height and set seed every year. Moss is a valuable part of a healthy lawn ecosystem, which can fill-in gaps, especially in shadier spots.

Garden Management
A wilder garden can feel like a magical space, with paths for exploration and beautiful native flowers alongside useful amenities like decking, lawns and greenhouses.

Restore

The best way to bring biodiversity back in an urban area is to coordinate a network of efforts across a neighbourhood, district, town or city. This will achieve a much greater impact than one garden alone, and this power is harnessed by organisations like Rewild My Street and initiatives like London’s National Park City. All groups start somewhere, so even if a local initiative doesn’t exist, then you could kick off local biodiversity recovery by starting such a scheme in your area.

But restoration doesn’t have to involve community engagement, and if you prefer to do things alone, then you can still create a modest impact on a local scale. Your garden may be an effective refuge for biodiversity, if you follow these steps to restore its health. More information about restoring gardens can be found in the Garden Management guide.

SUDS (Sustainable Urban Drainage Solutions) are features like rain gardens and swales that can reduce local flooding while boosting biodiversity. Even existing infrastructure can be retrofitted with reedbeds, marginal plants and riparian trees to improve the quality of habitat, filter incoming water and beautify the area. Native planting is key here – SUDS are aquatic features, so any seeds will spread quickly in floodwater – non-native species could invade sensitive ecosystems beyond your local area. 

SUDS aren’t restricted to streets, and there’s plenty of advice out there for landowners on installing rain gardens – you can even connect a pond to your gutter outflow, though this will become overwhelmed in winter. So a bog garden is useful for dealing with the overflow at the lowest point along the pond’s edge. Just be sure to create a rock/rubble-filled soakaway adjoining the bog, that will deal with heavy rain beyond its capacity, to avoid flooding your kitchen!

Wildflower meadows are perhaps the most well-known rewilding intervention in urban areas – they’re ideal for existing Modified Grassland habitats. They’re also relatively easy to achieve if you’re willing to do a bit of cutting every year in late summer. The establishment of a new meadow is typically carried out in autumn, or spring on heavy clay.

The first step in establishing a meadow is checking how deep your soil is – if it’s under 15cm deep then scarifying is your best bet (keep going with a scarifier/rake until you have a lot of bare earth). Over 15-20cm deep means you can use a rotavator to dig over the surface of the lawn (or sections of it) to create a fresh seedbed. Both rotavators and scarifiers cost about £50 to hire for a weekend, and make a lot of noise. 

Next, buy a cheap soil testing kit to check your soil pH in a few spots – below 5.5 is suitable for Acid Grassland; 5.5 – 6.5 is Neutral Grassland and beyond this is Calcareous Grassland. The final step is to order an appropriate seed mix from a seller like Habitat Aid (they supply locally-sourced mixes). Follow the instructions provided to get your seeds established, and if the grass returns too vigorously, consider planting Yellow Rattle and Eyebright to knock it back. You can find out more about Grassland Management in the relevant guide.

Ponds are an easy win in a garden, as they not only provide a stepping stone for aquatic life – they’re also a watering hole for landlubbers like mammals and birds. In short, if you want wildlife in your garden, you can’t go wrong with a pond (or three). Biodiverse ponds have a shallow margin, suitable for access, a deep end which remains ice-free year-round and a varied collection of native pond plants.

If you’re concerned about mosquitos, then a population of native Stickleback fish will keep their larvae under control, but they need a pond deep and large enough to avoid overheating. With plenty of native marginal plants, these fish won’t eat all your tadpoles, but they could stop newts from appearing. Your pond will suffer from algae as it gets established, but more plants (especially floating plants like waterlilies) will help balance out light and nutrient availability; just avoid duckweed as it will rapidly takes over and is almost impossible to eradicate.

Established trees are already present in many mature gardens & parks – these can provide benefits in the form of nest holes, shade, cover and roosting space for many different species. Isolated trees provide oversized benefits, like an island is an inhospitable sea, so even if they’re non-native it may be better to plant more native trees alongside them, rather than dig them out.

Planting trees in odd numbers will create a more natural effect, which can be beneficial in the long run for aesthetics and enjoyment of the space. Trees should be chosen based on their suitability to the location, soil type and climate – e.g. in the wild, a single Spindle or Wych Elm would not appear in the centre of an exposed dry grassland, but an Elder, a Hawthorn or a Pedunculate Oak might. Enrich the biodiversity around trees or at woodland edges by planting underwood species like Dogwood, Hazel, Bramble and Field Maple. These will create structural diversity, connecting the canopy to the ground flora.

Balance is key when working in urban landscapes – while a green roof is better than a flat roof, a solar roof is better still. The energy generated to power the building needs to come from somewhere, and this energy footprint is likely to have a bigger environmental impact elsewhere (with more power lost en route). Gardens are a place for play, relaxation, and practical things like composting, growing food, drying clothes and storing recycling bins. A truly sustainable (i.e. long-lasting) design, factors in all these elements, many of which play an important role in reducing the household’s environmental impact. More on this in the Garden Management guide.

In urban green spaces, biodiversity shouldn’t be the only priority, or even necessarily the highest. Creating safe, accessible parks and gardens in urban neighbourhoods is vital, as this lures children away from screens and can kick off a lifelong passion for wildlife. This is doubly important in economically-deprived neighbourhoods, where local green space may be the only accessible nature for many families. Accessibility is also important for older generations and those with limited mobility – in this case, non-slip, sealed surfaces are preferable for paths, as gravel and bark are too loose.

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