It’s obvious that bigger rewilding projects have a bigger impact on nature. But perhaps less obvious that this relationship isn’t a straight line – a 100m2 patch of land has more value to nature if it’s part of a larger project than if it stands alone, isolated. And that comes down to one of rewilding’s 3 D’s – ‘dispersal’.
Why is Dispersal So Important?
A diverse population of wildlife is healthier, as it has a bigger selection of adaptations that protect it from threats as varied as climate change, disease and predation.
Think of these as a pack of Top Trumps cards – the larger your hand, the more likely you are to beat your opponent, as you’ll have some kind of winning adaptation. A bigger pool of genes means a population is more likely to beat a threat, with the survivors passing on their genes to the next generation – basic evolutionary biology.
But to maintain this diverse gene pool, you need to mix up those genes and create new ones by frequently interbreeding between populations. That means animals and plant seeds/spores must move around the landscape, mating with distant individuals elsewhere.
Why is Urban Rewilding So Hard?
In a city or a town, movement between populations is more difficult, as there are barriers to dispersal, like roads, fences, and general urban development.
Some ecosystems can even be a barrier to dispersal, as animals and plant seeds aren’t adapted to colonise or move through them, like monoculture crops, tidy lawns, and conifer plantations.
Dispersal isn’t just important for keeping up a diverse collection of genes. It’s easy to lose a species entirely when there are low numbers present, as a single predator (like a cat), or a single event (like a new development), could wipe one or many species out.
So, maintaining connections between the wider landscape and isolated urban green spaces allows these urban areas to be replenished with species after extinction events. The urban spaces act as ‘sinks’ for biodiversity, while rural areas are like a tap that hasn’t been turned off, constantly spilling over and topping up abandoned ecosystems.
Are Wildlife Corridors the Answer?
Traditional conservation focused on the creation of ‘wildlife corridors’, but rewilders tend to do things a little bit differently.
Nature can move across some developed areas, and some plant seeds and animals travel by air, so joined-up pathways aren’t always essential.
That said, wildlife bridges and tunnels are important for larger animals and beneficial for smaller ones, especially when crossing major roads. In an ideal world, every city centre would be connected to the rural area around it by a contiguous green corridor. This might even be feasible, as rivers, riverbanks and railways provide that opportunity for many towns and cities.
A Joined-up Approach to Urban Rewilding
Given the importance of dispersal in urban diversity, you can see why a joined-up approach to nature is essential in towns and cities.
Rewilding urban areas isn’t something you do on a site by site basis – it needs to be holistic; taking into account habitats in the wider landscape. That doesn’t just mean the urban green spaces, but also the wilder areas that lie beyond the urban fringe – the ‘taps’ that will fill up your ‘sinks’.
A woodland species like a Great-Spotted Woodpecker might struggle to reach a forest at the heart of your city unless there are patches of woodland connecting it to the wider landscape. A newly-created wetland wouldn’t fulfill this need, so even a ‘green corridor’ only works for the specific types of wildlife that inhabit it. That means it’s vital to get a sense of what types of wildlife and habitats are found not just in your urban area, but beyond it, too.
Happily, councils are already mapping out different habitat types across the UK – this initiative is called ‘natural capital mapping’ – and the results may be available for you to use, helping inform your project designs. These maps can guide the creation of new habitats which not only benefit from incoming biodiversity, but also act as a stepping stone, connecting isolated patches of habitat in the urban core.
Bristol, Nottingham and Bradford-on-Avon worked with Ecosulis to map out the habitats across their urban areas, which will inform their land management strategies. If you work for a council, and you’re interested in this service, you can find out more about it on their website.
How to Design a Rewilded Planting Scheme
When you’re designing a planting scheme for an urban park, a housing development, or another green space, dispersal shouldn’t be the only priority.
There are 3 D’s in rewilding, not 1…
Dispersal, diversity and disturbance.
As we’ve discussed, dispersal is the top priority – connect your project to existing green spaces by avoiding the use of fences and walls where possible and identifying what type of habitat is most suitable for your site based on its context, soil type etc.
Viewed from above, green areas should weave through the project, rather than being siloed into enclosed courtyards and cut-off gardens, to optimise dispersal. Make the most of verges, playing fields and awkward corners, maximising the opportunity for native planting. Hedgerows and lines of trees can help birds and mammals to cross large open areas like car parks and meadows, and trees are also perfect for providing shade at the street level.
When it comes to diversity, check what native species are present in your local area. You can consult NBN Atlas for a detailed scientific list, visit a nature reserve, or commission an ecologist. Make sure that the conditions match your planting scheme – an exposed limestone hilltop will support very different plants compared with a sheltered clay valley. Planting the right trees in the right place isn’t just good for biodiversity – it also means they’ll actually survive and avoid ugly and costly mistakes.
Climate change resilience needn’t mean sourcing non-native trees from Southern Europe – but it does require consideration of water availability (i.e. root space/SUDS), suitability of species for the site, shade and reducing the extent of artificial surfaces that reflect heat, to maintain cool conditions that are good for both people and plants. You can ask for expert help when designing planting schemes – a good arborist will know what trees can go where.
Rewilding Local Parks - Creating Diversity
Diversity comes in a few different flavours, and you can think of these as acting at different scales.
At the smallest scale is genetic diversity, which you now know is important to protect species against disease and predation. Next up is species diversity – how many different species are present in an ecosystem – this determines the health of the ecosystem itself, just like genetics affect the health of the animal. Each species takes on a slightly different role, from grazing dominant grasses to eating disease-causing ticks. Lose one and you’ll probably be fine, unless it plays a ‘keystone’ role, like beavers, which are ‘ecosystem engineers’, shaping the way the whole habitat functions.
But the more species you have, the more resilient your ecosystem is to change (e.g. climate change), as you will have some organisms which are still suited to the new conditions. That’s why we recommend planting not just native plants, but a diverse range of native plants. These will attract a diverse range of other native wildlife, which depend on those plants.
Creating Messy Chaos in Urban Environments
Next up in scale (in the 3 D’s) is structural diversity. This sounds more complicated than it actually is.
When you step into a wild habitat, you’ll notice that, in most cases, every level of the ecosystem is occupied, from ground to canopy. Even in a grassland, there are small clusters of trees (copses), patches of scrub, ponds, rivers and wetlands. But in parks and gardens, we have a tendency to focus on one level – you might find huge areas which are nothing but grass, or woodlands with no open glades.
It’s generally the case that the edges of habitats – ‘ecotones’ – are richest in biodiversity. Many niches are created as an ecosystem transitions from high forest to low grassland or scrub to wetland. These margins are of exceptional value to wildlife, so a landscape that’s rich in wildlife will look like a lumpy mosaic of different habitats, slowly transitioning into one another.
This type of environment may be described as ‘messy’, but nature loves mess – wildlife thrives on diversity and disturbance. That doesn’t mean these places can’t also be valuable for people – paths through a mosaic landscape feel like a story unfolding – you never know what you’ll find around the next corner.
When designing new green spaces, it’s easy to focus in on one specific ecosystem – creating a large wildflower meadow, a continuous woodland or a wetland ecosystem. But concentrate instead on structural diversity – filling plant niches from ground cover and wetland species to high canopy; maximising edges – and you’ll create a more abundant and diverse environment that is also more engaging for the public.
Turning an Existing Site into a Rewilding Project
If you’re taking on an existing site, rather than designing a new project from scratch, there are a few interventions which can really help to kick off biodiversity.
British woodlands generally suffer from neglect – they have high canopies, few glades, low levels of understory vegetation, and were often planted in rows, regular patterns, or with regular spacing. They may be infested with non-native species, from Sycamore to Rhododendron and Himalayan Balsam, or be planted with an unnaturally dense mix of non-native conifers for timber production.
All of these issues affect biodiversity, and all should be a priority for the rewilder. A healthy, wild British woodland contains glades, rotting trunks and native trees without introduced invaders. The understory is lush and diverse, with not just bramble, but a mix of trees, climbers, ferns and other plants. On lower-lying land, ponds will form seasonally in the hollows created by storm-felled trees, which are left lying in place for fungi to colonise. Trees are irregularly-spaced, with light hitting the ground in places, allowing for intense competition between new saplings. Coppicing and felling maintains a mosaic of different densities across the woodland that promotes diversity in plant and animal life, including valuable sunlit glades that are full of butterflies in summer.
Elsewhere on your project, hedges should mimic more natural scrub formations – their edges slowly transitioning into grassland, wetland or woodland. Steep ‘wall’ hedges are out, and faded ‘wedges’ are in, with infrequent brushcutting used to knock these areas back. Traditional hedge-laying is a valuable technique that preserves our heritage and, in places, can create a dense habitat which is perfect for nesting birds. Coppicing can perform a similar function. Hedges should be native, highly diverse and suited to the conditions, with a variable density and scalloped edges that create sheltered ‘bays’, ideal for butterflies. Brambles and native climbers like Honeysuckle and Old Man’s Beard are to be encouraged, providing abundant nectar, seeds and fruit.
Lawns might feel like an obvious place to start creating biodiversity, but it’s worth bearing in mind that neglect is not the same thing as rewilding. Rewilders focus on optimising the 3 D’s, and that also applies to grassland ecosystems, where disturbance is an essential first (and ongoing) step in transitioning a manicured lawn towards a wildflower meadow. These habitats are often high in nutrients, which is great for grass, but bad for flowers, which tend to lose out when competing for light and space. Low nutrient soils are better, and this can be achieved in a number of different ways – by soil stripping; sowing the parasitic plant Yellow Rattle or even over a number of years by cutting grass and removing the arisings. If a diverse range of wildflowers are not already present, you can find a locally-sourced seed collection from Habitat Aid.
How to Maintain an Urban Rewilding Site
A well-designed rewilding project isn’t just a static site – maintenance is built in to the plan, allowing it to evolve over time.
In rewilding, we call this maintenance ‘disturbance’, as we’re effectively replicating the actions of wild animals and natural processes.
On larger sites, we might even bring in animals – perhaps a guild of herbivores – pigs, horses, cows, sheep and more. These can create a self-sustaining grassland ecosystem which is full of flowers in summertime. The herbivores not only graze randomly, but their dung also supports invertebrates and creates a spike in soil nutrients that leads to more diversity in plant life.
Coppicing and tree felling is a crucial part of work to maintain rewilding projects, replicating the actions of beaver, bison and other locally-extinct herbivores. But if you’re able to bring in beavers, they’ll do this better – realistically, though reintroductions are not going to be a possibility in all but the largest of urban rewilding sites.
Smaller projects will need to take a more hands-on approach. That means brushcutting and strimming rather than mowing, as it’s less likely to compact the ground, creating a uniform lawn. Resulting meadows can have a mix of different grass heights, with trees and shrubs scattered throughout – a structurally-diverse ‘wood pasture’.
Rewilders leave trees where they fall, to rot down and create a new home for fungi and invertebrates, but pile up grass clippings in heaps, to mimic grazing and dung.
Ponds and Pigs in Urban Projects
Pigs (ideally Wild Boar) are the perfect animal for larger rewilding projects, helping to ‘reset’ degraded lawns, while creating varied structure in the soil.
These animals plough out wallows – ephemeral ponds that are wonderful for biodiversity; but humans can do this, too. ‘Blue spaces’ – water in urban areas – are widely recognised as beneficial for mental health, particularly as they maintain a beautiful appearance into winter, when ‘green spaces’ often appear grey or brown.
Turning over small patches of soil from time to time with a rotavator, digging ponds and creating ‘scrapes’ is a good way to mimic pig activity and create new blue spaces, maintaining high biodiversity on your site into the future. But it’s worth noting that these interventions can also be hazardous to local residents – particularly young children and those with walking difficulties, so proper precautions should be taken.
The ongoing management of an urban rewilding site is complex, and the nuances too detailed to cover in a single article. Every intervention must not only take nature, but people into account, with accessibility a high priority for urban green spaces.
If you’d like to find out more about designing quality urban rewilding projects, or appoint a specialist to help, Ecosulis are the experts in the field. I work with them to advise landowners across the UK on how to maximise biodiversity in both urban and rural environments.
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