“The buddleias, brambles and bits of willow which have cracked through the concrete create a pretty interesting habitat for invertebrates, birds and bats.” says Jon Garner, Ecologist and Director at BioGains.
Ecologist and Director at BioGains, Jon Garner, joins the Trowers & Hamlins' natural capital team, to discuss some of the misconceptions around biodiversity net gain and ways to approach it.
It’s not what you’d necessarily expect to hear about a brownfield site. But, as
Jon Garner, ecologist and Director at BioGains, points out, appearances can be
deceptive when it comes to biodiversity.
“Where there is open soil, grass dominates, but on a formerly built-out site, it can
allow rare weeds and flowers to establish,” he explains.
This can present a challenge for developers trying to deliver the 10% biodiversity
net gain, which became law in February.
To deliver the uplift, sites need to be assessed and given a baseline biodiversity
‘score’ against which the 10% enhancement can be measured.
It’s easy to assume that the greener the site, the higher the baseline score will be, making it harder to achieve a 10% improvement. However, there are different types of greenery and grassland with different biodiversity ratings, just as brownfield sites can vary.
Biodiversity and brownfield sites
The sort of brownfield site described above, which perhaps hasn’t been touched for ten years, has established what is called an open mosaic habitat.
This can be valuable from a biodiversity point of view, particularly in an area without an abundance of similar habitats. It can have a biodiversity rating similar to that of an orchard.
Some brownfield sites may rate very low or even zero, but there is no way to know without an assessment.
The size of the site can add to the challenge particularly as the preferred option
from local authorities is for biodiversity net gain to be delivered on site.
There are benefits to onsite enhancement. For example, it can make residential
developments more attractive to buyers and neighbouring communities.
But, it’s a balancing act as residential sites will have competing pressures on land usage. Providing green space for residents to enjoy, perhaps for children to play or to walk dogs, doesn’t necessarily go hand in hand with a wildlife habitat.
“A local authority ecologist will look at the plans to
consider whether what is proposed is realistic,” says Garner.
Individual trees score reasonably well within the biodiversity net gain metric; on
bigger sites, a small community orchard would also rate well. If there is a lot of
space, some scrub or woodland planting is an option.
SUDS can be of high value because of the benefit of combining water drainage
with biodiversity habitats.
“The problem is that biodiversity net gain is measured by hectare, and some of
these habitats only cover a relatively small area,” he adds.
Getting an assessment and baseline established as early as possible, which is a
relatively cheap process, is key for developers buying land so the enhancement
options can be planned and costed.
Ongoing habitat management
Measures to improve biodiversity also require a 30-year management plan, so that needs to be considered when deciding what habitat to create, particularly onsite.
For example, wildflower grasslands need to be cut at specific times.
“You cut once the flowers have seeded, and most importantly, you remove arisings to help lower the nutrient level in the ground and stop the dominant grasses taking over,” explains Garner.
However, there may be an expectation from residents that the grass will be cut in the summer, which would result in the loss of biodiversity benefits.
Provision also needs to be made for someone to take on the maintenance
responsibility, and to be accountable if there are problems. This could be through a management company funded via a service charge, but if the developer exits the scheme, who is responsible?
This can be an advantage of off-site biodiversity net gain provision and using
a habitat bank. The habitat bank signs a section 106 agreement, which means
accepting liability.
Natural England has also set up conservation covenants as an alternative to Section 106 agreements.
These aren’t tried and tested and fall under a different area of law, which can be
off-putting – developers and land owners, and lawyers tend to prefer what is tried and tested, and S106 agreements are well understood. Habitat banks have to be accredited and are understandably subject to high levels of scrutiny, but the sites aren’t constrained by public access.
Mismatched biodiversity metrics
A fault in the metric is that woodlands aren’t rated as high as they should be
because of the time they take to become established.
Garner says a way to navigate this is to introduce scrubland: “Scrub habitat is
similar to a woodland in an ecological sense. It’s a stage before a woodland so
targeting scrub, you get there quicker.”
The problem is that ‘scrubland’ doesn’t sound very attractive, particularly if you are building homes.
For landowners turning a piece of land into a habitat bank can be a tempting
proposition for generating income. Navigating the regulations and requirements
takes skill and expertise, so while it can offer a high reward, it is also high risk.
Leasing land to a habitat bank is a lower-risk alternative. It means an income for 30 years, and the liability sits with the habitat bank, but the returns will be lower.
News headlines suggest habitat banks are direct competition for food-producing land, but Garner says there is plenty of land for both.
“There’s an awful lot of land that isn’t really cost-effective for delivering food production, and that is nearly always going to be suitable for biodiversity net gain,” he says.
While biodiversity net gain has been a part of planning policy for some time, the
new law has sharpened the focus and will undoubtedly change the development
landscape.
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