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Hedgerow study using artificial intelligence to help National Trust bring back its ‘blooming boundaries’

The National Trust is publishing research into the changes in hedgerows and density on its land in England and Wales since the start of the 20th Century, which will help inform its ambition for future conservation projects and aid plans to establish 4 million blossoming trees by 2030.

Hawthorn in flower at Stockbridge Down, Hampshire | © National Trust Images/John Miller
Hawthorn in flower at Stockbridge Down, Hampshire | © National Trust Images/John Miller

Results revealed during the conservation charity’s first ever Blossom Week – a week designed to celebrate the beauty of the wide variety of tree and hedgerow blossom – found that across England and Wales in 1900 there were just under 10,000km of boundaries on land now cared for by the National Trust.

Over the last 100 years, one third (33 per cent), nearly 3,300km, of the boundaries on land now cared for by the National Trust has disappeared, compared to 50 per cent of hedgerow loss across the rest of the country – suggesting that, while still a significant decline, National Trust places have fared better than the wider countryside.

This loss on land cared for by the conservation charity, is likely due to farmers following government policy, or because the loss occurred prior to acquisition.

A regional analysis shows that this loss appears to be fairly consistent across all regions and countries. The one key exception appears to be in the East of England where nearly half (48 per cent), over 400km, of boundaries recorded in the 1900 appear to have been lost.

In terms of hedgerow distribution, the South West had over 3,300km of boundaries (35 per cent) of the charities total at the turn of the century, whereby the South East and North West had the least amount of hedgerows with 1,350 and 1,500km of hedgerows respectively.

The charity and research partners ArchAI Ltd, used Artificial intelligence (AI) to unlock understanding from historic OS maps from the National Library of Scotland map collection. These data were compared to modern day mapping – to determine loss, retention and the creation of hedgerows over time on 100,000 hectares (247,105 acres) of land in its care.

In the UK hedgerow loss since the second world war - particularly from 1945 to 1990 - has been well-documented with 50 per cent of hedges lost due to changes to farming policy, increases in mechanisation to boost food production, urbanisation, increases in infrastructure, and also the neglect of hedges and a decline of traditional skills.

However, earlier historical changes have not been investigated at such a scale before.

Tom Dommett, Head of Historic Environment at the National Trust says: “National Trust places appear to have fared better than the wider countryside when it comes to the loss of hedgerows.

“In some cases, early acquisition by the Trust will have led to greater preservation of hedgerows in recognition of their landscape and wildlife value, while elsewhere the Trust has worked to restore and celebrate hedgerows and other historic boundaries.”

“For thousands of years our landscapes have been laced by an intricate web of hedgerows of varying types including Cumbrian kest hedges, rounded Welsh hedges that help the snow slide off during wintry weather, ancient Devon hedges atop earth and stone-faced banks, coppiced hedges and laid hedges.

“But our research shows how these different types of hedgerows have been lost due to the population growth and the advancement and needs of society.

“Hedges are important wildlife corridors, carbon stores and their bursts of blossom - blackthorn, hawthorn and dog rose, wild cherry, apple and plum - are not only beautiful but also critical for pollinators, while their fruits are an important source of winter food for birds.”

Explaining how Artificial Intelligence (AI) aided the research, Professor Matthew Heard, Head of Environmental Research and Data said: “Historic mapping provides a rich point-in-time snapshot of our landscapes – but this information is effectively ‘locked up’ in the images meaning that previously the analysis of the data has been a time consuming, manual process. However, the development of AI approaches presents an opportunity to ‘detect’ features of interest with much greater speed and at greater scales than ever before.

“This research will help us to build an understanding of the role hedges played in past landscapes, looking at national and regional variations and the extent and survival of hedgerows over time as well as the implications of this for landscape character, biodiversity, habitat connectivity, pollinator food sources and access to blossom for people.”

The density of boundary features – ie the number of kilometres of boundary we may expect to find within a single square kilometre was also better on National Trust land then the wider countryside with around 10km per square kilometre on land in the charity’s ownership in the 1900s compared to an average density of just under 7.5km at that time.

Results reveal a 19 per cent decrease in the density of boundaries based on the analysis on National Trust land since 1900 with some of the biggest losses in the North West (48 per cent reduction) and the East Midlands (47 per cent). More research is needed to unpick the stories behind the changes, but they may reflect, for instance, where smaller, mixed, rotational farming systems persisted for longer into the 20th Century preserving boundaries before rapid changes with the introduction of mechanisation and artificial fertilisers.

The data however does also suggest regions which have gained boundary density since 1900. Despite losing one third of its boundaries from 1900, the South East appears to now have a 21 per cent greater density of boundaries per square kilometre increasing from 6.5km in 1900 to nearly 8km today. While a resurgence of hedgerows is possible, it may also be the case that the density in 1900 drawn from the assessment of National Trust places is not representative of the region as a whole, for instance where the Trust cares for a disproportionate area of designed landscapes or open commons.

Matt added: “In recent times, hedges have often been flailed mechanically every year to help with maintenance. However, research has shown that this rather brutal way of hedgerow management impacts both the hedge itself, but also the nature that relies on it, hugely impacting on structure and reducing berry production.

“Historically hedges were less intensively managed across an estate with a sequence of management across several years as conditions allowed.

“We’re working with our tenants to improve the outcomes for nature and carbon of hedgerow management across our land – with more sympathetic management helping create better shaped and thicker hedgerows, which provide more resources for wildlife as well as shelter for livestock and crops.”

Tom concludes: “Looking at both hedgerow loss and boundary densities, our research paints a picture of a more complex, diverse landscape at the beginning of the 20th Century – almost certainly more blossom-filled and richer in nature.

“Since then, the story is of significant loss. But through this research – and by understanding the history of this loss, it presents us with the potential to map opportunity and possibility.

“In some cases it will be possible to identify and restore lost hedgerows, but the aim is not to ‘turn back the clock’ – rather it is hoped this research will help set the tone and that we may be inspired by the past to create new opportunities for hedgerows as well as revive old ones, all helping to support nature, capture carbon, add texture and beauty to our landscapes and to bring back blossom!”

Using the research, the National Trust now plans to scope the opportunities for hedgerow creation and restoration at key properties and engage in further research into hedgerow and other habitat histories. It is also advocating an approach of having wider hedgerows – to help benefit wildlife.

Hedgerow planting on National Trust land

Across a number of key countryside properties, such as Killerton in Devon, Dunham Massey in Cheshire and Wallington in Northumberland, over 220km of hedgerows have been planted in the last 20 years – with over 125km additional hedgerows planned over the next decade for these three properties alone as part of the Trust’s commitment to net zero.

Tim Dafforn, Countryside Manager at Killerton says: “We’ve surveyed our whole 6,500 acre (2,400 hectare) estate to identify the condition of our hedgerows so that we can fill any gaps, improve the hedgerows and plan future planting.

“We’ve planted 7km of new hedgerows recently – using blossoming trees such as hawthorn, blackthorn, wild cherry, rowan, spindle and elder along with species such as hornbeam that are more suited to our warming climate. We have also identified sites for an additional 25km to restore, equating to 125,000 new trees, which will be great for wildlife and improve habitat connectivity cross the whole estate.”

Paul Hewitt, Countryside Manager on the 13,500 acre (5,463 hectare) Wallington Estate says: “Working with our tenant farmers on the estate over the last few decades, we’ve been planting new hedgerows, restoring historic ones and widening many of the hedges so they can provide a greater benefit to wildlife.

“Wider hedgerows provide particular benefits of being habits in their own rights, acting as superhighways for wildlife to move around and join up with those habitats that already exist such as the woodlands and river corridors here.

“In the last 2 years, we’ve planted just over 13km of hedgerows (nearly 80,000 trees) with a further 10km being planted next winter. We’ve identified a minimum of 50km to restore here at Wallington.

“We’re hoping that some of the fruiting trees such as crab apples and rowans planted in our hedges will provide food to support the spread of pine martens from Kielder to north of us, to this area.”

Hedgerow benefits to nature

Commenting on the importance of hedgerows as habitats, Ben McCarthy, Head of Nature Conservation at the National Trust said: “Hedgerows are really important habitats providing food and shelter for many species as well as creating a physical network to help species move across our landscapes.

“For example, the early blossom of the blackthorn, hawthorn and cherry trees is an important nectar source for our early bumblebees and butterflies like the Brimstone whilst the autumnal fruit provides important food later in the year for our flocks of migrating and overwintering birds such as redwings and fieldfares.

“When allowed to grow, big, busy and riotous, hedges also provide great structural diversity in the landscape compared to the closely shared hedges that are now so common.

“Big bushy hedges provide more niches to support our wildlife and can complement in-field habitats by providing shelter and cover as well as making our landscapes more permeable for species to move across. All important for adapting to climate change.”

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