December 5, 2021

I, Science

The science magazine of Imperial College

Kruit Shrotri looks at why biodiversity has been falling in British woodlands
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Pine trees, Bristol

Many of us will take a summer walk through Britain’s woodlands and forests these coming months. From wild orchids to wandering hedgehogs, we will find a rich array of wildlife to enchant us.

But these woodlands have undergone drastic changes over the last century, and the consequences have led to a significant decline in wildlife. Conservationists estimate that more than half of Britain’s plant and animal species are in decline. A report launched two years ago by Sir David Attenborough found that endangered species have declined by almost 60% since the 1970s.

Deforestation, reforestation and a loss of ancient woodland

The decline in wildlife populations is largely a result of the deforestation practices that have taken place over the last few thousand years, and the reforestation practices that have taken place over the last century.

Whereas as much as 90% of Britain was woodlands 6,000 years ago, by 1900 woodlands made up just 5% of land, having been gradually depleted for timber production and cleared for agriculture.  This meant that in World War One, the country faced a severe timber shortage. As a result, the Government established the Forestry Commission in 1919. However, their remit was not to foster biodiversity. Rather it was to ensure a continuing source of timber through reforestation.

The Forestry Commission thus chose to reforest land with conifers, fast-growing trees that could meet timber demands. David Rumble is Head of Conservation at the Hampshire and Isle of Wight Wildlife Trust. “Conifers are a fast growing commercial crop,” he says. “But they are often densely planted to the detriment of ancient woodland features.”

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Ancient woodland

Ancient woodland is woodland that has existed for many centuries, long enough to nurture complex ecosystems that support a diverse range of wildlife. Conifers, on the other hand, are non-native to most parts on the country and so do not allow native wildlife to thrive. Furthermore, their uniformly dense canopies prevent light from reaching the woodland floor, often inhibiting the growth of many ground species.

“Truly ancient woodland patches have become smaller, under-managed and isolated from each other,” says Rumble. “And if a patch of habitat is too small or isolated, then it can’t support certain species. That leads to certain populations having a localised extinction.”

In fact, although reforestation efforts meant that woodland area in Britain increased from 5% to 10% in the last century, ancient woodland has decreased from 5% to just 2%.

The result has been a severe decline in British wildlife.

Managing woodlands today

Today there is a much greater awareness as to the importance of biodiversity. “Obviously many people think that biodiversity is inherently important,” says Rumble. “It’s also good for our health; evidence suggests that people’s well-being is enhanced by exposure to biodiversity.

“And of course there is great economic value it in, whether it be through pollination, woodland produce or regulation of local climate. For example, trees are very good at softening extremes in temperatures and ameliorating the impacts of flooding.”

Ashridge Park, Hertfordshire, UK | National Trust Woodlands carpAnd conservationists and foresters better understand the role that woodland and forest structures play in maintaining biodiversity, and practices have consequently changed. For example, the Forestry Commission now places an emphasis on fostering woodlands and forests with native trees. In England, Wales and Northern Ireland, where broadleaf trees are native, the Forestry Commission has planted twenty-six times as many broadleaves as conifers in the last year.

It also places an emphasis on fostering tree diversity within woodlands and forests, so that they provide a range of habitats to suit a range of wildlife. “We now recognise the importance of habitat diversity,” says Russell Anderson, a project manager working at the Forestry Commission. “The practice of restructuring forests is all about converting from uniformly-aged forests to a more diverse age structure, to create a patchwork of different habitats.”

Conservationists are also trying to improve biodiversity in Britain by reducing the fragmentation of habitats. In 2006, The Wildlife Trusts set up their ‘Living Landscapes’ project, which seeks to focus on conservation at the landscape scale. The impetus for this is based on the finding that habitats are able to support a greater number of species when joined together.

We’ve certainly come a long way over the last century in our ability to protect the habitats of British wildlife. But of course the very fact that so many species in Britain are still facing decline means that there is a great deal more work yet to be done. It’s certainly something to think about when you take your next summer woodland walk.

Kruti Shrotri is studying for an MSc in Science Communication

Images: Pine trees in Bristol by Matt GibsonThe old pathway, ancient woodland by debs-eyeWoodlands carpeted with English Bluebells in Spring by ukgardenphotos (Flickr, Creative Commons)