As spring arrives, we observe two important dates: World Rewilding Day (March 20) and the International Day of Forests (March 21). These observances underscore the crucial relationship between forests and wildlife. Forests are not merely collections of trees—they are dynamic ecosystems that provide sanctuary for most of Earth's terrestrial species, regulate our climate, and sustain human communities worldwide. This blog examines forests from global to local perspectives, exploring UK woodlands, London's urban canopy, and ancient forests—revealing why protecting these vital ecosystems matters for climate, wildlife, and humanity's future.
The State of Forests: Global and UK Perspectives
Forests cover 31% of Earth's land surface as vital habitats and the planet's "green lungs." They host 60,000 tree species and most land animals, including 80% of amphibians, 75% of birds, and 68% of mammals. As climate stabilisers, forests absorb 30% of fossil fuel CO₂ emissions yearly through carbon storage. Despite their importance, about 420 million hectares of forest have vanished since 1990, with 10 million hectares lost annually —equivalent to Scotland's area—fueling a biodiversity crisis.
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The UK's forest cover tells a story of decline and renewal. Currently at 13.2% woodland coverage (3.2 million hectares) —well below Europe's 38% average—the UK has seen its forests increase from 5-10% a century ago. However, half consists of commercial conifer plantations, and only 7% of native woodlands are healthy. Many ecologists would agree that true biodiversity requires native species, diverse ages, and connected habitats—priorities now driving UK conservation efforts.
Did you know London can be classified as a forest?
Beyond Big Ben and the Thames, London is remarkably green. Meeting UN forest criteria, the city boasts 8.4 million trees – one per resident. These trees span parks, streets, gardens, and reserves, creating a vast urban forest canopy throughout the city.
Looking at tree density, London impresses with 53 trees per hectare (5,300 per square kilometer) - comparable to traditional forests. With 20% tree cover, the city ranks among the world's greenest capitals. These trees provide crucial benefits: filtering pollution (2,261 tonnes annually), reducing heat, managing rainwater, and supporting wildlife. Their environmental services are worth hundreds of millions of pounds each year.
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St. James' Park, London, England.
London's forest cover has remained stable in recent decades despite urbanisation. Satellite data shows less than 1% change since the early 2000s, with only 56 hectares lost (a 0.33% decrease). Tree losses have been offset by new plantings. The city aims to increase canopy cover by 10% by 2050, from 20% to 22%, requiring around a million new trees in parks, streets, and private land. London's greenery varies by location, with more trees in outer boroughs than the city center. Common species include London plane, oak, birch, and sycamore trees. With 57% of trees on private land and 43% in public spaces, both residents and local authorities share responsibility for London's urban forest.
Perhaps the most powerful illustration of London’s arboreal abundance is this: if you look at a satellite image of London, you’ll see a vast expanse of green blotched among the grey. Large royal parks (Hyde Park, Richmond Park, etc.) stand out, but so do wooded commons and neighborhood parks. In summer, the city truly looks like it’s nestled in a forest. Patrick Barkham, writing in The Guardian quipped, “I strolled through a wood last week and didn’t even realise it. According to a UN definition, London can be classified as a forest”. This framing challenges us to value urban trees as much as rural woodland. It also underscores that conservation isn’t just a rural issue – our cities can be havens for nature too.
Ancient Woodlands: Living Time Capsules and Ecological Treasures
Not all forests are created equal. Some, known as ancient woodlands, have stood for centuries or even millennia, preserving unique biodiversity and heritage. In England, “ancient woodland” is defined as land that has been continuously wooded since at least the year 1600. These woods are relics – fragments of the original wild forests that once covered the land. They often harbor rich soils, old trees, and specialised species that simply can’t be found in newer plantations. Walking into an ancient woodland is like stepping back in time. A prime example is Oxleas Wood in southeast London—a designated Site of Special Scientific Interest (SSSI) spanning 77 hectares and believed to be over 8,000 years old. With oak, silver birch, hornbeam, and coppiced hazel, it is one of the few surviving ancient deciduous forests in the capital, offering not only ecological value but historical landmarks like Severndroog Castle.
Greater London has several ancient woodlands within its urban environment. Epping Forest, the largest at 2,400 hectares, lies on London's northeast edge. With continuous tree cover for over 3,000 years and roots possibly extending to the last Ice Age, it evolved from a medieval royal hunting ground to today's protected nature reserve. The forest hosts 55,000 ancient trees - the UK's largest collection - creating a vital ecosystem for diverse wildlife from fungi to birds.
In North London, Highgate Wood (28 hectares) and its neighbor Queen's Wood are remnants of the ancient Forest of Middlesex. Dating back to at least the 13th century, these woods feature ancient indicator species like wild service trees. Surrounded by city streets, these accessible medieval forests offer residents a rare chance to experience old-growth habitat within walking distance.
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Highgate Wood, North London, England.
In South London, remnants of the historic Great North Wood survive in nature reserves like Sydenham Hill Wood and Dulwich Wood. Once stretching from Deptford to Croydon, today over 20 scattered woodlands preserve ancient oaks and hornbeams amid residential neighborhoods. At Sydenham Hill Wood, woodpeckers and spring bluebells thrive next to city streets, offering glimpses of pre-urban London. As poet John Clare wrote of Epping Forest in 1841: "While giant London… was nothing but a guess among the trees". These ancient woodlands are living links to that past.
Ancient forests worldwide showcase nature's longevity. The Daintree Rainforest in Australia, at 180 million years old, predates the Amazon's 55 million years. Europe's Białowieża Forest preserves ancient oaks and European bison from the Ice Age. These forests are living museums of evolution, containing unique species and providing vital ecosystem services through their undisturbed ecological processes.
Ancient forests face global threats from logging, mining, and climate change. These ecosystems, built over centuries or millennia, cannot be replicated through simple replanting. That's why conservationists focus on saving existing natural forests rather than just creating new ones. This International Day of Forests reminds us to protect these irreplaceable old-growth forests for future generations.
Natural Woodlands, Native Species, and Urban Biodiversity
Conservation prioritises native species and natural regeneration. Native plants have deep connections with local wildlife - an English oak hosts hundreds of species, while non-native trees support far fewer. In the UK, DEFRA, The Forestry Commission, Natural England, NatureScot, Natural Resources Wales, and many others promote native trees (oak, beech, birch, rowan, hawthorn) and natural woodland management. In London, naturally regenerated woods show more biodiversity than manicured parks. Small wild areas and "rewilded" park corners provide crucial habitat for urban wildlife like butterflies, bats, foxes, and stag beetles.
London's ancient woodlands function as nature reserves that prioritise native flora. Highgate Wood shifted from exotic conifers to native species management in the 1960s, maintaining traditional practices like coppicing. Epping Forest continues pollarding to support species like hornbeam beetles. London's Biodiversity Action Plans focus on preserving native trees like English oak and hornbeam while controlling invasive species that threaten the ecosystem.
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Highgate Wood in North London, England.
Natural woodlands in cities provide vital social and educational opportunities. While only 16% of UK residents have woodland access within 500m, London bucks this trend. Many Londoners can access woods like Oxleas Wood, Wimbledon Common, and Richmond Park, which feature ancient trees and diverse wildlife. Even smaller urban sites like Camley Street Natural Park and Gunnersbury Triangle demonstrate thriving native vegetation, serving as educational spaces and sanctuaries for both people and wildlife.
Cities worldwide are embracing native habitat conservation through rewilding initiatives and green corridors. Urban biodiversity professional and co-founder of Gentian Dusty Gedge emphasises: "A city has the responsibility to deliver real, meaningful biodiversity". London exemplifies this through Biodiversity Net Gain requirements and habitat connectivity programs like the Great North Wood project. Native woodlands enhance ecological resilience while requiring minimal maintenance.
Mapping Trees and Enhancing Biodiversity in London
Managing urban forests requires data-driven solutions that combine technology and ecology. Using ultra-high-resolution imagery, we map individual trees, green roofs, and entire habitats across cities. These maps reveal vegetation patterns, potential species locations, and connectivity gaps—guiding urban planners and conservationists in planting efforts, protecting key areas, and monitoring changes over time.
A key example of our impact is the project we conducted in the London Borough of Lewisham. Using satellite data, we carried out a comprehensive study to catalogue trees, measure canopy cover, and assess habitat diversity. We mapped over 134,000 trees across the borough—revealing that Bellingham has the highest count (10,677), while Forest Hill boasts the greatest density at 50.4 trees per hectare. In contrast, Lewisham Central recorded both the lowest total (1,693) and the lowest density (25.6/ha), identifying it as a priority area for urban greening. The study also uncovered thousands of previously unrecorded trees and key wildlife corridors along railway embankments. This data enables councils to make targeted, evidence-based decisions—from focusing tree-planting in underserved areas to protecting vulnerable fragments of ancient woodland. By offering an “eagle-eye view of nature,” we help drive smarter, greener urban planning.
We also map green roofs and green infrastructure across London and beyond, identifying vegetated flat roofs and potential sites for mini-meadows to boost urban biodiversity. As our CEO Daniel White explains: "By harnessing advanced satellite technology and pioneering AI... we're turning ecological complexity into clarity," enabling a resilient future for both nature and enterprise.
Why Saving Forests and Biodiversity Matters
From the Amazon to urban woodlands, forests are vital for life on Earth. They regulate climate, clean air and water, and provide essential resources. They are crucial for biodiversity, with over half of all land species living in forests. Losing forests threatens species survival, disrupts climate patterns, and impacts communities who depend on them. Forest loss contributes 10-15% of global carbon emissions, making their protection one of the most cost-effective strategies to fight climate change, as recognised by the UN's Decade on Ecosystem Restoration.
Forests are vital for wildlife. From tigers and orangutans in tropical forests to dormice and woodpeckers in British woodlands, each species depends on these habitats for survival. Urban forests also support diverse wildlife - London's parks and gardens are home to foxes, hedgehogs, bats, and stag beetles. These animals not only enrich city life but provide essential services like pest control and pollination.
We face a clear challenge: stopping global forest loss while restoring and improving tree cover. This requires ending illegal logging, choosing deforestation-free products, and investing in native ecosystem restoration. In cities, we must prioritise urban nature through tree planting and green space creation.
This International Day of Forests reminds us that data and science confirm what we instinctively know: forests and wildlife need protection. While challenges remain urgent, progress is possible - we can reduce deforestation, restore habitats, and transform cities into biodiversity havens. By combining conservation efforts with data-driven insights, and with organisations like Gentian providing mapping tools alongside experts and volunteers on the ground, we're increasingly well-positioned to protect our forests and their inhabitants.
Forests are the green heart of our planet and our communities. By safeguarding ancient woodlands, expanding native tree cover, and integrating biodiversity into urban life, we honor the spirit of these international days not just with words, but with informed action. The health of our forests and the fate of our wildlife are intertwined with our own future. Let’s ensure that future is one where forests continue to thrive.
