Two decades of rewilding – a review

A twenty-year review shows rewilding brings nature roaring back 

Published January 2026

A two-decade ecological review at Knepp Wilding shows that rewilding has driven a dramatic recovery in wildlife on the 3500-acre estate in Sussex. Surveys reveal a 900% increase in breeding birds and a 500% rise in nightingales, alongside major gains in butterflies, dragonflies and other species. 

Endangered species like turtle dove and purple emperors have appeared at Knepp. Numbers of rare birds like nightingales have rocketed since Knepp started rewilding.   In some areas, butterfly species have doubled, while dragonflies and damselflies have increased by nearly 900%. 

As described in Isabella Tree’s book Wilding, Knepp was formerly unprofitable farmland. Tree and her husband, Charlie Burrell, chose a radical alternative: removing fences, breaking up Victorian drainage systems, allowing natural water flows to return, and leaving dead trees standing. 

Scrub and woodland quickly regenerated. Free-roaming animals were introduced to replace extinct ecological roles, including old English longhorn cattle, Exmoor ponies, Tamworth pigs, red and fallow deer, and later white storks and beavers. These animals now drive a dynamic mosaic of habitats that has proved “rocket fuel” for wildlife recovery. 

Isabella Tree, co-owner and co-founder of Knepp Wilding, said: 

“We have gone from a depleted, polluted, dysfunctional farmland to one of the most significant biodiversity hotspots in the UK. The uplift in biodiversity shows how much life the land can hold. We should be much more ambitious for our nature reserves and rewilding projects. 

“The UK has pledged to return 30% of land to nature by 2030, and it’s not happening fast enough. Rewilding is a powerful tool to get nature back.” 

Fleur Dobner, an ecologist at Knepp who worked on the review, added: 

“We’ve gone from a monoculture landscape to a rich mosaic of parkland, scrub, hedgerows, glades and grassland. The trend is strongly positive and still increasing year on year.” 

The review found: 

• A 916% increase in breeding bird abundance in the southern block since the initial Breeding Bird Survey in 2007 until present, and a +132% increase in species richness. 

• Common whitethroat has increased by 2200% from 2007 – 2025 on the Breeding Bird Survey transect. Other figures include: lesser whitethroat (+1000%), chiffchaff (+1150%), wren (+500%). 

• 2025 was a peak year for nightingales with 62 singing males. That’s up from just 9 in 1999, which represents a +511% increase in 25 years. And only 1 territory was recorded during the 2005 baseline monitoring conducted by Natural England. 

• A 600% increase in turtle doves, with 23 singing males in 2020 and 22 singing males in 2020. That’s up from just two in 2008.  

• 2025 was the second “biggest” year for purple emperor butterflies at Knepp, with 283 individuals counted in one day. Knepp currently holds one of the largest populations in the UK. 

• For butterflies, a 107% increase in species richness from 2005 – 2025 in two areas of Knepp. 

• One area gained around 96ha or 1.3million square metres of scrub habitat between 2001 and 2019, according to Queen Mary University.  

• A 871% increase in the abundance of dragonflies and damselflies from 2005 – 2025, and 53% increase in species richness along the Adur river restoration project. 

• For invertebrates, entomologist and ecologist Graeme Lyons found a total of 567 species in 2015 and 656 species in 2025 (+16%). There were 35 species of conservation status in 2015 and 46 species of conservation status in 2020, illustrating a ~31% increase over five years.