From the archive
1 Aug 2026
For three winters, in gales and torrential rain, Aaron Europa and Stu White of the Knepp estate spent their days waist-deep in Sussex clay, firing a lance of compressed air at the ground and hauling thorn bushes out whole. An air spade blasts heavy clay off a root system without tearing a root hair. Between the winters' digging and the spring nesting season that stopped them, they excavated 270 scrub trees entire - oak, sallow, hawthorn, blackthorn and dog rose - crown to root tip.
The digging was fieldwork for Nancy Burrell's doctorate at Oxford. Burrell grew up at Knepp and has watched it change since rewilding began in 2001, as longhorn cattle, Exmoor ponies and deer turned former arable fields into browsed parkland. Her question was carbon. Rewilding wins credit for wildlife but is waved aside on climate, and she suspected the missing piece was scrub, the thorny growth long dismissed as wasteland - and as unmeasurable.
She was right about the measurement. Standard carbon tools, built for plantations, predict a tree's mass from height and trunk diameter. But a blackthorn chewed by cattle for years grows nothing like a plantation tree. Below the browse line, roughly two and a half metres, it abandons any orderly reach for the sky and pours effort into thorns, resprouting and roots. Burrell built new equations, species by species, for plants shaped by being eaten.
The 270 excavated plants told the story. Below the browse line, the mean ratio of root to shoot was 1.06, against the 0.26 that standard accounting assumes: for every gram of leaf and thorn above ground, at least as much lay beneath, and that figure is conservative, since roots ran well beyond each plant. Above the browse line, out of the herbivores' reach, ratios settled back towards conventional values.
The implication runs past one estate. Scrub and hedgerow have spent decades written off as wasteland, good for nothing, and written off again as unmeasurable. If browsed scrub across the country carries anything like this weight below ground, the carbon ledger has been misreading one of its commonest landscapes - and the free-roaming animals doing the browsing may be part of the reason the roots are there at all.
Before clearing 'waste' scrub for a planting scheme, dig up one representative bush whole - a mattock, a trenching spade and a long afternoon will do it for anything under two metres - and weigh the roots against the top growth. If the roots match or outweigh the crown, that hedge is already a carbon store, and the case for leaving it standing writes itself.
Knepp Estate · Read the source