More than half a million trees have died beside a single 21-mile stretch of new carriageway, National Highways has admitted.
The trees were among 850,000 saplings planted along the A14 between Cambridge and Huntingdon as part of a £1.5 billion upgrade in 2020.
They died because of “poor soil” and “extreme heat”, according to an internal report by the government agency responsible for the country’s main roads, and it will cost an estimated £2.9 million to replant them.
National Highways previously felled 400,000 trees and shrubs as part of the development, but planting new trees was part of the permission to build.
However, the review said there has been an “unusually high fatality rate” and three-quarters of the saplings planted have died.
National Highways said it was due to poor soil and extreme heat, with it being likely more saplings perished in the heatwave which hit the UK last summer.
The government body said: “Replanting is expected to begin in October with the first batch of 162,000 trees already on order from a local nursery. All replanting work will be subject to a five-year establishment period.”
The internal document suggests the replanting plan will use more mulch to hold water, better tree guards, improved topsoil, and reviewing both the type of tree planted and the sapling’s age.
‘The scale of it really hits you’
County Councillor for South Cambridgeshire Edna Murphy has been campaigning for two years for National Highways to take responsibility and put it right.
She said: “The scale of it really hits you if you go up and down the A14, hundreds of thousands of trees, saplings planted and have just been left to die.
“It was actually the devil’s own job to get information out of National Highways. I tried the Freedom of Information Act, I tried asking nicely. Nothing worked.”
She added: “They’re just trying really hard now, to get some trees established, which can only be good. But we have to see if they actually do it.”
Tree experts have slammed the obsession over sapling planting being prioritised over aftercare. They said what has been left on the new carriageway are "nearly one million" plastic tree protection tubes, filled only with grass and dead twigs.
According to one expert, it takes up to 10 years for saplings to start absorbing carbon from the air and become beneficial against climate change.
Paul Gambill, CEO of Nori, a company which helps businesses offset their carbon emissions, said: "You plant the forest but you don’t start seeing carbon retention happening for at least 10 years after they’re planted.
“And then you have to maintain that forest and make sure it isn’t burned or cut down. Forests need to have a permanence of 100 years to be effective carbon stores."
In response to the review, National Highways Project Manager Martin Edwards said: “We take our responsibility to the local environment seriously. We’re pleased to be in a position where we have a clear route ahead for the replanting of trees on the A14 Cambridge to Huntingdon improvement scheme.
"This approach will result in planting the optimum species of tree, in the right areas, with tree planting set to begin in October.”