The conifers were felled on the 12 hectar site on the outskirts of Darwen, Lancashire, after a "health and safety survey."
United Utilities cleared the huge expanse of forest alongside the busy A666 claiming some of the trees, planted after the Second World War, were in danger of falling down.
But police and councillors have said that the cull was also ordered to discourage strangers from meeting for sexual intercourse at the known 'dogging' hotspot.
Jean Rigby, a local councillor, said: "The area will be replanted with native species that, in 20 years, people will see the benefit of.
"I'm more than happy this is being carried out - and it has a double whammy in terms of the sexual behaviour. I've heard anecdotally that since the trees have been cleared, it's quietened down a lot!"
Another councillor, Colin Rigby, said: "It's essential work that United Utilities are carrying out, and cutting the trees back also works as a deterrent to people who go dogging."
Sgt Mark Wilson, of Lancashire Police's Darwen Neighbourhood Policing team, explained: "It's an ongoing problem and very worrying for members of the public.
"It's far too early to tell if cutting the trees back has had any impact on the dogging situation, but we'll be paying regular attention to the area."
To minimise the impact on the local wildlife in Darwen, park rangers carried out the felling outside the bird breeding season with wildlife from the 20-metre deep strip than runs alongside the road, being moved to the wood behind.
United Utilities stressed that those cut down were commercial - and not protected - trees.
But Brian Jackson, of Friends of the Earth, said: "To remove thousands and thousands of mature trees is absurd. The conifer trees in this area are very valuable in providing windbreaks and attracting rainfall to the area."
Matthew Elliott, Chief Executive of the TaxPayers' Alliance, said: "It's awful that a public green space, an asset to the local community, has been destroyed mindlessly.
"If the law was enforced properly then there would be no need to chop down these trees.
The police and the council should work more closely with local residents to fight crime in order to prevent such a travesty happening again in future."
A spokesman for United Utilities said: "They were old and at risk of falling into the road causing an accident. Following a health and safety survey, a license was applied for and granted through the Forestry Commission to fell them.
"We are re-planting the area with natural broad leaf trees."
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