Darlington Council and the Darlington Forest Project planted the trees in Lakeside, Darlington.
Andrew Gibson, a member of the Darlington Forest Project, said: "As volunteers we've been planting trees. I am a runner so I go past and check on them. Over the course of a week or 10 days every single tree has gone, 300 trees have been taken down, it's a public right of way.
"If it was kids the smashed trees would have been discovered close by. It was maybe a dog walker or somebody who has taken issue thinking they've got their own right of way.
"It's absolutely appalling, it's a community project. It's better for the environment and better for the local area. It's just been trashed by someone."