" what's to stop the owner just removing the trees before applying for planning? " - nothing ,they often do . " a member of public can request that a tree in someone else's garden have a TPO applied to it. " - again ,this is not at all uncommon . But I'd like to add that TPO's can be lifted so that developments can be built . But in those cases ,as MarkT has pointed out ,there are planning requirements that replacement trees are planted to mitigate the loss of the protected tree .