I don't think I've ever seen a piece of marking tape on the ground Wendy.... The only way it's going to end up on the ground is by someone deliberately pulling it off which is highly unlikely.
I know it's plastic and yes there may be an alternative material that is bio degradable that could be used.. I'd choose this over deliberately pruning and clearing re-growth vegetation which is fragile to some extent after the fires. We need to minimise our impact on the environment not contribute to it...