This loophole is solved by making it that declaring the land as such status means the land is commited to that use for a minimum number of years that makes the conservation meaningful. Something like a decade minimum with a high bar for converting it for other usage afterwards. Farmers in the UK for instance already have some incentives to leave some fields alone.
Many capitalistic countries also have adverse possession laws, where if someone uses the land for X number of years, it becomes theirs.