This is a bit nuts in terms of "open space" preservation. I think its cool that a governmental entity would try such a tactic, especially using development codes, to save nature.
I know it is very burdensome to the property owner, but if the governmental body has such home rule powers, then it may be legal.
As for the property owners that are complaining in the article, they need to get themselves elected and rescind the law, if they dislike it so much.
What are yours?