Well, foraging hit prosperity at a time where you can't really do dick about it.
Your tax is already set for the season and your actions are spent too, so there is no way possible that you can dodge the prosperity loss.
This means you, at a minimum, have to spend 1 GB and a Regent Action, assuming Take 10, to restore Prosperity in that province.
If there was a structure, which made "Emergency Tax Relief" and dumped the tax by one or more levels, enough to offset the otherwise impending prosperity loss, then it would quite possibly be worth having it built and on retainer.
Assuming you are on stable Heavy Tax, then you can, in theory and pending DM allowance, offset up to 5 levels of prosperity loss, at the cost of the tax income of course.
Still, likely to be much preferred to the alternativy. Well, yes, it is much preferable to the alternative. I know.