are co-op reserves invested?

It's at the discretion of each building.

Decision being made by board?

Although I have seen them invested in other instruments than simple savings accounts, it's rare that they go into things like stock; more likely t-bills and the like.

Thanks everyone, very helpful.

Yes, the decision is made by the board.

For the most part, we're invested in CDs which we've "stepladdered" so they have staggered maturity dates. Since we do board elections every year, it's a safeguard against the possibility that a brand-new board would have immediate access to 100% of the building's reserves at any one time.