How can Obama justify his demand that states shutdown state parks?

So what if the federal government covers some of the costs of state parks?  Can't the state governments make up their own minds about whether they want to temporarily cover the difference?  On top of all this, the House Republicans (and some Democrats) have already passed a spending bill for the nation's parks, but Democrats in the Senate won't allow a vote on it.  Well, at least one governor has ignored Obama's demands on closures.  From The Hill newspaper:

Wisconsin Gov. Scott Walker (R) is defying orders from Washington, D.C., to close down several state parks that receive federal funding. 

Despite receiving a closure directive from the National Park Service, Wisconsin's Department of Natural Resources (DNR) has decided instead that parks partly funded by the federal government would stay open to the public.  

In the wake of this week's federal government shutdown, the U.S. Fish and Wildlife Service also placed barricades by a boat launch on the Mississippi River because it was on federal land. Wisconsin’s natural resources agency reopened it.  

State officials said they had legal authority to remove the barricades at the boat landing because of an agreement Wisconsin has had with the federal government since 1961.  

"We respect the magnitude of the process the federal government has had to undertake to close its properties and certain activities on properties they own and manage," Wisconsin's Natural Resources Secretary Cathy Stepp told department employees in an email obtained by The Hill. . . .