The U.S. gets up to 80% of sphagnum peat moss it uses from Canada. In Canada, the peat bog mass harvested each year is an estimated 1/60th of the mass that accumulates. About 0.02% of the 1.1 million km2 (422,000 square miles) of Canadian peat bog are used for peat moss mining. Some efforts are being made to restore peat bogs after peat mining, and some debate exists as to whether the peat bogs can be restored to their premining condition and how long the process takes. "The North American Wetlands Conservation Council estimates that harvested peatlands can be restored to 'ecologically balanced systems' within five to 20 years after peat harvesting." Some wetlands scientists assert that "a managed bog bears little resemblance to a natural one. Like tree farms, these peatlands tend toward monoculture, lacking the biodiversity of an unharvested bog."