The infestation, which (by November 2008) has killed about half of the province's lodgepole pines (33 million acres or 135,000 km²)[23][24] is an order of magnitude larger than any previously recorded outbreak.[25] One reason for unprecedented host tree mortality may be due to that the mountain pine beetles have higher reproductive success in lodgepole pine trees growing in areas where the trees have not experienced frequent beetle epidemics, which includes much of the current outbreak area.[26] In 2007 the outbreak spread, via unusually strong winds, over the continental divide to Alberta. An epidemic also started, be it at a lower rate, in 1999 in Colorado, Wyoming, and Montana. The United States forest service predicts that between 2011 and 2013 virtually all 5 million acres (20,000 km2) of Colorado’s lodgepole pine trees over five inches (127 mm) in diameter will be lost.[24]