OTTAWA — Finding the perfect real Christmas tree will be harder and more expensive this year. Canada, the world’s top exporter of natural Christmas trees, is grappling with a shortage that will likely be exacerbated by historic flooding in British Columbia, where some tree farms are underwater. …Canada exports about 2.3 million Christmas trees per year, with some 97 per cent going to the United States. While British Columbia does not export cut Christmas trees, it is a significant domestic supplier. That means shortfalls will have to be made up with supply from elsewhere, leaving fewer Canadian trees for export.“We can’t ship them because all the roads are closed,” said Arthur Loewen, whose tree farm in Chilliwack has been swamped. “We’re basically shut down until the water recedes.” Trees already cut and wrapped for wholesale buyers are piled up on wood pallets, surrounded by water. His self-serve fields… are 75 per cent flooded.