North America is the third largest of the seven continents and ranges from the Arctic tundra of Greenland and Alaska down to the arid semi-desert of Mexico and sub-tropical forest of Panama. The vegetation of the continent is diverse but has been modified extensively by man, however to the north, in parts of Canada, much of the vast expanse of boreal forest still exists. Inland, along the western side of much of the continent, run the Rocky Mountain range, extensively covered by mixed pine forest. Although the animal population of the continent was once diverse and widespread, encroachment by man on a grand scale, has severely reduced there numbers.