Original sentence: A native species is one that got to the island on its own by swimming, flying or walking over the ice.And these species are creating trouble for the forest.If you look at the mammals found here there are many more than 14.Many of our mammals, including moose, snowshow hare, red squirrels and mink, have been introduced through the island either on purpose or by accident.Snowshoe hare and moose in particular are having a detrimental effect on balsam fir stands in the park.That way we can see what the forest would look like if those animals weren't there.The Park has exclosures set up so that visitors can see the effect that introduced species are having on the forest.The creatures browse new growth of balsam fir and many other tree species, which is preventing the trees from growing and maturing.The exclosures are areas that are fenced off so that moose and snowshoe hare can't get in