derailments by washing out the tracks. When a beaver dam bursts, the resulting flash flood may overwhelm a culvert. Traditional solutions to beaver problems have been focused on the trapping and removal of all the beavers in the area. While this is sometimes necessary, it is typically a short-lived solution, as beaver populations have made a remarkable comeback in the United States (after near extirpation in the nineteenth century) and are likely to continually recolonize suitable habitat. Modern solutions include relatively cost-effective and low maintenance flow devices. Introduced to an area without its natural predators, as in Tierra del Fuego, beavers have flooded thousands of acres of land and are considered a plague. One notable difference in Tierra del Fuego from most of North America is that the trees in Tierra del Fuego cannot be coppiced as can willows, poplars, aspens, and other North American trees. Thus the damage by the beavers seems more severe. The beaver's disruption is not limited to human geography; beavers can destroy nesting habitat for endangered species. Warming temperatures in the Arctic allow beavers to extend their habitat further north, where their dams impair boat travel, impact access to food, affect water quality, and endanger downstream fish populations. Pools formed by the dams store heat, thus changing local hydrology and causing localized thawing of permafrost that in turn contributes to global warming. Stream life cycle Wetland creation If a beaver pond becomes too shallow due to sediment accumulation, or the tree supply is depleted, beavers will abandon the site. Eventually the dam will be breached and the water will drain out. The rich thick layer of silt, branches, and dead leaves behind the old dam is an ideal habitat for some wetland species. Meadow creation As the wetland fills up with plant debris and dries out, pasture species colonize it and the wetland may eventually become a meadow suitable for grazing in a previously forested area. This provides a valuable niche for many animals which otherwise would be excluded. Beaver dam creation also increases the plants the dams were made from (such as willows) to reproduce by cutting, encouraging the growth of adventitious roots. Riverine forest Finally the meadow will be colonized by riverine trees, typically aspens, willows and such species which are favoured by the beaver. Beavers are then likely to recolonize the area, and the cycle begins again. Bottomland Each time the stream