What is Tree line?
[[File: Tree line.jpg|thumb|250px|In this view of an alpine tree-line, the distant line looks particularly sharp. The foreground shows the transition from trees to no trees. These trees are stunted and one-sided because of cold and winds.]] The '''tree-line''' or '''timberline''' is the edge of the [[habitat]] at which [[tree]]s can grow. Beyond the tree-line, they are unable to grow as conditions are too bad. There are several types of tree lines defined in [[ecology]] and [[geology]]: * '''Arctic tree-line''' The farthest [[north]] in the [[Northern Hemisphere]] that trees can grow; farther north, it is too cold. * '''Antarctic tree-line''' The farthest [[south]] in the [[Southern Hemisphere]] that trees can grow; farther south, it is too cold as well. * '''Alpine tree-line''' The highest height where trees grow: higher up, it is too cold, or snow covers the ground for too much of the year. The [[climate]] above the tree-line is called an [[alpine climate]]. * '''Exposure tree-line''' On [[coast]]s and isolated mountains, the tree-line is often much lower than in corresponding altitudes inland and in larger, more complex mountain systems, because of strong [[wind]]s reduce tree growth. * '''Desert tree-line''' The places where trees cannot grow as there is too little [[rainfall]]. * '''Toxic tree-line''' The environment is too extreme for trees to grow. This can be caused by molten lava or hot rock ([[infrared]] radiation), any of several kinds of [[fumarole]] (steam, sulfur, acid), soil [[pH]], low [[oxygen]] conditions, salt concentrations (as near the [[Dead Sea]] or [[Great Salt Lake]]), [[sulfate]] levels, other natural causes, or by man made [[pollution]]. * '''Wetland tree-line''' The wettest ground on the margins of [[muskeg]]s and [[bog]]s that trees can grow in, below which the ground is too saturated with water, excluding [[oxygen]] from the [[soil]] that tree [[root]]s need to grow. However, no such line exists for [[swamp]]s, where trees, such as [[Taxodium|Bald cypress]] and the many [[mangrove]