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Forest migration
Forest migration is the movement of large seed plant dominated communities in geographical space over time.
The emphasis of forest migration is placed on the movement of the tree communities that make up the forest community. Though an individual tree is permanently fixed in a location, tree populations may migrate over the landscape through generations. Tree migration is controlled by two overlying forces: environmental suppression and dispersal capacity of the population by seed.〔 Though the true rate of forest expansion is difficult to quantify, efforts are being made to evaluate and predict past, current, and future rates and extents of forest movements.
==Forces controlling forest migrations==
Plant populations are governed by two major controlling forces.〔Sauer, J.D. 1988. Plant migration the dynamics of geographic patterning in seed plant species. University of California Press. Berkeley and Los Angeles, California.〕 The population expansion favoring force, positive force, is the sexual reproductive dispersal of the forest population. The population expansion limiting force, negative force, is the suppression by the environment of seed and plant success in an area. These two major forces compete and change through time causing advances and retreats in the borders of plant populations' regions. An advance in the range border of the forest population occurs when environmental suppressive forces are below the population's dispersal potential, thus allowing for seedling success outside the current range. Range border contractions occur when environmental suppressive forces increase to a point where seedling success is limited in the current range, thus no successive generation is established to replace the individuals within a portion of the current range through time. Though dispersal and environmental suppressive forces continually act, a static range boundary may occur when there is no change in the rate of these two factors.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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