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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 populations that make up the forest community. Though an individual tree is permanently fixed in a location, tree populations may migrate over the landscape through successful dispersal and establishment into new regions over the course of generations and/or a lack of regeneration in a portion of its previous habitat range, leading to subsequent population retreat. Tree migration is controlled by two overlying forces: environmental suppression and dispersal capacity of the population by seed. Though the true rate of forest migration is difficult to quantify, efforts are being made to evaluate past, current, and future rates and extents of forest movements.

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Forces controlling forest migrations
Forest migration happens by the occurrence of two processes: population expansion into new habitat range and population retreat from historical habitat range. These processes are governed by two competing forces. The positive force of forest migration, plant population expansion, is governed by the seed dispersal capacity of the tree species' population and seedling establishment success. The population expansion limiting force, negative force, is the suppression by the environment of the species' success in an area. Suppression by the environment could include human land use, disturbance, unfulfilled species-specific resource needs, and/or climatic stress.

These two major forces compete and change through time causing advances and retreats in the borders of plant populations' ranges. An advance in the range border of a tree population occurs when environmental suppressive forces beyond the historical range fall below the population's dispersal and establishment potential, thus allowing for seedling success in new territory. This creates a 'leading edge' of the tree population habitat range.

Range border contractions occur when environmental suppressive forces increase to a point where seedling success is limited in the current range. Regeneration failure in a portion of a species' habitat range creates a lagging or 'trailing edge'. 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.

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Current climate change and its effects
The Earth has entered another period of rapid climate change, known as global warming. Since the early 20th century, the global air and sea surface temperature has increased about 0.8 C-change, with about two-thirds of the increase occurring since 1980. It is important to consider this statistic as being a global average. The effects of climate change may be highly heterogeneous over the landscape, affecting different areas in different ways and magnitudes. Modern climate change will likely alter migration, persistence, and competition within and between plant communities. Also, the fact that forests are major constituents of habitat raises concerns on the effects of forest movement on climate change and greenhouse gas risk factors. Also some concern on the effects of forest migrations should be evaluated for wildlife because of the possibilities of forest fragmentations and extirpations.

It is important to consider that temperature is not the only relevant habitat range factor affected by climate change. Alterations in precipitation patterns, diurnal timing, seasonal intensity, and season length all can reduce the survivorship or reproductive ability of a plant species by disrupting phenology and genetic fitness of the population.

The ability of plant species to track climate change will be valuable information in predicting the future health, stability, and function of the Earth's forests in the coming decades and centuries. If forest populations cannot successfully migrate in response to climate change, the consequences could include disrupted reproductive cycles, population fragmentation, genetic bottlenecking, and extirpation. Knowledge of the genetic structure and phenotypic limits of plant species gives insight to the range of climatic shifts a species can endure before migration becomes necessary for a species to avoid climate change-induced extinction.

Generally, ideal tree habitat ranges are moving poleward for many species. The capacity for species to migrate in response to the ideal biogeographic range shifts has been questioned, especially in the context of extensive habitat fragmentation which occurs in modern-day landscapes.

Simulation models are presented which incorporate two factors, land use pattern and means of dispersal, to assess potential responses of forest species to climatic warming. Study areas displayed a range of human influence on the landscape, from heavily forested areas to areas dominated by urbanization and agriculture. The effect of establishing corridors (greenways) through fragmented landscapes is also assessed.

Results indicate that many species may be unable to track shifts in climatically-controlled range limits, resulting in widespread disequilibrium between vegetation and climate. A variety of mitigating options likely will be necessary to offset the negative consequences of climatic warming on biological diversity. Land use planners and managers are encouraged to incorporate climate warming into long-term planning.