As forests decline in temperate and tropical climates, highly-developed
countries and those striving for greater economic and social benefits
are beginning to utilize marginal forests of high-latitude and
mountainous regions for resources to satisfy human needs. The benefits
of marginal forests range from purely aesthetic to providing resources
for producing many goods and services demanded by a growing world
population. Increased demands for forest resources and amenities and
recent warming of high- latitude climates have generated interest in
reforestation and afforestation of marginal habitats in cold regions.
Afforestation of treeless landscapes improves the environment for human
habitation and provides for land use and economic prosperity. Trees are
frequently planted in cold climates to rehabilitate denuded sites, for
the amenity of homes and villages, and for wind shelter, recreation,
agroforestry, and industrial uses. In addition, forests in cold climates
reduce the albedo of the earth's surface in winter, and in summer they
are small but significant long-lived sinks for atmospheric carbon
dioxide. Finally, growth and reproductive success of forests at their
geographic limits are sensitive indices of climatic change. As efforts
to adapt forests to cold climates increase, however, new afforestation
problems arise and old ones intensify. Austral, northern, and
altitudinal tree limits are determined by many different factors.
Current hypotheses for high-latitude tree limits are based on low
growing-season temperatures that inhibit plant development and
reproduction.