Biology Reference
In-Depth Information
ductions for forestry and horticulture become important somewhat later
and have continued to the present. In the eastern United States, between
61 and 68% of plants, depending on location, that were introduced before
1900 and have become thoroughly naturalized were deliberately intro-
duced (Mack and Erneberg 2002).These percentages are likely to be low
because the manner of introduction of 31-37% of naturalized species
could not be determined with certainty. For Hawaii, about 57% of natu-
ralized species were deliberately introduced (Wester 1992). Since 1900,
the percentage of naturalized plants that were deliberately introduced has
tended to be even higher in many areas, including the United States,Aus-
tralia, and New Zealand (Mack and Erneberg 2002).
Many species of trees have been introduced to new regions for timber
production, fuelwood, creation of windbreaks, stabilization of stream
banks, or wetland reclamation. Australian eucalypts have been introduced
throughout the world for timber and fuelwood production and for use as
windbreaks. Russian olive (
Eleagnus angustifolia
) and Siberian elm (
Ulmus
pumila
), together with other species, were planted extensively in central
North America as windbreaks and landscaping trees. Several varieties of
tamarisk (
Tamarix
spp.) were used for stabilization of stream banks in the
southwestern United States in the early twentieth century. In Florida,
Australian melaleucas were planted in hopes that they would help reclaim
marshland by increasing transpiration of water. Russian olives, tamarisks,
and melaleucas have become very serious invaders in their areas of intro-
duction in North America.
In terms of number of alien species, horticultural attractiveness
accounts for more introductions of invasive woody plants in the United
States than any other perceived value (Reichard and White 2001). In Aus-
tralia, similarly, 65% of all plants that have become naturalized were intro-
duced for horticulture. Deliberate introduction for horticultural and
related use is responsible for establishment of many plants that reproduce
vegetatively (Py
v
ek 1997).
Animals have also been deliberately transported to new areas. Domes-
tic livestock, including cattle, horses, sheep, goats, and rabbits, have been
introduced to many oceanic islands or have become feral after their intro-
duction for husbandry.Various game and fur-bearing animals have been
released on islands or new continental areas or have escaped from farms.
Game birds and songbirds have been introduced to new geographical
areas for sport and pleasure. Game fish have been freely translocated to
new waters, both within and between continents. Fish and invertebrates
introduced for aquaculture or aquarium display have escaped or been
