'' can escape from gardens into nearby
wildlands. Many invasive
neophytes in Australia and New Zealand were originally garden escapees. The
Jerusalem thorn forms impenetrable thorny thickets in the
Northern Territory which can be several kilometers in length and width. Two other plants introduced as ornamental garden plants,
Asparagus asparagoides and
Chrysanthemoides monilifera, now dominate the herbaceous layer in many eucalyptus forests and supplant perennials, grasses, orchids, and lilies. Neophytes that compete aggressively, and which displace and repel populations of native species, may permanently change the
habitat for native species and can become an economic problem. For example, species of
Opuntia (prickly pears) have been introduced from America to Australia, and have become wild, thus rendering territories unsuitable for breeding; the same goes for
European gorse (
Ulex europaeus) in New Zealand.
Rhododendron species introduced as ornamental garden plants in the
British Isles crowd out island vegetation. The same can be seen in many acidic
peatlands in the Atlantic and subatlantic climates.
Robinia pseudoacacia was imported from America to
Central Europe for its rapid growth, and it now threatens the scarce
steppe and natural forest areas of the drylands. Examples in forests include
Prunus serotina which was initially introduced to speed up the accumulation of
humus. In North America,
Tamarisk trees, native to southern Europe and temperate parts of Asia, have proven to be problematic plants. In nutrient-poor heaths, but rich in grasses and bushes (
fynbos) in the region Cape in
South Africa, species of eucalyptus from Australia are growing strongly. As they are largely accustomed to poor soils, and in the Cape region they lack competitors for nutrients and parasites that could regulate their population, they are able to greatly modify the biotope. In
Hawaii, the
epiphytic fern
Phlebodium aureum, native to the tropical Americas, has spread widely and is considered an invasive plant. Particularly unstable ecosystems, already unbalanced by attacks or possessing certain characteristics, can be further damaged by escaped plants if the vegetation is already weakened. In the humid forests of Australia, escaped plants first colonize along roads and paths and then enter the interior of the regions they surround.
Thunbergia mysorensis, native to India, invaded the rainforests around the coastal city of
Cairns in
Queensland and even invades trees 40 m high. In
Central Australia, the Eurasian species
Tamarix aphylla grows along river banks, repelling native tree species, and wildlife that go together, lowers water levels and increases soil
salinity. As in the United States, tamarisks have proven to be formidable bio-invaders. The fight against this species of trees, which has spread widely since, appears to be almost hopeless. ==Related terms ==