Garden Refugee

Escaped plants are cultivated plants, usually garden plants, that are not originally native to an area, and due to their dispersal strategies, have escaped from cultivation and have settled in the wild and bred there, whether intentionally or unintentionally. Escaped plants are purposefully introduced plants that have naturalized in the wild and can develop into invasive plants, the settlement of which is to be assessed as problematic. Other commonly used terms include escaped garden plant, garden escapee, escaped ornamental or garden refugee.

Some plants are valued as ornamental plants since they are very adaptable and easy to grow, and therefore would escape cultivation and become weedy in various ecosystems with far-reaching ecological and economic consequences. They can also develop into invasive intruders, especially in fragile or unstable ecosystems. Occasionally, their spread can even be traced back to botanical gardens. Therefore, escaped plants are the subject of research in invasion biology. Some plants escaped from cultivation so long ago that they are currently considered roadside plants or wildflowers.

Dispersal

All garden refugees belong to the so-called hemerochoric plants. This term is used across the board for plants that have been introduced directly or indirectly by humans. The term also includes the unintentionally introduced plants that were introduced through seed pollution (speirochoric) or through unintentional transport (agochoric).

Plants escape from gardens in many ways, but one main cause of spread from the ornamental garden is by green waste dumping in bushland and road reserves and as well as by birds or other animals eating the fruits or seeds and dispersing them. Others are accidental hitchhikers that escape on ships, vehicles, and equipment. Garden escapees can be adventive, which means they can be established in an inappropriate area of origin site by human influence.

Occasionally, seed contamination also introduces new plants that could reproduce for a short period of time. The proportion of adventitious species in open ruderal corridors at such locations can exceed 30% of the flora of these locations. Further, ornamental alien plants can easily escape their confined areas (such as gardens and greenhouses) and naturalize if the climate outside changes to their benefit. In the US, there are over 5,000 escaped plants, many of which are escaped ornamentals.

Ecological threats

Many invasive neophytes in Australia and New Zealand were originally garden escapees. The Jerusalem thorn forms in the Northern Territory impenetrable thorny thickets 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 develop aggressively, which displace and repel large areas of native species in many humid and shady landscapes, permanently change the biotope pose in many parts of the world, and sometimes create 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'' has spread widely, and is considered an invasive plant.

Particularly unstable ecosystems, already unbalanced by attacks or possessing certain characteristics, can be massively damaged by neophytes because the final vegetation is already weakened. In the humid forests of Australia, neophytes 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

Garden escapees can fall within the definition of, and may have a relation to, these botanical terminologies below:

*Agriophyte: Refers to plant species that have invaded natural or near-natural vegetation and can survive there without human intervention. Established in their new natural habitats, they hereby remain part of natural vegetation even after human influence has ceased, and are independent of humans in their continued existence. Examples in Central Europe are waterweed, Douglas fir or Japanese knotweed, and the sweet chestnuts introduced by the Romans in Germany. The group of ornamental plants and even the poppy (both archaeophytes) that normally grow in fields colonized pioneering sites in floodplains and is therefore now part of natural vegetation.
*Epecophyte: Species of recent appearance, usually numerous and constant in the country, but confined to artificial habitats, such as meadows and ruderal vegetation. They are dependent on humans for existence that their habitats require constant renewal.
* Ephemerophyte: Species that are only introduced inconsistently, that die briefly from culture or that would disappear again without constant replenishment of seeds. In other words, they can establish themselves temporarily, but they are not in a position to meet all the conditions relating to the territory. A cold winter, or an unusual drought, can lead to the death of these plants; most of the time, they are not able to fight against the local flora in extreme conditions.
* Hemerochory: Plants or their seeds may have been transported voluntarily (introduction) or involuntarily by humans in a territory which they could not have colonized by their own natural mechanisms of dissemination, or at least much more slowly. They are able to maintain themselves in this new vital space without voluntary help from man. Many Central European cultivated and ornamental plants are hemorochoric – insofar as they have escaped and subsist independently of cultivation. These are the forms of hemerochory:
**Agochoric: Plants that are spread through accidental transport with, among other things, ships, trains, and cars. On land, agochoric plants used to be common in harbors, at train stations, or along railway lines. Australia, like New Zealand, has taken stringent measures to prevent the spread by seed or human transport. Agricultural implements imported into Australia must be thoroughly cleaned. Air travelers from other continents are forced to thoroughly clean the soles of their shoes.Tim Low: Feral Future. The Untold Story of Australia's Exotic Invaders, p. 73
**Ethelochoric: Deliberate introduction by seedlings, seeds, or plants in a new habitat by humans. Many cultivated plants which currently play an important role in human nutrition have been deliberately disseminated by humans. Wheat, barley, lentil, broad bean and flax, for example.
**Speirochoric: Unintentional introduction by seeds. As all seed samples also contain the seeds of the grasses of the field from which they were obtained, the trade-in seeds of useful plants has also allowed the spread of other species. Speirochoric plants are therefore sown on soil prepared by man and compete with useful plants. Wild chamomile, poppy, cornflower, corn buttercup are example of plants that were unintentionally scattered.

Example species

Examples of escaped plants and/or garden escapees include:

* '' Alchemilla mollis''
* '' Allium schoenoprasum''
* '' Allium ursinum''
* ''Anredera cordifolia''
* ''Aquilegia vulgaris''
* '' Araujia sericifera''
* '' Ardisia crenata''
* '' Asclepias tuberosa''
* '' Asparagus aethiopicus''
* ''Baccharis halimifolia''
* ''Bartlettina sordida

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