For protection of natural areas, it does not matter if invasive exotic plants are unintended introductions, or if they were introduced for cultivation. All are equally capable of altering native ecosystems.
Most exotic species that are not grown deliberately are agricultural or garden weeds, incidentally introduced with the crops, and it is in the interest of the grower to control them—no compulsion is usually necessary, neither is collective (voluntary or publicly funded) action required, other than on public lands.
Accidentally introduced exotic species, or weeds that have yet to spread to their full potential extent are the target of regulation, and may warrant collective efforts at eradication or control—but that's another discussion. Land owners who through no fault on their part become hosts to species that are difficult to control may feel that the Weed Act is unfair—but there is probably no constituency advocating neglect.
Conflicting interests arise when a species can be grown for profit or enjoyment, but spreads to other lands where it is damaging. Under present arrangements, growers profit, but don't bear the cost of control (or alternatively, the losses that accrue when there is no control on other lands). It seems unreasonable that land owners other than the growers, or that the public at large should bear the cost of collateral damage caused by growing of profitable species. This is a classic example of a negative externality . The cost of the crop or ornamental species spreading beyond where it is cultivated does not appear in the grower's accounts, although he profits in money or pleasure while society at large suffers a loss. One might go so far as to say that the grower steals his profit (or some portion of it) from the public at large—just to make the point clear.
This situation can only be corrected by collective (presumably government) action. The object of this discussion is to illuminate just what form that action should take (not to discuss which agricultural or horticultural species are invasive).
To start the discussion, here are some possibilities, listed irrespective of practicality.
- Prohibit the growing of the species altogether.
- Prohibit the growing of the species in locations where environmental factors make escape and spread likely, allowing it to be grown in environments where it is unlikely to become problematic.
- Require growers to control spread of the species (by listing as Noxious under the Weed Act) but also require growers to reimburse costs of control and lost property value to those who suffer them, including the public.
- Require all growers to collectively control the species outside of cultivation.
- Allow growing of the species under licence, with licence fees sufficient to cover (and applied to) control of the species out of bounds.
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