The Impact of Invasive Alien Species

Packages of unknown seeds which were sent from China to America have caused a bit of a stir recently. Despite the warning from the U.S. Department of Agriculture on not to open them, let alone to germinate them, some receivers did quite the contrary. In the end, it was an elaborate scheme to boost sales by getting false reviews. Warnings were given because the USDA has valid reasons mainly to protect the US crops and environment.

Plant movement, whether natural, un-intentional or intentional has various effects. Firstly, the spread of pests and diseases, secondly, recent concern of the spread of invasive alien species.

Invasive alien species (IAS) are any wildlife and plant species that are introduced or spread outside of their natural habitat and into a new foreign habitat or ecology that will cause damage or habitat destructions. In general, these species are not considered as problematic in their natural ecosystem of origin perhaps due to limited resources, unfavourable growing conditions or were kept under control. In many cases, these species have exponential growth and can become aggressive and be more successful in a new environment just because there are no natural predators, no control and optimum condition to thrive.

In the case of the Burmese python, like many other wildlife, they are brought in as pets. When they come bigger and unmanageable, they are usually released into the wild which is new to the unwanted pets. When the Burmese pythons were released into the Florida everglades, their increase in population resulted in decrease in the number of the native wildlife. Foxes, rabbits, raccoons, deer, opossums and bobcats which are native to the marshes were reported to being close to being wiped out.

In the UK, one of the well-known IAS plant is Rhododendron ponticum which was in introduced as an ornamental pot plant in the 1970s from its native region of Causacus. It forms a dense canopy, under low light conditions and once established they reduced the local biodiversity1. The roots also exude allelophatic chemical compounds (compounds that are harmless to the plants but can cause damages or growth enhancement to other surrounding plants) which results in no other plant growth under the canopy.

In the case of the mysterious random seeds appearing in the US, planting the seed and letting it fruit could release pollens of unknown genetic traits. If pollinated with local crops this can cause genetic drifts (random alteration of the genes) that can cause mutations and a drop in crop vigour or yield. It can also render established crops to become more susceptible to pest and disease.

The policy and guideline on IAS in the UK and Wales is available on the DEFRA website at, To name of some of the plants under management are: Nuttall’s waterweed (Elodea nuttallii), Chilean rhubarb (Gunnera tinctoria), Giant hogweed (Heracleum mantegazzianum), Floating pennywort (Hydrocotyle ranunculoides), Himalayan balsam (Impatiens glandulifera), Curly waterweed (Lagarosiphon major), American skunk cabbage (Lysichiton americanus), Parrot’s feather (Myriophyllum aquaticum).

In many cases, introduction of IAS across borders is because of beauty (introduced as ornamentals), pharmaceutical (introduced as medicinal herbs) and food (introduced as seeds/crops). Managing IAS in the UK and Wales is a heavy task, mainly because Great Britain is an Island. Therefore, when we are on holidays abroad and see an exotic species that may look good in the house or garden, do put into consideration how it is going to impact UK’s native species and the cost of mitigating aliens species especially when they become invasive and damaging.

1 Jones et al. (2019). Scientific Reports 9(2239).