The problem of moving plants and animals around the world.

It is a strange fact of nature that many species of plants and animals do much better somewhere that they did not originally evolve.  Oceanic islands are particularly attractive to foreign species and Charles Darwin observed that humans seem to be better than the Creator at selecting the inhabitants for islands.  Darwin gives examples of islands that have been transformed in just a few decades by invasive species.

Many people can name animals and plants that have been introduced and have gone on to thrive. In the UK red squirrels have been replaced by American grey squirrels and in Australia the introduced domestic cat has eaten its way through populations of other species.  Plants too have caused problems with Japanese knotweed and Paterson's curse being familiar problems in the UK & Australia respectively.

The repercussions of these invasives can be ecological changes, but the economic damage can be large.  In Australia as much as A$4 billion is spent annually on weed control and in the UK, it cost 10s of millions of pounds to clear the 2012 Olympic village site of knotweed.  These plant and animal problems are large and clearly visible.  Less obvious, at least to start with, are introduced diseases and invertebrate pests, but once they are doing damage the effects are very clear to see and the problem may be uncontrollable.  In the UK ash die-back is the current new problem but in Western Australia bush die-back has been a serious issue for decades.

The ecological impact of pests and diseases can be severe, with soil erosion following the death of plants being the worst impact.  However, the knock-on effects on herbivores, and pollinators, and the rest of the food web, is profound.  The UK countryside would be a much poorer place if alders, birch, hazels, hawthorns, beech, ash, honeysuckle, poplars, sloes, oaks, willows, and yews, were removed by pests and diseases.

Controlling an introduced pest or disease that has gone feral is often impossible and so preventing the introduction in the first place is the best strategy.  However, many of the potential problems cannot be spotted easily by quarantine officers.  Imported plants can look perfectly healthy but be infected. Significantly, all the plants listed above can harbour potentially devastating pests and diseases that are not present in the UK and other parts of Europe.

The ramifications of these imported diseases and pests can also be severe economic loss for the nurseries growing plants for landscaping or gardens.  All of the UK native plants listed above belong to groups that contain important ornamental plants.  It is easy to understand why nursery owners and their customers would welcome restrictions on the import of these plants.  The EU is planning to bring in new legislation in December 2019.  The legislation will list 39 genera of plants that are considered high risk. This is precisely what the EU is proposing, and it is seen by many people in the horticultural profession to be a sensible precaution to protect both the countryside and the nursery trade.

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