Pheasants and potatoes - How can numbers alone inform us about impact?

Invasive species are a real threat to our countryside. The distinction between which introduced species are causing a problem and which are not is often blurred. The pursuit of headlines and, more often than not, fundraising, adds to the confusion.

When the pheasant shooting season opens at the beginning of October pheasants are propelled to the front of this discussion. Despite the fact that the Game & Wildlife Conservation Trust (GWCT) has researched the net gain to nature, when best practice is followed (I have blogged about why this should be celebrated before) some involved in this non-indigenous discussion then manage to ignore this and just lob around statistics on the number of pheasants released 35 million (PACEC) as though that, in itself, is clear evidence of 'harm'.

Well, if high numbers of a non-indigenous species alone is supposed to demonstrate harm - let's think about that. Most farm crops are non-indigenous.

Potatoes were first domesticated in Peru and Chile and introduced to the British Isles around 1600AD, possibly from the wrecks of the Spanish Armada. Very quickly they became an important part of our diet. Initially they were grown in gardens and on smallholdings but it was not until the latter part of the eighteenth century that potatoes became popular as a field crop. Tubers were used for human consumption and for fattening pigs while the crop provided a good break in the cereal rotation.

If we take the UK's annual production of potatoes each year and divide it by the average weight of a potatoes per tonne we could estimate that we grow...

16,115,970,000 non-indigenous potatoes in the UK every year.

16 billion non-indigenous potatoes will keep us well fed. Do they do harm? No impact at all? Not even 16 billion? Well, just like the 35 million pheasants, there are impacts. Our farmers recognise, as do game keepers, that there are issues and strive to address or reduce them. For example, potato production regularly requires the control of slugs, for pheasants that might be foxes. As ever in conservation, the issues are complex; foxes eat slugs etc.

So it is not necessarily the act of growing a potato, or releasing a pheasant, that is the issue - it is the impacts on the environment. Both have impacts but the number of potatoes grown or pheasants released does not, on its own, tell us that they are causing 'harm'. Headlines about high numbers can serve us all in thinking though the issues - that is a good thing; as long as we consider all the issues.