Should corn be considered an invasive species in the Midwest?

Question

Per the United States Department of Agriculture (USDA) an invasive species is defined as:

• non-native (or alien) to the ecosystem under consideration

• whose introduction causes or is likely to cause economic or
  environmental harm or harm to human health

Corn in the Midwest, USA (often referred to as the Corn Belt) would seem to satisfy the first requirement as an invasive species as it is not native to this area. Regarding the second requirement, it could be argued that corn in the Midwest causes environmental harm because it is in place of many indigenous plants that many other animals rely on to survive. For example, habitat loss is considered a cause in the decline of the regal fritillary (Speyeria idalia) butterfly.

A Google search brought me to this Q&A site where many argued that corn is not an invasive species because it cannot survive or spread by itself without human intervention. I tend to agree with this logic but it does not seem to be within the scope of the USDA definition.

Should corn be considered an invasive species in the Midwest?

Answer 1

Should corn be considered an invasive species in the Midwest?

I agree with commenter Bryan Krause in that this question requires opinion -- but I think it only requires opinion as to the definition of what we consider "invasive".

The concept of an "invasive" species is highly contested among biologists. It is often used interchangeably with the terms non-native, non-indigenous, and alien.

Some people think we should consider a species as 'invasive' even if it is native to the region but is causing "economic or environmental harm or harm to human health". For example, the USDA considers Juniperus virginia a native species, despite its spread from plantings and its economic and ecological impacts in 'invaded' regions.

Answer 2

Species are only considered invasive if they become widely established in sustaining, wild populations. If the species is widely cultivated, but rarely or never escapes cultivation, it is not invasive. Even if it widely escapes cultivation, it may not necessarily be invasive because it might not be vigorous enough in the wild.

Corn has escaped and formed wild sustaining populations in North America, including in the Midwest. Here is BONAP's range map:

http://bonap.net/MapGallery/County/Zea%20mays.png

It shows that it is established in all lower 48 states as well as many of the Canadian provinces that border the US. However, if you look at the county-level distribution, you will see that it is spotty.

Given how widely it is cultivated in many of those states (it covers much of Iowa and Illinois, for instance) yet how sparsely it is established there (it only shows up as established in the wild in isolated counties in both states, this provides pretty strong evidence that it's not really that vigorous in the wild.

I have also observed corn plants growing in the wild in the US. They aren't particularly vigorous: there will be one plant here or there, and it never dominates or forms large monocultures. Those highlighted counties are where corn has formed some sustaining population. Not necessarily where it is vigorous, common, or abundant.

Want to see what a map of an invasive species looks like? Here is BONAP's map on garlic mustard, Alliaria petiolata, widely agreed to be invasive:

http://bonap.net/MapGallery/County/Alliaria%20petiolata.png

In spite of the fact that it is not cultivated, it is found in nearly all counties of broad regions from Wisconsin/Illinois east through New England. Furthermore, if you examine it in the wild, you find it forming huge monocultures, shutting out all sorts of other plants.

But back to corn:

The ecological damage caused by corn in North America is not caused by wild corn, i.e. not caused by corn as an invasive species. Rather, it is caused by the agriculture itself, specifically, by vast monocultures of corn and other crops, and various other aspects (fertilizer and other chemical applications) of yield-intensive agriculture.

So I think the answer here, even accounting for the high level of subjectivity in the definitions of "invasive", is definitively no.