Monarch Butterfly Decline and Ever More Intensive U.S. Farming

The decline of the monarch butterfly results from multiple causes. The one that gets the most play is logging (often illegal and done by the cartel) in its wintering ground in Mexico. Brad Plumer’s piece suggests a bigger reason is the rapid growth in intensive farming in the U.S. that has plowed under the small pieces of semi-wild land around the edges of farms that allowed monarchs (and many other species) to thrive.

Now a new study in the Journal of Animal Ecology suggests that the decline of milkweed is, in fact, the main factor here. The study, by a team of researchers from the University of Guelph, modeled the variations in butterfly populations. They found that habitat destruction in Mexico was no longer driving the decline — possibly because the country has put new conservation measures in place to protect those forests.

But butterfly populations were very sensitive to changes in milkweed. The study noted that milkweed plants had declined 21 percent between 1995 and 2013. These losses were concentrated in areas where monarchs breed — and 70 percent of the milkweed loss was located in agricultural areas. (The rest of the decline was on conservation lands or public areas such as the medians of roadways.)

And the outlook here is pretty bleak — the authors predicted that the monarch population would decline another 14 percent if milkweed loss continues.

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Still, not everyone’s convinced that herbicides are the only reason for the decline of native plants near agricultural fields. Another recent study by scientists at the US Department of Agriculture and Penn State found that herbicide-tolerant native plants around farmland in Pennsylvania were declining at the same rate as less-tolerant plants. That study suggests that other factors may be at work here.

The Penn State researchers pointed out that farmers have made a lot of changes in recent decades besides rising herbicide use — they’ve simplified their crop rotations, segregated crops and livestock, and employed new mechanical farming methods. What’s more, woodlots, hedgerows, pastures, and wetlands have all been cleared to make way for bigger fields. So there may be more going on than just GMOs and herbicides.

Much of this intensification of farming is the production of corn for high fructose corn syrup and the ever-growing corn-based industrial products. It’s not really to feed ourselves that we need to do this. We could mandate a certain amount of wild land per 100 acres or whatever in agricultural zones, but instead, we grow more corn to burn it in our cars.