Some Cold is Good! - Wilderness North

Celebrating 30 Years of Wilderness North  –          

Some Cold is Good!

There’s been a lot of frigid chatter (and we mean talk, not teeth) these days. A couple of weeks of below freezing temperatures hardly seems cause for celebration, but being glass-half-full people, we asked regional environmental researchers “What good is cold?” and got some great answers to share. We got quite a few, but you weren’t going outside anyway, were you? Many involve what we’ve always said up here: The cold keeps out the riff raff, or in these cases, the invasive species. Perhaps knowing these things – and that the forecast calls for more normal temps this week – will warm your heart, if not your fingers, toes and nose.

Good for Good Algae: Colder temperatures favor the growth of diatoms (algae enclosed in silica) and other “good” algae, while restricting the growth of potentially toxin-producing cyanobacteria, which are favored under warmer conditions, explains Chris Filstrup, a research at UMD’s Large Lakes Observatory and Minnesota Sea Grant.

Andrew Bramburger of the Natural Resources Research Institute at UMD takes it further: “Other than ice fishermen, most people didn’t venture out onto the lakes at that time of year – not even scientists. As the ‘ice-on’ period has become shorter and shorter, researchers have become increasingly interested in what is going on under the ice, and how important that might be for the rest of the year. When ice is clear and allows sunlight to penetrate into the water, a diatom algae called Aulacoseira islandica often grows in high abundance right on the bottom of the ice. It is a large, ‘juicy’ alga that contains lots of lipids and is a preferred food item for zooplankton. When the ice melts, A. islandica is suspended in the water column, where it can help to jump-start the food web for the coming summer. In years when little or no ice forms, or when ice doesn’t persist into the days with longer hours of daylight, the populations of A. islandica are smaller and don’t provide as much early-season food for zooplankton. Additionally, cold winters are good predictors of less intense thermal stratification of lakes during the following summer. Since intensely stratified lakes can be more prone to harmful algae blooms, cold winter temperatures can help keep our lakes healthier in the summer months.” See more on Andrew’s work in a June Breneman’s story, “Scientists find algae get ‘meaningful burst’ under ice.”

Freezing Out the Borers: Many insects survive the winter because they have a type of antifreeze that allows them to survive very cold temperatures … up to a point, notes Don Henne, assistant professor in Natural Resources Management at Lakehead University in Thunder Bay. What this means for the emerald ash borer is that cold temperatures can help kill many beetle larvae overwintering under the bark of ash trees, but it depends on how cold. He says studies conducted by scientists in Minnesota found that the colder it got, the more emerald ash borer larvae were killed, but temperatures would have to be -35° C (or -31° F) for several hours to achieve 98 percent kill. For cities like Thunder Bay and Winnipeg (which recently confirmed the presence of emerald ash borer), extremely cold temperatures could slow the rate of ash tree mortality and allow more time for emerald ash borer control programs to suppress the pest’s populations, even though many borer larvae do survive extreme cold. Learn more about the ash borer threat and where they’ve been confirmed at

George Host, director of the NRRI’s Forest and Land Initiative, says cold may help with another tree pest. “Our changing climate alters the relationships between trees and insect pests, sometimes for better and sometimes for worse. With warmer summers and longer growing seasons, invasive species like the emerald ash borer will feed more actively on the inner bark of ash trees, resulting in larger and healthier populations. The eastern larch beetle, responsible for killing off significant portions of Minnesota’s tamarack trees, typically produce one generation of beetles per summer, but could produce two or even three generations under warmer summer conditions. However, our current extreme cold temperatures from this extended polar vortex could put a damper on these insect pests. Extended periods of 20 to 30 below zero temperatures will kill off larvae hidden beneath the tree’s bark. While these frigid temperatures are tough on us and our pets and our vehicles, they should provide Minnesota’s trees with some welcome relief!

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