Similar to the weather patterns of the last several months, December 2019 showed quite a difference in the first half and the second half. During the early weeks, we had an average temperature of about 13 degrees with seven days of subzero. Along with this cold, we received nearly 20 inches of snow.

Going through a change in the second half, the temperature was close to 10 degrees warmer and about 8 inches of snow fell. A reading of nearly 40 degrees on Dec. 22 was the high for the month. The 10 days following the winter solstice averaged 28 degrees, with lots of clouds, mist, wet snow and rain — plenty of precipitation.

Winter is not only our coldest season, it is also our driest. December typically has only about 1.2 inches of precipitation for the whole month. Cold days are dry and snow that falls has little moisture content. But not so during the end of this December.

Though warmer with less snow, there was more precipitation. We seldom get rain at this time, but during the two days of Dec. 28 and 29, rain gave as much moisture as we usually get for the whole month. It brought interesting changes. Snow on the ground became wet and sticky. Slush and puddles formed on the roads and moving about was a bit difficult for us and others who live through these conditions.

While walking among the slush and puddles on the road on this wet 30-degree winter day, I noticed fewer tracks; critters are less active. This weather can cause harm for wildlife that live under the snowpack. Here, they find shelter in tunnels and homes. Wet snow can ruin this. But as I walked and looked at the woodland trees, I saw that some growths on their bark were taking advantage of this wet time: the lichens.

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Lichens are a strange and hardy form of life that abounds in the Northland, especially on trunks and branches of trees. Many lichens grow on soil and rocks, now under the snowpack. Others remain above the snow, on the tree bark, right out in winter weather. They may appear to be no more than gray, green, blue-green or yellow patches on the trees, almost looking like dried paint.

But living here, lichens are able to cope with winter. A closer look at lichens reveals that they consist of a combination of algae and fungi. These two organisms live in a mutualistic relationship that allows them to thrive. Algae are green with chlorophyll and are able to make food in the presence of sunlight. The filamentous fungi cells will hold needed moisture.

Though winter days may have plenty of sunlight, they are very dry and lichens go into a dormant phase unless there is a change from the normal weather.

And precipitation did come during a couple late December days. The fungi component of the lichen growth did its part and absorbed the available moisture. I could see as I passed by that the wet lichens looked larger and more colorful. Several species grow here, but most obvious were common greenshield lichen (flavoparmelia), gray shield lichen (parmelia) and yellow sunburst lichen (xanthoria). All were coated with available rain drops allowing their bodies to enlarge and show good color.

It was also interesting to note that when the cold and dry weather returned, the lichens went back to their dormant winter phase; waiting for the next damp opportunity. But for a short time in late December, the local lichens thrived in the moisture.

Larry Weber
Larry Weber