At this time of year, with deciduous trees fading into the background, evergreens become more visible and therefore more conspicuous to us. How can they stay so green and fare so well in Minnesota winters?
Evergreens do quite well in cold climates. They also thrive in less nutrient rich areas. One adaptation that allows them to do so is their needle-like leaves. The leaves are small and narrow and can remain on the tree for up to 40 years, although one to four years is a more common leaf lifespan. (So while spruce, pine and fir trees keep their leaves year-round, evergreens do actually lose leaves, just not all at once like deciduous trees.)
One essential ingredient for green plants to produce food is water. Winter, here in the Upper Mississippi River basin, is not real conducive for photosynthesis (the process through which green plants make food) because water has this annoying habit of making itself unavailable in winter, by freezing. By keeping living, green leaves on throughout the winter months, evergreens are able to take advantage of warm periods in which water becomes available to photosynthesize. Evergreen leaves are also covered by cutin, a waxy polymer, which helps them to retain the moisture that they do have in them. By keeping their leaves, these trees also reduce their nutrient loss rate, an important trait if you happen to live in an area with nutrient-poor soils.
One of the joys of being out in the winter world is to stand near large evergreens. Experiencing the soft sounds of wind blowing through their needles and the green color they offer in an otherwise color-muted landscape adds a counter-balance to the winter world in the upper Midwest. You dont have to travel to the Superior National Forest to experience big evergreens. Visit the Pine Bend Bluffs SNA in Inver Grove Heights to stand among some large white pine and to get a spectacular view of the Mississippi River valley. Before you go, be sure to visit the Department of Natural Resources webpage devoted to this site.
Tom Lewanski, Conservation Director