By Doyle Irvin, American Forests
There is an intimate relationship between wintry forests and the water cycle, and it deserves a little digging into. So, let’s take a look at the interworkings of snowpack — how forests affect it in different areas, some current debates about forest management practices and what the potential consequences may be for wildlife.
It’s fairly common knowledge that forested areas promote snowpack retention. Snow melts in the sun; trees provide shade. What’s less commonly talked about, and certainly surprised yours truly, is that the opposite is true in some climates — open fields were retaining snowpack for longer than forested areas. Researchers at the University of Washington were perplexed by this, and developed a study to attempt to answer why. Their study asserts that “this occurs because the dominant effect of forest cover shifts from slowing snowmelt by shading the snow and blocking the wind to accelerating snowmelt from increasing longwave radiation.”
Getting into the technicalities of short- and longwave radiation is beyond the scope of this post, but at its most basic form shortwave radiation is heat from the sun, and longwave radiation is heat from the Earth. The study found that winter snowmelt occurs more quickly under tree cover in areas where the mean temperatures are already above freezing — for example, warm Mediterranean climates like coastal areas in the Pacific Northwest. Essentially, trees radiate a little heat (they are less reflective than snow, absorbing more light), and it makes the difference in places already close to the melting point.
Do these findings change the current practice of planting trees to protect snowpack?
Not at large, no.
Most snowpack is found in places where winter is actually cold. What it does propose is a more nuanced approach to climate-specific forest and watershed management.
Speaking of nuanced approaches to forest management, there is currently growing steam behind proposals to thin the forests in the Sierra Nevada mountains in order to increase California’s water supply. The idea is that “just like crops, trees consume water.” These proposals are getting flak from many angles, with responses asserting that the studies are paid for by logging companies, and others simply excoriating the science involved — which are admitted by the proponents themselves as “back-of-the-envelope calculations.”
Environment Now’s study-in-response-to-this-study refutes the logging proposal for a variety of reasons. These include that the increases in water yield are very modest, that the increases are seasonally based (meaning that increases are limited to already-wet seasons when they are less needed) and that the thinning of the forest only makes room for vegetative regrowth, which would fill the vacuum within five to 10 years and make redundant all the logging performed.
If logging-for-water somehow does get mobilized, it is bad news for the snowpack (because the Sierras do actually get cold). Not only are trees vital anchors for avalanches, their duty in protecting snowpack is crucial to many animals who use snow for shelter from intense wayward freezes. Because snow is an incredible incubator, many species rely on it to survive the winter cold — everything from classic mammal examples, like bears, to insects whose survival is necessary if migratory birds are to have anything to eat come summer time.
Forested areas crucial to snowpack retention across the United States are in dire need of restoration. Beetles and blister rust are decimating forests across the country, putting wildlife from the Grizzly bear to the Pacific Salmon in danger. On top of wildlife, reducing forested areas also increases the chances of catastrophic floods. American Forests is hard at work planting millions of trees in the vital regions.