Mt. Nusatsum

Mt. Nusatsum

Wednesday, February 3, 2010

Snow on Trees

So one of my brothers who is a lot wiser and a little bit older than me  lives clear across this great country and he is also a loyal blog reader.  He was recently in the state of Vermont where he took this picture.  He's a deep thinker and always asks me seemingly innocuously simple questions, which never have simple answers.  A while back he asked me this one:  "What's the evolutionary advantage for some evergreens to hold such large amounts of snow on their branches in the winter time?"

It took me longer than I expected pondering this question, because I initially thought the answer was easy.  Keep in mind that while this blog is not a science forum, I do get intrigued by these kinds of questions as well.  There are reams of research on the  interception of snow by coniferous forests (evergreens) being a major factor in moderating winter snow pack in areas of deep snow.  They talk in technical terms such as sublimation, ablation and albedo of snow pack -- all really impressive stuff.  Less snow pack in a forest means growing seasons can be longer as a result of snow interception and conditions better for animals using the forest in the winter.  There is a ton of research about this topic in relation to clear cut logging, as it's well documented in areas of deep snow falls that snow packs in clear-cuts are deeper and stay longer for usually 15-25 years after logging until the new trees start intercepting snow.  This is an understood effect which researchers and forestry planners build into their plans to mitigate the effect of increasing the length and depth of deeper snow packs -- more good stuff.

Where I got stuck was trying to explain the area where I spend time in the winter -- western mountains with  alpine and semi-alpine zones.   I could find little information to help explain why even though many of these trees are shaped to shed snow, tending towards tight pyramidal shape, they can hold a lot of snow during big snowfalls. as evidenced in this picture I took last weekend.  The snow they do intercept and eventually shed creates huge tree wells - I know I've fallen in a few with my snowmobile! 

There is research about the importance of these tree wells for animals which use them to get under the snow to live and hunt (mice, weasels, etc).  The more interesting piece I found was that researchers had actually turned their mind to calculating the heat loss from the earth through tree wells in semi alpine forests.  Apparently tree wells can be a significant conduit for heat loss without the insulating snow blanket.  It suggests that these heat wells can moderate the temperature of the forest floor by keeping it colder.

When I went back to my brother's original question, I had to speculate a bit for the semi alpine and transition zone forests.  These trees, which can hold so much snow that they create tree wells big enough that you can disappear in them and not be found, may actually serve to maintain a cold environment.  The biggest enemy facing these semi-alpine forests is a warming climate where trees that have evolved to survive being solitary at high altitude can quickly be replaced by more aggressive 'forest' trees from lower altitudes.  These semi alpine forests and the plants associated with them have a vested interest in maintaining a long winter, they've adapted their life to it and the fewer lower elevation intruders the better.  I`m sure I have opened enough doors on this topic someone reading this post will want to do a thesis on it now.  Grizzly

1 comment:

  1. Very interesting post! Didn't know anything about tree wells before, now I'll be more aware as I'm walking in the forest.