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Merry Christmas and its very merry to be with the living this Christmas. 

The following incident occurred over the Thanksgiving weekend, must have been about 4:00 pm Saturday, November 28, 2009 as it became dark pretty shortly after.  Earlier and for several hours that day moderate wind gusts rustled through the crowns of the trees.  Weather turned and there was just a hint of snow an occasional very fine hail.  At that moment of the toppling it was a little bit sunny for a change, but with the occasional wind gust.

I figure now is a good moment to reflect on the subject of what to do in a forest should one encounters a massive tree falling in your path.  I have poked around the internet only to read one recent and gruesome account of errant tree dodging.  I never really though about it but yes, a full size pine tree should just about pulverize the head and shoulder of its victim.  That's gravity for you.   When it takes only a moment to release the energy collected in hundred and some odd years of growth, focusing it on a few hundred square feet of ground.  Just by comparison lightning, though more concentrated energy may be relatively benign.  Whereas lightning may actively seek its victim out in the shortest (and sometimes human aided path) from the negatively charged atmosphere to the ground, a tree (and assuming it were a random event) falls where it does.  Even if one were standing right next to it you would have a significant chance of coming out only worse for their nerves.  This is all strictly unaided tree falling and not felling of which seems to be well practiced art by foresters.  Generally well practiced except for the the subject of the previously mention account.  The take away from the official report was that its very important to quickly assess the danger your fellow tree harvesters warning you of, and not to mistake their concern for some less significant danger.  When your fellow foresters bellow "watch out", look up first or else you might avoid a minor danger only to jump into the path of a falling tree.

Given that a forest of any significance is littered with fallen trees, there would have to be at least a single significant tree fall each year for every few acres.  Certainly much more than say lightning strikes per acre per year, yet so many more people get struck.  Seems at least to be many more accounts of lightning strike than tree strikes.  Maybe this is just another media phenomenon 'struck by tree' might be less reported than 'struck by lightning'.  At any rate, what you might be curious about is what to do or what it is like to have a large tree cross you path.  First of all lets figure out the dimensions, the perspective may be a little poor in my camera but this tree pictured below spanned the distance of two power poles.  I paced it out to be an excess of 125 feet.  The top 15 feet entirely disintegrated by either the fall (the tip was pushed down by the heavier base right).    The diameter I would have to guess is a relatively skinny for its height at approximately 3 ft.  The breaking point was several feet in length not far up the trunk.  After reviewing various forestry publications I will just estimate the weight as being a simple cone with density of 34 lbs./ft^3

1/3 h Pi R^2 D -> 1/3 (125) 3.14 (3/2)^2  (34) -> 10K lbs -> 4.5 tons

I think that this might be a little light comparing it to some of the charts for a tree taller than 100 feet but certainly in the ball park.

As hazardous as it is to extrapolate off just a couple of data points (having witnessed the snow stressed breaking of 25 feet the top of an approximately 75 foot tree) and seeing much the damaged aftermath of many a snow, rain or wind storm you are pretty likely, if ever, to encounter a falling tree while there is a strong wind or else with a moderate to heavy snow or ice load.  In my judgment the time between the crack, and the moment where true direction of the fall could be determined was about 3 seconds.  Very fortunate for me, there was no competing sounds as my perspective was not the best (particularly initially looking directly up at it) to determine the direction of the fall.  Traveling by foot while reading paperback novel (Catherine Wells, Mother Grim)  I was quickly aware of the specific danger by the distinctive and significant crack.  In moving from the edge of the one lane road to the center in order to gain best advantage, I could see a moment later I was safely positioned.  The tree would land right where I was initially walking on the downhill side of the road and I could very comfortably achieved another 12 feet of safety before the tree hit the ground.  This second 3 seconds didn't compel me to scale the wall of the hill to get further away.  I was already decidedly so.
Seems my perception seems approximately correct as the time to fall should be about 3 seconds:

SQ(2h/g) -> 2 (125 ft) /32 ft/s^2 -> 2.8 seconds

The rotational inertia of the tree as it falls could easily account for the additional time.  I distinctly recall being thankful that I had not lost my page in the novel, but afterward I thought I should be much more grateful that I had not been listening to loud music or distracted by another noise, or that a car didn't happen to be driving by at precisely that moment.  I'm not sure my eyes, even directly facing the tree, could have helped more than my ears had done.  Other witnesses in cabins within the radius of a hundred yards claimed that there was a significant shaking both at the breaking and the crashing to earth.  I didn't feel much.  The owner of the house adjacent to the tree was pretty lucky too.  The tree landed all the way up his skinny driveway.  Both his truck and his house were within twenty feet of the fallen tree, but it did not look like he suffered much property damage.

8 December 2009

tree fallen, looking down drivewaytree fallen, street view
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