Why do pine trees make a thumping noise?
March 9, 2012 6:23 PM   Subscribe

Help me figure out why I hear and feel a thumping noise when I sit next to pine trees.

A little background: I was in San José, Costa Rica, last summer and ended up reading in a park that had a few pine trees scattered around (I don't know the species, however). I sat on the ground with my back resting against a pine trunk.

It wasn't long before I started hearing a bizarre thumping noise. From what I could feel from the ground, it should have been somebody jumping/stomping or people hurling bowling balls onto the soil from the nearby house's roof. I looked around--nobody. I looked (okay, creeped) at the adjacent house and nothing was going on. I looked up the tree and no critters were scampering around or woodpeckers going to town. This continued to happen, so I just accepted it as part of the experience abroad and thought nothing of it.

Fast forward to this month. I go to school at a college in southern Arkansas, and nearby there's a very primitive park (read: cleared footpaths) on a bluff overlooking a river. Along the bluff's edge are pine trees exclusively, with deciduous trees on the bluff's side. Last Friday, I was doing some reading and rested my back against a pine's trunk and--you guessed it--the same dull, thumping noise happened again.

The sound and sensation is similar to somebody whacking a carpeted floor with their hand: a very muffled bump that you can feel if you're sitting on the floor. But, like in Costa Rica, nobody (and nothing) was to be found. I felt the thumping noise in the ground and in the trunk, so I was wondering if the pine tree itself was responsible for this noise--sap moving around?--or if a parasite was tunneling around inside or below.

Anyone have any clue what's going on here? I'm sure there's a scientific explanation for it, but it's things like this that would have made the ancients believe in tree spirits & such. I'm not losing sleep over this mystery pine thumping, but it sure is weird.
posted by huxham to Science & Nature (9 answers total) 9 users marked this as a favorite
Bigfoot Wood Knocking?
posted by Sassyfras at 6:41 PM on March 9, 2012

Maybe Rube R. Nekker knows.
posted by Cortes at 6:41 PM on March 9, 2012

Best answer: Whoops, screwed up my links. Supposed to be this one.
posted by Cortes at 6:42 PM on March 9, 2012

I have experienced hearing insects that have infested a tree eating under/in the bark, but I can't imagine that it could be perceived as a "thumping" sound. Somehow I doubt that it is not related to the tree, or to insects.
posted by HuronBob at 7:05 PM on March 9, 2012

A rodent, underground.
posted by the Real Dan at 7:18 PM on March 9, 2012 [1 favorite]

Some squirrels cut pine cones from branches, in order to pick them up on the ground and eat them or store them for later. That could be it -- pine cones hitting the ground from a multi-story drop.
posted by Cool Papa Bell at 7:44 PM on March 9, 2012

Best answer: Rube R. Nekker, via Cortes, addressed the question I had for you-- wind conditions:

Trees? There is a large pine tree at my house that thumps under the right wind conditions ...
posted by Rube R. Nekker

Pine trees are stabilized by a stiff taproot and by a mass of lateral roots that act like guy wires.

The lateral roots are really tangled looking and full of elbows.

This is very tentative, but I think the thump occurs when wind pulls the lateral roots tight and irregularity in one root, such as an elbow, 'plucks' another root under tension like a finger plucking a big underground wooden guitar string.
posted by jamjam at 8:13 PM on March 9, 2012 [7 favorites]

Response by poster: jamjam: I forgot to mention that it was incredibly windy on the afternoon I went up to the Arkansas bluff. Your explanation makes sense of what I was experiencing: thumping in the ground (the lateral roots) and the tree trunk (link with the taproot).

I don't remember the specific weather conditions for the day I was in the Costa Rican park, but it stormed almost every day I was there, so I'm sure it was at least a little windy.
posted by huxham at 9:06 PM on March 9, 2012

whoa whoa whoa peoples ... it thumps against a roof, not a tree freestanding in the clearing!

ask me i am likely to tell you infrasound makes your eyeballs warble or the ents are saying hallo ...

but i like jamjams answer!
posted by Rube R. Nekker at 1:52 PM on March 10, 2012 [1 favorite]

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