I really do not like to becritical River but you could post a little more information perhaps a link to something. Alex
Alex ; the link sorry guy I assumed Anyway ; http://www.sciencealert.com/the-1-0...-pioneer-cabin-has-fallen-from-a-winter-storm
I agree. Carving the path through it probably weakened it. There was another tree with a road through it in Yosemite that fell in the 1960's I believe. So messing with the bases of these extraordinarily big trees doesn't have a very good record. They need to leave the trees alone. (The damage to these trees happened about 100 years ago.)
I lived in that part of California for several years. We drove through the tree about 15 years ago, when it was still permitted. Later on, they restricted it to walking only. (I have no idea why. If a tree is going to land on me I'd rather be in my car so I can drive away, or at least be protected by the steel roof!) It's very unlikely that the hole was a factor in the collapse. Sequoias have very shallow root systems, since they grow in a region with abundant rainfall. This was a "hundred-year flood" that loosened the topsoil, so the tree (and probably a few others that are not so famous or perhaps haven't even been noticed yet) just toppled over under its own weight as the damp soil became wet soil and finally turned to mud. So actually, removing a large portion of the tree's mass would be expected to make it less likely to fall over! I'm sure that the tourist shops will be selling bits of the tree at outrageous prices. And who's going to be sure that it was, in fact, from THAT TREE? Please Register or Log in to view the hidden image!
They were protecting the tree. Depends on the connections with the root system. Some kinds of trees have more or less specific connections between particular widths of xylem and phloem channels - the active "living" part of the tree just under the bark - and the roots directly connected to that width going into the ground. So removing that section of the circumference at the base starves a more or less circumferentially proportional section of the roots. The other roots will grow to compensate, but still that weakens the total spread and grip of the roots on the ground, and makes tipovers and blowdowns more likely.
The 'tunnel trees' usually had dead sections (from fires) at the base, and the tunnels removed those. however, it also removed some living to 'widen the tunnel', so yes, that widening could have contributed.
That would somewhat weaken the tree as well, for the same reason. I don't mean to imply the tunneling gets big blame (although fires the tree survives usually scar only one side - tunneling all the way through the opposite side is not merely enlarging a fire scar). Just that damage to a tree's trunk can weaken the root support, and enable tipups.