I took the girls for a walk today at the state university extension. They have a really nice area where the dogs can be off-lead semi-legally. There is a wide path that leads from the upper open field to an area that is being restored to a more natural mix of plants. The path between the two areas goes down a hill with many large Douglas fir trees on it.
Last month we had a bunch of windstorms on top of a very wet November. This combination led to several of the Doug firs deciding to lie down. They just uprooted themselves, big trees about 1.5 to 2 feet in diameter and 60 feet or more tall. Often two side-by-side trees went down, probably because the first took second with it. First, it's startling enough to see half a dozen very large trees down in a short walk. Second, the size of the root balls is shockingly small for such big trees. These big trees had rootballs that were maybe 10 feet in diameter and 6-8 feet deep. That's it!
I think perhaps the Doug firs are pack trees. They like to grow together, and they support one another. Does the one in my backyard get enough support, I wonder. My neighbors have several dougs, so I hope that is enough to keep mine happy. Certainly it's grown quite a bit in the time I've lived here.