They sure can break and the density of the wood in some of our Eucs would be too much I reckon...remember the Bistlecomb pine fiasco? At least this was one version of how the oldest living single organism on the planet ended up being cut down to read the rings!!!! Anyway rather than have my coloured version read this its well written and pretty fair, and interesting.
Oldest Living Tree Tells All, by Michael P. Cohen : Essays : Terrain.org