It's not how far the tree bends in the wind but whether it's uprooted.

From Alfred’s journal

The storm came through Tuesday night and I spent it flattened against the trunk, which is not dignified but works. By morning the big maple at the corner of the lot looked ruined. Half its leaves gone, one limb hanging by a strip of bark, the whole crown still swaying like it had not been told the wind stopped. I used to measure a tree by how still it held; I thought the ones that whipped around were the weak ones. But the little ornamental pear two yards over, the one that never moved much at all, was lying on its side with its roots in the air like a dog asking to be scratched. It's not how far the tree bends in the wind but whether it's uprooted. Switch was up in the maple by noon, running the bent limb end to end, and the thing held him.