Winds speeds in a storm are considered to be greatest at perhaps 30' above ground level.  And fully-fledged trees have three things working against them that this shelter does not have: 1) Huge surface area, which equates to high drag, 2) Moving center of gravity and 3) High leverage.  BTW, the 3D surface area of a single leaf is much more than one might expect due to its fractal geometry.  On the other hand, a domed cylinder has absolutely minimal surface area per volume.