I think its because so the plants can absorb more nutrients from the soil while being sturdy and wide so when the plant gets snowed on it doesn't break<span />
They have shallow, wide roots: To cover as much ground as possible, so the plant can absorb a sufficient amount of water before it freezes, and because the permafrost prevents the plants roots from going further down into the ground. <span />
Viscosity refers to the speed at which a substance can flow (i.e. the thickness of the substance/its ability to flow). I think that's the closest the English language gets.