I will not endorse Mother Jones. However, "outrunning" is straightforward. A forest can "move" a certain amount a year — it is not motion of individual trees, b

I will not endorse Mother Jones. However, "outrunning" is straightforward. A forest can "move" a certain amount a year — it is not motion of individual trees, but new trees and plants can grow where there were none before. If the extents of a forest are constrained by climate, and the boundaries of its climate zone moving at a speed which is slower than the trees can move, then the collection of organisms can meaningfully persist and be said to move north. If on the other hand the climate zones are moving too quickly, then sooner or later there will no longer exist a collection of trees and related organisms that functioned as this forest once did.