Read here. Scientists involved with the study of ancient and historical climates are well aware of the impact that nature's major cooling and warming oscillations have on the environment. Cold periods, such as the Little Ice Age (LIA), can be very destructive to plant life, literally causing vegetation to shift southward in the Northern Hemisphere seeking warmth. Once natural warming returns though, vegetation will shift back to its previous northern boundaries.
This is exactly what happened with the forests of northern Canada. After the LIA, the tree line shifted in some areas up to 200 kilometers farther north.(click image to enlarge)
Explorer in
1772: “I have observed during my several journeys in those parts that
all the way to the north of Seal River the edge of the wood is faced
with old withered stumps, and trees which have been flown (sic) down by
the wind….Those blasted trees are found in some parts extend to a
distance of twenty miles from the living woods, and detached patches of
them are much farther off; which is proof that the cold has been
increasing in these parts for some ages. Indeed some of the older
Northern Indians have assured me that they have heard their fathers and
grandfathers say, they remembered the greatest part of those places
where the trees are now blasted and dead, in a flourishing state.”