Alpine Tree Lines Offer Clues to MWP
By Paul Homewood
Further to yesterday’s post on Swiss glaciers, I came across this graph from HH Lamb’s “Climate, History and the Modern World”.
Based on work by La Marche and Markgraf, ( I believe in the 1970’s), it maps the upper tree lines over the past 6000 years in the White Mountains of California, and in the Swiss & Austrian Alps.
The lowering of the tree lines from around 2000 BC tells its own story. But also of interest is the fact that, despite the recent small recovery in the Alps, tree lines are still much lower in both regions than they were in the Middle Ages.
In the Alps, in particular, there is a clearly significant rebound in the couple of centuries up to 1000 AD, clear evidence of a rapid rise in temperatures. Recovery since the end of the LIA has been much smaller than a 1000 years earlier.
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NOT A LOT OF PEOPLE KNOW THAT 
You may also be interested in this report by Harvey Nichols from the late 1970s:
Historical Aspects of the Northern Canadian Treeline
Click to access Arctic29-1-38.pdf
ABSTRACT
From palynological studies it appears that northernmost dwarf spruces
of the tundra and parts of the forest-tundra boundary may be relicts from times of
prior warmth, and if felled might not regenerate. This disequilibrium may help
explain the partial incongruence of modern climatic limits with the present forest
edge. Seedlings established as a result of recent warming should therefore be found
within the northernmost woodlands rather than in the southern tundra.
Has a couple of maps and an old (1958) photo. 9 pages. Many references.