Climate warming reflected in new hardiness zone map   Lee E. Frelich
  Dec 22, 2006 05:52 PST 


The paleoecological record shows that with climate warming the existing
forests die suddenly when a threshold is reached, then there is a
transition lasting several centuries and then a new ecosystem with more
southerly species organizes itself.

Given the extreme rapidity of warming we are experiencing now, I would
expect a more extreme response than most of the previous changes in the
paleo record. We expect a 300 mile northward shift of tree species ranges
in the cold temperate and boreal zones.

Insects are heavily involved with the demise of existing forests in a
warming climate. Benign native insects have higher winter survival and if
the growing season is longer, higher reproductive rates, and basically they
increase fast enough to cause massive mortality of the existing forest. The
30 million acres of dead lodgepole pine in British Columbia caused by the
Mountain pine beetle, and the dead spruce forests in Alaska are early
examples (warming has a higher magnitude in the north, so responses occur
there first). Mountain pine beetle has now made it over the continental
divide, and with warmer winters, could move rapidly across the boreal
forest to Quebec, wiping out 100s of millions of acres of jack pine on the

One entomologist I talked to recently also thinks white pine could be
killed by this beetle across the cold-temperate zone of North America. In
MN we now have the Eastern tamarack beetle, a native insect which has had
higher survival since the year 2000, due to our very mild winters, and has
now killed 54,000 acres of tamarack forest. Of course, for this warming
event, unlike previous ones, we also have a lot of exotic tree diseases and
pests, and European earthworms that will all reinforce the impact of warming.

I have written a review paper on this topic, which I hope will be published
soon. I will be able to distribute copies once the review process is
complete and the embargo on distribution is lifted.


At 08:43 PM 12/21/2006, you wrote:

     The new hardiness zone map by the National Arbor Day Foundation shows
around a 150 mile nothern "migration" of zones for the eastern US.
   A comparison of the 1990 USDA map and the NADF 2006 map can be found
   As a garden center operator in suburban Cleveland, I can confirm a
number of "southern" plants are now successfully used in northern Ohio,
including southern magnolia, crape-myrtle, Japanese aucuba, and several
bamboos--I've even seen longleaf pine and deodar cedar.
   It will be interesting to see what effects the warming climate will
have on native forests. I would suspect the initial effects would be
reflected by insect pest populations(perhaps HWA infestations are
related to climate warming?)

Steve Galehouse