Steve:
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
way.
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.
Lee
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
here:
http://www.arborday.org/media/map_change.cfm
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 |
|