Balsam woolly adelgid   Jess Riddle
  Jul 10, 2006 08:01 PDT 

James,

If balsam woolly was more effective elsewhere than in the Smokies and
the Black Mountains, then it must have been beyond devastating.
Entire mountaintops of fraser fir were wiped out in the Smokies and
and Blacks. A few older trees have survived in both ranges, a stand
on Mount Guyot possible being the largest group, but those are the
exception. Mount Mitchell (6684'), in the Blacks, currently looks
much better than Clingmans Dome (6643'), in the Smokies. I have heard
the greater regeneration on Mitchell attributed to a heavier seed crop
at the time the adelgid moved through, rather than differences in
resistance. The only other fir population I have seen is the
southernmost one, near Richland Balsam on the Blue Ridge Parkway. I
have seen no old looking fir trees at that population, but it does
have larger regrowth trees.

The generation of fraser fir that have grown up post adelgid are still
relatively young with smooth bark, so they have not reached maximum
susceptibility yet; the balsam woolly adelgid feeds primarily through
cracks and fissures in the bark. I don't know if baseline data exists
to judge the susceptibility of the current generation.

I am far more optimistic for the future of fraser fir than I am for
our hemlocks, because fraser fir can reproduce before being killed by
balsam woolly adegid. Hence, they should be able to evolve smoother
bark and earlier reproductive age and minimize the impact of balsam
woolly adegid. If they can handle global warming, ozone pollution,
and acid deposition, they should be able to once again cover the high
peaks of the southern Appalachians. Conversely, hemlock woolly
adelgid kills two inch tall seedlings. Natural resistance and
environmental protection also appear less with hemlocks, so hemlock
may have to have help to recover.

Jess Riddle

On 7/5/06, James Smith wrote:
 
There must certainly be examples of diseases that have managed to wipe
out the host populations. Just because it's not terribly logical--even
in an implacable evolutionary way--doesn't mean that an organisim
wouldn't capitalise on a host's weaknesses to completely wipe them out.
I know almost nothing about the subject, but I would assume that thing
like that have occurred over the course of the history of life on Earth.

On the other hand, hasn't the balsam wooly adelgid shown signs that it's
not as effective on the trees in the Smokies and Blacks? Aren't the
newer generations of balsam trees coping with the introduced pests? Or
is it merely because the adelgids prefer older trees? Or did the
adelgids die off after the initial onslaught when almost all of our
balsam forests were destroyed?

If the balsam trees are, indeed, showing more resistance to the balsam
wooly adelgid, perhaps this bodes well for the eastern and carolina
hemlock species. Perhaps after they are initially wiped out, a newer
generation will be more likely to resist the pest.

Hasn't it been conjectured that a feline virus almost wiped out the
cheetah? Haven't genetic tests shown that at some time in the past the
breeding population of the entire species was reduced to just a few
dozen individuals? If so, then that would be an example of a disease
coming pretty darned close to completely wiping out a host.
RE: Balsam woolly adelgid   Matthew Hannum
  Jul 10, 2006 18:12 PDT 

How long have the adelgids been tearing through the Smokies?

I ask because when I look back upon some of my photos of the mountains
in 2004 on a road trip there, in certain areas there seem to be a lot
more dead trees in the woods than you'd think there should be... ghostly
straight, grey trunks of what I assume are evergreens... Could that be
the effects of the adelgid?
RE: Balsam woolly adelgid   James Smith
  Jul 10, 2006 19:50 PDT 


Yeah, that was the balsam wooly adelgid. It devastated the balsam trees.
Darned near wiped them out in some areas. To me, the most horrible
sights were in the high elevation areas along the Blue Ridge Parkway and
in the Great Smokies. Mount Mitchell, at one point, seemed to be nothing
more than a mass of dead snags. Still lots of dead trees standing up
there, but vigorous new growth of young trees, so it's not as bleak as
it was fourteen or fifteen years ago.
Re: Balsam woolly adelgid   Jess Riddle
  Jul 11, 2006 14:21 PDT 

Matthew,

Balsam woolly adelgid did kill entire stands of trees decades ago so
that now all that remains are stands of limbless snags. However, if
you were just seeing an unusually large number of snags in an area
that would still qualify as woods, you were probably looking at dead
red spruce. Spruce have been stressed by acid deposition and other
factors over recent decades and many in the park have died, especially
on the Tennessee side.

Jess Riddle