| hwa
spread |
James
Smith |
| Jul
23, 2007 06:44 PDT |
Okay, speaking here obviously as the layman that I am.
Over the past few years I've figured that hwa had pretty much
all but
killed our hemlocks. All of the places that I visited either had
completely dead stands of hemlocks, or the trees were already
heavily
infested and on their ways down to extinction. So I figured this
must be
the case over the entire range of the eastern and carolina
hemlocks.
However, most of my initial travels were done northward and
southward
along the eastern corridor of their southern habitat. Shenandoah
National Park--I couldn't find a single living hemlock. BRP from
Shenandoah south to GSMNP--the hemlocks all along this ribbon of
road
range from dead to very sick.
South Mountains State Park has a vast hemlock forest that is
beginning
its downhill slide. The tree that are not showing the effects of
the
sap-sucking monsters are totally infested. This is what I found
in just
about every area where I looked where the trees still only
"looked"
healthy.
However, over the past few months, I've made trips westward of
the
corridor of death where I had been spending most of my hiking
time.
Middle Tennessee showed me some fine stands where I couldn't
find any
evidence at all of the hwa. This past week I hiked extensively
in the
Allegheny highlands of West Virginia and saw only slight signs
of hwa,
and many, many, many thousands of acres of healthy hemlocks.
Considering that the variance in latitude and distance from
utterly
destroyed habitat and healthy habitat is slight, what is the
cause of
this? I seriously doubt that groves father west are less
susceptible to
the infestations--groves in north Georgia are dead and they're
farther
west than the groves I saw in WV.
I've read that the prime vector of hwa might be birds. If so,
are
certain species of birds carrying the adelgids up and down a
migration
corridor? And lacking this certain vector, hwa might be slower
to spread
westward by less reliable means (wind, etc.).
At any rate, just something this mailman has noticed in his
journeys
peak-bagging and waterfall wandering and forest watching
throughout the
South. |
| Re:
hwa, spread |
Kirk
Johnson |
| Jul
23, 2007 11:22 PDT |
Some think colder winters might be a limiting factor. In the
Allegheny
National Forest in NW Pennsylvania, there is no hwa infestation
(yet).
Although one affected tree was discovered (and destroyed) in SE
Elk County
in 2005.
Kirk Johnson
|
| Re:
hwa, spread |
Jess
Riddle |
| Jul
29, 2007 16:06 PDT |
James,
I've heard the same ideas on birds being the primary long
distance
dispersal vector and responsible for the relatively rapid spread
of
adelgid up and down the Appalachians. I have not heard a more
convincing explanation for the relative dispersal rates.
Jess
|
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